Myocardial blood flow in experimental cardiac hypertrophy in dogs.

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The effects of experimental myocardial hypertrophy on the coronary blood flow, myocardial 02 consumption, and coronary reserve capacity have been studied in unanaesthetized dogs, in which electromagnetic flowmeters had been chronically implanted. Myocardial hypertrophy was obtained by producing an arteriovenous fistula between the iliac vessels seven to 12 months before the experiments. In 15 dogs with systemic arteriovenous fistula, cardiac hypertrophy averaging 46% was obtained. These animals were arbitrarily divided into two groups. In the first (HI) hypertrophy averaged 32%, in the second (H2) hypertrophy was 67% on average. Eleven sham-operated dogs (group C) served as controls. Our findings show that, in experimental cardiac hypertrophy, coronary blood flow and 02 myocardial consumption at rest rise as the cardiac mass increases in size, whereas coronary resistance falls. Thus, coronary flow and 02 consumption per gram of myocardium in the animals with cardiac hypertrophy were not significantly different from those in the controls. In the dogs in group H2, the coronary reserve, measured as the percentage increase in the coronary flow from rest till peak flow during reactive hyperaemia, is therefore noticeably reduced, because it is partially utilized even at rest and, consequently, the possibility of an increase in flow after exercise or stress is diminished. In these conditions the supply of substrates to the myocardium can be normal at rest, whereas coronary flow and O2 supply may be inadequate only after a considerable increase in haemodynamic work.