QRS alternans during idiopathic ventricular tachycardia originating from the right coronary cusp of the aorta.

A 77-year-old man underwent electrophysiological testing for idiopathic ventricular tachycardia (VT) with QRS alternans exhibiting a left bundle branch block and left inferior axis QRS morphology. Successful radiofrequency catheter ablation was achieved at the site of the earliest ventricular activation in the right coronary cusp. Pacing at this site reproduced an excellent pace map with QRS alternans. Pacing from other sites in the ventricular outflow tracts reproduced neither an excellent pace map nor QRS alternans. This case demonstrates that VT with a single origin and multiple exits in the aortic root may exhibit QRS alternans.