Physiologic response to the inotropic and vasodilator properties of enoximone

In patients with chronic cardiac failure, improvement in ventricular function is observed after the administration of enoximone, a phosphodiesterase inhibitor with inotropic and vasodilator properties. The relative contributions of positive inotropy and vasodilation to the improvement in pump performance, however, remain uncertain. Therefore, findings from a series of dog experiments designed to resolve this issue are reviewed. Also, our current understanding of the physiologic response to enoximone in patients with cardiac failure, including the responses of myocardial oxygen consumption and efficiency, are considered. It is concluded that, enoximone produces a substantial (66 +/- 2% in dogs) increase in contractility, a relatively minor increase in heart rate (0 to 12%) and a decrease in systemic vascular resistance (-28 to -49%). These are the ranges of average responses based on review of published findings. These physiologic responses lead to an improvement in the pumping function of the failing heart; cardiac output (23 to 83%) and stroke work index (17 to 88%) are increased, and pulmonary capillary wedge pressure (-19 to -59%) and right atrial pressure (-29 to -60%) are decreased. The influence of enoximone on myocardial oxygen consumption is less consistent (-18 to +33%). Nevertheless, enoximone improves the efficiency of the failing heart.