Alterations of myocardial blood flow associated with experimental canine left ventricular hypertrophy secondary to valvular aortic stenosis.

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Abstract
Experimental renovascular hypertension or supravalvular aortic constriction results in left ventricular hypertrophy and impaired minimum coronary vascular resistance. However, these experimental models expose the coronary arteries to increased intra-arterial pressure, so that hypertensive vascular changes might be responsible for the impaired minimum coronary resistance. This study was performed to test the hypothesis that left ventricular hypertrophy in the absence of increased coronary pressure results in abnormalities of myocardial perfusion. Aortic valve stenosis was produced by plication of the noncoronary aortic cusp of 11 dogs at 6-8 weeks of age. Studies were carried out when the animals reached adulthood; mean left ventricular:body weight ratio was 7.1 +/- 0.4 as compared to 4.4 +/- 0.3 g/kg in 11 normal dogs (P less than 0.01). Under quiet resting conditions, myocardial blood flow measured with microspheres was significantly greater than normal in dogs with aortic stenosis. However, during maximum coronary vasodilation with adenosine, mean left ventricular blood flow in dogs with hypertrophy (3.29 +/- 0.39) was substantially less than in normal dogs (6.19 +/- 0.54 ml/min per g; P less than 0.01), whereas minimum coronary resistance was increased from 14.1 +/- 1.7 in normal dogs to 23.7 +/- 5.4 mmHg. min X g/ml (P less than 0.01). To examine the response of myocardial perfusion to cardiac stress, blood flow was measured during pacing at 200 and 250 beats/min. Compared with normal dogs, animals with hypertrophy had a subnormal increase in myocardial blood flow during tachycardia; this perfusion deficit was most marked in the subendocardium. These data demonstrate that left ventricular hypertrophy alone, without increased coronary artery pressure, is associated with impaired minimum coronary vascular resistance and with abnormalities of myocardial blood flow during pacing stress.