Ablation of ventricular tachycardia: Inside-out or outside-in?

Abstract

Sustained ventricular tachycardia (VT) causes significant morbidity and sudden death in patients with structural heart disease. Currently, right or wrong, VT ablation is often reserved as a treatment of last resort after the patient has received an implantable cardioverter-defibrillator (ICD), has failed an antiarrhythmic drug, and ultimately presents with VT storm. It is estimated that 35% of the patients with a primary prevention ICD will experience their first episode of ventricular arrhythmia within 3 years, with a 450% chance of subsequent ICD therapies. 1‐3 The incidence is even higher for patients with an ICD for secondary prevention indications. As patients live longer and more primary prevention ICDs are implanted, the number of VT ablations performed has also increased. The referral patterns for VT ablation over the past several years has expanded from ischemic heart disease to include more patients with nonischemic etiology such as arrhythmogenic right ventricular cardiomyopathy and dilated cardiomyopathy, where there is minimal endocardial low-voltage regions. Since the myocardial substrate is 3-dimensional, potential VT circuits can involve not only the subendocardial layer but also the intramural and the epicardial myocardium. While the prevalence of epicardial substrate in the population with nonischemic cardiomyopathy (NICM) remains ill-defined, many patients with NICM have more extensive bipolar low-voltage regions on the epicardium than the endocardium. 4 VT ablation was initially described in the postinfarction setting and involved surgical resection of the left ventricular aneurysm and subendocardial resection guided by intraoperative mapping to remove regions of abnormal and fractionated electrograms. 5,6 As technology has evolved over the past decades, the ability to “mimic” the surgical approach of “removing” the infarct zone by using a catheterbased approach became feasible, making the catheter-based ablation the preferred strategy in treating medically refractory VT. While endocardial ablation alone is able to control infarct-related VT with reasonable success, the same cannot be said of VT occurring in the setting of a nonischemic etiology primarily owing to the epicardial nature of the nonischemic substrate. 7‐11 Furthermore, despite an apparent initial successful ablation, depending on the underlying substrate, upward of 40% of the patients have recurrent VT. 12‐14 Some of the potential causes of ablation failure are related to broad complex circuits with multiple exits; inability to adequately identify appropriate ablation targets; progression of disease; thickness and density of the scar; and inability of the radiofrequency lesion to penetrate deep enough into the muscle to disrupt the circuit. In addition, in patients with VT whose substrate is nonischemic in nature, epicardial mapping can be limited by proximity to coronary vessels or insulated by epicardial fat. Sosa et al 15 first described the subxyphoid technique of epicardial mapping and ablation in the setting of VT related to Chagas disease. As more patients with nonischemic etiology of VT are referred for ablation, the number of patients requiring an epicardial approach has also increased. With improvements in the safety and in refinement techniques of epicardial mapping and ablation, the threshold to go epicardial has been lowered. In this issue of HeartRhythm, Tung et al 16 report their experience of epicardial VT ablation and the outcomes at a single tertiary referral center. The study design was a retrospective, nonrandomized study of 144 patients referred for VT ablation from 2004 to 2011, during which a total of 109 epicardial procedures were performed in 95 patients. Patients were divided into 3 groups: ischemic, nonischemic, and idiopathic. A comparison was made between patients who underwent both endo- and epicardial mapping and ablation to those who underwent endocardial ablation alone. A successful access to the pericardial space by using the method described by Sosa was achieved in 94%, with a major complication rate of 8.8% and bleeding in 6.7%. There was no procedure-related mortality and no tamponade or surgical intervention in any of the patients. The authors found that patients with ischemic VT who underwent combined endo- and epicardial ablation had a better outcome at 6 and 12 months compared to endocardial ablation alone. In contrast, for the nonischemic group, no difference was found between those who underwent combined endo- and epicardial ablation and those who underwent endocardial ablation alone. In our experience, patients with ICM have a