MECHANISM OF COCAINE-INDUCED MYOCARDIAL DEPRESSION IN DOGS

Cocaine causes pronounced depression of left ventricular function in conscious dogs immediately after intravenous administration. To examine this effect, 14 mongrel dogs were anesthetized with pentobarbital sodium (32 mg/kg) and instrumented with arterial and venous catheters and a Doppler blood flow transducer on the left circumflex coronary artery. Two weeks later, heart rate, blood pressure, coronary blood flow, and regional left ventricular ejection fraction (by two-dimensional echocardiography) were measured before and 1, 2, 5, and 10 minutes after cocaine (4 mg/kg i.v.), while the animals were fully conscious. Heart rate, blood pressure, and coronary blood flow were increased significantly at each time after cocaine. Regional ejection fraction, however, was depressed by 50±7%, 35±4%, and 21±4% at 1, 2, and 5 minutes after cocaine treatment, respectively. Ten minutes after cocaine treatment, regional ejection fraction had recovered to a level not significantly different from baseline. Because the observed myocardial depression after cocaine was accompanied by a large increase in the rate-pressure product, and presumably, myocardial oxygen consumption, this depression could have been secondary to increased myocardial oxygen demand not appropriately matched by an increase in coronary blood flow. To minimize the effects of cocaine on myocardial oxygen demand, a subset of six dogs received cocaine (4 mg/kg i.v.) while sedated with pentobarbital (25 mg/kg). In these dogs, cocaine did not significantly alter heart rate or blood pressure; however, regional ejection fraction was significantly depressed by 44±5% and 36±6% at 1 and 2 minutes after cocaine treatment, respectively. Significant depression of canine left ventricular function, in the absence of changes in major determinants of myocardial oxygen consumption, is consistent with a direct myocardial depressant action of cocaine.