Chronic angiotensin-converting-enzyme inhibition improves cardiac output and fluid balance during heart failure

The purpose of this study was to examine the sequential changes in renal and cardiovascular function produced by chronic Benazepril administration at different stages of heart failure in dogs. Heart failure was produced by rapid ventricular pacing in five dogs with a normally functioning renin- angiotensin system (angiotensin normal, AN) and six dogs chronically administered the angiotensin-converting-enzyme inhibitor (ACEI) Benazepril. After 7 days of pacing, cardiac output was significantly higher and total peripheral resistance (TPR) lower in the ACEI compared with the AN dogs. Cumulative sodium and water balance increased significantly in both groups, but after 7 days of pacing there were no significant differences between groups. However, the rate of increase in sodium and water balance was significantly less in the ACEI group. Effective renal plasma flow decreased in the AN and ACEI groups during pacing, but there were no between-group differences, and no significant changes in glomerular filtration rate (GFR) occurred in either group. In the AN dogs, pacing was continued for 7-21 days until the onset of decompensated heart failure. Urinary sodium excretion increased on the first day of ACEI infusion during this stage but returned to pre-ACEI levels during the next 2-3 days. No significant improvement in cardiac output was measured during ACEI in decompensated heart failure. These data suggest that chronic ACEI administration can improve renal and cardiac function in early heart failure without impairing GFR but is less effective in later, decompensated stages.