Background: The most common site of origin of idiopathic ventricular tachycardia (VT) is the right ventricular outflow tract. Idiopathic VT also can arise from the left ventricular outflow tract and the surrounding structures. Morphologic descriptions of 12-lead ECG characteristics of the aortic cusp region are limited.
Objective: The purpose of this study was to define unique ECG characteristics of the aortic cusp region by performing a systematic analysis of pacemapping of this region in patients with structurally normal hearts.
Methods: A combination of electroanatomic mapping, intracardiac echocardiography, and fluoroscopic guidance was used to study a total of 30 patients with structurally normal hearts undergoing left-sided ablation procedures. Each of the aortic valve cusps and the aortomitral continuity were paced at threshold and analyzed offline to determine unique ECG characteristics.
Results: Pacing from the left coronary cusp typically produced a multiphasic QRS morphology consistent with an M or W pattern in lead V(1) with a precordial transition (R>S) no later than V(2). Pacing from the right coronary cusp typically resulted in a left bundle-type pattern with a broad small R wave in V(2) and a precordial transition generally at V(3). Pacing from the aortomitral continuity resulted in a qR pattern that was not observed anywhere else in the left ventricular outflow tract. When comparing the right coronary cusp and left coronary cusp, the precordial transition was earlier in the left coronary cusp than in the right coronary cusp. Pacing the noncoronary cusp uniformly resulted in atrial capture.
Conclusion: When considering ablation of idiopathic VT, the aortic cusps and aortomitral continuity must be considered as possible foci. The 12-lead ECG, a readily and easily obtainable source of information, has useful characteristics for differentiating VTs arising from the cusp region.