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. 2017 Mar 17;23:58–86. doi: 10.12659/MSMBR.902557

Platelets Cellular and Functional Characteristics in Patients with Atrial Fibrillation: A Comprehensive Meta-Analysis and Systematic Review

Alexander Weymann 1,A,B,C,D,E,F,G,*, Sadeq Ali-Hasan-Al-Saegh 2,A,B,C,D,E,F,G,*, Anton Sabashnikov 3,4,A,B,C,D,E,F,G,*, Aron-Frederik Popov 3,A,B,C,D,E,F,G,*, Seyed Jalil Mirhosseini 2,A,B,C,D,E,F,G,, Luis Nombela-Franco 5,A,B,C,D,E,F,G, Luca Testa 6,A,B,C,D,E,F,G, Mohammadreza Lotfaliani 2,A,B,C,D,E,F,G, Mohamed Zeriouh 3,4,A,B,C,D,E,F,G, Tong Liu 7,A,B,C,D,E,F,G, Hamidreza Dehghan 8,A,B,C,D,E,F,G, Senol Yavuz 9,A,B,C,D,E,F,G, Michel Pompeu Barros de Oliveira Sá 10,11,12,A,B,C,D,E,F,G, William L Baker 13,A,B,C,D,E,F,G, Jae-Sik Jang 14,A,B,C,D,E,F,G, Mengqi Gong 7,A,B,C,D,E,F,G, Umberto Benedetto 15,A,B,C,D,E,F,G, Pascal M Dohmen 1,D,G,G, Fabrizio D’Ascenzo 16,A,B,C,D,E,F,G, Abhishek J Deshmukh 17,A,B,C,D,E,F,G, Giuseppe Biondi-Zoccai 18,19,A,B,C,D,E,F,G, Hugh Calkins 20,D,E, Gregg W Stone 21,D,E; Integrated Meta-Analysis of Cardiac Surgery and Cardiology-Group [IMCSC-Group]
PMCID: PMC5367840  PMID: 28302997

Abstract

Background

This systematic review with meta-analysis aimed to determine the strength of evidence for evaluating the association of platelet cellular and functional characteristics including platelet count (PC), MPV, platelet distribution width (PDW), platelet factor 4, beta thromboglobulin (BTG), and p-selectin with the occurrence of atrial fibrillation (AF) and consequent stroke.

Material/Methods

We conducted a meta-analysis of observational studies evaluating platelet characteristics in patients with paroxysmal, persistent and permanent atrial fibrillations. A comprehensive subgroup analysis was performed to explore potential sources of heterogeneity.

Results

Literature search of all major databases retrieved 1,676 studies. After screening, a total of 73 studies were identified. Pooled analysis showed significant differences in PC (weighted mean difference (WMD)=−26.93 and p<0.001), MPV (WMD=0.61 and p<0.001), PDW (WMD=−0.22 and p=0.002), BTG (WMD=24.69 and p<0.001), PF4 (WMD=4.59 and p<0.001), and p-selectin (WMD=4.90 and p<0.001).

Conclusions

Platelets play a critical and precipitating role in the occurrence of AF. Whereas distribution width of platelets as well as factors of platelet activity was significantly greater in AF patients compared to SR patients, platelet count was significantly lower in AF patients.

MeSH Keywords: Atrial Fibrillation, Blood Coagulation, Platelet Count

Background

As the most prevalent cardiac arrhythmia in the general population, atrial fibrillation (AF) is associated with a high risk of developing morbidities, such as thromboembolism, stroke and neurologic injury, major and minor organ injury or failure, and hospital re-admissions resulting in significantly increased health care costs [13]. Moreover, this situation might even exacerbate, since the number of AF patients is expected to double by 2050 [3].

The pathophysiological mechanism of increased prothrombotic tendency in patients with AF is highly intricate and multifactorial [4]. The association of increased platelet activity with atherosclerotic disease has been well documented [5]. Activated platelets have numerous vasoactive and prothrombotic factors [5,6]. Mean platelet volume (MPV) is a marker of platelet activation and function reflecting platelet size and changes either in terms of platelet stimulation or the rate of platelet production [6]. Virchow’s triad on prothrombotic state including arterial stasis, vessel wall abnormalities, and coagulant alternations in the hemostatic balance may play a major role in the development of supraventricular arrhythmia [7]. Platelets represent an important part of hemostatic balance and can directly affect prothrombotic state.

Various studies have reported the association of hemostatic markers with the occurrence of AF. However, so far the data from the studies have been largely inconclusive. This systematic review with meta-analysis aimed to determine the strength of evidence for evaluating the association of platelet cellular and functional characteristics including platelet count, MPV, platelet distribution width (PDW), platelet factor 4, beta thromboglobulin (BTG), and p-selectin with the occurrence of AF and consequent stroke.

Material and Methods

Literature search

A comprehensive literature search was conducted in electronic scientific databases (Medline/PubMed, Web of Science, Embase, and Google Scholar) from their inception through August 10, 2016 to identify relevant studies on the association of platelet cellular and functional characteristics with the occurrence of AF and consequent stroke. Predefined search terms were as follows: “platelet count”, “mean platelet volume”, “platelet distribution width”, “platelet factor 4”, “beta thromboglobulin”, “P-selectin”, and “atrial fibrillation” or “supraventricular arrhythmia”. No restrictions were applied regarding language, time of publication, or sample size of studies. To assess additional studies not indexed in common databases, all retrieved references of the enrolled studies, recent published review articles, and meta-analyses were also checked.

Study selection

Studies were included in the analysis when they met the following criteria: 1) human subjects; 2) cohort or case-control studies; 3) the study investigated the comparison between AF-cases and non-AF-population in terms of platelet biomarkers; 4) the study compared patients with and without stroke focusing on biomarkers. Abstracts without peer-review or from congress presentations only, as well as gray literature were not included.

Data extraction and outcome measures

Three investigators (S.A-H-S, S-J.M, and A.S) independently extracted the data. Discrepancies were resolved by a consensus standardized abstraction checklist used for recording data in each included study. Disagreements were discussed and resolved by senior authors (A.F-P, A.W, G.B.Z, and H.C). Author’s name, year of publication, country, design of study, sample size, mean age, gender, coexistent cardiovascular diseases and risk factors, such as diabetes mellitus, hypertension and history of myocardial infarction, percentage of used anti-coagulants, type of AF, and details of platelet markers were extracted. For exploration of heterogeneity among trials, subgroup analyses of disparities in the patients’ characteristics were performed for 1) the era of publication (before 2000 versus after 2000); 2) geographical area (Asia, Europe, Africa, North-America, South-America, and Oceania); 3) study design (case-control versus cohort); 4) size of patient cohort (≤300 versus >300); 5) mean age (≤60 years versus >60 years); 6) percentage of male patients (≤70% versus >70%); 7) presence of diabetes (≤30% versus >30%); 8) presence of hypertension (≤70% versus >70%); 9) history of cigarette smoking (≤0% versus >30%); 10) presence of myocardial infarction (≤20% versus >20%); 11) use of cardiovascular drugs, such as diuretics, angiotensin converting enzyme inhibitors, statins and beta-blockers (for each: ≤70% versus >70%); 12) AF-classification (chronic versus non-chronic; duration of AF ≥6 months and ≥1 attempt of electrical cardioversion to restore normal sinus rhythm were considered chronic AF and patients with duration of AF ≤6 months were considered non-chronic AF); 13) type of AF [paroxysmal (spontaneous termination of the arrhythmia within 7 days of its onset), persistent (sustained arrhythmia beyond 7 days), permanent (efforts to restore normal sinus rhythm have either failed or been forgone)]; and 12) anticoagulation (code-1: patients did not receive anticoagulants in both groups, code-2: all participants received anticoagulants in both groups, code-3: range of percentages between both groups >5 0%, code-4: range of percentages between both groups <50%, code-5: no information available about anticoagulation in both groups, and code-6: anticoagulation information not available for one group only).

Homogenization of extracted data

Continuous data were expressed as mean ± standard deviation (SD). For studies reporting interquartile ranges, the mean was estimated according to [minimum+maximum+2(median)]/4 and SD was calculated based on (maximum–minimum)/4 for groups with sample sizes of n ≤70 and (maximum–minimum)/6 for sample sizes of >70 [8].

Quality assessment and statistical analysis

The Newcastle-Ottawa scale was independently used by two investigators (S.A-H-S and M.G) to assess the quality of studies [9]. Total scores ranged from 0 (worst quality) to 9 (best quality) for case-control or cohort studies. Data were analyzed by STATA 11.0 using METAN and METABIAS modules. For non-categorical data, pooled effect size measured was weighted mean difference (WMD) with 95% CI. A p value <0.1 for Q test or I2 >50% showed significant heterogeneity among the studies. Heterogeneity among trials was examined by applying a random effect model when indicated. Publication bias was assessed using the Begg tests. A p value <0.05 was considered statistically significant.

Results

Literature search strategy and included studies

A total of 1,676 studies were retrieved from the literature search and screened databases, of which 1,005 studies (59.9%) were excluded after meticulous evaluation during the first review due to either unnecessary information (n=710), inadequate report of endpoints of interest (n=265) or report of non-matched data based on mean ±SD or median [minimum-maximum] (n=30). In total, 671 potentially relevant full-text articles were reviewed, and finally 73 studies were analyzed in the meta-analysis (Supplementary Table 1).

Association of platelet characteristics with AF

Platelet count

A total of 6,255 cases were selected from 45 studies, of which 2,964 were allocated to the AF group and 3,291 to the SR group. Patient populations in the selected studies ranged from 27 to 621 patients. Mean platelet count was 237.3×109/L in AF group and 240.04×109/L in SR (Tables 1, 2). Using a random effect model, pooled assessment effect analysis indicated that the mean platelet count was significantly lower in patients with AF than in patients with SR with WMD of −26.93 (95% CI: −28.35 to −25.51; p<0.001, Figure 1). Significant heterogeneity was observed among the studies (I2=93.5%; heterogeneity p<0.001).

Table 1.

Characteristics of included studies for meta-analysis of association of platelets characteristics and AF.

