Impaired regional subendocardial coronary flow reserve in conscious dogs with pacing-induced heart failure.

The purpose of the present investigation was to examine coronary flow and vasodilator reserve in conscious, chronically instrumented dogs with pacing-induced heart failure, a model of severe biventricular cardiomyopathy devoid of significant hypertrophy. Twelve dogs were studied after 28 days of rapid right ventricular pacing and were compared with six sham-operated controls. Left ventricular (LV) average transmural flow was significantly less in conscious dogs with pacing-induced heart failure, whereas the endocardial-to-epicardial flow ratio was not significantly different. In response to near maximal coronary vasodilation with adenosine, subepicardial coronary flow and vasodilator reserve were preserved in congestive heart failure (CHF), yet there was evidence of impaired subendocardial flow and vasodilator reserve, and the endocardial-to-epicardial ratio was significantly less. When the markedly elevated LV end-diastolic pressure was normalized in heart failure, there was restoration of subendocardial coronary flow reserve and a normalization of the endocardial-to-epicardial ratio. Thus, in CHF, there is impaired coronary flow and vasodilator reserve that is selective to the subendocardium of the LV. At this point in the heart failure process, this impairment is not associated with structural changes but is a consequence of the marked elevation in LV end-diastolic pressure.