Abstract
Cardiovascular mortality in peripheral artery disease (PAD) patients is higher in critical limb ischemia (CLI) than in intermittent claudication (IC). We sought to evaluate differential characteristics of coronary artery disease (CAD) severity and prognostic biomarkers for cardiovascular events between CLI and IC patients. Coronary angiography was performed on 242 PAD patients (age 73 ± 8 years) with either CLI or IC. High-sensitivity troponin T (hs-TnT), eicosapentaenoic acid–arachidonic acid ratio (EPA/AA), and lipoprotein(a), as biomarkers for prognostic factors, were measured from blood samples. The study patients were divided into a CLI-group (n = 42) and IC-group (n = 200). The Gensini score as an indicator of coronary angiographic severity was higher in the CLI-group than in the IC-group (39.1 ± 31.2 vs. 8.5 ± 8.3, p < 0.0001). Hs-TnT and lipoprotein(a) values were higher in the CLI-group than in the IC-group (0.152 ± 0.186 ng/mL vs. 0.046 ± 0.091, p < 0.0001, 45.9 ± 23.3 mg/dL vs. 26.2 ± 27.7, p = 0.0002, respectively) and EPA/AA was lower in the CLI-group than in the IC-group (0.22 ± 0.11 vs. 0.38 ± 0.29, p = 0.0049, respectively). Greater CAD severity, higher hs-TnT, and lipoprotein(a), and lower EPA/AA were observed in the CLI-group, which may explain higher cardiovascular events in patients with CLI.
Keywords: coronary artery, cardiovascular disease, peripheral artery disease, claudication, critical limb ischemia, cardiac biomarkers, cardiac catheterization
Peripheral arterial disease (PAD), which is caused by atherosclerotic occlusion of the arteries to the lower extremities, is an important manifestation of systemic atherosclerosis. PAD impairs not only quality of life but also the long-term prognosis of patients with atherosclerosis due to coexisting coronary artery disease, which is a major cause of mortality and morbidity in patients with PAD.1 2 Symptomatic PAD is usually classified into intermittent claudication (IC) and critical limb ischemia (CLI). Cardiovascular mortality in patients with PAD is higher in CLI than in IC.2 There are insufficient studies to indicate causes of higher cardiovascular morbidity and mortality in patients with CLI than in patients with IC.
The Gensini score is one of the coronary artery disease (CAD) scores determined by coronary angiogram.3 The coronary score was intended to take into account geometrically increasing severity of lesions, cumulative effect of multiple lesions, lesion location, and the influence of collaterals. The Gensini score is widely used for evaluation of coronary artery severity and has prognostic significance.4
Cardiac troponin T is a component of the contractile apparatus of cardiomyocytes and an established sensitive biomarker of myocardial cell injury. Cardiac troponin T measured by a highly sensitive assay predicts coronary heart disease, heart failure, and mortality.5 Elevated troponin T is reported to be associated with higher mortality and amputation rates in patients with PAD.6 Lipoprotein(a) [Lp(a)] is a genetic variant of low-density lipoprotein in which apolipoprotein B100 is linked by a disulfide bond to apolipoprotein(a), with a high degree of structural homology with plasminogen.7 8 Lp(a) can exert the development, growth, and disruption of atherosclerotic plaques through its effects on lipid accumulation, inflammation, and thrombosis.9 10 11 12 13 14 Lp(a) is a strong predictor of acute myocardial infarction.15 16 17 Dietary essential fatty acids are classified into n-3 (e.g., eicosapentaenoic acid [EPA]) and n-6 (e.g., arachidonic acid [AA]) groups, and the metabolites of these fatty acids have opposing effects on coronary artery disease. Dietary intake of fish-derived polyunsaturated fatty acid shows favorable outcome in patients with coronary artery disease.18 19 20 The Japan EPA lipid intervention study showed for the first time that additive administration of purified EPA reduced coronary events by 19% in patients with statin therapy.21 EPA/AA ratio is reported to be a strong predictor of cardiovascular events.22 23 24
The purpose of this study is to evaluate differential characteristics of coronary artery disease severity and prognostic biomarkers for cardiovascular events between CLI and IC patients and to assess causes of poorer outcomes in CLI patients than in IC patients.
