Relationship of high-sensitive C-reactive protein with cardiovascular risk factors, clinical presentation and angiographic profile in patients with acute coronary syndrome: An Indian perspective

Dear Editor

We would like to report our research findings about hs CRP and its correlation with conventional risk factors and angiographic severity of CAD among patients of acute coronary syndromes.

1. Introduction

Worldwide, atherosclerotic cardiovascular disease (CVD) including coronary artery disease (CAD) is estimated to be the leading cause of death and loss of disability-adjusted life years. Unfortunately, while the incidence and prevalence of CVD is now declining in the developed countries, it continues to increase exponentially in the developing nations. Reddy reported that from 1970 to 2015, mortality from CVD was projected to almost double in the developing countries while it was projected to decline during the same period in the developed nations.¹ The Global Burden of Diseases (GBD) study reported the estimated mortality from CAD in India to be roughly 1.6 million in the year 2000.²

Several modifiable and non-modifiable risk factors have been identified to cause CVD. The major modifiable risk factors include hypertension (HTN), diabetes (DM), smoking and hyperlipidemia and whereas non-modifiable risk factors include age, gender and family history of premature CAD. However, not all coronary events can be predicted by these risk factors. In particular, nearly half of all myocardial infarctions or stroke occurs among individuals without hyperlipidemia. Consequently, alternate risk assessment approaches are being explored to facilitate early and accurate identification of individuals at risk of having CVD. Since atherosclerosis is an inflammatory process, several markers of inflammation have been evaluated for this purpose. Among them, high-sensitive C-reactive protein (hs-CRP) has emerged as the most important CV risk marker. More than a simple marker of inflammation, hs-CRP may influence vascular vulnerability directly through several mechanisms including, enhanced expression of adhesive molecules, reduced nitric oxide, increased expression of endothelial PAI-1 and altered LDL uptake by macrophages. A scientific statement issued by Centre for Disease Control (CDC) and American Heart Association (AHA) has mentioned hs-CRP as the only inflammatory marker that can be used for risk prediction both for primary and secondary prevention of cardiovascular events.³ However, very limited information is available about the relationship between various CV risk factors and hs-CRP levels and the significance of elevated hs-CRP in Indian patients, who as compared to the western populations have vast differences in CVD epidemiology. Therefore, this study was sought to assess the relationship between the levels of hs-CRP and clinical profile, CV risk factors and the coronary angiographic findings in Indian patients presenting with acute coronary syndrome (ACS).

2. Material and methods

This cross-sectional study was conducted at a tertiary care center in North India. All consecutive patients who presented with ACS over a period of two years and who consented to be included in the study were enrolled. The study eligibility of every participant was determined by the principal author, a Consultant in Cardiology, who was also responsible for the final adjudication of the diagnosis of ACS. The study protocol was approved by the Intuitional Research and Ethical Committee.

2.1. Inclusion criteria

As mentioned above, all consecutive patients with ACS including unstable angina (UA), non-ST elevation myocardial infarction (NSTEMI) and ST elevation myocardial infarction (STEMI) were enrolled in to the study. UA was diagnosed if the patient had at least one of the following- angina chest discomfort at rest lasting for ≥ 20 min, recent onset (less than one month) angina of sufficient severity or exertional angina with a crescendo pattern, along with either ST segment depression ≥ 0.5 mm or T inversion ≥ 0.3 mV in any two contiguous leads. If the patient also had elevated Troponin T as a marker of myocyte necrosis, he was labeled to have suffered NSTEMI. However, for the diagnosis of STEMI, the patients needed to have symptoms consistent with acute myocardial infarction (AMI) [chest discomfort with or without radiation to arm(s)/jaw/back/epigastrium, weakness, diaphoresis, nausea, light headedness] of greater than 30 min duration, with ECG changes of STEMI i.e. ST elevation of at least 0.1 mV in 2 contiguous precordial leads or 2 limb leads or new/presumably new left bundle branch block.

2.2. Exclusion criteria

All patients with recent or ongoing infection or fever, chronic inflammatory disorders e.g. rheumatoid arthritis, systemic lupus erythematosus etc or any other condition which could have affected hs-CRP levels were excluded from the study.

