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J Am Coll Cardiol, 2006; 47:726-733, doi:10.1016/j.jacc.2005.09.055
(Published online 6 February 2006). © 2006 by the American College of Cardiology Foundation |
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* Department of Cardiology, Western Infirmary, Glasgow, Scotland
Cardiovascular Division, Brigham and Womens Hospital, Boston, Massachusetts
Duke University Medical Center, Durham, North Carolina
The Montreal Heart Institute, Montreal, Canada
|| Department of Cardiology, Green Lane Hospital, Auckland, New Zealand
¶ QE 11 Heart Function and Transplantation Clinic, Dalhousie University, Halifax, Nova Scotia, Canada
# Department of Medicine, Sahlgrenska University Hospital, Göteborg, Sweden
** ANMCO Research Center, Florence, Italy

Department of Cardiology University of Copenhagen, Copenhagen, Denmark

Leuven Coordinating Center, Leuven, Belgium
Manuscript received June 22, 2005; revised manuscript received August 22, 2005, accepted September 8, 2005.
* Reprint requests and correspondence: Prof. John McMurray, Department of Cardiology, Level 4, Western Infirmary, Glasgow, G11 6NT, Scotland, United Kingdom. (Email: j.mcmurray{at}bio.gla.ac.uk).
| Abstract |
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BACKGROUND: Angiotensin-converting enzyme inhibitors and ARBs interrupt the renin-angiotensin system by distinct mechanisms. It is not clear whether ARBs reduce atherosclerotic events such as myocardial infarction (MI) like ACE inhibitors. This evidence gap may reflect the nature of the studies conducted, to date. Placebo-controlled studies enrolled cohorts at low risk of atherosclerotic events (e.g., patients with chronic heart failure, most treated with an ACE inhibitor). One of the main active controlled trials was confounded by a blood pressure difference between treatments.
METHODS: We compared the effects of captopril, valsartan, and their combination on atherosclerotic events in 14,703 patients randomized in the Valsartan in Acute Myocardial Infarction Trial (VALIANT).
RESULTS: The number of individuals adjudicated as having a fatal or non-fatal MI in the captopril group was 559 (total investigator reported events 798), 587 (796) in the valsartan group, and 554 (756) in the combination group; valsartan versus captopril, p = 0.651 (0.965); combination versus captopril, p = 0.187 (0.350). Overall, all atherosclerotic events examined occurred at a similar frequency in the captopril and valsartan groups.
CONCLUSIONS: Angiotensin receptor blockers appear to be as effective as ACE inhibitors in reducing atherosclerotic events, even when used in addition to other secondary preventive treatments. These data, although not conclusive, also support the hypothesis that adding an ARB to an ACE inhibitor may have a small additional anti-infarction effect, a possibility that needs to be prospectively tested.
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It is still not clear, however, whether ARBs possess the broad spectrum of cardiovascular benefits, such as reduction in risk of myocardial infarction (MI), already demonstrated by ACE inhibitors. Angiotensin receptor blockers reduce the risk of hospital admission for worsening heart failure (and death) in patients with chronic heart failure (CHF) (46). In patients with hypertension, the ARB losartan reduced stroke more than the beta-blocker atenolol (but did not preferentially affect the risk of other adverse cardiovascular events, including MI), despite equal reduction in blood pressure (7). More recently, hypertensive patients treated with the calcium-channel blocker amlodipine had a lower risk of MI compared to those treated with valsartan (8). Angiotensin-converting enzyme inhibitors, on the other hand, clearly reduce the risk of atherosclerotic events including MI, stroke, and, possibly, unstable angina and the need for coronary revascularization (913). Recently, however, one ARB has been shown to reduce the development of atherosclerosis in an experimental animal model, and treatment with others has been shown to decrease blood markers of inflammation in patients with hypertension (1416).
An even more uncertain issue is whether adding an ARB to an ACE inhibitor might further reduce atherosclerotic events. This combination does reduce the risk of hospital admission for worsening heart failure (and cardiovascular death) in CHF, but its effect on MI, stroke, and other atherosclerotic events, especially MI, is not well defined (4,5,17).
