EFFECT OF ENALAPRIL IN DOGS WITH PACING-INDUCED HEART-FAILURE

A repeated-measures study was conducted on 5 dogs to clinically, radio graphically, and echocardiographically characterize the actions of the angiotensin-converting enzyme inhibitor, enalapril, before and after development of experimentally induced heart failure. Heart failure was artificially induced, using a surgically implanted programmable ventr icular pacemaker, which stimulated the heart at a rate of 245 beats/mi n until a low-output cardiomyopathic state developed. This condition w as then stabilized by decreasing the pacing rate to 190 beats/min. Pac ing-induced heart failure was successfully induced in a mean +/- SD 4. 2 +/- 1.95 weeks. The condition closely resembled the clinical, radiog raphic, and echocardiographic features of naturally acquired idiopathi c dilated cardiomyopathy in dogs. Enalapril was well tolerated by dogs , and clinical adverse reactions did not develop. Results of echocardi ographic studies indicated that enalapril treatment during the control period resulted in a significant (P < 0.05) increase in velocity of c ircumferential fiber shortening and a significant (P < 0.05) decrease in left ventricular ejection time. Therapeutic responses to enalapril were evident after development of heart failure. These included reduce d severity of clinical signs of disease, evidence of decreased radiogr aphically determined cardiac size (2 of 5 dogs), radiographic evidence of a reduction in pulmonary edema and congestion (4 of 5 dogs), signi ficant (P < 0.05) reductions in left atrial and ventricular chamber di mensions (left atrial dimension, diastolic left ventricular internal d imension as determined echocardiographically), and improvement in some echocardiographic indices of left ventricular performance (velocity o f circumferential fiber shortening and left ventricular ejection time) .