229 Endocardial and Epicardial Ablation Guided by Nonsurgical Transthoracic Epicardial Mapping to Treat Recurrent Ventricular Tachycardia EDUARDO SOSA. M.D.. MAURICIO SCANAVACCA, M.D., ANDRE D'AVILA. M.D. JOAO PICCIONI. M.D., OSVALDO SANCHEZ. M.D.. JOSE L. VELARDE, M.D., MARCIO SILVA, M.D., and BASILEO REOLAO, M.D. From the Heart Institute, University of Sao Paulo Medical School, Sao Paulo, Brazil; Nonsurgical Epicardial Ablation. Introduction: An epicardial site of origin of ventricu- lar tachycardia (VT) may explain unsuccessful endocardial radiofrequency (RF) catheter abla- tion. A new technique to map the epicardial surface of the heart through pericardial puncture was presented recently and opened the possihility of u.sing epicardial mapping to guide endo- cardial ahlation or epicardial catheter ahlation. We report the efficacy and .safety of these two approaches to treat 10 consecutive patients with VT and Chagas' disease. Methods and Results: Epicardial mapping was carried out with a regular steerable catheter introduced into the pericardial space. An epicardial circuit was found in 14 of 18 mapahle VTs induced in 10 patients. Epicardial mapping was used to guide endocardial ahlation in 4 pa- tients and epicardial ahlation in 6. The epicardial earliest activation site occurred 107 ± 60 msec earlier than the onset of the QRS complex. At the epicardial site used to guide endocar- dial ahlation, earliest activation occurred 75 ± 55 msec hefore the QRS complex. Epicardial mid-diastolic potentials and/or continuous electrical activity were seen in 7 patients. After 4.8 ± 2.9 seconds of epicardial RF applications, VT was rendered noninducihie. Hemopericardium requiring drainage occurred in 1 patient; 3 others developed pericardial friction without hemo- pericardium. Patients remain asymptomatic 5 to 9 months after the procedure. Interruption during endocardial pulses occurred after 20.2 ± 14 seconds (P - 0.004), hut VT was always reinducihie and the patients experienced a poor outcome. Conclusion: Epicardial mapping does not enhance the effectiveness of endocardial pulses of RF. Epicardial applications of RF energy can safely and effectively treat patients with VT and Chagas' disease. (J Cardlova.sc Electrophysiol. Vol. 9. pp. 229-239. March 199H) ventricular tachycardia, catheter ablation, radiofrequency, mapping, eplcardium Introduction It has been suggested that 15% of isehemic ven- tricular tachycardias (VTs) have the crucial por- tion of the reentrant circuit located in a subepi- Prcsenied in abstract form at ihe 70th Scientific Sessions of the American Heart Association. Orlando, Florida, November 1997. Address for correspondence: Edtiardo Sosa. M.D.. Institiito do Corav'ao. Grupo de ArHtniia. Av, Eneas de Carvaiho Aguiar, 44- Cerqueira Cesar. CEP 05403-000. Sao Pairlo. Brazil. Fax: 55-11- 2822354; E-mail: sosa@decx6.incnr.usp.br Manuscript received 6 October 1997; Accepted for publication 14 Januarv 1998. cardial layer of viable muscle, which may make endocardial pulses of radiofrequency (RF) en- ergy less effective and account for the disparity of results published by different investigators.' i-" There- fore, it became fundamental to differentiate an epi- cardial from an endocardial circuit during this era of RF catheter ablation. A new transthoracic technique to perform ex- tensive epicardial mapping through pericardial puncture in the eleclrophysiology (EP) laboratory was described recently by our group.'^ Accord- ing to this methodology, it was possible to iden- tify different VTs related lo an epicardial circuit in a specific subset of patients with VT and Cha-