CLINICAL RESEARCH: ACUTE CORONARY SYNDROME
Elevated Placental Growth Factor Levels Are Associated With Adverse Outcomes at Four-Year Follow-Up in Patients With Acute Coronary Syndromes
Timo Lenderink, MD*, ,*,
Christopher Heeschen, MD ,
Stephan Fichtlscherer, MD ,
Stefanie Dimmeler, MD,
Christian W. Hamm, MD||,
Andreas M. Zeiher, MD,
Maarten L. Simoons, MD*,
Eric Boersma, PhD* for the CAPTURE Investigators
* Department of Cardiology, Atrium Medical Centre, Heerlen, the Netherlands
Department of Cardiology, Thoraxcenter, Erasmus Medical Center Rotterdam, Rotterdam, the Netherlands
Department of Surgery, Ludwig-Maximilians-University, Munich, Germany
Department of Cardiology, J. W. Goethe University, Frankfurt, Germany
|| Department of Cardiology, Kerckhoff Heart Center, Bad Neuheim, Germany
Manuscript received April 10, 2005;
revised manuscript received July 7, 2005,
accepted August 9, 2005.
* Reprint requests and correspondence: Dr. Timo Lenderink, Department of Cardiology, Atrium Medical Centre Heerlen, H. Dunantstr. 5, 6419 PC Heerlen, the Netherlands. (Email: t.lenderink{at}atriummc.nl).
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Abstract
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OBJECTIVES: This study sought to evaluate the predictive value of baseline placental growth factor (PlGF) for long-term cardiovascular events in acute coronary syndromes (ACS).
BACKGROUND: A biomarker of vascular inflammation, PlGF is identified as a powerful predictor for short-term outcome in patients with ACS.
METHODS: In 544 patients who were enrolled in the placebo arm of the c7E3 Fab Anti Platelet Therapy in Unstable REfractory angina (CAPTURE) trial, PlGF levels were determined as well as markers of myocardial necrosis (troponin T [TnT]), general inflammation (high-sensitivity C-reactive protein [hsCRP]), and platelet activation (soluble CD40 ligand [sCD40L]). Cox proportional hazard regression analyses were applied to evaluate the relationship between biomarkers and the occurrence of all-cause death or non-fatal myocardial infarction during a median follow-up period of four years.
RESULTS: Patients with PlGF levels in the fourth and fifth quintile (>27 ng/l) had higher mortality than those with lower levels (10.8% vs. 3.2%; hazard ratio [HR], 3.3; 95% confidence interval [CI], 1.6 to 7.1), as well as a higher incidence of the composite end point of death or myocardial infarction (27.6% vs. 11.3% events; HR, 2.6; 95% CI, 1.7 to 3.9). The relationship between PlGF and the composite end point remained significant after adjustment for TnT, sCD40L, and hsCRP (adjusted HR, 3.3; 95% CI, 2.0 to 5.4).
CONCLUSIONS: In patients with ACS, elevated plasma levels of PlGF are associated with adverse cardiac outcomes during long-term follow-up. These data suggest that PlGF as a more specific marker of vascular inflammation should be considered for risk stratification of patients with ACS rather than general markers of inflammation.
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Abbreviations and Acronyms
| | ACS = acute coronary syndrome | | hsCRP = high-sensitivity C-reactive protein | | PlGF = placental growth factor | | sCD40L = soluble CD40 ligand | | TnT = troponin T |
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Vascular inflammation is now believed to play an important role in atherosclerosis (1). Markers of general inflammation such as high-sensitivity C-reactive protein (hsCRP) (2), interleukin-6 (3), and serum amyloid (4) are associated with adverse outcomes in patients with coronary heart disease. However, placental growth factor (PlGF), a member of the vascular endothelial growth factor (VEGF) family, was recently shown to be strongly up-regulated in early and advanced atherosclerotic lesions. Increasing evidence suggests that PlGF acts as a primary inflammatory instigator of atherosclerotic plaque instability (5). Indeed, recently it has been shown that PlGF is an independent biomarker of short-term adverse outcome in patients with chest pain that is suspicious for an acute coronary syndrome (ACS) (6).