Methods
Study Patients
The study included a total of 242 patients with symptomatic PAD who underwent endovascular therapy (EVT). The ankle–brachial index and duplex ultrasonography were routinely used to confirm the diagnosis of PAD. The study patients were divided into IC and CLI based on lower extremity conditions. IC was defined as Rutherford classification 2 to 3, while CLI was defined as Rutherford classification 4 to 6.25
Study Protocols
All the study patients underwent coronary angiography and lower limb angiography before the day of EVT. Coronary angiography and lower limb angiography were performed with usual methods via a radial, brachial or femoral artery. Serum Lp(a), high-sensitivity troponin T, EPA, AA, low-density cholesterol, high-density cholesterol, triglyceride, and hemoglobin A1c levels were measured in the fasting state before EVT. All the study patients underwent EVT based on the findings from a lower limb angiogram.
Coronary Angiography and Lower Limb Angiography
All coronary angiograms were scored for luminal narrowing using a modified American Heart Association/American College of Cardiology classification.26 Patients were designated as having angiographically smooth normal coronary arteries, nonsignificant CAD (visible plaque resulting in < 50% luminal stenosis), or significant CAD (at least one major epicardial vessel with ≥50% stenosis). The severity of their CAD was calculated based on angiographic disease of their native vessels before revascularization. Quantitative angiographic scoring was performed using the Gensini score that quantifies CAD severity by a nonlinear points system for degree of luminal narrowing.3 Lower limb angiography showed culprit lesions for symptomatic PAD.
Blood Sampling
Venous blood was drawn from all patients in the fasting state. Levels of low-density lipoprotein cholesterol, high-density cholesterol, triglyceride, and hemoglobin A1c were measured. Serum levels of Lp(a) were measured using a latex agglutination turbidimetric immunoassay (Sekisui Medical Co., Tokyo, Japan). Serum high-sensitivity troponin T levels were measured using high-sensitivity assay with electrochemiluminescence detection (Roche Diagnostics Co., Tokyo, Japan), the normal range was less than 0.014 ng/mL (cut off value for acute myocardial infarction of 0.1 ng/mL). Plasma levels of EPA and AA were measured using gas chromatography (SRL Co., Tokyo, Japan). The values of EPA/AA ratio were calculated for analysis.
Statistical Analysis
Data were expressed as mean ± SD. Continuous variables were compared using the Student t-test. Chi-square analysis was used to test the differences between proportions. Fisher exact test was used when the expected value for a cell was < 5. Lp(a) values were logarithmically transformed to statistically analyze Lp(a) as a continuous variable. All statistical analyses were performed using JMP version 10 (SAS Inc., Chicago, IL). Statistical significance was defined as a p-value less than 0.05 (two tailed).
Results
Patient clinical characteristics are shown in Table 1. Laboratory findings are indicated in Table 2. Values of high-sensitivity troponin T, LP(a) were higher in the CLI group than in the IC group, while EPA/AA ratio was lower in the CLI group than in the IC group. Coronary angiographic findings showed a higher incidence of significant coronary artery stenosis in at least one major coronary artery and greater values of Gensini score in the CLI group than in the IC group (Table 3). Lower limb angiographic findings are shown in Table 4.
Table 1. Patients' clinical characteristics.
| Clinical characteristics | IC | CLI | p-Value |
|---|---|---|---|
| Men/women | 156/44 | 30/12 | 0.3679 |
| Age (y) | 72 ± 8 | 74 ± 11 | 0.2965 |
| Body mass index (kg/m2) | 22.1 ± 4.2 | 22.1 ± 7.9 | 0.9856 |
| Hypertension | 163 (82%) | 32 (76%) | 0.4020 |
| Diabetes mellitus | 102 (51%) | 32 (76%) | 0.0024 |
| Hypercholesterolemia | 84 (42%) | 10 (24%) | 0.0224 |
| Smoking (current or ex-smoker) | 107 (54%) | 16 (38%) | 0.0685 |
| CKD | 143 (72%) | 32 (76%) | 0.5629 |
| Hemodialysis | 77 (39%) | 18 (43%) | 0.6005 |
| Rutherford class | |||
| 2 | 98 (49%) | ||
| 3 | 101 (51%) | ||
| 4 | 12 (29%) | ||
| 5 | 28 (67%) | ||
| 6 | 2 (4%) | ||
| Statin use | 136 (68%) | 25 (60%) | 0.2899 |
| Aspirin use | 184 (92%) | 38 (90%) | 0.7444 |
| Clopidogrel use | 180 (90%) | 36 (86%) | 0.4149 |
| Cilostazol use | 22 (52%) | 129 (65%) | 0.1405 |
Abbreviations: CLI, critical limb ischemia, CKD, chronic kidney disease; IC, intermittent claudication.
