Which of the following drugs has a positive inotropic effect. Select all that apply.

Choice A rationale

Epinephrine is a potent catecholamine that stimulates alpha-1, beta-1, and beta-2 adrenergic receptors. Stimulation of beta-1 receptors in the myocardium increases the concentration of intracellular calcium, which enhances the force of contraction. This positive inotropic effect is vital in emergency settings like cardiac arrest or severe shock to improve stroke volume and mean arterial pressure. It increases myocardial oxygen consumption, which must be carefully monitored in patients with underlying coronary artery disease.

Choice B rationale

Digoxin is a cardiac glycoside that exerts a positive inotropic effect by inhibiting the sodium-potassium ATPase pump. This inhibition leads to an increase in intracellular sodium, which subsequently slows the calcium-sodium exchanger, resulting in higher intracellular calcium levels available for myocardial contraction. Digoxin also has negative chronotropic effects by increasing vagal tone. It is commonly used in heart failure to improve contractility and in atrial fibrillation to control the ventricular rate.

Choice C rationale

Metoprolol is a selective beta-1 adrenergic antagonist (beta-blocker). Its primary action is to block the effects of catecholamines on the heart, which leads to a decrease in heart rate (negative chronotropy) and a decrease in the force of contraction (negative inotropy). While it is beneficial for long-term management of heart failure and hypertension by reducing myocardial workload and protecting against arrhythmias, it does not have the positive inotropic effect required by the question.

Choice D rationale

Nitroglycerin is a potent vasodilator that primarily acts on venous smooth muscle to decrease preload and, at higher doses, on arterial smooth muscle to decrease afterload. By reducing the volume of blood returning to the heart and the resistance the heart must pump against, it lowers myocardial oxygen demand. It does not directly increase the contractile force of the heart muscle; therefore, it is considered a nitrate vasodilator rather than a positive inotropic agent.

Choice E rationale

Amlodipine is a dihydropyridine calcium channel blocker that primarily targets vascular smooth muscle to cause systemic vasodilation. By inhibiting the influx of calcium ions into vascular cells, it reduces peripheral vascular resistance and blood pressure. While it affects calcium channels, its action is focused on the vasculature rather than increasing the strength of myocardial contraction. In fact, some calcium channel blockers can have a mild negative inotropic effect by reducing available calcium in cardiomyocytes.