Ablation of Unstable Ventricular Tachycardia and Ventricular Fibrillation

A body of work has developed to supplement the classic methods of activation and entrainment mapping for cases of hemodynamically unstable ventricular tachycardia (VT). Definition of the arrhythmic substrate and ablation can be performed during sinus rhythm. Preoperative imaging such as computed tomography scan or magnetic resonance imaging may help guide the mapping strategy. Special equipment includes an electroanatomic mapping system, which is necessary to construct a 3-dimensional rendering of ventricular geometry and scar location; irrigated-tip radiofrequency ablation catheter, which is optimal for mapping and ablation; intracardiac echocardiography, which may facilitate transseptal access to perform transmitral left ventricular mapping and monitoring of complications such as cardiac tamponade; and a percutaneous left ventricular assist device to optimize hemodynamic status. Targets for substrate ablation include VT exit sites identified by pace mapping, sites identified by brief resetting and entrainment mapping, late and fractionated potentials, sites with local abnormal ventricular activity, and channels between dense (“electrically unexcitable”) scar. Ablation to ‘homogenize’ the scar area is an alternative effective approach. For ventricular fibrillation (VF), mapping is performed to identify the focal origin of triggers. Targets for focal VF are premature ventricular contractions (PVC) triggers preceded by Purkinje potentials or from the ventricular outflow tract or papillary muscle. Sources of difficulty include epicardial and intramyocardial VT circuits, and for VF ablation PVC triggers that are difficult to induce.