Note: Mean ± SD.
Table 2. Laboratory findings.
| Findings | IC | CLI | p-Value |
|---|---|---|---|
| HbA1c (%) | 6.4 ± 1.5 | 6.5 ± 1.6 | 0.1511 |
| LDL cholesterol (mg/dL) | 83.3 ± 25.4 | 88.2 ± 33.5 | 0.2932 |
| HDL cholesterol (mg/dL) | 45.3 ± 13.1 | 38.1 ± 12.3 | 0.0015 |
| Triglyceride (mg/dL) | 143.5 ± 94.5 | 113.0 ± 37.1 | 0.0456 |
| High-sensitivity Troponin T (ng/mL) | 0.046 ± 0.091 | 0.152 ± 0.186 | < 0.0001 |
| Lp(a) (mg/dL) | 26.2 ± 27.7 | 45.9 ± 23.3 | 0.0002 |
| EPA/AA | 0.38 ± 0.29 | 0.22 ± 0.11 | 0.0049 |
| ABI | 0.67 ± 0.28 | 0.48 ± 0.29 | 0.0004 |
Abbreviations: AA, arachidonic acid; ABI, ankle brachial index; CLI, critical limb ischemia; EPA, eicosapentaenoic acid; HDL, high-density lipoprotein; IC, intermittent claudication; LDL, low-density lipoprotein; Lp(a), lipoprotein (a).
Note: Mean ± SD.
Table 3. Findings of coronary angiography.
| Findings | IC | CLI | p-Value |
|---|---|---|---|
| Significant coronary stenosis in at least one major coronary artery | 44 (22%) | 25 (60%) | < 0.0001 |
| Gensini score | 8.5 ± 8.3 | 39.1 ± 31.2 | < 0.0001 |
Abbreviations: CLI, critical limb ischemia; IC, intermittent claudication.
Note: Mean ± SD.
Table 4. Findings of lower limb angiography.
| Findings | IC | CLI | p-Value |
|---|---|---|---|
| Locations of culprit lesions | |||
| Iliac artery | 70 | 15 | < 0.0001 |
| SFA | 135 | 18 | |
| BTK | 3 | 13 | |
| CTO | 57 (38%) | 21 (54%) | 0.1813 |
Abbreviations: BTK, below the knee; CLI, critical limb ischemia; CTO, chronic total occlusion; IC, intermittent claudication; SFA, superficial femoral artery.
Note: Mean ± SD.
Discussion
This study showed that the CLI group had a higher incidence of diabetes mellitus, significant coronary artery stenosis in at least one major coronary artery, higher values of high-sensitivity troponin T and Lp(a), and lower ratio of EPA/AA than the IC group. Those findings may explain higher incidences of major adverse coronary and cerebral events in CLI patients.
CLI is defined as limb pain that occurs at rest or impending limb loss that is caused by severe compromise of blood flow to the affected extremity. CLI patients showed extremely poorer prognosis than IC patients due to higher rates of cardiovascular events.2 Evaluation of the mechanisms of higher rates of cardiovascular events are needed for improvement of prognosis in CLI patients.
