Prognostic Value of Systemic Endothelial Dysfunction in Patients With Acute Coronary Syndromes
Further Evidence for the Existence of the “Vulnerable” Patient
Background— Endothelial vasodilator dysfunction may serve as a marker integrating the vascular risk of an individual; however, whether systemic vasodilator function predicts disease progression and cardiovascular event rates in patients with manifest acute coronary syndromes (ACS) is unknown.
Methods and Results— In 198 patients with angiographically documented ACS, forearm blood flow (FBF) responses to acetylcholine (ACH; 10 to 50 μg/min) and sodium nitroprusside (SNP; 2 to 8 μg/min) were measured by venous occlusion plethysmography before hospital discharge within 5 days of an episode of an ACS. Cardiovascular events (cardiovascular death, myocardial infarction, and ischemic stroke) served as outcome variables over a mean follow-up period of 47.7±15.1 months. Patients who experienced cardiovascular events during follow-up (n=31) had a significantly reduced vasodilator response to ACH (P<0.05) and SNP (P<0.05). By multivariate analysis, vasodilator response to ACH and elevated troponin T serum levels were the only significant (P<0.05) independent predictors of a poor prognosis, even after adjustment for traditional cardiovascular risk factors, concurrent medication, invasive treatment strategy, and C-reactive protein serum levels. Recovery of endothelium-dependent vasoreactivity as assessed by repeated FBF assessment 8 weeks after the index measurement after the ACS predicted further event-free survival in a subset of 78 patients.
Conclusions— Systemic endothelium-dependent vasoreactivity predicts recurrence of instability and cardiovascular event rates in patients with ACS. Furthermore, the recovery of systemic endothelial function is associated with event-free survival. Assessment of systemic vasoreactivity, measured by a minimally invasive test, provides important prognostic information in addition to that derived from traditional risk factor assessment in patients with ACS.
Received February 1, 2004; de novo received May 14, 2004; accepted June 29, 2004.
Rupture or endothelial erosion of a coronary plaque with subsequent thrombosis represents the pathomorphological substrate of acute coronary syndromes.1,2 Clinically, the transition from stable coronary artery disease to acute coronary syndromes coincides with elevated levels of inflammatory markers like C-reactive protein, amyloid A, or interleukin-6,3–5 which suggests that local inflammatory mechanisms may contribute to plaque instability.6,7 More recently, acute coronary syndromes were shown to be associated with a transient acute, widespread coronary inflammatory process, not confined to the culprit artery responsible for the acute coronary syndrome, but correlated with systemic levels of C-reactive protein.8 Moreover, the persistence of elevated systemic inflammatory markers was shown to predict recurrence of coronary instability in patients surviving an acute coronary syndrome.9,10 These observations prompted the hypothesis that there may be not only isolated or multiple inflamed vulnerable plaques or a locally vulnerable endothelium but also some inflamed patients who remain vulnerable for a period of weeks and months and who could be identified by persistent elevation of systemic inflammatory markers.11
The vascular endothelium is a primary target for inflammatory mediators. Functionally, endothelial inflammatory activation is associated with a profound impairment in endothelium-dependent vasodilator function.12–14 As such, endothelial function may be regarded as an integral index of all inflammatory mediators present in an individual and thus may represent the vascular phenotype of an inflamed patient. Therefore, we tested the hypothesis that assessment of systemic endothelial vasodilator function provides prognostic information in patients suffering from an acute coronary syndrome and is capable of identifying the vulnerable patient who is prone to experience recurrence of instability.
A total of 198 patients were studied within 5 days of an acute coronary syndrome, which was defined as angina at rest and alterations of the ST segment, excluding ST elevation, with or without elevation of troponin T. In all patients, the culprit lesion was documented by coronary angiography.
Patients with impaired left ventricular ejection fraction (<45%) as assessed by echocardiography were excluded. Moreover, patients with any evidence of inflammatory or malignant disease were excluded. Screening tests were performed by evaluation of the patient’s history, white blood cell count, and, if required, urinary test or radiograph of the chest.
