To the Editor:
The findings by Gulati and associates supported an association between exercise capacity and survival in women.1 They also state that their results provide a “clear clinical rationale for routine stress testing in asymptomatic women.”
Although we find these results intriguing, we would like more information. If clinicians decide to stress-test their patients, how would the results be used? The results would be easier to appreciate if tables were included with absolute risks of mortality for varying Framingham risk and exercise capacity scores.
Additional information would help establish the clinical value of exercise capacity. In particular, it is important to know how much the findings are modified by excluding patients with coronary ischemia or known chronic diseases or by adding age or other cardiovascular risk factors to the regression equation. If the findings are substantially changed, then exercise capacity may be a marker for other disease, rather than an independent risk factor. Although the investigators adjusted for the Framingham risk score, there is no reason to assume that the effect of age and other cardiovascular risk factors have the same association with mortality in the St James data set as these factors have on coronary heart disease risk in the Framingham data set.
References
Response
We thank Dr Levy and colleagues for their interest in our report.1 Our findings demonstrate that exercise capacity provides additional prognostic information, beyond that provided by traditional cardiac risk factors. Given this, we feel that there is a rationale for measuring exercise capacity by routine exercise stress testing in asymptomatic women. When any risk factor is identified, the question always remains whether we can intervene on the risk factor and alter prognosis. There is some evidence that maintaining or improving exercise capacity over time is associated with an improved survival in asymptomatic men2 and myocardial infarction survivors.3 Nonetheless, we do agree with the editorial by Drs Mark and Lauer4 that there is no evidence available at this time describing the impact of intervention on one’s exercise capacity and that this is an area in need of further study. At this point, a standardized stress test will provide a clinician with a quantifiable measure to assist a patient in assessing his or her future risk of death.
To address the question of those with coronary ischemia, it must be emphasized that only asymptomatic women were included in this study. We are unable to answer how many women were excluded because of symptoms, but we believe this number was small. Nonetheless, no data were collected on them, and no symptomatic woman underwent a stress test. We did exclude 91 patients with a past history of any cardiac disease, including coronary artery disease, in order to have a group of asymptomatic women free of any underlying heart disease that could confound the findings.
Our models adjust for cardiac risk factors using the Framingham Risk Score.5 We also performed a multivariate analysis that included individual cardiac risk factors, including age. The estimated effects of exercise capacity are essentially the same as those of our Figure 3, which adjusted separately for Framingham Risk Score and age. We chose to present our findings using the Framingham Risk Score because of its simplicity and applicability in clinical practice.
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- Exercise Capacity and the Risk of Death in Women