There are few studies to assess differences of CAD severity between IC and CLI patients. Although it is unclear why CLI patients have higher coronary artery severity than IC patients, higher incidence of diabetes mellitus, higher Lp(a) values, and lower EPA/AA may be related with coronary artery disease progression. Greater coronary artery lesion severity may be related with greater values of serum high-sensitivity troponin T in CLI patients, compared with IC patients. Lp(a) values are increased in an inflammatory condition.27 Although Lp(a) is usually genetically determined, CLI with inflammatory condition may elevate Lp(a) level. There are few studies to assess Lp(a) values between CLI and IC patients. Lp(a) level is a reliable biochemical marker for survival in patients with critical limb ischemia.28 An elevated Lp(a) level of > 24 mg/dL incurred a 107 and 45% increase in mortality at 3 and 5 years, respectively.28 A lower serum EPA/AA ratio is associated with a greater risk of cardiovascular disease, especially coronary heart disease.29 Linnemann et al have reported that high-sensitivity troponin T is frequently elevated in PAD and is associated with higher rates of not only mortality but also limb amputation.6 In their study, a prevalence of elevated high-sensitivity troponin T (> 0.01 ng/mL) was higher in CLI patients (Rutherford categories 4 and 5) than in IC patients (Rutherford categories 2 and 3). These results support our study results in terms of high-sensitivity troponin T. Elevated high-sensitivity troponin T concentration is also associated with an impaired renal function.6 However, there were no significant differences of incidences of chronic renal disease and hemodialysis in our study.
Our study demonstrated that CLI patients had greater severity of coronary artery lesions, higher values of high-sensitivity troponin T and Lp(a), and lower values of EPA/AA. These findings may support higher rates of mortality, cardiovascular events in CLI patients. The diagnosis of CLI thus predicts a poor prognosis for life and limb. Patients with CLI should undergo aggressive assessment of coronary artery conditions and biomarkers for future prediction of cardiovascular events in addition to limb evaluation. Furthermore, patients should have aggressive modification of their cardiovascular risk factors and coronary revascularization if necessary.
The high rate of patients on hemodialysis and suffering from diabetes mellitus was shown in our study. Our hospital has a large hemodialysis center which sees almost all patients with hemodialysis in our medical care zone. The leading cause of hemodialysis was diabetes mellitus in our hemodialysis center. PAD patients with hemodialysis in the hemodialysis center were referred to our cardiovascular center. That was the reason why our study indicated high rate of patients with hemodialysis and diabetes mellitus.
Our study has several limitations. First, the sample size was relatively small. Second, patient enrollment for this study was selective because the only patients who underwent EVT were included for the study. Third, prognosis of our study patients was not evaluated in this study. Therefore, we were not able to evaluate which factors predicted cardiovascular mortality in our study. Long follow-up data are needed to determine the prognostic factors for cardiovascular mortality in our study population.
Conclusion
Greater severity of coronary artery disease, higher high-sensitivity troponin T and Lp(a) values, and lower EPA/AA were observed in the CLI patients, which may explain higher cardiovascular events in patients with CLI than with IC.
Funding
The authors received no financial support for the research and/or authorship of this article.
Footnotes
Conflict of Interest The authors declare no potential conflicts of interests with respect to the authorship and/or publication of this article.