For the follow-up period, all patients were given aspirin (100 mg/d) and β-blocker therapy. For forearm blood flow (FBF) measurements, vasoactive medications such as calcium channel blockers, ACE inhibitors, and long-acting nitrates were withheld at least 24 hours before the study. In contrast, aspirin, β-blockers, and statins were not discontinued.
FBF measurements were performed as described previously.13 In brief, all FBF measurements were performed in the morning in a quiet, temperature-controlled room at 22°C (72°F). Patients were asked to refrain from drinking alcohol or caffeine and from smoking for 12 hours before the examination. Under local anesthesia (<1.5 mL of 2% mepivacaine; Astra Pharmaceuticals) and sterile conditions, a 22-gauge catheter (Braun-Melsungen) was inserted into the brachial artery of the nondominant arm (left in most cases) for the infusion of drugs or saline. This arm was elevated above the level of the right atrium. All patients were allowed to rest for 20 minutes after catheter placement to achieve stable baseline measurements before data collection. FBF (mL · min−1 · 100 mL−1 forearm volume) was measured with venous occlusion plethysmography (model EC-4; D.E. Hokanson), with calibrated mercury-in-silastic strain gauges applied to the widest part of the forearm. Upper arm cuffs were intermittently inflated to 40 mm Hg for 10 seconds every 15 seconds to temporarily prevent venous outflow (rapid cuff inflator E-10; D.E. Hokanson). To exclude hand circulation from the blood flow, a wrist cuff was inflated to suprasystolic pressure. Flow measurements were recorded, and 6 readings were obtained for each measurement. Drug infusions were administered with a constant-rate infusion pump (Braun-Melsungen). Basal measurements were obtained after intra-arterial sodium chloride (0.9%) infusion (rate 1 mL/min). For the assessment of endothelium-dependent vasodilation, acetylcholine (Ciba Vision GmbH) was infused intra-arterially in increasing dosages of 10 to 50 μg/min with infusion rates of 0.8 to 1.2 mL/min. Sodium nitroprusside (Schwarz Pharma) was infused for assessment of endothelium-independent vasodilation in increasing dosages of 2 to 8 μg/min with infusion rates of 0.8 to 1.2 mL/min.
Analysis of the plethysmographic recordings was performed on the day of the measurement by a technician. All blood samples were obtained on the day of FBF measurement after puncture of the brachial artery.
Clinical long-term follow-up was performed with a questionnaire that was sent to patients; additionally, a telephone contact was performed. All information regarding potential cardiovascular events was validated by source data, including the analysis of coronary angiograms, discharge letters, or charts of hospital stays. Cardiovascular death was defined as death due to a myocardial or cerebral infarction or documented sudden cardiac death. Myocardial infarction was defined as an elevation of creatine kinase serum levels >2 times the upper limit or new ST elevations (>0.1 mV) in ≥2 leads. Ischemic stroke was defined as clinical evidence of stroke without intracranial hemorrhage on brain imaging studies. Because ACE inhibitors and statins influence both endothelial vasodilator function and disease progression, all medical therapy, especially with ACE inhibitors and lipid-lowering drugs, was documented. For the present analysis, we focused exclusively on hard end points, namely, death, myocardial infarction, and stroke.
Data are expressed as mean±SD. Statistical comparisons were made by the Student t test or by the nonparametric Mann-Whitney U test. Differences in forearm vascular reactivity to acetylcholine or sodium nitroprusside were examined by the general linear model procedure. Cumulative event rates were estimated by Kaplan-Meier survival curves for categorical variables. Probability values were determined by use of the log-rank statistic. For Kaplan-Meier analyses, vasodilator function of the forearm to acetylcholine or sodium nitroprusside was calculated as area under the curve (AUC) and divided into quartiles or tertiles, respectively. In addition, Cox regression analysis was used to examine the potential relationships between continuous variables and events during the follow-up period. Multivariate analysis with Cox regression techniques was performed to examine potential interactions among the entered covariates. The variables included in the model were FBF response to acetylcholine, PCI procedure, extent of coronary artery disease, C-reactive protein and troponin T serum levels, arterial hypertension, LDL cholesterol level, smoking, diabetes mellitus, and concurrent chronic medication with ACE inhibitors or statins.