Inflammatory processes of atherosclerosis are sustained after acute interventional or medical treatment and trigger cardiovascular events during long-term follow-up (7,8). Therefore, we studied the relationship between baseline levels of PlGF and the incidence of all-cause mortality or non-fatal myocardial infarction during a four-year follow-up in ACS patients who were enrolled in the CAPTURE trial. We related our findings to other markers, for example, one of general inflammation, such as hsCRP and soluble CD40 ligand (sCD40L).
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Methods
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Patients and treatment.
The c7E3 Fab Anti Platelet Therapy in Unstable REfractory angina (CAPTURE) protocol has been described in detail (9). Briefly, patients were eligible if they had refractory unstable angina, defined as chest pain at rest with concomitant electrocardiographic abnormalities compatible with myocardial ischemia (ST-segment depression, ST-segment elevation, or T-wave inversion), and one or more episodes of typical chest pain or electrocardiographic abnormalities during at least 2 h of treatment with intravenous heparin and nitrates. The most recent ischemic episode should have occurred within 48 h before enrolment, corresponding to Braunwald class III unstable angina. All patients had undergone coronary angiography, and percutaneous coronary intervention was scheduled within 18 to 24 h after the start of the study medication. After giving informed consent, patients were randomly assigned to abciximab (ReoPro, Centocor B.V., Leiden, the Netherlands; 0.25-mg/kg bolus plus 10 µg/min continuous infusion) or placebo. Study medication was started within 2 h of randomization and continued until 1 h after the procedure. All patients received aspirin, heparin, and nitrates, whereas beta-blockers, calcium channel antagonists, and other cardiovascular drugs were given at the discretion of the investigator.
Analytical techniques.
Plasma samples drawn at the time of randomization were available for determination of troponin T (TnT), hsCRP, sCD40L, and PlGF. Because TnT (10,11) and sCD40L (12) have been shown to interact with the treatment effect of abciximab, the present analysis was restricted to the 544 patients receiving placebo in whom blood samples were available (86% of patients receiving placebo). Blood samples were collected a mean of 8.7 h (standard deviation, 4.9) after the onset of symptoms, but before percutaneous coronary intervention and before the incidence of adverse events. Measurement of cardiac marker levels was performed blinded to the patients’ histories. Levels of PlGF and sCD40L were measured by enzyme-linked immunosorbent assay (both from R&D Systems, Wiesbaden, Germany). Total imprecision (expressed as coefficient of variation) for PlGF was 7.3%. For sCD40L, a diagnostic threshold level of 5.0 µg/l was used. Levels of TnT were determined using a one-step enzyme immunoassay based on electrochemiluminescence technology (Roche Diagnostics, Mannheim, Germany). A diagnostic threshold value of 0.01 µ/l was used. Levels of hsCRP were measured using the Behring BN II Nephelometer (Dade Behring, Deerfield, Illinois). A diagnostic threshold value of 10 mg/l was used.
A cut-off value for PlGF of 27 ng/l was used in this study based on the difference of number of events between the third and fourth quintile (see the Results section), which was almost equal to the 25 ng/l based on additional receiver-operating characteristic analyses and looking at the maximal sum of sensitivity and specificity per 1 ng/l.
Study end points.
End points of the present analysis were all-cause mortality and the composite of all-cause mortality and non-fatal myocardial infarction. Follow-up at six months was part of the study protocol. Myocardial infarction during the index hospitalization was defined by creatine kinase (CK)-MB or CK levels exceeding three times the upper limit of normal in two samples and an increase by 50% over the previous value, or an electrocardiogram (ECG) with new significant Q waves in two or more contiguous leads. Myocardial infarction after discharge was defined by CK-MB or CK levels exceeding two times the upper limit of normal or new significant Q waves in two or more contiguous leads. A clinical end point committee adjudicated these events. Survival status and information on myocardial infarction were collected for the patients who were alive six months after randomization. Follow-up data were obtained from the treating physician, the general practitioner, the patient, or municipal registries and were not adjudicated.