First Author Year Country Design N-AF N-SR Age-AF Age-SR Male-AF Male-SR AC-AF AC-SR Type of AF NOS
Karatas [20] 2016 Turkey Case-control 40 581 65.7 56.4 70 75 100 100 ND 8
Drabik [21] 2015 Poland Case-control 47 50 60.8 59.4 65.9 64 38.3 26 Persistent 9
Drabik [21] 2015 Poland Case-control 41 50 60.6 59.4 46.3 64 51.2 26 Paroxysmal 9
Idriss [22] 2015 Egypt Case-control 21 20 34.2 29.3 28.5 70 33.3 0 ND 7
Akdag [23] 2015 Turkey Case-control 96 52 63.6 64.5 64 56 54.1 ND Combined 9
Akyuz [24] 2015 Turkey Case-control 40 50 63 61.5 72.5 72 20 14 Combined 7
Chavaria [25] 2015 USA Case-control 40 250 70.6 60.7 65 84 ND ND ND 6
Erdogan [26] 2014 Turkey Case-control 34 33 70.5 68.6 47 51.5 66.6 0 Permanent 9
Xu (without comorbidities) [27] 2014 China Cohort 57 58 65.1 67 50.9 50 50.9 15.5 ND 7
Xu (with comorbidities) [27] 2014 China Cohort 57 58 68.95 67 52.6 50 49.1 15.5 ND 7
Acet (PAF) [28] 2014 Turkey Case-control 71 63 63 61.1 42 46 ND ND Paroxysmal 9
Acet (persistent and permanent) [28] 2014 Turkey Case-control 63 63 64.6 61.1 41 46 ND ND Combined 9
Arik (with INR 2–3) [29] 2014 Turkey Case-control 125 123 70.4 68.9 41.6 39.8 ND ND Permanent 8
Arik (with abnormal INR) [29] 2014 Turkey Case-control 125 123 70 68.9 36 39.8 ND ND Permanent 8
Distelmaier [30] 2014 USA Case-control 66 132 73.5 73.5 61 61 ND ND ND 7
Gungor [31] 2014 Turkey Case-control 117 60 48.3 46.1 60.6 55 75.2 8.3 Combined 9
Sonmez [32] 2014 Turkey Cohort 52 33 70 70 34.6 39.3 59.6 36.3 Persistent 7
Ulu [33] 2014 Turkey Case-control 25 32 ND ND ND ND ND ND ND 7
Turgut [34] 2013 Turkey Case-control 81 81 64 62 51 53 28 20 ND 7
Jaremo (healthy control) [35] 2013 Sweden Cohort 58 24 69 66 79.3 54.1 12.06 0 ND 8
Jaremo (disease control) [35] 2013 Sweden Cohort 58 72 69 74 79.3 56.9 12.06 41.6 ND 8
Berge [36] 2013 Norway Cohort 63 126 75 75 71.4 70.6 8 33 Combined 9
Ertas (without stroke) [37] 2013 Turkey Case-control 87 24 69 38 44 58 58 ND ND 6
Ertas (with stroke) [37] 2013 Turkey Case-control 39 24 71 38 36 58 51 ND ND 6
Sahin [38] 2013 Turkey Case-control 72 72 65.1 64.7 48.2 51.3 ND ND Persistent 7
Tekin [39] 2013 Turkey Case-control 107 112 74 73 31 40 ND ND ND 7
Turfan (without CVA) [40] 2013 Turkey Cohort 77 58 63 56 57.4 51.7 44.3 0 ND 7
Turfan (with CVA) [40] 2013 Turkey Cohort 63 58 69 56 52.4 51.7 41.3 0 ND 7
Feng [41] 2012 China Case-control 185 189 65.9 65.7 62.7 60.8 76.8 83.1 Combined 8
Acevedo [42] 2012 Chile Case-control 130 20 67 ND ND ND 0 0 Combined ND
Hayashi [43] 2011 Japan Case-control 14 13 53.1 62.8 93 92 100 100 Paroxysmal 7
Hayashi [43] 2011 Japan Case-control 14 13 60.1 62.8 93 92 100 100 ND 7
Fu [44] 2011 China Case-control 90 79 54.1 54.8 70 57 22 0 Combined 8
Hou (disease control) [45] 2010 China Case-control 26 26 65.2 64.5 57.6 57.6 7.6 11.5 ND 8
Hou (healthy control) [45] 2010 China Case-control 26 26 65.2 65.4 57.6 57.6 7.6 0 ND 8
Alberti [46] 2009 Italy Case-control 17 34 68.1 60.8 94.1 23.5 0 0 Persistent 7
Choudhury (disease control) [47] 2008 UK Case-control 121 71 62.58 64.04 76 72 37.2 47.4 ND 6
Choudhury (healthy control) [47] 2008 UK Case-control 121 65 62.58 62.03 76 68 37.2 0 ND 6
Colkesen [48] 2008 Turkey Case-control 103 87 63 45 55 21 50 14 Paroxysmal 8
Blann [49] 2008 UK Case-control 54 28 65 64 64.8 60.7 60 0 ND 6
Topaloglu (disease control) [50] 2007 Turkey Case-control 18 28 37 32 ND ND ND ND ND 6
Topaloglu (healthy control) [50] 2007 Turkey Case-control 18 20 37 35 ND ND ND ND ND 6
Yip [51] 2006 Taiwan Case-control 62 20 66.2 65.3 66.1 60 58.1 0 ND 7
Heeringa [52] 2006 UK Cohort 162 324 78 77 51 51 ND ND ND 8
Inoue (with comorbidities) [53] 2004 Japan Case-control 159 92 ND ND ND ND ND ND ND 7
Inoue (lone AF) [53] 2004 Japan Case-control 87 19 ND ND ND ND ND ND ND 7
Conway [54] 2004 UK Case-control 106 41 69 67 63 61 86 0 Permanent 6
Conway [55] 2004 Turkey Case-control 37 37 67 68 72.9 67.56 ND ND Persistent 6
Atalar (paroxysmal AF) [56] 2003 Turkey Case-control 15 22 45 47 60 63.6 0 0 Paroxysmal 6
Atalar (permanent AF) [56] 2003 Turkey Case-control 25 22 51 47 64 63.6 0 0 Permanent 6
Kamath [57] 2003 UK Case-control 31 31 61 66 61.3 41.9 0 0 Combined 6
Kamath [57] 2003 UK Case-control 93 31 66 66 63.4 41.9 0 0 Permanent 6
Kamath [58] 2002 UK Case-control 29 29 61 65 55.17 41.3 37.9 0 Paroxysmal 7
Kamath [58] 2002 UK Case-control 87 29 65 65 63.2 41.3 37.9 0 Permanent 7
Kamath [59] 2002 UK Case-control 93 50 70 70 62.4 64 0 0 ND 6
Kamath [60] 2002 UK Case-control 34 23 73 ND 20 ND 0 0 ND 6
Li-Saw-Hee [61] 2001 UK Case-control 23 20 65 63 69.6 85 69.6 0 Paroxysmal 8
Li-Saw-Hee [61] 2001 UK Case-control 23 20 65 63 69.6 85 100 0 Persistent 8
Li-Saw-Hee [61] 2001 UK Case-control 23 20 67 63 69.6 85 100 0 Permanent 8
Mondillo [62] 2000 Italy Case-control 45 35 67.6 66.3 80 85.7 55 0 Permanent 7
Li-Saw-Hee [63] 2000 UK Case-control 52 60 68 66 80 75 0 0 ND 6
Li-Saw-Hee [64] 1999 UK Case-control 25 25 60 58 20 20 ND ND ND 6
Minamino [65] 1999 UK Case-control 28 28 64 64 71.4 71.4 7 14 ND 6
Minamino [66] 1997 Japan Case-control 45 45 63 63 73.3 73.3 ND ND ND 6
Kahn [67] 1997 Canada Case-control 50 31 ND ND ND ND 0 0 ND 7
Sohara [68] 1997 Japan Case-control 21 9 59.1 59 ND ND 0 0 Paroxysmal 6
Lip GY [69] 1996 UK Case-control 51 26 70.4 ND ND ND 0 0 ND 6
Nagao [70] 1995 Japan Case-control 17 19 81.5 78.4 47.1 47 0 0 ND 8
Sohara [71] 1994 Japan Case-control 19 9 60 ND 76.9 ND 0 0 Paroxysmal 6
Gustafsson (with stroke) [72] 1990 Sweden Case-control 20 40 77 77 ND ND 0 0 ND 8
Gustafsson (without stroke) [72] 1990 Sweden Case-control 20 40 77 77 ND ND 0 0 ND 8
Yamauchi (without valvular heart disease) [73] 1986 Japan Case-control 73 57 47 36 ND 89.5 0 0 ND 6
Yamauchi (with valvular heart disease) [73] 1986 Japan Case-control 26 57 55 36 ND 89.5 0 0 ND 6
Table 2.

Information about markers and their levels in each study.