2.3. Clinical evaluation and investigations

Once enrolled into the study, all patients underwent detailed clinical assessment, biochemical investigations and coronary angiography. Clinical evaluation included detailed history regarding the presenting symptoms, presence or absence of various conventional CV risk factors, socioeconomic status (SES) of the patients, followed by general physical and cardiovascular system examination including height, weight, calculation of body-mass index (BMI), waist-to-hip ratio (WHR) measurement and blood pressure (BP) measurement. BMI was calculated as weight (in kg)/height² (in meters). The patients with BMI > 30 kg/m² were considered obese. Waist and hip circumferences were measured in the standing position, using a non-stretchable standard tape measure. The waist circumference was measured at the narrowest point between the costal margin and iliac crest and hip circumferences at the level of the widest diameter around the buttocks. Central obesity was defined as the WHR > 0.9 for males and >0.8 for females.

All patients also underwent a complete dental examination by a trained dentist to look for definitive evidence of periodontitis. The examination consisted of determination of suppuration index, plaque index (PI), gingival index (GI), pocket depth (PKT), bleeding index (BI), attachment loss measurements (AL), and tooth mobility. Missing and deciduous teeth were also recorded.^4,5

The biochemical investigations included routine blood investigation such as hemoglobin level, white blood cell count, blood urea, serum creatinine, serum electrolytes levels, fasting blood glucose (FBG) estimation, fasting lipid profile and hs-CRP measurement. Fasting lipid profile was performed using commercial kits from Boehringer Mannheim. Low-density lipoprotein (LDL) cholesterol was calculated by using the Friedewald equation: LDL cholesterol = total cholesterol – [(Triglycerides/5) + high-density lipoprotein (HDL) cholesterol].

The hs-CRP estimation was done at the time of presentation and the analysis was done by turbidimetry immunoassay using QUANTA Reagent kit (latex) manufactured by Tulip corporation, USA. Values of ≤1 mg/l, 1–3 mg/l and >3 mg/l were labeled as low risk, intermediate risk and high risk, respectively.

The selective coronary angiography was performed in all patients who consented for the same (71.8% of all). The timing of coronary angiography was determined in accordance with the accepted treatment protocols for the patients with ACS. Images in multiple views were obtained by standard technique to access both the extent and severity of disease. Significant CAD was defined as at least 70% reduction in the diameter of major epicardial coronary arteries i.e. left anterior descending (LAD), left circumflex (LCx) or right coronary artery (RCA) and their branches; or 50% luminal narrowing of the left main coronary artery (LMCA). Patients were classified as having single-vessel disease (SVD), double-vessel disease (DVD) or triple vessel disease (TVD) accordingly. Presence of significant CAD in LMCA was classified as DVD.

2.3.1. Criteria for CV risk factors, metabolic syndrome (MS) and SES

For the purpose of the present study, DM was defined as deranged FBG level ≥ 126 mg/dl or a patient who was already on treatment for diabetes. HTN was defined as 2 or more BP readings of >140 mmHg systolic BP or >90 mmHg diastolic BP, or a patient who was already on anti-hypertensive medication. Smoking was defined as the regular smoking of tobacco in any form currently or within the last 1 year. A positive family history of premature CAD was defined as the presence of documented CAD in a first-degree relative before 55 years of age in males and before 65 years of age in females. Dyslipidemia was defined by presence of any one of the following: LDL cholesterol > 130 mg/dl, TG ≥ 150 mg/dl or HDL cholesterol <40 mg/dl in men and <50 mg/dl in women.

The MS was defined using the National Cholesterol Education Program- Adult Treatment Panel III criteria as presence of ≥3 of the following vascular risk factors – waist circumference > 102 cm in men or > 88 cm in women, fasting triglycerides ≥ 150 mg/dl, HDL-cholesterol < 40 mg/dl in men or <50 mg/dl in women, BP ≥ 130/85 mmHg or use of blood pressure medication, and FBG ≥ 110 mg/dl.⁶

For determination of SES of the patients, modified Kuppuswamy's scale⁷ was used which included education (maximum 7 points), profession (maximum 10 points) and income (maximum 12 points). The patients were categorized in to lower, middle and upper SES if the total points were ≤10, 11–25 or >25, respectively.

2.4. Statistical analysis

The data was analyzed using Statistical Package for Social Sciences (SPSS) Version 15.0. Values were expressed as mean (±standard deviation) or as percentages. Comparisons between the groups were done using student's unpaired t test or chi-square test wherever appropriate. A p < 0.05 was considered statistically significant.

3. Results

We studied 337 subjects including 287 (85.2%) males and 50 (14.8%) females. The mean age of the subjects was 58.32 ± 11.24.