Statistical significance was assumed if the null hypothesis could be rejected at the P=0.05 level. All statistical analysis was performed with SPSS for Windows 11.5 (SPSS Inc).
Baseline characteristics of the 198 patients are summarized in Table 1. The mean duration of follow-up was 47.7±15.1 months (range 11 to 1650 days). During follow-up, a total of 31 patients experienced a cardiovascular event (Table 2). Four patients died of cardiovascular causes, 24 had myocardial infarction, and 3 experienced an ischemic stroke.
Clinical Determinants of Prognosis
Patients who had a recurrent major cardiovascular event after surviving an episode of an acute coronary syndrome did not differ from patients with an uneventful course of disease with regard to classic risk factors for CAD, with the exception of diabetes, which was more frequently observed in patients with CV events during follow-up. Moreover, pharmacological treatment for secondary prevention did not differ between groups (Table 1). As expected, patients with recurrence of instability had significantly elevated troponin T levels, higher C-reactive protein serum levels, and more frequently underwent invasive revascularization procedures for treatment of the acute coronary syndrome qualifying for inclusion in the study. Serum LDL cholesterol levels were slightly but nonsignificantly lower in patients with recurrence of instability. Multivariate analysis with the Cox regression model revealed that elevated troponin T serum level was the only remaining independent predictor for a poor outcome after an episode of an acute coronary syndrome.
Systemic Vasoreactivity and Prognosis
As illustrated in Figure 1A, patients who had a recurrent major cardiovascular event during follow-up had a significantly blunted dose-dependent forearm vasodilator response to the endothelium-dependent mediator acetylcholine and to the endothelium-independent mediator sodium nitroprusside (Figure 1B).
Figure 2A shows the cumulative proportion of patients without recurring cardiovascular events according to quartiles of acetylcholine-induced FBF responses. The incidence of recurring cardiovascular events increased significantly with decreasing vasodilator responses to the intra-arterial infusion of acetylcholine. Although there was an overall association between major cardiovascular events and the vasodilator response to sodium nitroprusside, Kaplan-Meier analysis failed to achieve statistical significance.
Cox regression analysis with FBF responses to acetylcholine measured as AUC of the dose-response relation as a continuous variable also demonstrated a significant association with recurrence of cardiovascular events (P=0.03). In addition, the use of either the maximal acetylcholine response or the maximum percent increase from baseline in response to acetylcholine gave essentially identical results (P<0.01 and P=0.04, respectively). Thus, impaired systemic endothelial vasodilator function, measured in the forearm circulation, is associated with a significantly higher incidence of recurring cardiovascular events after an acute coronary syndrome.
To identify systemic vasodilator dysfunction as an independent predictor for recurrence of cardiovascular events, a multivariate analysis using the Cox regression model was performed, which included the classic risk factors for coronary artery disease, the extent of coronary artery disease, the use of PCI, the presence of ACE inhibitor or statin therapy for secondary prevention, and the established risk markers C-reactive protein and troponin T serum levels. As shown in Table 3, systemic endothelial vasodilator function remained a statistically significant independent predictor (RR 0.54, 95% CI 0.32 to 0.89), as did the serum marker troponin T (RR 2.12, 95% CI 1.0 to 4.4), whereas C-reactive protein levels or LDL cholesterol levels lost their significance once acetylcholine-mediated FBF responses were forced into the multivariate model. To exclude a potentially confounding effect of PCI to predict recurrence of cardiovascular events in our patient population, we performed an additional multivariate analysis restricted exclusively to patients undergoing PCI for treatment of the culprit lesion. Of these 144 patients, stent-PCI was performed in 122 patients with bare metal stents, whereas 22 patients underwent balloon angioplasty without stent implantation. No patient in the present study population underwent bypass surgery for treatment of the acute coronary syndrome. A total of 44 patients received glycoprotein IIb/IIIa inhibitors, which have been shown to affect endothelial vasodilator function,15 during the PCI procedure. As illustrated in Table 4, multivariate analysis restricted to the 144 patients who underwent PCI revealed similar results compared with the total study population, with P<0.02 for acetylcholine-induced blood flow responses, P<0.05 for troponin T, and P=0.29 for C-reactive protein serum levels. Thus, systemic endothelial vasodilator capacity provides additional prognostic information compared with the established risk markers to predict recurrence of instability in patients with acute coronary syndromes, even in those patients undergoing aggressive early revascularization procedures.
