C-reactive protein, clinical presentation, and ischemic activity in patients with chest pain and normal coronary angiograms

Patients

We studied 164 consecutive patients who were referred to our CPNCA clinic from September 1996 to February 2002. All had typical anginal chest pain on effort and/or at rest, and completely normal coronary angiograms. As part of their clinical characterization, all patients underwent clinical and risk factor assessment, baseline 12-lead electrocardiogram (ECG), M-mode and two-dimensional echocardiography, and provocative testing for coronary artery spasm with hyperventilation or ergonovine.

Ten patients with left bundle branch block on the baseline ECG, two with dilated cardiomyopathy, six with coronary artery spasm, five with systemic inflammatory conditions, and one with prostatitis were excluded. In addition, three patients who returned an incomplete angina questionnaire were also excluded from study.

We, thus, enrolled 137 patients (mean age, 57 ± 9 years; 33 men), all of whom completed a standardized angina and cardiovascular risk factor questionnaire and also underwent exercise treadmill stress testing and 24-h continuous ECG Holter monitoring. Venous blood samples were taken at study entry and kept frozen at −80°C for measurement of serum high-sensitivity C-reactive protein (hs-CRP) concentration at a later time.

The study protocol was approved by the local research ethics committee, and all subjects signed informed written consent before study entry.

Angina and cardiovascular risk factor questionnaires

Temporal onset of pain, number of anginal episodes per week, average duration of episodes, triggers of chest pain, association of chest pain with exertion, presence of chest pain at rest, and classical risk factors such hyperlipidemia, diabetes mellitus, hypertension, and current or past smoking were investigated.

Chest pain weekly occurrence was subsequently grouped in three categories: <2, 2 to 4, and ≥5 episodes per week. Average duration of individual anginal episodes was also grouped in three categories: < 5, 5 to 20, and >20 min. The circumstance of occurrence of angina was also noted, that is, exertional chest pain, pain at rest, and their combination.

24-h continuous ambulatory ECG monitoring

Three-channel 24-h Holter monitors with amplitude-modulated recording (Marquette 8500, Marquette Electronics Inc., Milwaukee, Wisconsin) were used to record ST-segment changes during patients routine daily activities; ST-segment analyses (Marquette 8000 laser Holter, version 5) were performed after each recording was completely edited and artifacts removed. Ischemic episodes were defined as horizontal or downsloping ST-segment depression >1.0 mm (0.1 mV) measured at 0.08 s after the J-point and persisting for ≥1 min. Holter recordings were analyzed independently by two investigators who were blind to the patients’ clinical data.

Treadmill exercise stress testing

All treadmill exercise tests were carried out in the morning between 9:00 amand 10:30 amafter patients discontinued cardiac medications for at least 48 h. The Bruce protocol was used in all patients (CASE Marquette 12, Marquette Electronics, Milwaukee, Wisconsin). Three ECG leads (V₂to V₅and aVF) were continuously monitored during the test. A standard 12-lead ECG was printed and blood pressure measured (cuff sphygmomanometer) at baseline, at the end of each stage, at peak exercise, as well as at the onset of chest pain and/or significant ST-segment depression. Time to 1-mm ST-segment depression and total exercise time were recorded. Patients’ recovery was continuously monitored until the return of ST-segment to baseline levels, or for up to 6 min when tests were negative.

The exercise test was terminated when one or more of the following end points were reached: physical exhaustion, progressive severe angina, ST-segment depression ≥3 mm, dyspnea, and severe arrhythmias.

A test was considered “positive” when ≥1 mm ST-segment (horizontal or downsloping) at 0.08 s from the J-point was observed in two contiguous leads. In patients with positive test results, duration of exercise, heart rate-blood pressure product at 1 mm ST-segment depression and at peak exercise, and total ST-segment depression (mm) were measured. In patients with negative tests results, duration of exercise and rate pressure product were measured at peak exercise.

