RESULTS OF ELECTROPHYSIOLOGIC STUDIES IN PATIENTS WITH ACUTE CHAGASICMYOCARDITIS

Background: As the acute stage of Chagas' myocarditis is rarely detect ed, little is known about the electrophysiologic characteristics of th at stage. Hypothesis: This investigation was undertaken to conduct an electrophysiologic study of the properties of the heart during the acu te phase of Chagasic myocarditis. Methods: We studied eight patients w ho had positive xenodiagnosis, positive mice culture, and positive com plement fixation test for Chagas' disease. Results: Tryanosoma cruzi w ere identified in all of the patients' stained blood samples. Right ve ntricular endomyocardial biopsies were obtained, evidencing a distinct infiltrate of lymphocytes that confirmed the diagnosis of acute myoca rditis. The cardiac dimensions and the ventricular systolic and diasto lic function were preserved in all patients. The electrocardiogram evi denced conduction defects in two patients. The signal-averaged electro cardiogram displayed late potentials in three patients. In the electro physiologic study, atrial fibrillation or flutter was induced in four patients. When compared with control patients, Chagasic patients were found to have greater values of atrial threshold, A-H interval, and at rioventricular (AV) nodal effective refractory period. The H-V interva l was mildly prolonged in two patients, but the dynamic AV nodal condu ction was preserved (1:1 conduction during right atrial stimulation at a cycle length of 400 ms) in all the Chagasic patients. The ventricul ar parameters were within normal limits, and no sustained ventricular arrhythmia could be induced. Conclusions: Patients with mild acute Cha gasic myocarditis may suffer from electrical abnormalities and arrhyth mias that an more evident at the supraventricular level and the AV jun ction.