Data analysis.
Continuous variables were summarized by median values with corresponding 25th and 75th percentiles. Discrete variables were summarized in terms of frequencies and percentages. Kaplan-Meier analyses were performed to evaluate the incidence of events over time. Univariable and multivariable Cox proportional hazards regression analyses were applied to evaluate the relationship between PlGF and long-term outcome. We adjusted for age, gender, history of diabetes, and ST-segment depression on the qualifying ECG and the biomarkers sCD40L, hsCRP, and TnT (thresholds were: >5.0 µg/l, >10 mg/l, and >0.01 µg/l, respectively). The p values were two-sided, with p  0.05 being considered significant.
The main results are presented for 544 patients who entered the trial. Additional analyses were performed in the subgroup of patients who survived the first six months, with events counted after this period.
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Results
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Patients with PlGF levels above 27 ng/l had significantly higher levels of hsCRP than those with lower PlGF levels (64.7% vs. 26.2%, p < 0.0001). Also, patients with elevated PlGF levels more often had a history of smoking (47.9% vs. 37.5%; p = 0.02). Other established risk factors were evenly distributed over the two PlGF groups.
The median follow-up duration was 48 months (25th and 75th percentile: 38, 55) with 46 (25th and 75th percentile: 38, 54) months of follow-up beyond 30 days. During follow-up, 31 patients had died and 60 had experienced a non-fatal myocardial infarction. A total of 21 deaths and 21 non-fatal myocardial infarctions occurred after 30 days.
Analyses based on quintiles showed a noticeably higher calculated annual incidence of death and non-fatal myocardial infarction in the fourth and fifth quintiles (Fig. 1). Long-term mortality of patients with elevated PlGF levels was 10.8%, compared with 3.2% in those without elevated PlGF levels (crude hazard ratio, 3.3; 95% confidence interval (CI), 1.6 to 7.1; p = 0.002) (Fig. 2). The composite end points of death and non-fatal myocardial infarction occurred in 27.6% and 11.3% of patients (crude hazard ratio, 2.6; 95% CI, 1.7 to 3.9; p < 0.001) (Fig. 3).
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Figure 1 Bar graphs of the calculated annual incidence of death or non-myocardial infarction according to placental growth factor (PlGF) status grouped in quintiles.
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Figure 2 Kaplan-Meier curves of death during four-year follow-up according to placental growth factor status. In the right panel, 49 patients who died or experienced myocardial infarction (MI) before the 30-day follow-up were excluded. Dotted line = placental growth factor >27 ng/l.
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Figure 3 Kaplan-Meier curves of death or myocardial infarction (MI) during four-year follow-up according to placental growth factor status. In the right panel, 49 patients who died or experienced MI before the 30-day follow-up were excluded. Dotted line = placental growth factor >27 ng/l.
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In the patients who survived the first 30 days, the incidence of all-cause mortality during extended follow-up was 8.7% in those with elevated baseline PlGF and 2.6% in those without elevated PlGF (crude hazard ratio, 3.2; 95% CI, 1.4 to 7.6; p = 0.007). The composite end point occurred in 16.2% of patients with elevated PlGF levels and in 5.7% of patients without elevated PlGF levels (crude hazard ratio, 2.9; 95% CI, 1.5 to 5.3; p = 0.001).
After adjustment for multiple baseline characteristics and TnT, sCD40L and hsCRP PlGF remained significant predictors for the incidence of death or myocardial infarction during the four years after admission (adjusted hazard ratio, 3.0; 95% CI, 1.1 to 7.9; p = 0.026; Table 1), as well as during long-term follow-up in six-month survivors (adjusted hazard ratio, 3.3; 95% CI, 2.0 to 5.4; p < 0.001) (Table 1).