References
- 1.Criqui M H, Langer R D, Fronek A. et al. Mortality over a period of 10 years in patients with peripheral arterial disease. N Engl J Med. 1992;326(6):381–386. doi: 10.1056/NEJM199202063260605. [DOI] [PubMed] [Google Scholar]
- 2.Norgren L Hiatt W R Dormandy J A Nehler M R Harris K A Fowkes F G; TASC II Working Group. Inter-Society Consensus for the Management of Peripheral Arterial Disease (TASC II) J Vasc Surg 200745(Suppl S):S5–S67. [DOI] [PubMed] [Google Scholar]
- 3.Gensini G G. A more meaningful scoring system for determining the severity of coronary heart disease. Am J Cardiol. 1983;51(3):606. doi: 10.1016/s0002-9149(83)80105-2. [DOI] [PubMed] [Google Scholar]
- 4.Eapen D J, Manocha P, Ghasemzedah N. et al. Soluble urokinase plasminogen activator receptor level is an independent predictor of the presence and severity of coronary artery disease and of future adverse events. J Am Heart Assoc. 2014;3(5):e001118. doi: 10.1161/JAHA.114.001118. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.Saunders J T, Nambi V, de Lemos J A. et al. Cardiac troponin T measured by a highly sensitive assay predicts coronary heart disease, heart failure, and mortality in the Atherosclerosis Risk in Communities Study. Circulation. 2011;123(13):1367–1376. doi: 10.1161/CIRCULATIONAHA.110.005264. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Linnemann B, Sutter T, Herrmann E. et al. Elevated cardiac troponin T is associated with higher mortality and amputation rates in patients with peripheral arterial disease. J Am Coll Cardiol. 2014;63(15):1529–1538. doi: 10.1016/j.jacc.2013.05.059. [DOI] [PubMed] [Google Scholar]
- 7.Gaubatz J W, Heideman C, Gotto A M Jr, Morrisett J D, Dahlen G H. Human plasma lipoprotein [a]. Structural properties. J Biol Chem. 1983;258(7):4582–4589. [PubMed] [Google Scholar]
- 8.McLean J W, Tomlinson J E, Kuang W J. et al. cDNA sequence of human apolipoprotein(a) is homologous to plasminogen. Nature. 1987;330(6144):132–137. doi: 10.1038/330132a0. [DOI] [PubMed] [Google Scholar]
- 9.Sorensen K E, Celermajer D S, Georgakopoulos D, Hatcher G, Betteridge D J, Deanfield J E. Impairment of endothelium-dependent dilation is an early event in children with familial hypercholesterolemia and is related to the lipoprotein(a) level. J Clin Invest. 1994;93(1):50–55. doi: 10.1172/JCI116983. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Nielsen L B, Nordestgaard B G, Stender S, Niendorf A, Kjeldsen K. Transfer of lipoprotein(a) and LDL into aortic intima in normal and in cholesterol-fed rabbits. Arterioscler Thromb Vasc Biol. 1995;15(9):1492–1502. doi: 10.1161/01.atv.15.9.1492. [DOI] [PubMed] [Google Scholar]
- 11.Nielsen L B, Stender S, Jauhiainen M, Nordestgaard B G. Preferential influx and decreased fractional loss of lipoprotein(a) in atherosclerotic compared with nonlesioned rabbit aorta. J Clin Invest. 1996;98(2):563–571. doi: 10.1172/JCI118824. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Nielsen L B, Stender S, Kjeldsen K, Nordestgaard B G. Specific accumulation of lipoprotein(a) in balloon-injured rabbit aorta in vivo. Circ Res. 1996;78(4):615–626. doi: 10.1161/01.res.78.4.615. [DOI] [PubMed] [Google Scholar]
- 13.Nielsen L B, Grønholdt M L, Schroeder T V, Stender S, Nordestgaard B G. In vivo transfer of lipoprotein(a) into human atherosclerotic carotid arterial intima. Arterioscler Thromb Vasc Biol. 1997;17(5):905–911. doi: 10.1161/01.atv.17.5.905. [DOI] [PubMed] [Google Scholar]
- 14.Boffa M B, Marcovina S M, Koschinsky M L. Lipoprotein(a) as a risk factor for atherosclerosis and thrombosis: mechanistic insights from animal models. Clin Biochem. 2004;37(5):333–343. doi: 10.1016/j.clinbiochem.2003.12.007. [DOI] [PubMed] [Google Scholar]