Overall, 69 (20.5%), 68 (20.2%) and 200 (59.3%) patients had hs-CRP levels <1 mg/l, 1–3 mg/l and >3 mg/l, respectively. Table 1 shows relationship of hs-CRP levels with the gender and Table 2 shows the relationship between hs-CRP levels and the SES. The female patients had higher levels of hs-CRP with 76% having values >3 mg/l as compared to only 56.5% male patients (p = 0.02). A total of 104 patients (30.9%) belonged to lower SES, 207 (61.4%) to middle SES and 26 (7.7%) to upper SES. The prevalence of high hs-CRP (>3 mg/l) was significantly higher in the lower SES (78.8%) as compared to the upper SES (46.2%, p < 0.05).

Table 1.

Levels of hs-CRP in relation to gender profile of the patients.

Gender	hs-CRP categories			p
	<1 mg/l n = 69	>1–3 mg/l n = 68	>3 mg/l n = 200
Females n = 50	4 (8)	8 (16)	38 (76)	0.02
Males n = 287	65 (22.6)	60 (20.9)	162 (56.5)

Values in parentheses represent proportion of the population belonging to the particular gender.

Table 2.

Levels of hs-CRP in relation to the socioeconomic status of the patients.

Risk factor	Hs-CRP categories			χ2	p
	<1 mg/l n = 69	>1–3 mg/l n = 68	>3 mg/l n = 200
Lower SE Class, n = 104	6 (5.8)	16 (15.4)	82 (78.8)	27.237	<0.001
Middle SE Class, n = 207	57 (27.5)	44 (21.3)	106 (51.2)	19.368	<0.001
Upper SE Class, n = 26	6 (23.1)	8 (30.8)	12 (46.2)	2.486	0.289

Values in parentheses represent proportion of the population in the particular socioeconomic class.

Table 3 shows values of hs-CRP according to the different CV risk factors. The smokers were found to have significantly higher proportion of patients with higher CRP (55.3% with >3 mg/l as compared to 18.8% with <1 mg/l, p = 0.03 for comparison with non-smokers). Similarly, the patients with MS, central obesity and periodontitis were also found to have greater prevalence of elevated hs-CRP levels. In contrast, no statistically significant association was seen between hs-CRP levels and HTN, DM and dyslipidemia.

Table 3.

Levels of hs-CRP in relation to various cardiovascular risk factors.

Risk factor	hs-CRP categories			p
	<1 mg/l n = 69	>1–3 mg/l n = 68	>3 mg/l n = 200
Smoker, n = 170	32 (18.8)	44 (25.9)	94 (55.3)	0.031
Metabolic syndrome, n = 62	4 (6.5)	10 (16.1)	48 (77.4)	0.002
Central obesity, n = 114	24 (21.1)	14 (12.3)	76 (66.7)	0.032
Periodontitis, n = 102	10 (9.8)	16 (15.7)	76 (74.5)	<0.001
Hypertension, n = 136	30 (22.1)	22 (16.2)	84 (61.8)	0.315
Diabetes, n = 102	26 (25.5)	14 (13.7)	62 (60.8)	0.088
Dyslipidemia, n = 195	33 (16.9)	36 (18.5)	126 (64.6)	0.058
Premature CAD, n = 52	2 (3.8)	8 (15.4)	42 (80.8)	0.001

Values in parentheses represent proportion of the population with the particular risk factor.

Overall, 52 patients had presented with premature CAD (age of onset <45 years). Among them, the majority (80.8%) had high hs-CRP levels with only few (3.8%) having hs-CRP levels within the normal limits (<1 mg/l, p = 0.001).

Figs. 1 and 2 depict relationship between hs-CRP levels and the type of ACS and the angiographic extent of CAD, respectively. Nearly two-thirds of the patients with STEMI had hs-CRP levels above 3 mg/l as compared to only half with UA/NSTEMI (p value < 0.001). Similarly, majority of the patients with SVD had hs-CRP levels <1 mg/l whereas most of the patients with TVD had elevated (>3 mg/l) hs-CRP levels (p < 0.001).

Fig. 1.

Levels of hs-CRP in relation to the type of ACS (p < 0.001 for comparison between STEMI and UA/NSTEMI).

Fig. 2.

Levels of hs-CRP in relation to the angiographic extent of CAD (p < 0.001 for comparison).

