Comparative hemodynamic effects of digoxin vs nitroprusside in conscious dogs with aortocaval fistula-induced chronic left ventricular volume overload and normal systolic performance

Abstract

We compared the effects of IV digoxin (0.04 mg/kg) and nitroprusside (NP) (1.2 and 1.8 μg/kg/min) on left ventricular (LV) performance in six preinstrumented conscious dogs with chronic volume overload and congestive heart failure (CHF) produced by an aortocaval fistula. At 3 and 6 hours after digoxin administration (serum level, 3.5 ± 0.6 ng/ml), there were no changes in heart rate, LV systolic (LVSP) and end-diastolic (LVEDP) pressures, LV dimensions, LV dP dt max , or percent minor diameter shortening as compared to control values in the resting state, after beta blockade, or during phenylephrine infusion. By contrast, NP produced a significant reduction ( p < 0.05) in LVEDP (16 ± 3 to 10 ± 3 mm Hg) at the smaller dose which caused no change in mean aortic pressure. The larger dose of NP further reduced LVEDP and evoked significant ( p < 0.05) decreases in LVSP (124 ± 5 to 117 ± 7 mm Hg), mean aortic pressure (85 ± 3 to 78 ± 5 mm Hg), and LV end-diastolic dimension (LVEDD) (53.0 ± 5.5 to 52.0 ± 5.7 mm), while augmenting LV dP dt max (3288 ± 266 to 3647 ± 130 mm Hg/sec). Beta blockade with IV propranolol (2.0 mg/kg) prevented the rise in LV dP dt max after high-dose NP administration but did not alter the reductions in mean aortic pressure, LVEDP, and LVEDD. This study indicates that NP, but not digitalis, has a favorable effect on LV hemodynamics in the volume-overloaded heart with normal LV systolic contraction and high-output CHF resulting from increased blood volume and reduced LV diastolic compliance. At least part of the apparent improvement in LV performance observed with high-dose NP is sympathetically mediated since it can be attenuated by beta blockade.