QRS Morphology Shift Following Catheter Ablation of Idiopathic Outflow Tract Ventricular Tachycardia

Abstract

A 42-year-old patient without structural heart disease was referred for catheter ablation of salvos of outflow tract ventricular tachycardia (VT). Activation mapping of the clinical VT (VT1) revealed the earliest ventricular activation site at the right ventricular outflow tract (RVOT). Catheter ablation at this site led to a slight QRS shift of the VT morphology (VT2). Activation mapping of VT2 established the site of origin at the commissure between the right (RCC) and left (LCC) coronary cusps. This case is indicative of the presence of myocardial fibers displaying preferential conduction properties from the RCC-LCC commissure to a breakout site at the RVOT. A 42-year-old patient was referred for catheter ablation of symptomatic salvos of idiopathic ventricular tachycardia (VT). Structural heart disease was excluded by means of transthoracic echocardiography, cardiac magnetic resonance imaging, and exercise stress testing. The electrocar-diogram (ECG) during VT displayed a left bundle branch block pattern (LBBB) with an inferior axis, R-wave in lead I, and precordial transition in lead V4 (Figure 1A). The QRS morphology was suggestive of a right ventri cular outflow tract (RVOT) site of origin (SOO). An electro-physiologic study was performed in a fasting state without sedation. Antiarrhythmic drugs (β-blocker) were stopped at least five half-times before the procedure. High-density activation mapping of the clinical VT (VT1) was performed using a three-dimensional nonfluoro-scopic mapping system (CARTO ® 3; Biosense Webster, Diamond Bar, CA, USA) via a multipolar catheter (DecaNav catheter, 2-8-2 interelectrode spacing; Biosense Webster, Diamond Bar, CA, USA). A contact force-sensing catheter (SmartTouch™; Biosense Webster, Diamond Bar, CA, USA) was used for validation of the earliest activation site and ablation (contact force up to 8 g). Activation mapping of the RVOT revealed the earliest activation site at the posterior septum (−23 ms) (Figures 2A and 2C). The unipolar signal at this site displayed a small initial r-wave with a steep negative dV/dT. Radio-frequency (RF) energy delivery (25-30 W, 43°C) at this site led to a slight QRS shift of the VT morphology. The ECG morphology of the second VT (VT2) was characterized by LBBB with an inferior axis, a lower-amplitude R-wave in lead I, and a precordial transition in lead V4 (Figure 1B). Of note, the most prominent change was seen in lead V1, where the rS pattern shifted to a QS pattern with notching on the downward deflection, which is suggestive of a right coronary cusp (RCC)-left coronary cusp (LCC) com-missure SOO. Following the change in QRS morphology, 4334