Myocardial blood flow in left ventricular hypertrophy developing in young and adult dogs

This study was performed to test the hypothesis that growth of coronary vasculature would be facilitated if myocardial hypertrophy occurred during the period of normal body growth rather than in mature adult animals. Left ventricular hypertrophy was produced by banding the ascending aorta in eight young dogs 7 wk of age and in nine adult dogs. Adult dogs were studied 2 mo after aortic banding, whereas young dogs were allowed to grow to adulthood before study. Left ventricular weight-to-body weight ratios were increased to 6.88 ± 0.36 g/kg in the young dogs and 6.64 ± 0.47 in adult dogs; both were significantly greater than seven normal control animals (4.32 ± 0.05; each P < 0.01). Myocardial blood flow per gram measured with microspheres during quiet resting conditions was significantly higher in young dogs with left ventricular hypertrophy than in normal dogs. Myocardial blood flow rates during maximum coronary vasodilation with adenosine (4 μmol·kg^-1·min^-1 iv) were similar in all three groups. However, since mean coronary perfusion pressure was higher in the dogs with aortic banding, minimum coronary vascular resistance per gram of myocardium was significantly higher in both young (21.1 ± 3.1 mmHg·ml^-1·min·g) and adult dogs with left ventricular hypertrophy (21.8 ± 2.2) than in the normal dogs (16.8 ± 3.1; each P < 0.01). Mean coronary vascular resistance for the total left ventricle was similar in all three groups of animals, suggesting that growth of coronary vasculature did not occur as the myocardium underwent hypertrophy. These data indicate that left ventricular hypertrophy beginning at 7 wk of age and continuing during the subsequent period of normal body growth results in impairment of minimum coronary vascular resistance similar to that seen when hypertrophy begins after the animals have reached adulthood.