And the correct answer is D. Ryan receptor mutations lead to DADs, or delayed after depolarizations, and triggered activity by causing abnormal calcium leak from the SR that leads to inward current through the electrogenic sodium-calcium exchanger. So calcium current through the sacralemmal calcium channel normally triggers calcium release from the internal calcium store, the sarcoplasmic reticulum, through ryanidine receptor channels, a process known as excitation-contraction coupling. The calcium release from the SR then leads to contraction of cardiac myocytes. Catecholaminergic polymorphic ventricular tachycardia, CPVT, also called exercise-induced ventricular tachycardia, is characterized by a normal baseline ECG and arrhythmias with either exercise or high catecholamine states, including catecholamine infusions with isoproteranol. Mutations in the ryanidine receptor lead to spontaneous SR calcium release in the setting of high calcium loads that are present during exercise or high catecholaminergic states. The cytoplasmic calcium is removed from the cell by the electrogenic sodium-calcium exchanger, where one calcium ion goes out and three sodium ions go in, leading to an inward current. The inward current produces delayed after depolarizations, which, if big enough, can trigger action potentials and arrhythmias. The action potential prolongation seen in Long QT syndrome leads to reactivation of the sacralemmial calcium channel and early after depolarizations, EADs. Arrhythmogenic cardiomyopathy is caused by mutations of dense mesomal proteins, and it is associated with epsilon waves, not CPVT.

ryanodine receptors

catecholaminergic polymorphic ventricular tachycardia

calcium leaks

delayed after depolarizations

arrhythmias