Protection against sudden coronary occlusion by induced mild chronic volume hypertrophy in dogs

A model of mild chronic volume hypertrophy in the dog has been described which consists of establishing a small arteriovenous (A-V) shunt. The model was utilized to evaluate the protection afforded by mild chronic volume hypertrophy against sudden coronary occlusion. Eight animals were studied, 4 with a single shunt (mean estimated 25% increase in cardiac output) and 4 with a double shunt (mean estimated 57% increase in cardiac output). The A-V shunt resulted in the expected volume hypertrophy by roentgenographic and cardiac weight criteria, but was small enough to produce no signs of exercise intolerance, cardiac failure, or definite electrocardiographic changes. After 6 months, the A-V fistulae were surgically closed and 2 weeks later, under normal hemodynamic conditions, the heart was challenged by sudden, permanent ligation of the left circumflex coronary artery at its origin. The time from ligation to death was measured and compared with 10 control animals without such fistulae. Death occurred in 2 to 13 min in the control animals; in contrast, 5 of the 8 animals with mild chronic volume hypertrophy survived longer than any control animal, and 2 were long-term survivors. The actuarial estimate of the difference in survival was significant (p=0.007) and indicated that the fistulae reduced the hazard of coronary ligation by a factor of 6. A single small shunt afforded protection similar to a double one. Therefore, mild chronic volume hypertrophy induced by a small A-V fistula in the normal dog protects against sudden coronary occlusion. We speculate that the procedure may have a role in the multifactorial prophylactic management of coronary artery disease in asymptomatic high risk subjects, instead of an inapplicable exercise program.