Recovery of Systemic Endothelial Vasodilator Function Predicts Event-Free Survival
Because previous studies demonstrated that inflammation-associated “stunning” of the endothelium is a transient phenomenon that resolves after elimination of the inflammatory stimulus,12,13,16 we tested the hypothesis that spontaneous recovery of systemic endothelial vasodilator function after an acute coronary syndrome might predict a beneficial course of disease. For this purpose, in 78 patients who initially did not experience recurrence of instability, we repeated FBF measurements under identical conditions 8 weeks after the index assessment during the acute coronary syndrome. In this patient cohort, a total of 11 events occurred subsequently after the repeated assessment of systemic endothelial function.
As illustrated in Figure 3A, FBF responses to acetylcholine remained severely depressed in those patients who had recurrence of instability >8 weeks after the initial event, whereas acetylcholine-induced FBF responses profoundly improved in those patients who had an uneventful follow-up. When the patient population was divided into tertiles according to the extent of improvement in acetylcholine-induced FBF responses within 8 weeks after an acute coronary syndrome, it was revealed that recurrence of instability was observed predominantly in those patients, in whom FBF responses to acetylcholine did not increase within 8 weeks after an acute coronary syndrome (Figure 3B). Moreover, receiver operating characteristic curve analysis revealed the significant predictive power of change in acetylcholine-induced FBF responses to predict recurrence of instability during follow-up (AUC 0.77; P=0.003; 95% CI 0.664 to 0.874 ). No such association was observed for FBF responses to the endothelium-independent vasodilator sodium nitroprusside (Figure 3C). Thus, recovery of endothelial vasodilator capacity is a significant determinant of a beneficial clinical course in patients with acute coronary syndromes.
The results of the present study demonstrate that impaired systemic endothelial vasodilator function is associated with future cardiovascular events in patients surviving an episode of an acute coronary syndrome. Moreover, endothelial vasodilator capacity of the forearm circulation appears to provide additional information compared with the inflammatory marker C-reactive protein to predict the recurrence of instability, which suggests that the assessment of systemic endothelial vasodilator function indeed provides an integrated index of all inflammatory mediators present in an individual and thus reflects the vascular phenotype of an inflamed patient. Finally, this is the first study to document that an improvement of systemic endothelial vasodilator dysfunction within a short time period of 8 weeks after an acute coronary syndrome is associated with significantly fewer future cardiovascular events.
We and others have previously demonstrated that dysfunction of either the coronary or peripheral vascular endothelium constitutes an independent predictor of cardiovascular events that provides valuable prognostic information in addition to that derived from conventional risk factor assessment.17–23 However, all of these previous studies were performed exclusively in patients either at risk or with established atherosclerotic diseases and purposely excluded patients with acute coronary syndromes. The present study considerably extends these previous findings by demonstrating that endothelial dysfunction is a systemic disorder that not only represents a critical element in the pathogenesis of atherosclerotic disease and its progression but, more importantly, predicts recurrence of instability in patients who survived an acute coronary syndrome. Inasmuch as the persistence of elevated systemic inflammatory markers predicts recurrence of instability,9,10 the vascular phenotype appears to reflect persistent inflammatory endothelial activation of the systemic circulation in patients who had coronary plaque rupture/erosion with ensuing acute coronary syndromes. Thus, the assessment of systemic endothelial vasodilator function appears to be able to identify the inflamed patient who remains vulnerable after an episode of acute coronary syndrome.
