A 58-year-old patient is recovering in the intensive care unit after a myocardial infarction (MI). The nurse notes an order for the beta-blocker metoprolol. What is the purpose of this drug?

Choice A rationale While some beta-blockers have a minor effect on vasodilation, their primary purpose in a post-MI patient is not to dilate the coronary arteries. Beta-blockers reduce myocardial oxygen demand by decreasing heart rate, contractility, and blood pressure. Vasodilators, such as nitrates or calcium channel blockers, are the drugs of choice for dilating coronary arteries. Choice B rationale After an MI, circulating catecholamines (epinephrine and norepinephrine) can increase heart rate and contractility, which raises myocardial oxygen demand and can extend the size of the infarct. Metoprolol, a beta-blocker, competitively blocks these catecholamines at the beta-1 adrenergic receptors, thereby reducing heart rate and myocardial contractility. This action decreases oxygen consumption and prevents further cardiac damage. Choice C rationale Beta-blockers like metoprolol have a negative inotropic effect, meaning they decrease the force of myocardial contraction. A positive inotropic effect, which increases the force of contraction, is seen with drugs like digoxin or dopamine and would be counterproductive in a post-MI setting where the goal is to reduce the heart's workload. Choice D rationale While metoprolol does lower blood pressure as a secondary effect by decreasing heart rate and reducing cardiac output, its primary purpose in a post-MI patient is to reduce the workload of the heart and decrease myocardial oxygen demand. The reduction in blood pressure is a beneficial side effect, but it is not the main indication for its use in this context.