First author markers Levels
Karatas [20] PC, MPV, PDW PC [AF: 230±69.3 vs. SR: 240±77.5]
MPV [AF: 9.5±1.7 vs. SR: 8.7±1]
PDW [AF: 13.9±1.7 vs. SR: 13.4±1.4]
Drabik [21] PC, PF4 PC [AF: 202±20.5 vs. SR: 219±16.5]
PF4 [AF: 66.1±10.25 vs. SR: 50.55±10.45]
Drabik [21] PC, PF4 PC [AF: 210.25±15.75 vs. SR: 219±16.5]
PF4 [AF: 62.72±7.95 vs. SR: 50.55±10.45]
Idriss [22] P-selectin P-selectin [AF: 85.9±42.1 vs. SR: 38±7.8]
Akdag [23] PC, MPV PC [AF: 265.5±73.4 vs. SR: 248.2±67.2]
MPV [AF: 8.9±1.1 vs. SR: 7.8±1]
Akyuz [24] PC, MPV PC [AF: 277±79 vs. SR: 264±82]
MPV [AF: 9.8±0.6 vs. SR: 8.4±0.6]
Chavaria [25] PC PC [AF: 242.2±54.1 vs. SR: 243.2±66.2]
Erdogan [26] PC, MPV, P-selectin PC [AF: 245.6±114.9 vs. SR: 238.4±66.6]
MPV [AF: 7.82±1.2 vs. SR: 7.68±0.7]
P-selectin [AF: 25.86±11.89 vs. SR: 23.95±8.49]
Xu (without comorbidities) [27] PC, MPV PC [AF: 205±31 vs. SR: 209±41]
MPV [AF: 10.6±1.9 vs. SR: 8.7±0.8]
Xu (with comorbidities) [27] PC, MPV PC [AF: 206±42 vs. SR: 209±41]
MPV [AF: 11.7±2 vs. SR: 8.7±0.8]
Acet (PAF) [28] PC PC [AF: 248.9±59 vs. SR: 259.8±95.9]
Acet (persistent and permanent) [28] PC PC [AF: 268±98 vs. SR: 259.8±95.9]
Arik (with INR 2–3) [29] PC, MPV, PDW PC [AF: 259±54.3 vs. SR: 255.75±41.5]
MPV [AF: 7.56±0.63 vs. SR: 7.63±0.68]
PDW [AF: 17.05±0.86 vs. SR: 17.52±0.71]
Arik (with abnormal INR) [29] PC, MPV, PDW PC [AF: 238.75±41.16 vs. SR: 255.75±41.5]
MPV [AF: 8.26±0.63 vs. SR: 7.63±0.68]
PDW [AF: 17.50±1.13 vs. SR: 17.52±0.71]
Distelmaier [30] PC PC [AF: 202±14.75 vs. SR: 215±14.16]
Gungor [31] PC, MPV PC [AF: 249.4±59.4 vs. SR: 253.4±61.1]
MPV [AF: 8.99±0.65 vs. SR: 9.14±0.98]
Sonmez [32] PC PC [AF: 231±60 vs. SR: 247±67]
Ulu [33] PC, MPV PC [AF: 236.4±63.9 vs. SR: 233.3±86.2]
MPV [AF: 11.47±0.93 vs. SR: 10.37±1.07]
Turgut [34] PC, MPV PC [AF: 274±82 vs. SR: 253±83]
MPV [AF: 9±0.2 vs. SR: 8.4±0.2]
Jaremo (healthy control) [35] PC PC [AF: 241±64 vs. SR: 260±78]
jaremo (disease control) [35] PC, P-selectin PC [AF: 241±64 vs. SR: 265±84]
P-selectin [AF: 102±53 vs. 74±44]
Berge [36] PC, P-selectin PC [AF: 230±7.5 vs. SR: 261.25±4.16]
P-selectin [AF: 31.2±3.72 vs. 31.52±2.05]
Ertas (without stroke) [37] PC PC [AF: 232±55 vs. 258±54]
Ertas (with stroke) [37] PC PC [AF: 240±82 vs. 258±54]
Sahin [38] MPV MPV [AF: 8.31±1.12 vs. SR: 7.99±1.39]
Tekin [39] PC, MPV PC [AF: 242±90 vs. SR: 243±67]
MPV [AF: 9.49±1.08 vs. SR: 9.09±1.13]
Turfan (without CVA) [40] PC, MPV PC [AF: 264±94 vs. SR: 213±72]
MPV [AF: 9.1±1 vs. SR: 8.6±1.3]
Turfan (with CVA) [40] PC, MPV PC [AF: 245±73 vs. SR: 213±72]
MPV [AF: 9.7±0.9 vs. SR: 8.6±1.3]
Feng [41] PC, MPV PC [AF: 213.3±82.5 vs. SR: 217.6±81.7]
MPV [AF: 9.95±1.32 vs. SR: 9.02±1.16]
Acevedo [42] P-selectin P-selectin [AF: 219±141 vs. 145±29]
Hayashi [43] PC PC [AF: 260±83 vs. 190±77]
Hayashi [43] PC PC [AF: 200±14 vs. 258±54]
Fu [44] PC, P-selectin PC [AF: 210±55.5 vs. SR: 221.1±51.1]
P-selectin [AF: 33.4±7.4 vs. 29.2±6.5]
Hou (disease control) [45] P-selectin P-selectin [AF: 32±5 vs. 32±4.9]
Hou (healthy control) [45] P-selectin P-selectin [AF: 32±5 vs. 33±7]
Alberti [46] PC PC [AF: 185.6±10 vs. 243.3±9.5]
Choudhury (disease control) [47] PC, MPV, P-selectin PC [AF: 259.9±66.3 vs. SR: 261.1±63.4]
MPV [AF: 7.6±1.4 vs. SR: 7.8±0.9]
P-selectin [AF: 61±7 vs. SR: 55.25±6.8]
Choudhury (healthy control) [47] PC, MPV, P-selectin PC [AF: 259.9±66.3 vs. SR: 266.9±56.1]
MPV [AF: 7.6±1.4 vs. SR: 7.4±0.97]
P-selectin [AF: 61±7 vs. SR: 40.75±5.25]
Colkesen [48] PC, MPV PC [AF: 242±73 vs. SR: 236±53]
MPV [AF: 10±2 vs. SR: 8.3±1.5]
Blann [49] P-selectin P-selectin [AF: 72.5±7.5 vs. SR: 46.25±6.25]
Topaloglu (disease control) [50] PF4 PF4 [AF: 115.39±7.56 vs. SR: 97.96±25.51]
Topaloglu (healthy control) [50] PF4 PF4 [AF: 115.39±7.56 vs. SR: 6.95±2.49]
Yip [51] PC PC [AF: 204±57 vs. SR: 209±49]
Heeringa [52] P-selectin P-selectin [AF: 31.3±10.1 vs. SR: 31.8±13.1]
Inoue (with comorbidities) [53] BTG, PF4 BTG [AF: 74.5±3.3 vs. SR: 43.9±3.3]
PF4 [AF: 21.6±1.5 vs. SR: 14.7±1.9]
Inoue (lone AF) [53] BTG, PF4 BTG [AF: 77±4.9 vs. SR: 46.3±5.5]
PF4 [AF: 23.1±2.1 vs. SR: 17.7±3.1]
Conway [54] P-selectin P-selectin [AF: 53.5±4 vs. SR: 50.75±6.75]
Conway [55] P-selectin P-selectin [AF: 54.75±5.75 vs. SR: 51.25±6.25]
Atalar (paroxysmal AF) [56] BTG, PF4 BTG [AF: 175.35±11.55 vs. SR: 161.7±8.4]
PF4 [AF: 72.45±11.55 vs. SR: 56.7±12.6]
Atalar (permanent AF) [56] BTG, PF4 BTG [AF: 191.1±14.7 vs. SR: 161.7±8.4]
PF4 [AF: 81.9±12.6 vs. SR: 56.7±12.6]
Kamath [57] PC, BTG, P-selectin PC [AF: 280±81 vs. SR: 253±51]
BTG [AF: 90.03±13.3 vs. SR: 71.98±10.5]
P-selectin [AF: 38±6 vs. SR: 36±11]
Kamath [57] PC, BTG, P-selectin PC [AF: 264±75 vs. SR: 253±51]
BTG [AF: 92.13±11.02 vs. SR: 71.98±10.5]
P-selectin [AF: 39±10 vs. SR: 36±11]
Kamath [58] PC, BTG, P-selectin PC [AF: 279±73 vs. SR: 252±53]
BTG [AF: 89.51±13.9 vs. SR: 66.93±8.13]
P-selectin [AF: 38±11 vs. SR: 34±10]
Kamath [58] PC, BTG, P-selectin PC [AF: 266±76 vs. SR: 252±53]
BTG [AF: 93.97±10.5 vs. SR: 66.93±8.13]
P-selectin [AF: 39±10 vs. SR: 34±10]
Kamath [59] PC, BTG PC [AF: 253±77 vs. SR: 261±62]
BTG [AF: 92.4±11.9 vs. SR: 69.3±10.5]
Kamath [60] PC, BTG, P-selectin PC [AF: 253±67 vs. SR: 270±49]
BTG [AF: 88.2±16.8 vs. SR: 67.72±11.5]
P-selectin [AF: 37±10 vs. SR: 36±9]
Li-Saw-Hee [61] P-selectin P-selectin [AF: 37±3 vs. SR: 36±4]
Li-Saw-Hee [61] P-selectin P-selectin [AF: 50.5±6.5 vs. SR: 36±4]
Li-Saw-Hee [61] P-selectin P-selectin [AF: 216.5±30.5 vs. SR: 36±4]
Mondillo [62] BTG, PF4 BTG [AF: 80.11±31.29 vs. SR: 40.95±8.75]
PF4 [AF: 6.82±1.68 vs. SR: 4.02±0.84]
Li-Saw-Hee [63] P-selectin P-selectin [AF: 205.25±47.75 vs. SR: 125.75±17.25]
Li-Saw-Hee [64] BTG, P-selectin BTG [AF: 34±6 vs. SR: 33±11]
P-selectin [AF: 73±33 vs. SR: 144±78]
Minamino [65] BTG BTG [AF: 84±19.45 vs. SR: 43.22±8.32]
Minamino [66] BTG BTG [AF: 87.65±47.4 vs. SR: 55.72±22.02]
Kahn [67] PC PC [AF: 230±98 vs. SR: 233±49]
Sohara [68] BTG, PF4 BTG [AF: 38±27.3 vs. SR: 22.8±7.85]
PF4 [AF: 16.4±18.2 vs. SR: 3.37±2.26]
Lip GY [69] PC, BTG PC [AF: 242±67 vs. SR: 224±63]
BTG [AF: 187±30 vs. SR: 99.75±25.25]
Nagao [70] BTG, PF4 BTG [AF: 43.8±23.2 vs. SR: 31.9±12.7]
PF4 [AF: 9.06±7.04 vs. SR: 5.68±3.53]
Sohara [71] BTG, PF4 BTG [AF: 31.1±29.9 vs. SR: 22.8±7.8]
PF4 [AF: 9.8±15.9 vs. SR: 3.4±2.2]
Gustafsson (with stroke) [72] PC, BTG, PF4 PC [AF: 179±18.5 vs. SR: 238.75±15.75]
BTG [AF: 40.1±5.8 vs. SR: 25.47±2.62]
PF4 [AF: 5.77±2.02 vs. SR: 2.55±0.45]
Gustafsson (without stroke) [72] PC, BTG, PF4 PC [AF: 172.25±8.75 vs. SR: 238.75±15.75]
BTG [AF: 36.25±2.75 vs. SR: 25.47±2.62]
PF4 [AF: 3.77±1.07 vs. SR: 2.55±0.45]
Yamauchi (without valvular heart disease) [73] BTG, PF4 BTG [AF: 49.4±35.8 vs. SR: 31.2±14]
PF4 [AF: 18.6±27.2 vs. SR: 11.6±8.2]
Yamauchi (with valvular heart disease) [73] BTG, PF4 BTG [AF: 64.1±52.8 vs. SR: 31.2±14]
PF4 [AF: 34.1±45.5 vs. SR: 11.6±8.2]
Figure 1.

Figure 1

Forest plot of weighted mean difference (WMD) for association between platelet count and occurrence of AF.

MPV

A total of 3,609 cases were included from 19 studies, of which 1,646 were allocated to the AF group and 1,963 to the SR. Patient populations of the included studies ranged from 57 to 621 patients. Mean level of MPV was 9.22 FL in the AF group and 8.40 FL in the SR group (Tables 1, 2). Pooled analysis revealed that MPV level was significantly higher in patients with AF compared to those with SR with WMD of 0.61 (95% CI: 0.56 to 0.65; p<0.001, Figure 2) using a random effect model. There was a significant heterogeneity among the studies (I2=94.3%; heterogeneity p<0.001).

Figure 2.

Figure 2

Forest plot of weighted mean difference (WMD) for association between level of mean platelet volume and occurrence of AF.

PDW

A total of 1,117 cases were included from three studies, of which 290 were allocated to the AF group and 827 to the SR group. Using a random effect model, pooled analysis revealed that PDW was statistically lower in the AF group than in the SR group with WMD of −0.22 (95% CI: −0.37 to −0.08; p=0.002, Supplementary Figure 1). There was significant heterogeneity among the studies (I2=87.4%; heterogeneity p<0.001)

BTG

A total of 1,781 patients were included from 22 studies, of whom 1,043 were allocated to the AF group and 738 to the SR. Mean level of BTG was 83.62 ng/mL in patients with AF and 58.72 ng/mL in those with SR (Tables 1, 2). Pooled analysis revealed that the mean level of BTG was significantly higher in AF patients compared to those with SR with WMD of 24.69 (95% CI: 24.07 to 25.32; p<0.001, Figure 3) with considerable heterogeneity among the studies (I2=97.6%; heterogeneity p<0.001).

Figure 3.

Figure 3

Forest plot of weighted mean difference (WMD) for association between level of beta thromboglobulin and occurrence of AF.

PF4

A total of 1,220 cases were selected from 16 studies, of which 651 were allocated to the AF group and 569 to the SR group. Mean levels of PF4 were 41.43 ng/mL in the AF group and 24.78 ng/mL in the SR group (Tables 1, 2). Pooled analysis showed that the level of PF4 was remarkably higher in patients suffering AF compared to controls with WMD of 4.59 ng/mL (95% CI: 4.33 to 4.86; p<0.001, Figure 4) using a random effect model. There was significant heterogeneity among the studies (I2=99.6%; heterogeneity p<0.001).

Figure 4.

Figure 4

Forest plot of weighted mean difference (WMD) for association between level of platelet factor 4 and occurrence of AF.

P-selectin

A total of 2,725 cases were included from 24 studies, of which 1,469 were allocated to the AF group and 1,256 to the SR. Mean level of P-selectin was 69.52 ng/mL in the AF group and 51.51 ng/mL in the SR group (Tables 1, 2). Using a random effect model, pooled analysis showed that the level of P-selectin was significantly higher in the AF group compared to the SR group with WMD of 4.90 ng/mL (95% CI: 4.36 to 5.45; p<0.001, Figure 5). Significant heterogeneity was observed among the studies (I2=98.6%; heterogeneity p<0.001).

Figure 5.

Figure 5

Forest plot of weighted mean difference (WMD) for association between level of P-selectin and occurrence of AF.

Association of platelet characteristics with the incidence of stroke in patients with AF

Five studies examined the association of platelet markers with stroke (Table 3). Platelet count and MPV were investigated in at least two studies which were included in the meta-analysis (Table 3). According to pooled assessment analysis, the level of MPV (number of studies=2, WMD of 0.97, 95% CI: 0.70 to 1.24; p<0.001 and I2=95%%; heterogeneity p<0.001, Supplementary Figure 2) was significantly higher in patients with stoke compared to those without major cerebrovascular events. Pooled analysis showed that platelet count (number of studies=4, WMD of 7.23, 95% CI: −4.96 to 19.42; p=0.245 and I2=35.2%%; heterogeneity p=0.21, Supplementary Figure 3) was not significantly different in patients with or without stroke.

Table 3.

Included studies about relationship between platelet characteristics with clinical adverse events in patients with AF.

First Author Country and year Study design Number Mean age AC in patients with adverse events AC in patients without adverse events Platelet markers
Bayar [74] Turkey-2015 Case-control 90 65.3 MPV [AF: 11.1±1.3 vs. SR: 9.1±1]
Ertas [37] Turkey-2013 Case-control 126 70 58 51 PC [AF: 240±82 vs. SR: 232±55]
Turfan [40] Turkey-2013 Cohort 140 66 44.3 41.3 PC [AF: 245±73 vs. SR: 264±94]
MPV [AF: 9.7±0.9 vs. SR: 9.1±1]
Kahn [67] Canada-1997 Case-control 75 72.7 100% 100% PC [AF: 253±82 vs. SR: 230±98]
Gustafsson [72] Sweden-1990 Case-control 40 70 PC [AF: 188±37 vs. SR: 148±8.7]
BTG [AF: 40.1±5.8 vs. SR: 36.25±2.75]
PF4 [AF: 5.77±2.05 vs. SR: 3.77±1.07]

Publication bias and subgroup analysis

Begg tests suggested that there might be publication bias for studies examining the levels of MPV and BTG (Supplementary Figures 48). Details of subgroup analysis are reported in Supplementary Tables 2 and 3.