4. Discussion

Epidemiological studies have revealed that the prevalence of CVD in India is increasing along with the prevalence of conventional risk factors for CVD. Present health transition from predominance of infections to the preponderance of cardiovascular disorders, such as HTN, DM and CVD is now responsible for 53% of all deaths in India. Indians have one of the highest rates of heart disease in the world and the disease also tends to be more aggressive and manifests at a younger age. Consequently, prevention of CVD has become one of the most important public health challenges of our times. Several modifiable and non-modifiable factors such as HT, DM, smoking etc are recognized as major risk factors for CVD and aggressive correction of these play vital role in CVD prevention. However, not all adverse CV events can be predicted or explained by these conventional risk factors, which limits our ability to accurately identify the individuals who are at “high risk” of developing CVD. Therefore, a host of alternate risk assessment approaches such as imaging of subclinical atherosclerosis, detection of vascular inflammation etc are being evaluated to overcome this limitation and to provide more accurate risk estimates in any given individual.

Numerous studies have provided the evidence that inflammation plays a central role in the occurrence of CVD.^8–10 Accordingly, several mediators of the inflammatory response, including acute-phase proteins, cytokines and cellular adhesion molecules have been evaluated as potential indicators of the risk of a first acute atherothrombotic event, as well as of recurrent complications after initial presentation.¹¹ As the prototypical acute-phase reactant, hs-CRP has been the focus of much of the clinical investigation.¹² Various epidemiological studies have demonstrated that hs-CRP is a strong predictor of future cardiovascular events.^13–15 The relationship between baseline hs-CRP and future CV events in most cases has been proven independent of the major traditional risk factors evaluated in daily clinical practice. In terms of clinical application, hs-CRP seems to be a stronger predictor of CV events than LDL cholesterol, and it adds prognostic information at all levels of calculated Framingham risk and at all levels of MS. Using widely available high sensitivity assays, hs-CRP levels of ≤1, 1 to 3, >3 mg/l correspond to low, moderate and high risk groups for future CV events. An added advantage of hs-CRP is that its levels have been shown to be stable with little or no diurnal variation,¹⁶ making hs-CRP the most commonly used and best standardized inflammatory marker of CV and metabolic disorders.¹⁷ Unfortunately, very limited information is available about hs-CRP levels and their relationship with CV risk factors or incident CVD in Indian studies. Our study therefore provides important insights in to this aspect which is eminently pertinent to day-to-day clinical practice.

In our study, women were found to have higher hs-CRP levels as compared to men. This is consistent with the previous population studies that have shown that the levels of hs-CRP are usually higher in women in healthy populations.¹⁸ Whether this information implies the need to have gender-specific cut-off values of hs-CRP for prediction of CV risk needs to be evaluated in large-scale outcome studies.¹⁹

For many decades and across multiple nations, differences in SES have been consistently associated with variations in CVD and mortality rates. Low SES is associated with an increased risk of CAD with greater morbidity and mortality.²⁰ However, the mechanisms by which low SES leads to adverse cardiovascular outcomes are not very well known. Previous studies have shown that the patients belonging to low SES tend to have higher CRP levels, suggesting a link between inflammation and increased risk of CVD in these individuals. Lubbock et al²¹ in their study showed that after adjustment for traditional cardiovascular risk factors and potential confounding variables, lower income and education remained associated with higher CRP levels. Similarly, Sethi et al²² also found that significantly higher number of patients with high hs-CRP (>3 mg/l) were from low SES. In our study, we too found that the patients from low SES had significantly higher prevalence of elevated hs-CRP levels as compared to those from upper SES.

In our study, higher hs-CRP levels were also found to be associated with smoking, MS and central obesity. These findings were consistent with several previous studies showing similar results.^23–29 It has been shown that the hs-CRP levels are not only elevated in patients with MS but may also predict the development of MS.³⁰

During the last two decades, there has been an increasing interest in the impact of oral health on atherosclerosis and subsequent CVD. The advent of the inflammation paradigm in coronary pathogenesis stimulated research in chronic infections caused by a variety of micro-organisms – such as Chlamydia pneumoniae, Helicobacter pylori, and cytomegalovirus – as well as dental pathogens. Several epidemiological studies investigating the relation between infections – including dental infections – and various clinical manifestations of atherosclerotic vascular disease have been published suggesting periodontal disease as a risk factor for CVD. Results of our study documented higher hs-CRP levels of >3 mg/l being significantly associated with periodontitis. It was seen that amongst patients with high hs-CRP (>3 mg/l), the incidence of periodontitis was 38% whereas in low hs-CRP (<1 mg/l) it was only 14.5%, which were in accordance with data shown by Slade et al,³¹ Glurich et al³² and Noack et al.³³ Similarly Joshipura et al³⁴ have published cross-sectional data from the prospective male health professionals' follow-up study, where self-reported periodontal disease was analyzed in a sample of 468 men with respect to a variety of biomarkers of CAD. Their results showed, in part, that periodontal disease was associated with higher levels of CRP, thereby supporting the hypothesis that periodontal disease might also be causally linked with CAD.

