Mechanisms responsible for the cardiotoxic effects of cocaine.

Cocaine can induce lethal cardiovascular events, including myocardial infarction and ventricular fibrillation. The mechanisms responsible for these cardiotoxic effects of cocaine remain largely to be determined. Cocaine has both sympathomimetic (inhibition of neuronal uptake of norepinephrine) and local anesthetic (Na+ channel blockade) properties. Neurotransmitters released from cardiac sympathetic nerves bind to both alpha- and beta-adrenergic receptors eliciting a cascade of intracellular responses. Stimulation of beta-adrenergic receptors activates adenylate cyclase, increasing cyclic AMP levels, whereas alpha-adrenergic receptor stimulation activates phospholipase C, increasing inositol trisphosphate. These second messengers, in turn, elicit increases in cystolic calcium. Elevations in cystolic calcium can provoke oscillatory depolarizations of the cardiac membrane, triggering sustained action potential generation and extrasystoles. Cocaine also acts as a local anesthetic by inhibiting sodium influx into cardiac cells, which impairs impulse conduction and creates an ideal substrate for reentrant circuits. Thus, the adrenergic and anesthetic properties of cocaine could act synergistically to elicit and maintain ventricular fibrillation. Adrenergic receptor activation would trigger the event whereas sodium channel blockade would create the reentrant substrate to perpetuate the malignant arrhythmias.