Discussion

The incidence of cardiovascular diseases has been dramatically increasing in developed and developing countries in recent decades [1]. AF represents one of the most critical and prevalent cardiac arrhythmias precipitating morbidity and mortality in short- and long-term periods of time and adversely affecting patient’s quality of life [1,2]. Despite the wide range of investigations on diagnosis and treatment of AF conducted and published in recent years, the pathophysiology of this multifactorial disease is not completely understood [2]. Due to a number of complex mechanisms that are involved in the development of AF the current controversies regarding diagnosis and treatment of AF seem to be justifiable [2,3]. Among other things the mechanism of oxidation and release of free radical oxygen has been defined as one of the main precipitating mechanisms in development of AF [2]. Also, the Virchow’s triad, which plays a critical role in predicting AF and includes arterial stasis, vessel wall abnormalities, and coagulant alternations in the hemostatic balance, indicates that prothrombotic state is another important pathophysiological mechanism of AF. However, the exact mechanism involving prothrombotic state in AF is ambiguous [6,7]. Nevertheless, it is known that platelets are involved in both thrombosis and inflammation becoming a key factor in pathogenesis of cardiovascular diseases [6]. In the present study, we attempted conducting a meticulous and multilateral investigation on platelets cellular and functional characteristics in patients with AF compared to patients with sinus rhythm. Our findings revealed that from statistical and clinical points of view, AF was significantly associated with reduced platelet count. However, an undeniable fact is that a considerable heterogeneity among the studies was present in this analysis. A subgroup analysis revealed that the type of AF (chronic or non-chronic) could probably be a factor of heterogeneity: there was an inverse relationship between the occurrence of AF and platelet count in non-chronic AF, while such an association was not observed in patients with chronic AF. On the other hand, reduced platelet count was not observed in paroxysmal and permanent AF, while this relationship only existed in persistent AF. In general, it can be concluded that the type of AF is one of the heterogeneity factors in platelet count analysis. Barura et al. reported that exposure to cigarette smoking could change the hemostatic process through multiple mechanisms including alteration of the function of endothelial cells, platelets, and coagulation factors [10]. However, our subgroup analysis demonstrated that platelet count was not significantly reduced in cigarette smokers with AF compared to smokers with SR, while lower platelet count was observed in non-smokers with AF compared to smokers with SR. This can be explained by the fact that cigarette smoking can disturb the actual platelet count via increasing aggregation and adhesion of the platelets [10]. In fact, we believe that the occurrence of AF is strongly associated with reduced platelet count while the type of AF, cigarette smoking, and the geographical area of the studies represent factors of heterogeneity.

MPV is also an important biomarker of platelet activity. Large platelets secrete many critical mediators of coagulation, inflammation, thrombosis, and atherosclerosis. A close relationship has been found between MPV and cardiovascular risk factors, such as diabetes mellitus, hypertension, and hypercholesterolemia [11,12]. The results of this study revealed that the average MPV was significantly higher in AF patients than in SR patients, thus implying the direct relationship between MPV and the risk of AF. According to our subgroup analysis, study sample size and diabetes mellitus could probably result in heterogeneity. Our findings also showed that levels of the platelet markers were notably higher in both chronic and non-chronic AF patients compared to the SR group. Interestingly, Sansanayudh et al. recently found an association between elevated MPV and CAD. Patients with CAD and slow coronary blood flow showed larger MPV compared to controls [13]. The mean difference in MPV in patients with an acute coronary event was higher than those with stable coronary disease [13]. They suggested that MPV might be used for risk stratification or to add diagnostic accuracy to the traditional risk stratification markers in patients with CAD [13].

PWD is a platelet biomarker and predictive factor in cardiovascular diseases. Varastehravan et al. indicated that PDW in patients with ST-segment elevation myocardial infarction could be used for prediction of ST-segment resolution and clinical outcomes [14]. According to the results of the present study, PDW was greater in patients with AF than those with SR and thus had a direct relationship to the risk of AF. However, due to the limited number of studies on PDW no subgroup analysis could be performed to examine heterogeneity factors. Nevertheless, our evidence shows that AF might be associated with both larger volume of platelets as well as distribution width.

Platelet activation is demonstrated by the release of platelet granules and their components into the circulation. BTG and platelet factor 4 (PF4) represent specific platelet proteins of alpha-granules, which can be secreted into surrounding medium during cell activation [15,16]. Based on the results of this study, increased levels of BTG might be also directly related to the risk of AF. Our subgroup analysis revealed the type of AF (chronic or non-chronic), history of CS, and gender as factors of heterogeneity. The present study also indicated that the level of PF4 was remarkably higher in AF patients compared to those with SR, while the level of BTG and PF4 were significantly increased compared to SR patients in both chronic and non-chronic AF as well as paroxysmal and permanent AF. Therefore, it can be suggested that platelet activity and release of specific proteins from their granules may also play a vital role in pathophysiology of AF.

P-selectin, an integral membrane glycoprotein of platelets and endothelial cells, is involved in the onset of atherosclerosis and cardiovascular diseases [17]. P-selectin functions as a cell adhesion molecule (CAM) on the surfaces of activated endothelial cells, which line the inner surface of blood vessels, and activated platelets. In unactivated endothelial cells, it is stored in α-granules [17]. The present study revealed that P-selectin marker was notably higher in AF patients compared to SR group. The subgroup analysis proposed the type of studies and the type of AF as factors of heterogeneity. In brief, cohort studies did not show any relationship between the level of P-selectin and occurrence of AF, whereas case-control studies strongly confirmed this relationship. It is necessary to mention that the number of cohort studies was remarkably less than case-control studies. Increased level of P-selectin was observed in both chronic and non-chronic AF in our meta-analysis. On the other hand, this association was found in persistent and permanent AF but not in paroxysmal AF. Overall, taking into account the evidence from the present study, platelet count and other biomarkers may considerably influence the development of AF underlying the role of platelets in pathophysiology of AF as well as the predictive function of platelet factors.

The results of our study showed that the level of MPV was obviously higher in AF patients with stroke as compared to AF patients without cerebrovascular events. However, we found no association between platelet count and the occurrence of stroke.

There is a hypothesis that cardiac risk factors might also affect the occurrence of AF. Feng et al. proposed a hypothesis that the relationship between hemostatic markers and AF became insignificant after stratifying based on cardiovascular disease status [18]. Our results showed that cardiac risk factors including diabetes, hypertension, and history of MI were not recognized as heterogeneity factors. However, it should be mentioned that an important cardiac risk factor affecting our results was cigarette smoking.

Lip et al. argued that using anticoagulants could reduce the level of hemostatic factors in AF patients, and consequently, differences in receiving anticoagulants in various studies could be considered as a factor of heterogeneity [19]. According to the results of our subgroup analyses of platelet count and level of MPV and PF4, differences in using anticoagulants could possibly play a considerable role in the occurrence of heterogeneity. It should also be noted that in our meta-analysis on non-experimental studies more heterogeneity was found which may be explained by the following reasons: 1) biases are less controlled, 2) more confounding factors, and 3) differences in defining outcomes. As a result, performing analysis on non-experimental studies, finding associations, effect size, and estimating heterogeneity as well as appropriate method for finding the factors of heterogeneity should be the aim of such meta-analyses.

Conclusions

In summary, considering the results of this study, we strongly state that platelets play a critical and precipitating role in the occurrence of AF as the volume and distribution width of platelets as well as the factors of platelet activity appeared to be significantly higher in AF patients compared to SR patients. On the other hand, AF was associated with lower platelet count. Therefore, emphasizing the potential predictive role of platelet factors in the occurrence of AF, we strongly recommend adding cellular and functional characteristics of platelets to the diagnostic criteria of AF in the future.

Supplementary Files

Supplementary Figure 1.

Forest plot of weighted mean difference (WMD) for association between level of platelet distribution width and occurrence of AF.

Supplementary Figure 2.

Forest plot of weighted mean difference (WMD) for association between level of mean platelet volume and occurrence of stroke.

Supplementary Figure 3.

Forest plot of weighted mean difference (WMD) for association between level of platelet count and occurrence of stroke.

Supplementary Figure 4.

Funnel plot for publication bias of studies investigating of platelet count.

Supplementary Figure 5.

Funnel plot for publication bias of studies investigating of mean platelet volume.

Supplementary Figure 6.

Funnel plot for publication bias of studies investigating of beta thromboglobulin.

Supplementary Figure 7.

Funnel plot for publication bias of studies investigating of platelet factor-4.

Supplementary Figure 8.

Funnel plot for publication bias of studies investigating of P-selectin.

Supplementary Table 1.

Included and excluded studies.

Clinical outcomes and biomarkers Studies were identified and screened [n] Studies were excluded according to title, abstract or full text [n] Studies were included [n]
Platelet count 285 252 33 approved articles with totally 45 enrolled data for meta-analysis
Mean platelet volume 140 125 15 approved articles with totally 19 enrolled data for meta-analysis
Platelet distribution width 11 9 2 approved articles with totally 3 enrolled data for meta-analysis
Beta thromboglobulin 66 51 15 approved articles with totally 22 enrolled data for meta-analysis
Platelet factor 4 54 44 10 approved articles with totally 16 enrolled data for meta-analysis
P-selectin 115 97 18 approved articles with totally 24 enrolled data for meta-analysis

Supplementary Table 2.

Extra details of characteristics of each study for exploration of heterogeneity factors.

