Isolated T wave alternans.

Two patients with isolated T wave alternans are reported, with their vectocardiograms, their response to carotid sinus stimulation, and the response to calcium infusion in one of them with documented severe hypocalcemia. Eleven cases of the literature are briefly reviewed. The alternans of the T wave appears with severe QT prolongation, QT alternans, and an increased tendency to ventricular fibrillation. The findings are consistent with the hypothesis that T wave alternans may be the electrocardiographic manifestation of the transmembrane action potential alternans and could be related in some cases to hypocalcemia.