Indeed, by multivariate analysis, impaired systemic endothelial vasodilator function provided significant additional information compared with C-reactive protein serum levels to predict the recurrence of cardiovascular complications after an acute coronary syndrome. Moreover, those patients in whom systemic endothelial vasodilator function improved over 8 weeks after the acute coronary syndrome suffered significantly less frequently from recurring cardiovascular events compared with patients whose endothelial vasodilator function remained impaired over time. Taken together, these data indicate that systemic endothelial dysfunction may be regarded as a marker of the inherent atherosclerotic risk, integrating the balance of proinflammatory and antiinflammatory mediators acting on the vascular wall. Indeed, we previously demonstrated that elevated levels of the antiinflammatory cytokine interleukin-10, which exerts potent endothelial protective functions in experimental and human studies,24,25 ameliorate the increased risk associated with the persistence of elevated levels of the inflammatory marker C-reactive protein serum in patients with acute coronary syndromes.26
The exposure of endothelial cells to proinflammatory stimuli induces procoagulant activity,27 leads to expression of cell surface adhesion molecules,28,29 and impairs bioavailability of the potent platelet inhibitor nitric oxide.30,31 Thus, systemic endothelial activation may indeed contribute to a thrombogenic blood to trigger recurrence of instability in inflamed patients.
Importantly, the prognostic value of systemic endothelial vasodilator function was independent of classic risk factors, such as troponin positivity, in patients with acute coronary syndromes but provided additional information compared with the inflammatory serum marker C-reactive protein. Thus, assessment of systemic endothelial vasodilator function contributes specific and independent prognostic value in patients with acute coronary syndromes. However, further studies are required to prospectively validate a cutoff value of endothelial vasodilator capacity for optimized risk prediction in patients with acute coronary syndromes.
In summary, systemic endothelial dysfunction is a major predictor of recurrence of instability in patients with acute coronary syndromes. Assessment of the vascular phenotype might provide an integrated index of systemic inflammatory activation of the vascular wall and thus enable the identification of the inflamed, “vulnerable” patient at risk.
This study was supported by the Deutsche Forschungsgemeinschaft (SFB 553 Project C5). The authors gratefully acknowledge Margret Müller-Ardogan for expert technical assistance.
Virmani R, Kolodgie FD, Burke AP, Farb A, Schwartz SM. Lessons from sudden coronary death: a comprehensive morphological classification scheme for atherosclerotic lesions. Arterioscler Thromb Vasc Biol. 2000; 20: 1262–1275.
Libby P, Ridker PM. Novel inflammatory markers of coronary risk: theory versus practice. Circulation. 1999; 100: 1148–1150.
Buja LM, Willerson JT. Role of inflammation in coronary plaque disruption. Circulation. 1994; 89: 503–505.
Biasucci LM, Liuzzo G, Grillo RL, Caligiuri G, Rebuzzi AG, Buffon A, Summaria F, Ginnetti F, Fadda G, Maseri A. Elevated levels of C-reactive protein at discharge in patients with unstable angina predict recurrent instability. Circulation. 1999; 99: 855–860.
Bogaty P, Poirier P, Simard S, Boyer L, Solymoss S, Dagenais GR. Biological profiles in subjects with recurrent acute coronary events compared with subjects with long-standing stable angina. Circulation. 2001; 103: 3062–3068.
Maseri A, Fuster V. Is there a vulnerable plaque? Circulation. 2003; 107: 2068–2071.
Hingorani AD, Cross J, Kharbanda RK, Mullen MJ, Bhagat K, Taylor M, Donald AE, Palacios M, Griffin GE, Deanfield JE, MacAllister RJ, Vallance P. Acute systemic inflammation impairs endothelium-dependent dilatation in humans. Circulation. 2000; 102: 994–999.
Fichtlscherer S, Rosenberger G, Walter DH, Breuer S, Dimmeler S, Zeiher AM. Elevated C-reactive protein levels and impaired endothelial vasoreactivity in patients with coronary artery disease. Circulation. 2000; 102: 1000–1006.