First Author Geographic Area Total N Total age Total male Total DM Total HTN Total MI Total Diuretic Total ACEI Total. Statin Total BB AC-code Chronic or not CS
Karatas [20] European 621 61.05 72.5 23 45.5 ND ND ND 0 ND 2 Non-chronic 64
Drabik [21] European 97 60.1 64.95 20 48.85 17.3 ND 52.25 53.15 60.6 4 Non-chronic 22.85
Drabik [21] European 91 60 55.15 16.4 46.05 26.2 ND 54.05 47.45 57.25 4 Non-chronic 20
Idriss [22] Africa 41 31.75 49.25 0 0 ND ND ND ND 11.9 4 ND 34.5
Akdag [23] European 148 64.05 60 16.5 22 ND ND ND ND ND 6 ND 23.5
Akyuz [24] European 90 62.25 72.25 29 42.5 ND 14.5 20.75 32.5 23 4 ND 34.25
Chavaria [25] North American 290 65.65 74.5 29.05 65.65 4.5 ND ND ND ND 5 ND 55.05
Erdogan [26] European 67 69.55 49.25 10 65 ND 18 53.5 10 43.3 3 chronic 6
Xu (without comorbidities) [27] Asian 115 66.05 50.45 37.4 53.1 ND ND 42.6 29.55 43.55 4 chronic 38.25
Xu (with comorbidities) [27] Asian 115 67.975 51.3 36.5 57.5 ND ND 40.8 26.05 40.95 4 chronic 31.25
Acet (PAF) [28] European 134 62.05 44 16.5 18 ND ND ND ND ND 5 Non-chronic 21.5
Acet (persistent and permanent) [28] European 126 62.85 43.5 21.5 24 ND ND ND ND ND 5 ND 28.5
Arik (with INR 2–3) [29] European 248 69.65 40.7 6.05 68.95 ND 27 59.25 ND 59.7 5 chronic 13.7
Arik (with abnormal INR) [29] European 248 69.45 37.9 6.85 65.35 ND 24.2 55.65 ND 61.3 5 chronic 12.1
Distelmaier [30] North American 198 73.5 61 24 60.5 25 ND ND ND ND 5 Non-chronic ND
Gungor [31] European 177 47.2 57.8 3.3 14.75 ND ND ND ND 10.6 3 ND 23.15
Sonmez [32] European 85 70 36.95 10.6 63.25 ND 14.1 47.15 15.4 35.55 4 Non-chronic ND
Ulu [33] European 57 ND ND ND ND ND ND ND ND ND 5 ND ND
Turgut [34] European 162 63 52 100 65.5 ND 6.5 23.5 18 16.5 4 chronic 41.5
Jaremo (healthy control) [35] European 82 67.5 66.7 ND ND ND ND ND ND ND 4 ND 2.55
jaremo (disease control) [35] European 130 71.5 68.1 12.75 43.75 9.1 28.65 26.25 25.05 55.9 4 ND 9.45
Berge [36] European 189 75 71 8 48 ND 19 21 34.5 28 4 ND ND
Ertas (without stroke) [37] European 111 53.5 51 ND ND ND ND ND ND ND 6 ND 2
Ertas (with stroke) [37] European 63 54.5 47 ND ND ND ND ND ND ND 6 ND 5
Sahin [38] European 144 64.9 49.75 100 66.5 ND ND ND ND ND 5 Non-chronic 44.5
Tekin [39] European 219 73.5 35.5 13.5 68.5 ND ND ND ND ND 5 chronic 19
Turfan (without CVA) [40] European 135 59.5 54.55 ND ND ND ND ND ND ND 4 ND 55.5
Turfan (with CVA) [40] European 121 62.5 52.05 ND ND ND ND ND ND ND 4 ND 50.6
Feng [41] Asian 374 65.8 61.75 17.65 53.2 ND 23 41.95 44.85 42.5 4 ND 25.65
Acevedo [42] South American 150 ND ND ND ND ND ND ND ND ND 1 Non-chronic ND
Hayashi [43] Asian 27 57.95 92.5 14.5 48.5 ND ND 40.5 26 ND 2 Non-chronic ND
Hayashi [43] Asian 27 61.45 92.5 11.05 52 ND ND 37 26 ND 2 chronic ND
Fu [44] Asian 169 54.45 63.5 ND ND ND ND ND 12.9 6.1 4 ND 42.45
Hou (disease control) [45] Asian 52 64.85 57.6 ND ND ND ND 40.3 ND 11.45 4 Non-chronic 26.9
Hou (healthy control) [45] Asian 52 65.3 57.6 ND ND ND ND 21.15 ND 7.65 4 Non-chronic 26.9
Alberti [46] European 51 64.45 58.8 ND ND ND ND ND ND ND 1 Non-chronic ND
Choudhury (disease control) [47] European 192 63.31 74 10.5 66.4 ND 33.15 55.7 46.5 43.7 4 ND ND
Choudhury (healthy control) [47] European 186 62.305 72 4.1 31.8 ND 17.75 26.85 14.45 21.9 4 ND ND
Colkesen [48] European 190 54 38 18.5 41.5 ND ND ND 28 ND 4 Non-chronic ND
Blann [49] European 82 64.5 62.75 ND 27 ND 16.5 19 ND 18.5 3 ND 12.6
Topaloglu (disease control) [50] European 46 34.5 ND ND ND ND ND ND ND ND 5 ND ND
Topaloglu (healthy control) [50] European 38 36 ND ND ND ND ND ND ND ND 5 ND ND
Yip [51] Asian 82 65.75 63.05 ND ND ND ND ND ND ND 3 chronic ND
Heeringa [52] European 486 77.5 51 17.5 25 22.5 31.65 ND ND 16.55 5 ND 20.9
Inoue (with comorbidities) [53] Asian 251 ND ND ND ND ND ND ND ND ND 5 ND ND
Inoue (lone AF) [53] Asian 106 ND ND ND ND ND ND ND ND ND 5 ND ND
Conway [54] European 147 68 62 7.5 26.5 ND ND ND ND ND 3 chronic 16
Conway [55] European 74 67.5 70.23 12.95 37 1.85 ND ND ND ND 5 Non-chronic 16.2
Atalar (paroxysmal AF) [56] European 37 46 61.8 0 35.9 ND ND ND ND 17.845 1 Non-chronic ND
Atalar (permanent AF) [56] European 47 49 63.8 0 35.9 ND ND ND ND 17.845 1 chronic ND
Kamath [57] European 62 63.5 51.6 ND ND ND ND ND ND ND 1 Non-chronic ND
Kamath [57] European 124 66 52.65 ND ND ND ND ND ND ND 1 chronic ND
Kamath [58] European 58 63 48.235 6.85 24.1 ND ND ND ND ND 4 Non-chronic 5.15
Kamath [58] European 116 65 52.25 5.15 30.45 ND ND ND ND ND 4 chronic 5.15
Kamath [59] European 143 70 63.2 5.35 29.565 ND ND ND ND ND 1 ND ND
Kamath [60] European 57 ND ND ND ND ND ND ND ND ND 1 ND ND
Li-Saw-Hee [61] European 43 64 77.3 2.15 10.85 ND ND ND ND ND 3 Non-chronic 13.65
Li-Saw-Hee [61] European 43 64 77.3 2.15 13 ND ND ND ND ND 3 Non-chronic 11.52
Li-Saw-Hee [61] European 43 65 77.3 6.52 23.9 ND ND ND ND ND 3 chronic 11.52
Mondillo [62] European 80 66.95 82.85 ND ND ND ND ND ND ND 3 chronic 33.75
Li-Saw-Hee [63] European 112 67 77.5 3.85 12.5 ND ND ND ND ND 1 ND 13.3
Li-Saw-Hee [64] European 50 59 20 ND ND ND ND ND ND ND 5 chronic 20
Minamino [65] European 56 64 71.4 21.5 25 ND ND ND ND 19.5 4 chronic 37.5
Minamino [66] Asian 90 63 73.3 12.5 23.5 ND ND ND ND 14.5 5 chronic 39
Kahn [67] North American 81 ND ND ND ND ND ND ND ND ND 1 ND ND
Sohara [68] Asian 30 59.05 ND ND ND ND ND ND ND ND 1 Non-chronic ND
Lip GY [69] European 77 ND ND ND ND ND ND ND ND ND 1 chronic ND
Nagao [70] Asian 36 79.95 47.05 ND ND ND ND ND ND ND 1 ND ND
Sohara [71] Asian 28 ND ND ND ND ND ND ND ND ND 1 Non-chronic ND
Gustafsson (with stroke) [72] European 60 77 ND ND ND ND ND ND ND ND 1 ND ND
Gustafsson (without stroke) [72] European 60 77 ND ND ND ND ND ND ND ND 1 ND ND
Yamauchi (without valvular heart disease) [73] Asian 130 41.5 ND ND ND ND ND ND ND ND 1 ND ND
Yamauchi (with valvular heart disease) [73] Asian 83 45.5 ND ND ND ND ND ND ND ND 1 ND ND

Supplementary Table 3.

Subgroup-analysis

Subgroup Studies (N) WMD (95% CI) I-squared and Heterogeneity-p-value and Effect-p-value respectively
Platelet count

Year of publication
 >2000 41 −24.04 (−25.52 to −22.56) 91.1% and 0.001 and 0.001
 ≤2000 4 −60.67 (−65.22 to −55.62) 92.8% and 0.001 and 0.001

Geographic area
 Asian 7 13.8% and 0.324 and 0.284
 European 35 −3.88 (−10.98 to 3.21) 94% and 0.001 and 0.001
 Africa - −30.05 (−31.59 to −28.50)
 North American 3 0.0% and 0.401 and 0.001
 South American - −12.23 (−16.39 to −8.08)
 Australia -

Design of study
 Cohort 8 −29.32 (−31.25 to −27.40) 91.6% and 0.001 and 0.001
 Case-control 37 −24.10 (−26.20 to −22.01) 93.8% and 0.001 and 0.001

Number of population
 >300 2 −6.33 (−19.68 to 7.02) 0.0% and 0.689 and 0.353
 ≤300 43 −27.16 (−28.59 to −25.74) 93.7% and 0.001 and 0.001

Mean Age
 >60 years 34 −27.90 (−29.34 to −26.46) 94.5% and 0.001 and 0.001
 ≤60 years 7 −0.76 (−9.25 to 7.12) 76.7% and 0.001 and 0.860

Male
 >70% 8 −29.82 (−31.76 to −27.88) 85.8% and 0.001 and 0.001
 ≤70% 31 −16.15 (−18.44 to −13.86) 90.6% and 0.001 and 0.001

Diabetes mellitus
 >30% 1 21.00 (−4.40 to 46.40)
 ≤30% 28 −22.68 (−24.24 to −21.12) 88.3% and 0.001 and 0.001

Hypertension
 >70%
 ≤70% 29 −22.52 (−24.07 to −20.96) 88.4% and 0.001 and 0.001

History of MI
 >20% 2 −11.74 (−15.35 to −8.13) 9.7% and 0.293 and 0.001
 ≤20% 3 −15.44 (−22.10 to −8.77) 31.1% and 0.234 and 0.001

Medication: Diuretic
 >70%
 ≤70% 11 −28.43 (−30.31 to −26.56) 88.1% and 0.001 and 0.001

Medication: ACEI
 >70%
 ≤70% 17 −25.60 (−27.33 to −23.88) 89.6% and 0.001 and 0.001

Medication: Statin
 >70%
 ≤70% 18 −25.90 (−27.64 to −24.15) 88.4% and 0.001 and 0.001

Medication: Beta-Blocker
 >70%
 ≤70% 17 −25.40 (−27.11 to −23.68) 89.3% and 0.001 and 0.001

Anti-coagulant status codes
 1 9 −54.79 (−58.44 to −51.15) 93.4% and 0.001 and 0.001
 2 3 1.69 (−17.11 to 20.53) 67.3% and 0.047 and 0.860
 3 3 −3.15 (−17.55 to 11.23) 0.0% and 0.890 and 0.667
 4 19 −25.27 (−27.00 to −23.53) 90.9% and 0.001 and 0.001
 5 8 −10.84 (−14.41 to 7.24) 38.3% and 0.124 and 0.001
 6 3 −6.34 (−21.47 to 8.77) 70.8% and 0.033 and 0.411

AF
 Chronic 12 −2.15 (−7.34 to 3.02) 35.6% and 0.106 and 0.414
 Non-chronic 11 −21.73 (−24.45 to −19.01) 95.5% and 0.001 and 0.001

Type of AF
 Paroxysmal 5 −5.29 (−11.24 to 0.64) 67.8% and 0.015 and 0.081
 Persistent 3 −41.86 (−46.34 to −37.38) 97.4% and 0.001 and 0.001
 Permanent 5 −4.55 (−11.58 to 2.46) 64.6% and 0.023 and 0.204

Cigarette smoking
 >30% 9 2.31 (−4.14 to 8.77) 67.3% and 0.002 and 0.482
 ≤30% 17 −9.11 (−12.70 to −5.52) 46.6% and 0.018 and 0.001

Mean platelet volume

Year of publication
 >2000 All of studies: after 2000
 ≤2000

Geographic area
 Asian 3 1.37 (1.16 to 1.58) 95.9% and 0.001 and 0.001
 European 16 0.56 (0.51 to 0.61) 93.1% and 0.001 and 0.001
 Africa
 North American
 South American
 Australia

Design of study
 Cohort 4 1.37 (1.14 to 1.60) 94.7% and 0.001 and 0.001
 Case-control 15 0.57 (0.52 to 0.62) 93.6% and 0.001 and 0.001

Number of population
 >300 2 0.90 (0.67 to 1.13) 0.0% and 0.666 and 0.001
 ≤300 17 0.59 (0.54 to 0.64) 94.9% and 0.001 and 0.001

Mean Age
 >60 years 15 0.61 (0.56 to 0.66) 94.8% and 0.001 and 0.001
 ≤60 years 3 0.33 (0.13 to 0.54) 95.2% and 0.001 and 0.001

Male
 >70% 4 0.67 (0.50 to 0.83) 95.6% and 0.001 and 0.001
 ≤70% 14 0.59 (0.54 to 0.64) 94.7% and 0.001 and 0.001

Diabetes mellitus
 >30% 2 0.59 (0.53 to 0.65) 42.3% and 0.188 and 0.001
 ≤30% 14 0.60 (0.52 to 0.67) 95.8% and 0.001 and 0.001

Hypertension
 >70%
 ≤70% 16 0.59 (0.55 to 0.64) 95.1% and 0.001 and 0.001

History of MI Studies have not data about history of myocardial infarction

Medication: Diuretic
 >70%
 ≤70% 8 0.57 (0.52 to 0.62) 95.5% and 0.001 and 0.001

Medication: ACEI
 >70%
 ≤70% 10 0.60 (0.55 to 0.65) 96.4% and 0.001 and 0.001

Medication: Statin
 >70%
 ≤70% 10 0.66 (0.61 to 0.72) 95.1% and 0.001 and 0.001

Medication: Beta-Blocker
 >70%
 ≤70% 11 0.58 (0.53 to 0.63) 96.4% and 0.001 and 0.001

Anti-coagulant status codes
 1
 2 1 0.80 (0.26 to 1.33)
 3 2 −0.07 (−0.31 to 0.16) 8.7% and 0.295 and 0.530
 4 10 0.67 (0.62 to 0.73) 95.1% and 0.001 and 0.001
 5 5 0.43 (0.33 to 0.53) 94.6% and 0.001 and 0.001
 6 1 1.10 (0.75 to 1.45)

