Role of Ablation Therapy in Ventricular Arrhythmias Mithilesh K. Das, MD, MRCP, FACC * , Gopi Dandamudi, MD, Hillel Steiner, MD Krannert Institute of Cardiology, 1800 North Capitol Avenue, Indianapolis, IN 46202, USA Sustained ventricular tachycardia (VT) and ventricular fibrillation (VF) are associated with a poor prognosis because of an increased risk for sudden cardiac death (SCD), particularly in pa- tients who have structural heart disease (SHD) [1]. In addition, frequent nonsustained VT (NSVT), premature ventricular complexes (PVCs), or ven- tricular couplets may cause tachycardia-induced cardiomyopathy, a rare consequence of these arrhythmias. In the present era, the implantable cardioverter defibrillator (ICD) is the mainstay therapy for primary and secondary prevention of SCD. Recurrent VT develops in 20% and 40% to 60% in patients who receive an ICD for primary and secondary prophylaxis for SCD, respectively [2]. ICDs terminate most ventricular arrhythmia (VA) episodes. ICDs do not prevent recurrence of VAs or change the underlying substrate of VA, however. In fact, there is evidence that ICDs may increase the incidence of VA. Repeated ICD shocks reduce quality of life and increase mortality. Recur- rent VAs in these patients often are treated with antiarrhythmic agents with only moderate success. Furthermore, these drugs are associated with an increased risk of proarrhythmia, systemic toxicity, and increased defibrillation threshold (especially amiodarone). Catheter ablation is the treatment of choice to cure or reduce the recurrences of VA in patients who have an ICD [3]. Catheter ablation can be life-saving for electrical storms (ES), defined as three separate episodes of VT or VF within a 24-hour period, each separated by 5 minutes. ES is an independent predictor of short-term mor- tality and occurs in 3.5% and 20% of patients who have an ICD implanted for primary and secondary prophylaxis, respectively. Catheter ablation is also the treatment of choice for symptomatic idiopathic VT or PVCs. Polymorphic VT or VF initiated by a single monomorphic PVC also can be treated with catheter ablation. A recent randomized trial showed that ablation therapy in patients who have an ICD implanted for secondary prophylaxis reduces the risk for ICD therapy by 65% during a 2-year follow up as compared with the patients who do not receive ablation therapy. Catheter ablation of VT or VF in the electro- physiology (EP) laboratory remains a challenging procedure. Patients who have SHD often have poor hemodynamic tolerance to the VA induced in the EP laboratory. Catheter ablation of VA requires a precise understanding of cardiac EP, the VA mechanism, and mapping techniques. Most VAs can be ablated endocardially. Epicar- dial ablation is needed for VTs with an epicardial circuit or focal source. The purpose of this article is to describe current mapping techniques and indications and to discuss the present status of catheter ablation for VA. Mechanisms of ventricular arrhythmia VA mechanism, like any arrhythmia, has either a focal source or a reentrant circuit. Sustained monomorphic VT (SMMVT) occurs predomi- nantly because of reentry in patients who have SHD, whereas a focal VT or a PVC occurs because of enhanced automaticity or triggered activity in patients who have normal hearts and rarely, in patients who have SHD (Box 1, Table 1). Dr. Steiner is a recipient of a Fellowship Grant from The American Physicians Fellowship for Medicine in Israel. * Corresponding author. E-mail address: midas@iupui.edu (M.K. Das). 0733-8651/08/$ - see front matter. Published by Elsevier Inc. doi:10.1016/j.ccl.2008.03.010 cardiology.theclinics.com Cardiol Clin 26 (2008) 459–479