Crp assessment

Fasting blood samples were collected in tubes containing citrate, and were drawn and centrifuged immediately. Serum was then aliquoted and stored at −80°C until analysis. No specimen inadvertently thawed during storage. C-reactive protein measurements were performed on the COBAS Integra (Roche Diagnosis Limited, East Sussex, United Kingdom) using the CRP-latex assay in both the high-sensitivity application (analytical range, 0.2 to 12 mg/l) and the normal application (analytical range, 2 to 160 mg/l). Analytical precision of the hs-CRP–latex assay was 7.6% at a level of 1.02 mg/l, 3.3% at 1.79 mg/l, and 1.3% at a level of 4.36 mg/l. Samples outside the analytical range of the hs-CRP–latex assay were analyzed by the CRP-latex assay in the normal application. The analytical precision of the normal CRP-latex assay was 2.4% at a level of 29.5 mg/l and 1.3% at a level of 113 mg/l.

Statistical analysis

Baseline demographic and biochemistry analytical information is presented as mean ± SD for continuous variables and as absolute number (percentage) for categorical variables. Comparison of hs-CRP levels among patients with different chest pain duration, different number of weekly episodes, and different circumstances of occurrence of angina was carried out with one-way analysis of variance. When this analysis showed statistical significance, post-hoc Bonferroni test was applied to assess individual differences. To evaluate whether cardiovascular risk factors would alter these results, univariate analysis of variance was carried out. Comparison of hs-CRP levels among patients with positive or negative exercise stress test or Holter monitoring was carried out using the Student ttest. To assess the relationship of the results of exercise stress testing and 24-h ECG monitoring with the severity of anginal symptoms, the chi-square test was applied. The Spearman rank correlation test was used to assess the relation between hs-CRP concentration and ST-segment depression in the 24-h Holter, the maximal ST-segment depression and the heart rate-blood pressure product at 1-mm ST-segment depression in the exercise stress test. Logistic regression analysis was carried out to assess independent predictors for positive (≥1 mm ST-segment depression) or negative (<1 mm ST-segment depression) exercise stress test and Holter results.

Traditional risk factors used in the multivariable analyses included smoking history, diabetes, diagnosis of hypertension, and cholesterol levels. Statistical analysis was performed using SPSS for Windows (version 10.0, SPSS Inc., Chicago, Illinois). All p values are two-tailed, and confidence intervals (CI) have been calculated at the 95% level.

Clinical characteristics and hs-CRP levels

Baseline hs-CRP levels in the whole patient population ranged from 0.1 to 17.2 mg/l (mean 2.0 ± 2.5 mg/l).

Patients with prolonged angina episodes (>20 min) had significantly higher hs-CRP levels (3.9 ± 4.1 mg/l) than patients with moderate (5 to 20 min) duration of pain (1.5 ± 1.4 mg/l; p < 0.001) and those with short-lasting (<5 min) episodes (1.5 ± 1.3 mg/l; p < 0.001). Similarly, patients with a greater number of chest pain episodes (≥5 per week) had significantly higher levels of hs-CRP (2.9 ± 3.3 mg/l) than patients with two to four episodes (1.6 ± 1.7 mg/l; p = 0.015) and those with <2 episodes of chest pain (1.3 ± 1.2 mg/l; p = 0.004), as shown in Figure 1. These significant differences were maintained after adjustment for traditional risk factors; hs-CRP concentration was nonsignificantly (p = 0.6) higher in patients with both exertional and rest pain (2.2 ± 2.5 mg/l) compared with patients with exertional chest pain only (1.8 ± 2.5 mg/l) or those with predominantly rest chest pain (1.7 ± 1.7 mg/l).

• Download figure
• Open in new tab
• Download powerpoint

Figure 1

Error barsgraph showing high-sensitivity C-reactive protein (hs-CRP) concentrations (mean ± 2 SE) compared with number of chest pain episodes per week (A)and duration of chest pain episodes (B).

Exercise stress testing, 24-h ECG holter data, and hs-CRP levels

In patients with a positive exercise stress test, hs-CRP level was significantly higher (2.6 ± 2.8 mg/l) than in patients with a negative exercise stress test result (1.1 ± 1.1 mg/l; p < 0.001). Similarly, patients with ischemic episodes during 24-h Holter monitoring had higher hs-CRP levels (3.4 ± 3.1 mg/l) compared with patients without ST-segment shifts (0.9 ± 0.7 mg/l; p < 0.001). These differences remained significant after adjustment for traditional risk factors.