AF
 Chronic 7 0.58 (0.53 to 0.63) 96.6% and 0.001 and 0.001
 Non-chronic 3 0.85 (0.58 to 1.13) 88.6% and 0.001 and 0.001

Type of AF
 Paroxysmal 1 1.70 (1.20. to 2.19)
 Persistent 1 0.32 (−0.09 to 0.73)
 Permanent 3 0.39 (0.28 to 0.51) 97.1% and 0.001 and 0.001

Cigarette smoking
 >30% 8 0.68 (0.62 to 0.74) 94.7% and 0.001 and 0.001
 ≤30% 7 0.45 (0.36 to 0.54) 94.8% and 0.001 and 0.001

BTG

Year of Publication
 >2000 11 29.31 (28.57 to 30.04) 88.6% and 0.001 and 0.001
 ≤2000 11 12.67 (11.49 to 13.85) 95.5% and 0.001 and 0.001

Geographic area
 Asian 8 30.31 (29.51 to 31.11) 77% and 0.001 and 0.001
 European 14 15.91 (14.92 to 16.91) 96.2% and 0.001 and 0.001
 Africa
 North American
 South American
 Australia

Design of study
 Cohort All of studies are “case-control”
 Case-control

Number of population
 >300 All of studies are “number less than 300 population”
 ≤300

Mean Age
 >60 years 11 15.79 (14.74 to 16.84) 94.2% and 0.001 and 0.001
 ≤60 years 6 13.01 (9.94 to 16.08) 90.1% and 0.001 and 0.001

Male
 >70% 3 39.01 (33.37 to 44.65) 0.0% and 0.600 and 0.001
 ≤70% 9 19.98 (18.28 to 21.68) 90.9% and 0.001 and 0.001

Diabetes mellitus
 >30%
 ≤30% 7 25.36 (23.30 to 27.42) 80.8% and 0.001 and 0.001

Hypertension
 >70%
 ≤70% 7 25.36 (23.30 to 27.42) 80.8% and 0.001 and 0.001

History of MI No Data

Medication: Diuretic No Data

Medication: ACEI
 >70% No Data
 ≤70%

Medication: Statin
 >70% No Data
 ≤70%

Medication: Beta-Blocker
 >70%
 ≤70% 4 27.17 (23.22 to 31.12) 89.1% and 0.001 and 0.001

Anti-coagulant status codes
 1 14 14.70 (13.63 to 15.78) 93.6% and 0.001 and 0.001
 2
 3 1 39.16 (29.56 to 48.75)
 4 3 27.83 (24.92 to 30.73) 85.5% and 0.001 and 0.001
 5 4 29.83 (29.03 to 30.63) 97.8% and 0.001 and 0.001
 6

AF
 Chronic 8 24.21 (22.11 to 26.30) 96.7% and 0.001 and 0.001
 Non-chronic 5 17.74 (14.40 to 21.08) 31.3% and 0.213 and 0.001

Type of AF
 Paroxysmal 4 17.60 (13.57 to 21.63) 48.3% and 0.121 and 0.001
 Persistent
 Permanent 4 25.90 (23.39 to 28.40) 80.5% and 0.002 and 0.001

Cigarette smoking
 >30% 3 39.01 (33.37 to 44.65) 0.0% and 0.600 and 0.001
 ≤30% 3 18.64 (16.00 to 21.27) 97.2% and 0.001 and 0.001

Platelet factor 4

Year of Publication
 >2000 9 6.38 (6.04 to 6.72) 99.8% and 0.001 and 0.001
 ≤2000 7 1.78 (1.36 to 2.20) 81.6% and 0.001 and 0.001

Geographic area
 Asian 7 6.75 (6.32 to 7.17) 51.5% and 0.054 and 0.001
 European 9 3.25 (2.91 to 3.59) 99.8% and 0.001 and 0.001
 Africa
 North American
 South American
 Australia

Design of study
 Cohort All of studies are “case-control”
 Case-control

Number of population
 >300 All of studies are “number less than 300 population”
 ≤300

Mean Age
 >60 years 6 2.27 (1.93 to 2.61) 94.6% and 0.001 and 0.001
 ≤60 years 7 58.31 (55.83 to 60.80) 99.6% and 0.001 and 0.001

Male
 >70% 1 2.80 (2.23 to 3.36)
 ≤70% 5 11.60 (9.55 to 13.66) 89.3% and 0.001 and 0.001

Diabetes mellitus
 >30%
 ≤30% 4 15.25 (12.79 to 17.72) 69.6% and 0.020 and 0.001

Hypertension
 >70%
 ≤70% 4 15.25 (12.79 to 17.72) 69.6% and 0.020 and 0.001

History of MI
 >20% 1 15.55 (11.43 to 19.67)
 ≤20% 1 12.17 (8.38 to 15.95)

Medication: Diuretic No Data

Medication: ACEI
 >70%
 ≤70% 2 13.71 (10.92 to 16.50) 28.7% and 0.236 and 0.001

Medication: Statin
 >70%
 ≤70% 18 13.71 (10.92 to 16.50) 28.7% and 0.236 and 0.001

Medication: Beta-Blocker
 >70%
 ≤70% 4 15.25 (12.79 to 17.72) 69.6% and 0.020 and 0.001

Anti-coagulant status codes
 1 9 1.90 (1.48 to 2.32) 90.6% and 0.001 and 0.001
 2
 3 1 2.80 (2.23 to 3.36)
 4 2 13.71 (10.92 to 16.50) 28.7% and 0.236 and 0.001
 5 4 8.18 (7.75 to 8.61) 99.9% and 0.001 and 0.001
 6

AF
 Chronic 2 2.93 (2.37 to 3.49) 97.3% and 0.001 and 0.001
 Non-chronic 5 13.07 (10.71 to 15.43) 23.9% and 0.262 and 0.001

Type of AF
 Paroxysmal 4 11.86 (8.98 to 14.75) 6.1% and 0.363 and 0.001
 Persistent 1 15.50 (11.43 to 19.67)
 Permanent 1 2.93 (2.37 to 3.49) 97.3% and 0.001 and 0.001

Cigarette smoking
 >30% 1 2.80 (2.23 to 3.36)
 ≤30% 2 13.71 (10.92 to 16.50) 28.7% and 0.236 and 0.001

P-selectin

Year of Publication
 >2000 23 4.92 (4.37 to 5.47) 98.6% and 0.001 and 0.001
 ≤2000 1 −71.00 (−104.1 to −37.80)

Geographic area
 Asian 3 1.90 (0.42 to 3.38) 78.9% and 0.009 and 0.012
 European 19 5.30 (4.71 to 5.89) 98.8% and 0.001 and 0.001
 Africa 1 47.90 (29.57 to 66.22)
 North American
 South American 1 74.0 (46.63 to 101.36)
 Australia

Design of study
 Cohort 3 −0.27 (−1.16 to 0.61) 81.2% and 0.005 and 0.547
 Case-control 21 8.04 (7.35 to 8.74) 98.6% and 0.001 and 0.001

Number of population
 >300 1 −0.50 (−2.61 to 1.61)
 ≤300 23 5.29 (4.72 to 5.86) 98.6% and 0.001 and 0.001

Mean Age
 >60 years 19 4.95 (4.38 to 5.53) 98.8% and 0.001 and 0.001
 ≤60 years 3 4.46 (2.38 to 6.54) 95.2% and 0.001 and 0.001

Male
 >70% 8 5.42 (4.72 to 6.12) 99.5% and 0.001 and 0.001
 ≤70% 14 4.09 (3.19 to 4.99) 95.5% and 0.001 and 0.001

Diabetes mellitus
 >30%
 ≤30% 15 4.70 (4.08 to 5.31) 99.0% and 0.001 and 0.001

Hypertension
 >70%
 ≤70% 16 5.54 (4.93 to 6.15) 99.0% and 0.001 and 0.001

History of MI
 >20% 1 −0.50 (−2.61 to 1.61)
 ≤20% 2 4.11 (1.41 to 6.82) 87.1% and 0.005 and 0.003

Medication: Diuretic
 >70%
 ≤70% 7 5.24 (4.53 to 5.96) 99.0% and 0.001 and 0.001

Medication: ACEI
 >70%
 ≤70% 8 5.25 (4.54 to 5.96) 98.9% and 0.001 and 0.001

Medication: Statin
 >70%
 ≤70% 6 4.60 (3.87 to 5.34) 98.8% and 0.001 and 0.001

Medication: Beta-Blocker
 >70%
 ≤70% 10 3.67 (3.02 to 4.33) 98.0% and 0.001 and 0.001

Anti-coagulant status codes
 1 5 5.46 (2.88 to 8.03) 97.2% and 0.001 and 0.001
 2
 3 6 9.20 (7.99 to 10.42) 99.5% and 0.001 and 0.001
 4 10 4.19 (3.50 to 4.87) 98% and 0.001 and 0.001
 5 3 0.81 (−0.85 to 2.47) 91.4% and 0.001 and 0.342
 6

AF
 Chronic 6 5.94 (4.28 to 7.60) 99.4% and 0.001 and 0.001
 Non-chronic 8 3.09 (1.94 to 4.23) 92.2% and 0.001 and 0.001

Type of AF
 Paroxysmal 2 1.40 (−0.58 to 3.39) 2.1% and 0.312 and 0.166
 Persistent 2 8.17 (6.10 to 10.25) 96.2% and 0.001 and 0.001
 Permanent 5 6.13 (4.47 to 7.79) 99.5% and 0.001 and 0.001

Cigarette smoking
 >30% 2 4.76 (2.68 to 6.84) 95.4% and 0.001 and 0.001
 ≤30% 15 5.41 (4.55 to 6.27)

Footnotes

Declaration of interest

The authors declare that there is no conflict of interest.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplementary Figure 1.

Forest plot of weighted mean difference (WMD) for association between level of platelet distribution width and occurrence of AF.

Supplementary Figure 2.

Forest plot of weighted mean difference (WMD) for association between level of mean platelet volume and occurrence of stroke.

Supplementary Figure 3.

Forest plot of weighted mean difference (WMD) for association between level of platelet count and occurrence of stroke.

Supplementary Figure 4.

Funnel plot for publication bias of studies investigating of platelet count.

Supplementary Figure 5.

Funnel plot for publication bias of studies investigating of mean platelet volume.

Supplementary Figure 6.

Funnel plot for publication bias of studies investigating of beta thromboglobulin.

Supplementary Figure 7.

Funnel plot for publication bias of studies investigating of platelet factor-4.

Supplementary Figure 8.

Funnel plot for publication bias of studies investigating of P-selectin.

Supplementary Table 1.

Included and excluded studies.

Clinical outcomes and biomarkers Studies were identified and screened [n] Studies were excluded according to title, abstract or full text [n] Studies were included [n]
Platelet count 285 252 33 approved articles with totally 45 enrolled data for meta-analysis
Mean platelet volume 140 125 15 approved articles with totally 19 enrolled data for meta-analysis
Platelet distribution width 11 9 2 approved articles with totally 3 enrolled data for meta-analysis
Beta thromboglobulin 66 51 15 approved articles with totally 22 enrolled data for meta-analysis
Platelet factor 4 54 44 10 approved articles with totally 16 enrolled data for meta-analysis
P-selectin 115 97 18 approved articles with totally 24 enrolled data for meta-analysis

Supplementary Table 2.

Extra details of characteristics of each study for exploration of heterogeneity factors.

