Which antianginal drug acts primarily by inhibiting the late sodium current in cardiac myocytes?

Ranolazine is the antianginal agent that primarily functions by inhibiting the late sodium current in cardiac myocytes. This mechanism is particularly beneficial in managing angina because it helps to reduce intracellular calcium overload, which can occur during ischemic conditions. By inhibiting the late sodium current, ranolazine decreases the influx of sodium into the cell, which indirectly reduces the amount of calcium that enters through sodium-calcium exchange mechanisms. This modulation of cardiac myocyte sodium and calcium levels leads to improved myocardial relaxation and decreased oxygen demand, providing relief from angina symptoms.

The other options provided, such as verapamil and diltiazem, are calcium channel blockers that primarily work by inhibiting calcium entry into the cells, leading to vasodilation and a decrease in heart rate but do not primarily target the late sodium current. Propranolol, as a beta-blocker, reduces heart rate and myocardial contractility but operates through a different mechanism, primarily affecting adrenergic receptors rather than sodium currents. These pharmacological differences highlight ranolazine's unique mechanism of action as a critical treatment option in the management of angina.