A group of cardiologists hypothesized that a new ACE inhibitor improves outcomes among patients with left ventricular dysfunction whether they have heart failure or not. The cardiologists assessed the role of the new ACE inhibitor in patients who were at high risk for cardiovascular events but who did not have left ventricular dysfunction or heart failure. A total of 8,560 high-risk patients (age ≥55) with evidence of vascular disease or diabetes plus one other cardiovascular risk factor but with no known history of heart failure were randomly assigned at a ratio of 1:1 to receive the new ACE inhibitor or placebo for a mean of 5 years. The primary outcome was death from cardiovascular causes. A total of 261 patients assigned to receive the new ACE inhibitor (6.1%) died from cardiovascular causes, compared to 346 patients assigned to receive placebo (8.1% percent) (relative risk = 0.75; p

Question

A group of cardiologists hypothesized that a new ACE inhibitor improves outcomes among patients with left ventricular dysfunction whether they have heart failure or not.  The cardiologists assessed the role of the new ACE inhibitor in patients who were at high risk for cardiovascular events but who did not have left ventricular dysfunction or heart failure.  A total of 8,560 high-risk patients (age ≥55) with evidence of vascular disease or diabetes plus one other cardiovascular risk factor but with no known history of heart failure were randomly assigned at a ratio of 1:1 to receive the new ACE inhibitor or placebo for a mean of 5 years.  The primary outcome was death from cardiovascular causes.  A total of 261 patients assigned to receive the new ACE inhibitor (6.1%) died from cardiovascular causes, compared to 346 patients assigned to receive placebo (8.1% percent) (relative risk = 0.75; p < 0.05).  Which of the following conclusions can be drawn from these results?

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Explanation: 11ec2b69_bdf6_c882_8f63_2161d87c7b8f_MD0005_00 In this study, a group of cardiologists assessed the role of a new ACE inhibitor in patients at high risk for cardiovascular events but who did not have left ventricular dysfunction or heart failure. Participants were randomly assigned at a ratio of 1:1 to receive the new ACE inhibitor or placebo for a mean of 5 years. The study results showed that 6.1% of patients in the new ACE inhibitor group died from cardiovascular causes and 8.1% of patients in the placebo group died from cardiovascular causes. The study estimated that the relative risk (RR) = 0.75and p < 0.05. RR < 1.0 indicates that the treatment (ie, new ACE inhibitor) reduced the rate of death from cardiovascular causes compared to placebo. The change in risk (RR = 0.75 compared to RR = 1.0, the null value) represents a reduction of (1.0 − 0.75)/1.0 = 0.25, or 25%(Choice B). The p-value corresponds to a test of RR = 1.0 (ie, the null value), so a significant result (p < 0.05) means that the RR is significantly different from 1 at a 5% significance level. Therefore, treatment with the new ACE inhibitor had a significant effect on the rate of death from cardiovascular causes (Choice D). Because the RR is significantly different from the null value (RR = 1.0), a confidence interval (CI) constructed at the same significance level (ie, 5% significance level produces a 95% CI) will exclude the null value. Therefore, a 95% CI for the RR reported by this study would exclude the null value. (Choice C) The rate of death from cardiovascular causes was 8.1% (or 0.081) in the placebo group and 6.1% (or 0.061) in the new ACE inhibitor group, so the RR for the placebo group compared to the new ACE inhibitor group is 0.081/0.061 = 1.33. This means that the rate of death from cardiovascular causes was 33% higher among patients assigned to placebo. Educational objective: Relative risk (RR) is a measure of association between an exposure and an outcome. For RR < 1.0, the exposure decreases the risk of the outcome (ie, protective factor). For RR = 1.0, there is no association between the exposure and the outcome. For RR > 1.0, the exposure increases the risk of the outcome. Confidence intervals that contain the null value (RR = 1.0) indicate that the association is not statistically significant.

A Group of Cardiologists Hypothesized That a New ACE Inhibitor