First Author Geographic Area Total N Total age Total male Total DM Total HTN Total MI Total Diuretic Total ACEI Total. Statin Total BB AC-code Chronic or not CS
Karatas [20] European 621 61.05 72.5 23 45.5 ND ND ND 0 ND 2 Non-chronic 64
Drabik [21] European 97 60.1 64.95 20 48.85 17.3 ND 52.25 53.15 60.6 4 Non-chronic 22.85
Drabik [21] European 91 60 55.15 16.4 46.05 26.2 ND 54.05 47.45 57.25 4 Non-chronic 20
Idriss [22] Africa 41 31.75 49.25 0 0 ND ND ND ND 11.9 4 ND 34.5
Akdag [23] European 148 64.05 60 16.5 22 ND ND ND ND ND 6 ND 23.5
Akyuz [24] European 90 62.25 72.25 29 42.5 ND 14.5 20.75 32.5 23 4 ND 34.25
Chavaria [25] North American 290 65.65 74.5 29.05 65.65 4.5 ND ND ND ND 5 ND 55.05
Erdogan [26] European 67 69.55 49.25 10 65 ND 18 53.5 10 43.3 3 chronic 6
Xu (without comorbidities) [27] Asian 115 66.05 50.45 37.4 53.1 ND ND 42.6 29.55 43.55 4 chronic 38.25
Xu (with comorbidities) [27] Asian 115 67.975 51.3 36.5 57.5 ND ND 40.8 26.05 40.95 4 chronic 31.25
Acet (PAF) [28] European 134 62.05 44 16.5 18 ND ND ND ND ND 5 Non-chronic 21.5
Acet (persistent and permanent) [28] European 126 62.85 43.5 21.5 24 ND ND ND ND ND 5 ND 28.5
Arik (with INR 2–3) [29] European 248 69.65 40.7 6.05 68.95 ND 27 59.25 ND 59.7 5 chronic 13.7
Arik (with abnormal INR) [29] European 248 69.45 37.9 6.85 65.35 ND 24.2 55.65 ND 61.3 5 chronic 12.1
Distelmaier [30] North American 198 73.5 61 24 60.5 25 ND ND ND ND 5 Non-chronic ND
Gungor [31] European 177 47.2 57.8 3.3 14.75 ND ND ND ND 10.6 3 ND 23.15
Sonmez [32] European 85 70 36.95 10.6 63.25 ND 14.1 47.15 15.4 35.55 4 Non-chronic ND
Ulu [33] European 57 ND ND ND ND ND ND ND ND ND 5 ND ND
Turgut [34] European 162 63 52 100 65.5 ND 6.5 23.5 18 16.5 4 chronic 41.5
Jaremo (healthy control) [35] European 82 67.5 66.7 ND ND ND ND ND ND ND 4 ND 2.55
jaremo (disease control) [35] European 130 71.5 68.1 12.75 43.75 9.1 28.65 26.25 25.05 55.9 4 ND 9.45
Berge [36] European 189 75 71 8 48 ND 19 21 34.5 28 4 ND ND
Ertas (without stroke) [37] European 111 53.5 51 ND ND ND ND ND ND ND 6 ND 2
Ertas (with stroke) [37] European 63 54.5 47 ND ND ND ND ND ND ND 6 ND 5
Sahin [38] European 144 64.9 49.75 100 66.5 ND ND ND ND ND 5 Non-chronic 44.5
Tekin [39] European 219 73.5 35.5 13.5 68.5 ND ND ND ND ND 5 chronic 19
Turfan (without CVA) [40] European 135 59.5 54.55 ND ND ND ND ND ND ND 4 ND 55.5
Turfan (with CVA) [40] European 121 62.5 52.05 ND ND ND ND ND ND ND 4 ND 50.6
Feng [41] Asian 374 65.8 61.75 17.65 53.2 ND 23 41.95 44.85 42.5 4 ND 25.65
Acevedo [42] South American 150 ND ND ND ND ND ND ND ND ND 1 Non-chronic ND
Hayashi [43] Asian 27 57.95 92.5 14.5 48.5 ND ND 40.5 26 ND 2 Non-chronic ND
Hayashi [43] Asian 27 61.45 92.5 11.05 52 ND ND 37 26 ND 2 chronic ND
Fu [44] Asian 169 54.45 63.5 ND ND ND ND ND 12.9 6.1 4 ND 42.45
Hou (disease control) [45] Asian 52 64.85 57.6 ND ND ND ND 40.3 ND 11.45 4 Non-chronic 26.9
Hou (healthy control) [45] Asian 52 65.3 57.6 ND ND ND ND 21.15 ND 7.65 4 Non-chronic 26.9
Alberti [46] European 51 64.45 58.8 ND ND ND ND ND ND ND 1 Non-chronic ND
Choudhury (disease control) [47] European 192 63.31 74 10.5 66.4 ND 33.15 55.7 46.5 43.7 4 ND ND
Choudhury (healthy control) [47] European 186 62.305 72 4.1 31.8 ND 17.75 26.85 14.45 21.9 4 ND ND
Colkesen [48] European 190 54 38 18.5 41.5 ND ND ND 28 ND 4 Non-chronic ND
Blann [49] European 82 64.5 62.75 ND 27 ND 16.5 19 ND 18.5 3 ND 12.6
Topaloglu (disease control) [50] European 46 34.5 ND ND ND ND ND ND ND ND 5 ND ND
Topaloglu (healthy control) [50] European 38 36 ND ND ND ND ND ND ND ND 5 ND ND
Yip [51] Asian 82 65.75 63.05 ND ND ND ND ND ND ND 3 chronic ND
Heeringa [52] European 486 77.5 51 17.5 25 22.5 31.65 ND ND 16.55 5 ND 20.9
Inoue (with comorbidities) [53] Asian 251 ND ND ND ND ND ND ND ND ND 5 ND ND
Inoue (lone AF) [53] Asian 106 ND ND ND ND ND ND ND ND ND 5 ND ND
Conway [54] European 147 68 62 7.5 26.5 ND ND ND ND ND 3 chronic 16
Conway [55] European 74 67.5 70.23 12.95 37 1.85 ND ND ND ND 5 Non-chronic 16.2
Atalar (paroxysmal AF) [56] European 37 46 61.8 0 35.9 ND ND ND ND 17.845 1 Non-chronic ND
Atalar (permanent AF) [56] European 47 49 63.8 0 35.9 ND ND ND ND 17.845 1 chronic ND
Kamath [57] European 62 63.5 51.6 ND ND ND ND ND ND ND 1 Non-chronic ND
Kamath [57] European 124 66 52.65 ND ND ND ND ND ND ND 1 chronic ND
Kamath [58] European 58 63 48.235 6.85 24.1 ND ND ND ND ND 4 Non-chronic 5.15
Kamath [58] European 116 65 52.25 5.15 30.45 ND ND ND ND ND 4 chronic 5.15
Kamath [59] European 143 70 63.2 5.35 29.565 ND ND ND ND ND 1 ND ND
Kamath [60] European 57 ND ND ND ND ND ND ND ND ND 1 ND ND
Li-Saw-Hee [61] European 43 64 77.3 2.15 10.85 ND ND ND ND ND 3 Non-chronic 13.65
Li-Saw-Hee [61] European 43 64 77.3 2.15 13 ND ND ND ND ND 3 Non-chronic 11.52
Li-Saw-Hee [61] European 43 65 77.3 6.52 23.9 ND ND ND ND ND 3 chronic 11.52
Mondillo [62] European 80 66.95 82.85 ND ND ND ND ND ND ND 3 chronic 33.75
Li-Saw-Hee [63] European 112 67 77.5 3.85 12.5 ND ND ND ND ND 1 ND 13.3
Li-Saw-Hee [64] European 50 59 20 ND ND ND ND ND ND ND 5 chronic 20
Minamino [65] European 56 64 71.4 21.5 25 ND ND ND ND 19.5 4 chronic 37.5
Minamino [66] Asian 90 63 73.3 12.5 23.5 ND ND ND ND 14.5 5 chronic 39
Kahn [67] North American 81 ND ND ND ND ND ND ND ND ND 1 ND ND
Sohara [68] Asian 30 59.05 ND ND ND ND ND ND ND ND 1 Non-chronic ND
Lip GY [69] European 77 ND ND ND ND ND ND ND ND ND 1 chronic ND
Nagao [70] Asian 36 79.95 47.05 ND ND ND ND ND ND ND 1 ND ND
Sohara [71] Asian 28 ND ND ND ND ND ND ND ND ND 1 Non-chronic ND
Gustafsson (with stroke) [72] European 60 77 ND ND ND ND ND ND ND ND 1 ND ND
Gustafsson (without stroke) [72] European 60 77 ND ND ND ND ND ND ND ND 1 ND ND
Yamauchi (without valvular heart disease) [73] Asian 130 41.5 ND ND ND ND ND ND ND ND 1 ND ND
Yamauchi (with valvular heart disease) [73] Asian 83 45.5 ND ND ND ND ND ND ND ND 1 ND ND

Supplementary Table 3.

Subgroup-analysis

Subgroup Studies (N) WMD (95% CI) I-squared and Heterogeneity-p-value and Effect-p-value respectively
Platelet count

Year of publication
 >2000 41 −24.04 (−25.52 to −22.56) 91.1% and 0.001 and 0.001
 ≤2000 4 −60.67 (−65.22 to −55.62) 92.8% and 0.001 and 0.001

Geographic area
 Asian 7 13.8% and 0.324 and 0.284
 European 35 −3.88 (−10.98 to 3.21) 94% and 0.001 and 0.001
 Africa - −30.05 (−31.59 to −28.50)
 North American 3 0.0% and 0.401 and 0.001
 South American - −12.23 (−16.39 to −8.08)
 Australia -

Design of study
 Cohort 8 −29.32 (−31.25 to −27.40) 91.6% and 0.001 and 0.001
 Case-control 37 −24.10 (−26.20 to −22.01) 93.8% and 0.001 and 0.001

Number of population
 >300 2 −6.33 (−19.68 to 7.02) 0.0% and 0.689 and 0.353
 ≤300 43 −27.16 (−28.59 to −25.74) 93.7% and 0.001 and 0.001

Mean Age
 >60 years 34 −27.90 (−29.34 to −26.46) 94.5% and 0.001 and 0.001
 ≤60 years 7 −0.76 (−9.25 to 7.12) 76.7% and 0.001 and 0.860

Male
 >70% 8 −29.82 (−31.76 to −27.88) 85.8% and 0.001 and 0.001
 ≤70% 31 −16.15 (−18.44 to −13.86) 90.6% and 0.001 and 0.001

Diabetes mellitus
 >30% 1 21.00 (−4.40 to 46.40)
 ≤30% 28 −22.68 (−24.24 to −21.12) 88.3% and 0.001 and 0.001

Hypertension
 >70%
 ≤70% 29 −22.52 (−24.07 to −20.96) 88.4% and 0.001 and 0.001

History of MI
 >20% 2 −11.74 (−15.35 to −8.13) 9.7% and 0.293 and 0.001
 ≤20% 3 −15.44 (−22.10 to −8.77) 31.1% and 0.234 and 0.001

Medication: Diuretic
 >70%
 ≤70% 11 −28.43 (−30.31 to −26.56) 88.1% and 0.001 and 0.001

Medication: ACEI
 >70%
 ≤70% 17 −25.60 (−27.33 to −23.88) 89.6% and 0.001 and 0.001

Medication: Statin
 >70%
 ≤70% 18 −25.90 (−27.64 to −24.15) 88.4% and 0.001 and 0.001

Medication: Beta-Blocker
 >70%
 ≤70% 17 −25.40 (−27.11 to −23.68) 89.3% and 0.001 and 0.001

Anti-coagulant status codes
 1 9 −54.79 (−58.44 to −51.15) 93.4% and 0.001 and 0.001
 2 3 1.69 (−17.11 to 20.53) 67.3% and 0.047 and 0.860
 3 3 −3.15 (−17.55 to 11.23) 0.0% and 0.890 and 0.667
 4 19 −25.27 (−27.00 to −23.53) 90.9% and 0.001 and 0.001
 5 8 −10.84 (−14.41 to 7.24) 38.3% and 0.124 and 0.001
 6 3 −6.34 (−21.47 to 8.77) 70.8% and 0.033 and 0.411

AF
 Chronic 12 −2.15 (−7.34 to 3.02) 35.6% and 0.106 and 0.414
 Non-chronic 11 −21.73 (−24.45 to −19.01) 95.5% and 0.001 and 0.001

Type of AF
 Paroxysmal 5 −5.29 (−11.24 to 0.64) 67.8% and 0.015 and 0.081
 Persistent 3 −41.86 (−46.34 to −37.38) 97.4% and 0.001 and 0.001
 Permanent 5 −4.55 (−11.58 to 2.46) 64.6% and 0.023 and 0.204

Cigarette smoking
 >30% 9 2.31 (−4.14 to 8.77) 67.3% and 0.002 and 0.482
 ≤30% 17 −9.11 (−12.70 to −5.52) 46.6% and 0.018 and 0.001