The number of ischemic episodes during the 24-h ECG Holter monitoring was significantly correlated with hs-CRP concentration (Spearman r = 0.65; p < 0.001). When analysis was limited to the 86 patients with a positive exercise stress test result, both ST-segment depression at peak exercise and rate pressure product at 1-mm ST-segment depression correlated significantly with hs-CRP levels (Spearman r = −0.43; p < 0.001 and Spearman r = −0.42; p < 0.001, respectively) (Fig. 2).

• Download figure
• Open in new tab
• Download powerpoint

Figure 2

Spearman correlations among high-sensitivity C-reactive protein (hs-CRP) concentrations, number of episodes of ST-segment depression during 24-h electrocardiogram Holter monitoring (A), ST-segment depression during exercise stress testing (B), and rate-pressure product (RPP) at 1-mm ST-segment depression during exercise stress testing (C).

Binary logistic regression showed that hs-CRP was the only variable able to predict exercise stress test results (odds ratio [OR], 1.7; 95% CI, 1.2 to 2.2) and the presence of ST-segment depression episodes during 24-h ECG Holter monitoring (OR, 3.8; 95% CI, 2.3 to 6.2).

Crp, endothelial dysfunction, and myocardial ischemia in syndrome X

Yudkin et al. (17)showed in a cross-sectional study of healthy subjects that CRP concentrations were related to biochemical markers of endothelial dysfunction. Fichtlscherer et al. (11)reported that elevated CRP levels in patients with coronary artery disease were associated with a profound impairment of systemic endothelial vascular reactivity. More importantly, they also reported that normalization of CRP levels over time was associated with a significant improvement of endothelium-dependent flow responses. Further data endorsing a role of CRP in endothelial dysfunction were gathered by Pasceri et al. (12), who reported that CRP induced the expression of ICAM-1 and VCAM-1 in both umbilical vein and coronary artery endothelial cells. These findings suggest that CRP was not merely an inflammatory marker but also a potential cause of impaired endothelial function.

We have previously shown that plasma ET-1, a powerful microvascular vasoconstrictor agent, is raised in patients with syndrome X and that “high” plasma ET-1 levels were associated with an earlier onset of chest pain during exercise (4)and with a reduced coronary flow response during rapid atrial pacing (10). Recently, Desideri et al. (5)found that syndrome X patients had an increased responsiveness of ET-1 to glucose loading, suggesting that these patients were more susceptible to releasing ET under stressful circumstances.

The mechanisms responsible for myocardial ischemia in patients with CPNCA remain poorly understood, but increased vasoconstrictor and abnormal vasodilator responses, due to endothelial dysfunction, have been suggested as possible candidates (6,7). Reversible myocardial perfusion defects in areas supplied by arteries showing endothelial dysfunction, the production of transmyocardial lactate (21), lipid hydroperoxides and conjugated dienes (22)during atrial pacing, and a decrease of pH and oxygen saturation (23)in the coronary sinus of patients with syndrome X undergoing atrial pacing, indicate that myocardial ischemia may indeed be responsible for chest pain and ECG changes in these patients. More recently, using cardiac magnetic resonance, Buchthal et al. (3)and Panting et al. (2)have objectively shown the presence of myocardial ischemia in syndrome X patients.

Previous studies from our group showed the occurrence of increased ICAM-1 and VCAM-1 levels in syndrome X patients that were comparable to elevations in coronary artery disease patients and significantly larger than levels found in healthy individuals (9). Taken together, these findings and the results of the present study suggest that inflammatory mechanisms may be responsible, at least in part, for endothelial dysfunction and increased disease activity in patients with cardiac syndrome X.

Conclusions

High-sensitivity C-reactive protein correlates with symptoms and ECG markers of myocardial ischemia in CPNCA patients. Whether hs-CRP is related to the pathogenesis of angina in these patients deserves further investigation.