Linear ablation lesions for control of unmappable ventricular tachycardia in patients with ischemic and nonischemic cardiomyopathy

Background-Conventional activation mapping is difficult without inducible, stable ventricular tachycardia (VT). Methods and Results-We evaluated 16 patients with drug refractory, unimorph ic, unmappable VT. Nine patients had ischemic and 7 had nonischemic cardiom yopathy. All patients had implantable defibrillators and had experienced 6 to 55 VT episodes during the month before treatment. Patients underwent bip olar catheter mapping during baseline rhythm. The amount of endocardium wit h an abnormal electrogram amplitude was estimated using fluoroscopy in 3 pa tients and a magnetic mapping system (CARTO) in 13 patients. For the magnet ic mapping, normal endocardium was defined by an amplitude >1.5 mV; this me asurement was based on sinus rhythm maps in 6 patients who did not have str uctural heart disease. Radiofrequency point lesions extended linearly from the "dense scar," which had a voltage amplitude <0.5 mV, to anatomic bounda ries or normal endocardium. To limit radiofrequency applications, 12-lead E CG during VT and pacemapping guided placement of linear lesions. No new ant iarrhythmic drug therapy was added. The amount of endocardium demonstrating an abnormal electrogram amplitude ranged from 25 to 127 cm(2). A total of 8 to 87 radiofrequency lesions (mean, 55) produced a median of 4 linear les ions that had an average length of 3.9 cm (range, 1.4 to 9.4 cm). Twelve pa tients (75%) have been free of VT during 3 to 36 months of follow-up (media n, 8 months); 4 patients had VT episodes at 1, 3, 9, and 13 months, respect ively. Only one of these patient had frequent VT. Conclusions-Radiofrequency linear endocardial lesions extending from the de nse scar to the normal myocardium or anatomic boundary seem effective in co ntrolling unmappable VT.