However, in our study we did not find significant association between elevated hs-CRP levels and HTN, DM or dyslipidemia. These findings were quite unexpected and contrary to the previous literature on this subject.^35–41 It is possible that the concomitant lifestyle modification and antidiabetic and lipid-lowering agents in some of these patients might have confounded this relationship.^42–47 In addition, genetic factors may also have contributed to the lack of association between hs-CRP levels and HTN, DM and dyslipidemia. CRP levels are a complex phenotype with both genetic and environmental determinants. Recent work has highlighted the impact of genetic variants on CRP levels.⁴⁸ Baseline levels of CRP show a clear heritability of approximately 40% in studies of families⁴⁹ whereas Brull et al⁵⁰ have shown a genetic determinant in both baseline levels and response to stimulation, which may involve separate mechanisms. Moreover, genetic variants on the CRP locus and other loci may influence the effect of dietary and lifestyle factors on hs-CRP levels and may contribute to inter- individual variability of plasma hs-CRP concentrations. In addition, these genetic variants have been shown to affect even the CRP response to pharmacological agents such as fenofibrate.⁵¹ Unfortunately, due to logistic reasons, we could not evaluate the impact of these measures on the relationship between hs-CRP and HTN, DM and dyslipidemia.

In present study, elevated hs-CRP levels were significantly more common in patients with premature CAD as compared to the older patients. Similar results were observed in a study where hs-CRP levels were increased significantly (p < 0.0001) in patients of premature CAD as compared to controls and hs-CRP levels were in high risk range in all the young patients.⁵²

The patients with STEMI are known to have higher peak hs-CRP levels as compared to those with UA/NSTEMI.⁵³ Moreover, a study by Brunetti et al⁵⁴ reported that plasma CRP concentrations showed a different release curve with Q-wave AMI in comparison with non Q-wave AMI and patients with UA. The higher increase in CRP levels during Q-wave MI than in non Q-wave MI seems to be linked to the extension of myocardial damage, rather than to the pre-existing inflammation. Similar results were obtained in the present study also.

In our study, we found significant correlation between the extent of CAD and hs-CRP levels, similar to several previous studies.^54,55 Nyandak et al⁵⁵ observed a significant correlation between the hs-CRP levels and the extent of CAD as well as the angiographic stenosis score. A study from Zairis and colleagues also reported that hs-CRP concentration correlated with the stenosis complexity in patients with acute coronary syndrome.⁵⁶ These findings suggest that higher hs-CRP level also reflect increased disease burden apart from being just an indicator of the presence of ACS. It further corroborates the belief that inflammation is not only an important trigger mechanism of ACS related to plaque rupture, but also a promoter of chronic atherosclerosis.

5. Limitations

Our study had several limitations that merit attention. As discussed above, due to logistic reasons, we could not assess the impact of ongoing pharmacological and non-pharmacological measures on hs-CRP levels. However, high prevalence of elevated hs-CRP levels along with a significant association with the angiographic extent of CAD found in our study suggests that the ongoing therapies, if at all, did not materially affect the overall pattern of hs-CRP levels in these patients. Another important limitation of our study was that we measured hs-CRP levels in patients with ACS whereas the prognostic value of hs-CRP for CV risk prediction has been established largely in patients with stable CAD or those with CAD. Nevertheless, the findings of the present study have helped demonstrate important associations between hs-CRP levels and the different aspects of CAD (CV risk factors, type of ACS, angiographic extent of CAD, etc) in Indian patients which had been lacking thus far.

6. Conclusions

The present study, for the first-time, demonstrated that in Indian patients presenting with ACS, the hs-CRP levels correlate with several CV risk factors such as smoking, MS, obesity etc, lower SES, clinical evidence of periodontitis, the type of ACS and the angiographic severity of CAD. We also found that the hs-CRP levels were higher in women as compared to men implying a need to have different gender-specific cut-off values for hs-CRP for prediction of CV risk. However, we did not find any significant association between hs-CRP levels and HTN, DM and dyslipidemia which needs to be explored in future, larger studies.