- 15.Maher V MG, Brown B G, Marcovina S M, Hillger L A, Zhao X Q, Albers J J. Effects of lowering elevated LDL cholesterol on the cardiovascular risk of lipoprotein(a) JAMA. 1995;274(22):1771–1774. [PubMed] [Google Scholar]
- 16.Kamstrup P R, Benn M, Tybjaerg-Hansen A, Nordestgaard B G. Extreme lipoprotein(a) levels and risk of myocardial infarction in the general population: the Copenhagen City Heart Study. Circulation. 2008;117(2):176–184. doi: 10.1161/CIRCULATIONAHA.107.715698. [DOI] [PubMed] [Google Scholar]
- 17.Kamstrup P R, Tybjaerg-Hansen A, Steffensen R, Nordestgaard B G. Genetically elevated lipoprotein(a) and increased risk of myocardial infarction. JAMA. 2009;301(22):2331–2339. doi: 10.1001/jama.2009.801. [DOI] [PubMed] [Google Scholar]
- 18.Lavie C J, Milani R V, Mehra M R, Ventura H O. Omega-3 polyunsaturated fatty acids and cardiovascular diseases. J Am Coll Cardiol. 2009;54(7):585–594. doi: 10.1016/j.jacc.2009.02.084. [DOI] [PubMed] [Google Scholar]
- 19.Weitz D, Weintraub H, Fisher E, Schwartzbard A Z. Fish oil for the treatment of cardiovascular disease. Cardiol Rev. 2010;18(5):258–263. doi: 10.1097/CRD.0b013e3181ea0de0. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 20.Iso H, Kobayashi M, Ishihara J. et al. Intake of fish and n3 fatty acids and risk of coronary heart disease among Japanese: the Japan Public Health Center-Based (JPHC) Study Cohort I. Circulation. 2006;113(2):195–202. doi: 10.1161/CIRCULATIONAHA.105.581355. [DOI] [PubMed] [Google Scholar]
- 21.Yokoyama M, Origasa H, Matsuzaki M. et al. Effects of eicosapentaenoic acid on major coronary events in hypercholesterolaemic patients (JELIS): a randomised open-label, blinded endpoint analysis. Lancet. 2007;369(9567):1090–1098. doi: 10.1016/S0140-6736(07)60527-3. [DOI] [PubMed] [Google Scholar]
- 22.Kondo T, Ogawa K, Satake T. et al. Plasma-free eicosapentaenoic acid/arachidonic acid ratio: a possible new coronary risk factor. Clin Cardiol. 1986;9(9):413–416. doi: 10.1002/clc.4960090905. [DOI] [PubMed] [Google Scholar]
- 23.Kashiyama T, Ueda Y, Nemoto T. et al. Relationship between coronary plaque vulnerability and serum n-3/n-6 polyunsaturated fatty acid ratio. Circ J. 2011;75(10):2432–2438. doi: 10.1253/circj.cj-11-0352. [DOI] [PubMed] [Google Scholar]
- 24.Domei T, Yokoi H, Kuramitsu S. et al. Ratio of serum n-3 to n-6 polyunsaturated fatty acids and the incidence of major adverse cardiac events in patients undergoing percutaneous coronary intervention. Circ J. 2012;76(2):423–429. doi: 10.1253/circj.cj-11-0941. [DOI] [PubMed] [Google Scholar]
- 25.Rutherford R B, Baker J D, Ernst C. et al. Recommended standards for reports dealing with lower extremity ischemia: revised version. J Vasc Surg. 1997;26(3):517–538. doi: 10.1016/s0741-5214(97)70045-4. [DOI] [PubMed] [Google Scholar]
- 26.Austen W G Edwards J E Frye R L et al. A reporting system on patients evaluated for coronary artery disease. Report of the ad hoc committee for grading of coronary artery disease, council on cardiovascular surgery, American Heart Association Circulation 197551(4, Suppl):5–40. [DOI] [PubMed] [Google Scholar]
- 27.Langsted A, Kamstrup P R, Nordestgaard B G. Lipoprotein(a): fasting and nonfasting levels, inflammation, and cardiovascular risk. Atherosclerosis. 2014;234(1):95–101. doi: 10.1016/j.atherosclerosis.2014.01.049. [DOI] [PubMed] [Google Scholar]
- 28.Cheng S W, Ting A C. Lipoprotein (a) level and mortality in patients with critical lower limb ischaemia. Eur J Vasc Endovasc Surg. 2001;22(2):124–129. doi: 10.1053/ejvs.2001.1431. [DOI] [PubMed] [Google Scholar]
- 29.Ninomiya T, Nagata M, Hata J. et al. Association between ratio of serum eicosapentaenoic acid to arachidonic acid and risk of cardiovascular disease: the Hisayama Study. Atherosclerosis. 2013;231(2):261–267. doi: 10.1016/j.atherosclerosis.2013.09.023. [DOI] [PubMed] [Google Scholar]