Myocardial flow during tachycardia in dogs with chronic left ventricular hypertrophy.

The effect of pacing-induced tachycardia on transmural myocardial blood flow distribution was studied in 16 awake dogs with left ventricular hypertrophy secondary to modified aortic coarctation banding done at 7-10 wk of age. They were studied between 11 and 50 mo of age. In those dogs with mild and moderate left ventricular hypertrophy, the blood flow distribution was normal during resting conditions and remained normal during an increased heart rate of 250 beats/min. In the six dogs with severe hypertrophy (left ventricle/body wt greater than 7.0 g/kg) a reduced flow to the endocardial layers was present during resting conditions (endocardial/epicardial 0.91 +/- 0.09), but during tachycardia the endocardial-to-epicardial ratio normalized to 1.26 +/- 0.08 (mean +/- SEM). These data indicate that, in dogs with significant left ventricular hypertrophy, the vasoregulator mechanism functions adequately to maintain normal transmural myocardial blood flow distribution during tachycardia. In addition, studies were carried out to compare the magnitude of hypertrophy with the hemodynamic load secondary to coarctation banding.