Ergonovine testing and forearm plethysmography in cocaine-related myocardial ischemia

Cardiovascular disorders associated with cocaine use: myths and truths

Cocaine produces a pattern of cardiovascular responses that are associated with apparent myocardial ischemia, arrhythmias, and other life-threatening complications in some individuals. Despite recent efforts to better understand the causes of cocaine-induced cardiovascular dysfunction, there remain a number of unanswered questions regarding the specific mechanisms by which cocaine elicits hemodynamic responses. This review will describe the actions of cocaine on the cardiovascular system and the evidence for the mechanisms by which cocaine elicits hemodynamic and pathologic responses in humans and animals. The emphasis will be on experimental data that provide the basis for our understanding of the mechanisms of cardiovascular toxicity associated with cocaine. More importantly, this review will identify several controversies regarding the causes of cocaine-induced cardiovascular toxicity that as yet are still debated. The evidence supporting these findings will be described. Finally, this review will outline the obvious deficits in our current concepts regarding the cardiovascular actions of cocaine in hope of encouraging additional studies on this grave problem in our society.

Endothelium-dependent vasorelaxation is impaired in cocaine arteriopathy

OBJECTIVES

This study sought to assess endothelium-dependent vasorelaxation in long-term users of cocaine.

BACKGROUND

Cocaine use has been associated with myocardial infarction, stroke and intestinal infarction. Previously demonstrated effects of the drug, including increased heart rate and blood pressure and increased vascular tone, do not explain the sporadic nature of these vascular events or the occurrence of ischemia remote from acute administration. Abnormal endothelial function could contribute to focal vasospasm and thrombosis and predispose to premature atherosclerosis, all of which have been demonstrated in cocaine users with myocardial infarction.

METHODS

Using plethysmography, we studied the change in forearm blood flow in response to intraarterial acetylcholine and nitroprusside in 10 long-term cocaine users and 13 control subjects of similar age who had not used cocaine; sample size was based on a 70% power to detect a 20% reduction in flow with acetylcholine between subjects and control subjects. Using graded doses of intracoronary acetylcholine (from 10(-9) to 10(-6) mol/liter), we studied a second group of 10 cocaine users with angiographically normal or near-normal arteries.

RESULTS

Mean forearm blood flow during acetylcholine infusion was significantly lower in cocaine users than in control subjects (p = 0.02). During nitroprusside infusion, there was no difference (p = 0.2) between cocaine users and control subjects. Cigarette smoking did not explain the differences between cocaine users and control subjects. Acetylcholine elicited coronary vasoconstriction in 8 of 10 subjects.

CONCLUSIONS

We conclude that endothelium-dependent vasorelaxation is impaired in long-term users of cocaine.

Intracoronary versus intravenous effects of cocaine on coronary flow and ventricular function

BACKGROUND

Cocaine use has been associated with cardiomyopathy and ischemic coronary syndromes. However, the pathophysiological mechanisms responsible for these syndromes are not clear and have been suggested to involve direct effects of cocaine on myocyte contractility and coronary resistance as well as indirect effects via altered autonomic tone, secondary mediators, and myocardial metabolism. We sought to distinguish direct from indirect effects of cocaine on ventricular function and coronary resistance by comparison of the administration of intracoronary cocaine (0.12 to 0.36 mg/min constant infusion) with intravenous cocaine (5 mg/kg bolus infusion) in an in vivo anesthetized pig preparation.

METHODS AND RESULTS

To control for changes in coronary resistance secondary to autoregulation and myocardial metabolism, the left anterior descending coronary artery was perfused at constant coronary pressure and the interventricular vein was cannulated for coronary venous oxygen saturation measurement. Coronary blood flow, regional percent segment shortening, myocardial oxygen consumption, and serum cocaine concentrations were measured. Intracoronary cocaine produced a dose-dependent decrease in percent segment shortening in the absence of significant changes in coronary flow or systemic hemodynamics. In contrast, intravenous cocaine had mild biphasic effects on coronary resistance with an initial brief vasodilation (30.0 +/- 5% increase in flow from control) followed by more prolonged vasoconstriction (17.0 +/- 3.3% decrease in flow from control), which were independent of autoregulation or myocardial metabolism. In addition, intravenous cocaine caused an early 48% decrease in percent segment shortening, at which time the measured cocaine concentration was 20.1 micrograms/mL blood. This was comparable to the intracoronary cocaine concentration of 17.1 micrograms/mL blood, which produced a similar 48% decrease in percent segment shortening.

CONCLUSIONS

We conclude that the effects of acute cocaine exposure on ventricular function are predominantly direct but of brief duration and therefore probably not clinically relevant. The effects of cocaine on coronary tone are predominantly indirect and biphasic, with early vasodilation followed by mild and more prolonged vasoconstriction. In the absence of coronary stenosis or ventricular hypertrophy, this small amount of vasoconstriction is unlikely to cause ischemia.