The aim of this report, therefore, is to describe, in detail, the comparative effects of an ACE inhibitor (captopril), an ARB (valsartan), and their combination on atherosclerotic events in the Valsartan in Acute Myocardial Infarction Trial (VALIANT) (1820).
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Trial end-points. The primary end point of VALIANT was all-cause mortality. The secondary end points included cardiovascular mortality and a number of composites of cardiovascular mortality and non-fatal cardiovascular events including MI, hospitalization for heart failure, stroke, and resuscitation after cardiac arrest.
The Clinical End Points Committee (CEC) in VALIANT adjudicated all deaths and the first non-fatal event in the composite described above. As in the report of the primary results of VALIANT, the analyses of time to first events in the present report were carried out using CEC adjudicated end points, with the exception of hospitalized angina and revascularization (i.e., coronary artery bypass grafting [CABG] or percutaneous coronary intervention), which were not adjudicated. Conversely, we used investigator-reported diagnoses to calculate the total number of events that occurred.
Statistical analysis. Rates of baseline clinical characteristics are reported as means with standard deviations or frequencies and percents. The number of patients experiencing an event (and rates) was estimated using the Kaplan-Meier method, and a log-rank test was used for statistical comparisons. Cox proportional hazards models were used to calculate p values and hazard ratios with 95% confidence intervals. To compare the total number of atherosclerotic events reported per patient rather than the number of patients with events, we employed a negative binomial regression model with an offset adjustment to account for differential periods of follow-up between patients (24). Because beta-blockers and statins also reduce the risk of atherosclerotic events, we also examined whether treatment with either of these drugs at baseline modified the effect of randomized therapy. The interaction of each concomitant medication with the two treatment arms was included into the previously developed multivariable models. The SAS statistical software (SAS Institute Inc., Cary, North Carolina) was used for all statistical analyses. The p values of 0.025 were used as critical values for statistical significance for each of the two valsartan treatments with captopril alone.
| Results |
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Composite atherosclerotic end points. Table 3 shows a hierarchy of composite atherosclerotic end points, including cardiovascular death. There was no statistically significant difference between treatments for any composite end point.
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Interactions between randomized therapy and background treatment given at baseline. Background beta-blocker treatment did not modify the effect of study treatment. There was, however, an interaction between statin treatment taken at baseline and randomized therapy (Fig. 2). Patients receiving a statin at baseline appeared to have a significantly (interaction p value = 0.013) lower risk of MI with combination therapy than with captopril alone (and, conversely, patients not taking a statin at baseline had a similar rate of infarction in both the combination treatment and captopril only groups). There was a qualitatively similar interaction for the composite outcome of cardiovascular death or MI.
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| Discussion |
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By contrast, it has not been clear whether ARBs also reduce coronary events. This lack of evidence may be related to the nature of the studies conducted, to date, with these agents. The presently completed placebo-controlled studies have been conducted in patient cohorts with a low risk of atherosclerotic events (i.e., patients with CHF, many already treated with an ACE inhibitor) with little resultant power to detect a treatment difference between the ARB and placebo (4,6). The remaining large studies have been active-controlled studies in hypertensive subjects (7,8). Here, for equal blood pressure reduction, treatment with losartan led to a lower risk of stroke (but not of MI) compared to atenolol (7). In the recent Valsartan Antihypertensive Long-term Use Evaluation trial (VALUE), the risk of both stroke and MI were higher in patients treated with valsartan compared to those treated with amlodipine although blood pressure was reduced more in the amlodipine group, particularly in the first year when the difference in MI was most pronounced (the systolic/diastolic difference was 4.0/2.1 mm Hg at 1 month and 2.0/1.6 mm Hg at 6 months) (8).
VALIANT, therefore, provides an excellent opportunity to evaluate the comparative effect of ARBs and ACE inhibitors on atherosclerotic events (and on the effect of combined ACE inhibitor-ARB treatment, compared to ACE inhibitor monotherapy) (18,19).