Mean platelet volume

Year of publication
 >2000 All of studies: after 2000
 ≤2000

Geographic area
 Asian 3 1.37 (1.16 to 1.58) 95.9% and 0.001 and 0.001
 European 16 0.56 (0.51 to 0.61) 93.1% and 0.001 and 0.001
 Africa
 North American
 South American
 Australia

Design of study
 Cohort 4 1.37 (1.14 to 1.60) 94.7% and 0.001 and 0.001
 Case-control 15 0.57 (0.52 to 0.62) 93.6% and 0.001 and 0.001

Number of population
 >300 2 0.90 (0.67 to 1.13) 0.0% and 0.666 and 0.001
 ≤300 17 0.59 (0.54 to 0.64) 94.9% and 0.001 and 0.001

Mean Age
 >60 years 15 0.61 (0.56 to 0.66) 94.8% and 0.001 and 0.001
 ≤60 years 3 0.33 (0.13 to 0.54) 95.2% and 0.001 and 0.001

Male
 >70% 4 0.67 (0.50 to 0.83) 95.6% and 0.001 and 0.001
 ≤70% 14 0.59 (0.54 to 0.64) 94.7% and 0.001 and 0.001

Diabetes mellitus
 >30% 2 0.59 (0.53 to 0.65) 42.3% and 0.188 and 0.001
 ≤30% 14 0.60 (0.52 to 0.67) 95.8% and 0.001 and 0.001

Hypertension
 >70%
 ≤70% 16 0.59 (0.55 to 0.64) 95.1% and 0.001 and 0.001

History of MI Studies have not data about history of myocardial infarction

Medication: Diuretic
 >70%
 ≤70% 8 0.57 (0.52 to 0.62) 95.5% and 0.001 and 0.001

Medication: ACEI
 >70%
 ≤70% 10 0.60 (0.55 to 0.65) 96.4% and 0.001 and 0.001

Medication: Statin
 >70%
 ≤70% 10 0.66 (0.61 to 0.72) 95.1% and 0.001 and 0.001

Medication: Beta-Blocker
 >70%
 ≤70% 11 0.58 (0.53 to 0.63) 96.4% and 0.001 and 0.001

Anti-coagulant status codes
 1
 2 1 0.80 (0.26 to 1.33)
 3 2 −0.07 (−0.31 to 0.16) 8.7% and 0.295 and 0.530
 4 10 0.67 (0.62 to 0.73) 95.1% and 0.001 and 0.001
 5 5 0.43 (0.33 to 0.53) 94.6% and 0.001 and 0.001
 6 1 1.10 (0.75 to 1.45)

AF
 Chronic 7 0.58 (0.53 to 0.63) 96.6% and 0.001 and 0.001
 Non-chronic 3 0.85 (0.58 to 1.13) 88.6% and 0.001 and 0.001

Type of AF
 Paroxysmal 1 1.70 (1.20. to 2.19)
 Persistent 1 0.32 (−0.09 to 0.73)
 Permanent 3 0.39 (0.28 to 0.51) 97.1% and 0.001 and 0.001

Cigarette smoking
 >30% 8 0.68 (0.62 to 0.74) 94.7% and 0.001 and 0.001
 ≤30% 7 0.45 (0.36 to 0.54) 94.8% and 0.001 and 0.001

BTG

Year of Publication
 >2000 11 29.31 (28.57 to 30.04) 88.6% and 0.001 and 0.001
 ≤2000 11 12.67 (11.49 to 13.85) 95.5% and 0.001 and 0.001

Geographic area
 Asian 8 30.31 (29.51 to 31.11) 77% and 0.001 and 0.001
 European 14 15.91 (14.92 to 16.91) 96.2% and 0.001 and 0.001
 Africa
 North American
 South American
 Australia

Design of study
 Cohort All of studies are “case-control”
 Case-control

Number of population
 >300 All of studies are “number less than 300 population”
 ≤300

Mean Age
 >60 years 11 15.79 (14.74 to 16.84) 94.2% and 0.001 and 0.001
 ≤60 years 6 13.01 (9.94 to 16.08) 90.1% and 0.001 and 0.001

Male
 >70% 3 39.01 (33.37 to 44.65) 0.0% and 0.600 and 0.001
 ≤70% 9 19.98 (18.28 to 21.68) 90.9% and 0.001 and 0.001

Diabetes mellitus
 >30%
 ≤30% 7 25.36 (23.30 to 27.42) 80.8% and 0.001 and 0.001

Hypertension
 >70%
 ≤70% 7 25.36 (23.30 to 27.42) 80.8% and 0.001 and 0.001

History of MI No Data

Medication: Diuretic No Data

Medication: ACEI
 >70% No Data
 ≤70%

Medication: Statin
 >70% No Data
 ≤70%

Medication: Beta-Blocker
 >70%
 ≤70% 4 27.17 (23.22 to 31.12) 89.1% and 0.001 and 0.001

Anti-coagulant status codes
 1 14 14.70 (13.63 to 15.78) 93.6% and 0.001 and 0.001
 2
 3 1 39.16 (29.56 to 48.75)
 4 3 27.83 (24.92 to 30.73) 85.5% and 0.001 and 0.001
 5 4 29.83 (29.03 to 30.63) 97.8% and 0.001 and 0.001
 6

AF
 Chronic 8 24.21 (22.11 to 26.30) 96.7% and 0.001 and 0.001
 Non-chronic 5 17.74 (14.40 to 21.08) 31.3% and 0.213 and 0.001

Type of AF
 Paroxysmal 4 17.60 (13.57 to 21.63) 48.3% and 0.121 and 0.001
 Persistent
 Permanent 4 25.90 (23.39 to 28.40) 80.5% and 0.002 and 0.001

Cigarette smoking
 >30% 3 39.01 (33.37 to 44.65) 0.0% and 0.600 and 0.001
 ≤30% 3 18.64 (16.00 to 21.27) 97.2% and 0.001 and 0.001

Platelet factor 4

Year of Publication
 >2000 9 6.38 (6.04 to 6.72) 99.8% and 0.001 and 0.001
 ≤2000 7 1.78 (1.36 to 2.20) 81.6% and 0.001 and 0.001

Geographic area
 Asian 7 6.75 (6.32 to 7.17) 51.5% and 0.054 and 0.001
 European 9 3.25 (2.91 to 3.59) 99.8% and 0.001 and 0.001
 Africa
 North American
 South American
 Australia

Design of study
 Cohort All of studies are “case-control”
 Case-control

Number of population
 >300 All of studies are “number less than 300 population”
 ≤300

Mean Age
 >60 years 6 2.27 (1.93 to 2.61) 94.6% and 0.001 and 0.001
 ≤60 years 7 58.31 (55.83 to 60.80) 99.6% and 0.001 and 0.001

Male
 >70% 1 2.80 (2.23 to 3.36)
 ≤70% 5 11.60 (9.55 to 13.66) 89.3% and 0.001 and 0.001

Diabetes mellitus
 >30%
 ≤30% 4 15.25 (12.79 to 17.72) 69.6% and 0.020 and 0.001

Hypertension
 >70%
 ≤70% 4 15.25 (12.79 to 17.72) 69.6% and 0.020 and 0.001

History of MI
 >20% 1 15.55 (11.43 to 19.67)
 ≤20% 1 12.17 (8.38 to 15.95)

Medication: Diuretic No Data

Medication: ACEI
 >70%
 ≤70% 2 13.71 (10.92 to 16.50) 28.7% and 0.236 and 0.001

Medication: Statin
 >70%
 ≤70% 18 13.71 (10.92 to 16.50) 28.7% and 0.236 and 0.001

Medication: Beta-Blocker
 >70%
 ≤70% 4 15.25 (12.79 to 17.72) 69.6% and 0.020 and 0.001

Anti-coagulant status codes
 1 9 1.90 (1.48 to 2.32) 90.6% and 0.001 and 0.001
 2
 3 1 2.80 (2.23 to 3.36)
 4 2 13.71 (10.92 to 16.50) 28.7% and 0.236 and 0.001
 5 4 8.18 (7.75 to 8.61) 99.9% and 0.001 and 0.001
 6

AF
 Chronic 2 2.93 (2.37 to 3.49) 97.3% and 0.001 and 0.001
 Non-chronic 5 13.07 (10.71 to 15.43) 23.9% and 0.262 and 0.001

Type of AF
 Paroxysmal 4 11.86 (8.98 to 14.75) 6.1% and 0.363 and 0.001
 Persistent 1 15.50 (11.43 to 19.67)
 Permanent 1 2.93 (2.37 to 3.49) 97.3% and 0.001 and 0.001

Cigarette smoking
 >30% 1 2.80 (2.23 to 3.36)
 ≤30% 2 13.71 (10.92 to 16.50) 28.7% and 0.236 and 0.001

P-selectin

Year of Publication
 >2000 23 4.92 (4.37 to 5.47) 98.6% and 0.001 and 0.001
 ≤2000 1 −71.00 (−104.1 to −37.80)

Geographic area
 Asian 3 1.90 (0.42 to 3.38) 78.9% and 0.009 and 0.012
 European 19 5.30 (4.71 to 5.89) 98.8% and 0.001 and 0.001
 Africa 1 47.90 (29.57 to 66.22)
 North American
 South American 1 74.0 (46.63 to 101.36)
 Australia

Design of study
 Cohort 3 −0.27 (−1.16 to 0.61) 81.2% and 0.005 and 0.547
 Case-control 21 8.04 (7.35 to 8.74) 98.6% and 0.001 and 0.001

Number of population
 >300 1 −0.50 (−2.61 to 1.61)
 ≤300 23 5.29 (4.72 to 5.86) 98.6% and 0.001 and 0.001

Mean Age
 >60 years 19 4.95 (4.38 to 5.53) 98.8% and 0.001 and 0.001
 ≤60 years 3 4.46 (2.38 to 6.54) 95.2% and 0.001 and 0.001

Male
 >70% 8 5.42 (4.72 to 6.12) 99.5% and 0.001 and 0.001
 ≤70% 14 4.09 (3.19 to 4.99) 95.5% and 0.001 and 0.001

Diabetes mellitus
 >30%
 ≤30% 15 4.70 (4.08 to 5.31) 99.0% and 0.001 and 0.001

Hypertension
 >70%
 ≤70% 16 5.54 (4.93 to 6.15) 99.0% and 0.001 and 0.001

History of MI
 >20% 1 −0.50 (−2.61 to 1.61)
 ≤20% 2 4.11 (1.41 to 6.82) 87.1% and 0.005 and 0.003

Medication: Diuretic
 >70%
 ≤70% 7 5.24 (4.53 to 5.96) 99.0% and 0.001 and 0.001

Medication: ACEI
 >70%
 ≤70% 8 5.25 (4.54 to 5.96) 98.9% and 0.001 and 0.001

Medication: Statin
 >70%
 ≤70% 6 4.60 (3.87 to 5.34) 98.8% and 0.001 and 0.001

Medication: Beta-Blocker
 >70%
 ≤70% 10 3.67 (3.02 to 4.33) 98.0% and 0.001 and 0.001

Anti-coagulant status codes
 1 5 5.46 (2.88 to 8.03) 97.2% and 0.001 and 0.001
 2
 3 6 9.20 (7.99 to 10.42) 99.5% and 0.001 and 0.001
 4 10 4.19 (3.50 to 4.87) 98% and 0.001 and 0.001
 5 3 0.81 (−0.85 to 2.47) 91.4% and 0.001 and 0.342
 6

AF
 Chronic 6 5.94 (4.28 to 7.60) 99.4% and 0.001 and 0.001
 Non-chronic 8 3.09 (1.94 to 4.23) 92.2% and 0.001 and 0.001

Type of AF
 Paroxysmal 2 1.40 (−0.58 to 3.39) 2.1% and 0.312 and 0.166
 Persistent 2 8.17 (6.10 to 10.25) 96.2% and 0.001 and 0.001
 Permanent 5 6.13 (4.47 to 7.79) 99.5% and 0.001 and 0.001

Cigarette smoking
 >30% 2 4.76 (2.68 to 6.84) 95.4% and 0.001 and 0.001
 ≤30% 15 5.41 (4.55 to 6.27)

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