Fichtlscherer S, Rössig L, Breuer S, Vasa M, Dimmeler S, Zeiher AM. Tumor necrosis factor antagonism with etanercept improves systemic endothelial vasoreactivity in patients with advanced heart failure. Circulation. 2001; 104: 3023–3025.
Heitzer T, Ollmann I, Koke K, Meinertz T, Munzel T. Platelet glycoprotein IIb/IIIa receptor blockade improves vascular nitric oxide bioavailability in patients with coronary artery disease. Circulation. 2003; 108: 536–541.
Bhagat K, Vallance P. Inflammatory cytokines impair endothelium-dependent dilatation in human veins in vivo. Circulation. 1997; 96: 3042–3047.
Suwaidi JA, Hamasaki S, Higano ST, Nishimura RA, Holmes DR, Lerman A. Long-term follow-up of patients with mild coronary artery disease and endothelial dysfunction. Circulation. 2000; 101: 948–954.
Schächinger V, Britten MB, Zeiher AM. Prognostic impact of coronary vasodilator dysfunction on adverse long-term outcome of coronary heart disease. Circulation. 2000; 101: 1899–1906.
Heitzer T, Schlinzig T, Krohn K, Meinertz T, Münzel T. Endothelial dysfunction, oxidative stress, and risk of cardiovascular events in patients with coronary artery disease. Circulation. 2001; 104: 2673–2678.
Halcox JPJ, Schenke WH, Zalos G, Mincemoyer R, Prasad A, Waclawiw MA, Nour KRA, Quyyumi AA. Prognostic value of coronary vascular endothelial dysfunction. Circulation. 2002; 106: 653–658.
Perticone F, Ceravolo R, Pujia A, Ventura G, Iacopino S, Scozzafava A, Ferraro A, Chello M, Mastroroberto P, Verdecchia P, Schillaci G. Prognostic significance of endothelial dysfunction in hypertensive patients. Circulation. 2001; 104: 191–196.
Gokce N, Keaney JF Jr, Hunter LM, Watkins MT, Menzoian JO, Vita JA. Risk stratification for postoperative cardiovascular events via noninvasive assessment of endothelial function: a prospective study. Circulation. 2002; 105: 1567–1572.
Targonski PV, Bonetti PO, Pumper GM, Higano ST, Holmes DR Jr, Lerman A. Coronary endothelial dysfunction is associated with an increased risk of cerebrovascular events. Circulation. 2003; 107: 2805–2809.
Gunnett CA, Heistad DD, Berg DJ, Faraci FM. IL-10 deficiency increases superoxide and endothelial dysfunction during inflammation. Am J Physiol Heart Circ Physiol. 2000; 279: H1555–H1562.
Heeschen C, Dimmeler S, Hamm CW, Fichtlscherer S, Boersma E, Simoons ML, Zeiher AM. Serum level of the antiinflammatory cytokine interleukin-10 is an important prognostic determinant in patients with acute coronary syndromes. Circulation. 2003; 107: 2109–2114.
Pasceri V, Willerson JT, Yeh ETH. Direct proinflammatory effect of C-reactive protein on human endothelial cells. Circulation. 2000; 102: 2165–2168.
Szmitko PE, Wang CH, Weisel RD, de Almeida JR, Anderson TJ, Verma S. New markers of inflammation and endothelial cell activation: part I. Circulation. 2003; 108: 1917–1923.
Venugopal SK, Devaraj S, Yuhanna I, Shaul P, Jialal I. Demonstration that C-reactive protein decreases eNOS expression and bioactivity in human aortic endothelial cells. Circulation. 2002; 106: 1439–1441.
Verma S, Wang CH, Li SH, Dumont AS, Fedak PW, Badiwala MV, Dhillon B, Weisel RD, Li RK, Mickle DA, Stewart DJ. A self-fulfilling prophecy: C-reactive protein attenuates nitric oxide production and inhibits angiogenesis. Circulation. 2002; 106: 913–919.