Influence of Enoximone on Myocardial Energetics in Patients with Idiopathic Dilated Cardiomyopathy

Abstract

Enoximone may influence myocardial energetics by vasodilation, which may reduce and by inotropism which may increase myocardial energy demand. To separate both pharmacological properties, the influence of enoximone on myocardial oxygen consumption and its hemodynamic determinants was analyzed and compared to the effects of the pure vasodilator nitroprusside. The relationship between myocardial oxygen consumption and left ventricular hemodynamics was evaluated in 22 patients with idiopathic dilated cardiomyopathy (NYHA stages II-III). During control, myocardial oxygen consumption per beat [MVO2 (beat)] correlated closely with left ventricular systolic stress-time integral (STI) (r = 0.74; p less than 0.001). The ratio of MVO2 (beat) and STI was used as an inverse measure of the economy of myocardial contraction. Following nitroprusside (10 patients) the STI decreased by 35% (p less than 0.005) and MVO2 (beat) by 30% (p less than 0.005). MVO2 (beat)/STI did not significantly change. Following enoximone (12 patients), STI decreased by 60% (p less than 0.001), MVO2 (beat) by 19% (p less than 0.001), and MVO2 (beat)/STI increased from 1.31 +/- 0.16 to 2.72 +/- 0.78 nl.cm2/100 g.dyn.s (p less than 0.001). In summary, vasodilation by nitroprusside decreased MVO2 (beat) in proportion to its major determinant, STI; the economy of myocardial contraction remained unchanged. Compared to nitroprusside, enoximone reduced the economy of contraction. Thus, with enoximone, the energy-saving effect of vasodilation is counteracted by increased energy demand due to the inotropic stimulation of the myocardium. Global myocardial oxygen consumption depends on the balance of both pharmacological properties.