[Changes in myocardial metabolism induced by drugs used during intensive care]

More and more patients with coronary heart disease (CAD) are admitted to intensive care units. The drugs used to treat these patients have various effects on the myocardium which must be known in order to avoid worsening the CAD. This review examines the metabolic effects on the myocardium of the most commonly used drugs in intensive care. The physiology of myocardial oxygen supply is first recalled with regard to the coronary circulation, myocardial oxygen extraction and consumption. Digitalis glycosides do not affect the coronary circulation, but the decrease myocardial oxygen consumption in patients with heart failure, mainly by lowering heart rate. Dihydropyridine calcium blockers (nifedipine, nicardipine) increase coronary blood flow, despite a decrease in arterial blood pressure. Their effects on myocardial oxygen consumption are mediated by a sympathetic reflex. Verapamil decreases the heart rate and myocardial inotropism, and is responsible for coronary vasodilation. The result is a decrease in myocardial oxygen consumption. Diltiazem and bepridil have almost similar effects: they decrease myocardial oxygen consumption and increase blood supply to the heart. It has been recently shown that verapamil was the most depressant calcium channel blocking agent, and that it resulted in the most important decrease in myocardial metabolism. Beta-blocking agents decrease myocardial metabolism, except those with an important intrinsic sympathomimetic activity, such as pindolol. Amiodarone can be considered as an alpha and beta blocking drug: its main effect is to counteract the effects of endogenous catecholamines on myocardial metabolism. The sympathomimetic amines (noradrenaline, adrenaline, isoprenaline, dopamine, dobutamine) increase, to different extents, myocardial oxygen consumption. Vasodilators, such as the nitrates or sodium nitroprusside, decrease cardiac filling pressures, and increase myocardial blood flow, thus lowering myocardial oxygen consumption. Phosphodiesterase inhibitors (amrinone, enoximone) have both an inotropic and a vasodilating effect. They decrease cardiac afterload, and increase blood supply to the myocardium; this compensates for the increase in myocardial oxygen consumption due to the increase in myocardial contractility. Because all the drugs used in intensive care have different effects on myocardial metabolism, their reasoned use should avoid an inappropriate increase in oxygen demand.