DIVERGENT EFFECTS OF INTRAVENOUS DOBUTAMINE AND NITROPRUSSIDE ON LEFTATRIAL CONTRIBUTION TO VENTRICULAR FILLING IN DOGS WITH CHRONIC HEART-FAILURE

The left atrial (LA) contribution to left ventricular (LV) filling is often attenuated in patients with heart failure. It remains uncertain, however, whether therapy with positive inotropic agents or vasodilato rs improves or further impairs this maladaptation. In the present stud y, the effects of intravenous dobutamine and nitroprusside on the LA c ontribution to LV filling was examined in seven dogs with chronic hear t failure produced by multiple sequential intracoronary microembolizat ions. Pulsed Doppler echocardiography was used to measure mitral inflo w velocity before and after an intravenous infusion of dobutamine (4 m u g/kg/min) and an intravenous infusion of nitroprusside (3 mu g/kg/mi n). The percent LA contribution to LV filling was calculated as the ra tio of the time-velocity integral of the LA component of mitral inflow velocity (Ai) to the time-velocity integral of total diastolic inflow velocity (Ti) times 100. Dobutamine increased LV filling pressure, LV end-diastolic wall stress, LV end-diastolic stiffness, and Ei, but ha d no effect on Ai or the percent LA contribution to filling (14% +/- 3 % vs 12% +/- 2%) (p < 0.34). In contrast, nitroprusside decreased LV f illing pressure, LV end-diastolic wall stress, and end-diastolic stiff ness, and increased Ei, Ai, and the percent LA contribution to LV fill ing (12% +/- 2% vs 17% +/- 2%) (p < 0.01). The results indicate that d obutamine and nitroprusside have divergent effects on the LA contribut ion to LV filling. In dogs with chronic heart failure, dobutamine appe ars to impair LA contribution to the LV filling by augmenting LA workl oad, whereas nitroprusside appears to elicit greater LA contribution t o LV filling by reducing the LA workload.