Not only was valsartan compared to an evidence-based dose of a proven ACE inhibitor, but these treatments were used on top of extensive background anti-platelet, beta-blocker, and statin treatment, as well as coronary revascularization (18,19). Furthermore, this large patient cohort, as anticipated, accrued a substantial number of atherosclerotic events (18,19).
We found that the risk of the individual atherosclerotic events studied was comparable in the valsartan and captopril groups as were the rates of the fatal and non-fatal cardiovascular composite end points. This assessment was based on a large number of individual events (e.g., approximately 800 MIs per treatment group compared to <400 per group in the VALUE study) and very large numbers of patients experiencing any atherosclerotic event (over 2,000 per treatment group for the composite of cardiovascular death, MI, hospitalization for angina, or stroke).
It is of interest that the risk of recurrent MI and stroke tended to be less in the valsartan added to captopril group compared to the captopril monotherapy group and that these apparent differences occurred early after randomization. It is important to note, however, that these effects were identified in a retrospective analysis, are modest in size, and are not statistically significant. There is, however, experimental evidence to support the hypothesis that there might be more clinical benefit from both agents used together than either alone. One or more greater blockade of the action of angiotensin II or the putative, protective, effects of augmentation of bradykinin with ACE inhibitors and enhanced stimulation of the AT2 receptor with ARBs may be relevant (13,14). Whatever the mechanism, blood pressure was slightly (2.2 mm Hg systolic) but significantly (p < 0.001) lower in the combination treatment group than in the captopril group after randomization. In the VALUE study, a comparably small difference was associated with a lower incidence of MI in the amlodipine-based treatment group, though the difference in that trial occurred in individuals with a much higher baseline blood pressure (compared to the relatively low blood pressure in VALIANT) (8). Arguably, however, a recent placebo-controlled trial with nifedipine in patients with ischemic heart disease suggests that blood pressure reduction is not the whole explanation for the differences observed in coronary events in these various studies (26).
The value of combining an ARB with an ACE inhibitor in patients with stable coronary heart disease (or at high risk of developing coronary disease) should, however, be clarified by the ONgoing Telmisartan Alone and in Combination with Ramipril Global Endpoint trial (ONTARGET). In this study, "full-dose" ARB is being added to full-dose ACE inhibitor unlike in VALIANT (17). This approach was not possible in VALIANT, where treatment was initiated and quickly titrated in the acute phase of MI, because there is concern about excessive lowering of blood pressure in this relatively unstable situation (27). For that reason, a submaximal target dose of valsartan (80 mg twice daily as opposed to 160 mg twice daily) was employed in VALIANT. In this setting, even addition of this reduced dose of valsartan to full-dose captopril led to an excess of adverse events related to hypotension. Hypotension is likely to be less frequent and of less concern in the patients enrolled in the ONTARGET study.
In a post-hoc analysis, we found that there was an interaction between baseline statin therapy and valsartan. Such findings must be interpreted cautiously and may arise from the play of chance. However, mechanistic interactions between cholesterol and the renin-angiotensin system (RAAS) and between statins and inhibitors of the RAAS (and valsartan specifically) have been described (2830). Whether or not there is a therapeutic interaction that favorably influences clinical outcomes may be worthy of exploration in other datasets.
There are limitations to the current analysis. Though we had a very large number of events, not all of these were adjudicated. Adjudication practice varies between trials and for individual types of event. Of all events examined here, the greatest concern is probably that investigator designated hospitalized angina may not always have accurately identified a true acute coronary syndrome. Our analysis could also have been confounded by the proportion of patients discontinuing treatment differing between treatment groups. However, the difference was small, and, if anything, would have tended to reduce the effect of combination therapy. The proportion stopping treatment for reasons other than death was 21.6% in the captopril group, 20.5% in the valsartan group, and 23.4% in the combination group (p < 0.05).
In summary, this analysis of the very large and high-risk cohort of patients with acute MI in VALIANT suggests that ARBs are as effective as ACE inhibitors in reducing atherosclerotic events, even when given in addition to other secondary preventive treatments. These data also suggest, but do not prove, that adding an ARB to an ACE inhibitor may have a small additional anti-infarction effect.
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