Exercise Tolerance as a Guide to Therapeutic Efficacy for Heart Failure
The Potential for Angiotensin Receptor Blockers
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The early trials of efficacy of therapy for heart failure focused on exercise tolerance as a guide to symptom relief. Patients with heart failure usually seek medical help because of an impairment of their exercise capacity, and it seemed reasonable to use quantitative assessment of this capacity to guide our therapeutic efforts. Indeed, early studies of nitrates1 and of captopril2 3 suggested a significant improvement in peak exercise capacity when these drugs were added to conventional therapy. The duration of these studies, which were designed to demonstrate short-term improvement, was usually 3 to 6 months.
Then why has exercise tolerance fallen out of favor in the continuing effort to document efficacy of therapy? A number of reasons can be cited. Peak exercise time during a progressively loaded test has a very subjective end point dependent on the motivation of both the patient and the examiner. The end point can be made more quantitative by the collection of expired gas to calculate peak oxygen consumption and to document that the subject surpassed the anaerobic threshold,4 but this adds considerable complexity to a multicenter study. Furthermore, demonstration of a statistically significant increase in exercise time does not …