Arterial Vasodilator Therapy in Heart Failure: Haemodynamic Response Patterns Predictive of Changes in Exercise Capacity

Abstract

When the peripheral vascular resistance is abnormally high, the heart can be considered to be pumping inefficiently in that much of its effort is wasted in overcoming the extra high load. Patients with such conditions are liable to have reduced exercise capacity (ExC). It is unclear whether selective arterial vasodilation in these patients can improve ExC. In a double-blind crossover comparative study of the effects of felodipine versus placebo in 10 patients with heart failure in NYHA class III, all patients decreased systemic vascular resistance (SVR) and increased cardiac index (CI), not only at rest but also during exercise. Since heart rate (HR) did not change, the increase in CI was due to increased stroke volume (SV). This beneficial haemodynamic response did not, however, correlate with functional response to the drug. A mixed exercise response was obtained, with 3 patients showing an increase, 3 a decrease, and 4 no change in ExC with felodipine. Therefore, we investigated whether an alternative way of characterizing haemodynamic response would explain why individual patients responded differently to the same drug. We tested the hypothesis that vasodilator therapy would enhance ExC if it were able to alter the load facing the heart in such a way that the cardiac pump needed to impart less hydraulic power output to maintain the same degree of physical exercise. Patients who could perform with felodipine the same submaximal exercise for less cardiac effort than with placebo were the ones who could increase their ExC during the vasodilator therapy. The converse was also true. We conclude that exercise response to vasodilator therapy depended on whether the failing heart was rendered able to pump more efficiently by the drug.