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Table 1. Multivariable Adjusted Hazard Ratios for the Incidence of Death or Myocardial Infarction During Long-Term Follow-Up
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Discussion
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In this study we demonstrate that elevated baseline levels of PlGF, a more specific marker of vascular inflammation, are associated with adverse long-term outcomes in patients with ACS. The predictive value of PlGF was independent of hsCRP, a biomarker of general inflammation. Interestingly, baseline PlGF was also associated with an increased risk of cardiovascular complications during extended follow-up in patients who survived the first six months.
These data add to the growing evidence showing that hsCRP as a classic systemic acute-phase protein might not be specific enough for the inflammation process involved in vascular atherosclerosis (13). Therefore, hsCRP levels collected in ACS patients seem to be less useful as a tool for cardiovascular risk stratification and patient management. In contrast, PlGF as a more specific marker of vascular inflammation providing independent predictive value for the short-term cardiovascular outcome is not hampered by the occurrence of an ACS (5,6). We have shown its usefulness as a determinant of long-term outcome. It is important to note in this respect that the prognostic value of baseline PlGF was independent of biomarkers of platelet activation (soluble CD40-ligand) and myocardial necrosis (TnT).
We observed both an early divergence of the curves shortly after onset of symptoms as well as an impressive late divergence of the curves after two years of follow-up. These findings support the pathophysiological concept of a chronic (vascular) inflammatory basis of atherosclerosis with an acute superimposed process in the setting of an ACS (14). The present data suggest that chronic inflammatory processes in the coronary vessel wall may indeed result in the repetitive occurrences of cardiovascular events during long-term follow-up (1,15,16). In patients with ACS, early percutaneous coronary intervention, as performed in the present CAPTURE trial, obviously prevents adverse cardiac events during short-term (six-month) follow-up. Long-term events, however, apparently require a more effective and/or specific anti-inflammatory treatment, such as blocking of the PlGF receptor or reducing the activity of circulating PlGF levels by administration of soluble VEGF receptor 1 (17). Future studies of anti-inflammatory therapies should assess a potential additional long-term benefit in patients with ACS. The baseline PlGF level may serve as a powerful indicator for the targeted use of anti-inflammatory therapy in patients at high risk for the rapid progression of coronary atherosclerosis. Follow-up PlGF levels could then be used as indicators for the effect of such therapy.
We acknowledge that this investigation has some limitations. First, the long-term follow-up data, which were obtained from multiple sources, were not adjudicated by an independent clinical event committee. Thus, the applied criteria for myocardial infarction might have differed between investigators and some events may actually have been missed. Second, no information is available on long-term medical treatment (such as statin or angiotensin-converting enzyme inhibition therapy), which might have influenced patient outcome. Accordingly, we recognize that there was information bias in our data. However, it is rather unlikely that this would have resulted in a differential bias between patients with or without elevated PlGF levels. In this respect, it should be emphasized that the investigators who collected long-term follow-up (E. B. and T. L.) were blinded to any information on baseline data (including biomarker levels). Importantly, between patients with high and low PlGF levels, there was no difference in the prevalence of hypercholesterolemia, which was the primary reason for the initiation of statin treatment at the time of the CAPTURE study. We think therefore that further prospective studies should be performed using this post-hoc defined criteria of PlGF elevation and preferably more time intervals.
Conclusions.
In patients with ACS, increased plasma levels of PlGF are associated with adverse cardiac outcomes during long-term follow-up. Placental growth factor as a marker of vascular inflammation should be considered for risk stratification in patients with ACS rather than general markers of inflammation such as hsCRP.
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Footnotes
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The CAPTURE study was supported by Centocor B. V., Leiden, the Netherlands.
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References
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Abstract
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