The electrocardiogram in chronic chagasic myocarditis

Abstract

1. 1. Electrocardiographic abnormalities were present in 113 (86.92 per cent) out of 130 cases of the chronic form of Chagas' disease studied in the “Pabellón de Cardiología Luis H. Inchauspe”, Policlínico Ramos Mejía, Buenos Aires. 2. 2. In the abnormal group of electrocardiograms, the highest incidence was shown by the following findings: right bundle branch block, 55.7 per cent; ventricular extrasystoles, 53.9 per cent; primary T-wave changes, 42.4 per cent; P-wave abnormalities, 23.0 per cent; left ventricular enlargement, 22.1 per cent. 3. 3. A comparative study of sixty-three cases of chagasic with sixty-five cases of nonchagasic right bundle branch block showed that the former is more frequently accompanied by other electrocardiographic abnormalities. The association of right bundle branch block with primary T-wave changes and multiple and polymorphous ventricular extrasystoles was found very valuable for the diagnosis of chronic chagasic myocarditis. In more than 50 per cent of the chagasic cases of right bundle branch block, there was pronounced left-axis deviation of the QRS. Chagas' disease was found to be an important cause for right bundle branch block in Buenos Aires, and it is possible that it is the most important of all in endemic areas in the country. Right bundle branch block in a patient with the chronic form of Chagas' disease would indicate that chronic myocarditis is actually present in at least 85 per cent of the cases. 4. 4. Contrasting with right bundle branch block, left bundle branch block is seldom seen in chronic chagasic myocarditis. The possible reasons for this difference are discussed. An explanation is advanced which depends on the two following facts: (a) the degree of inflammatory involvement seems to be usually about the same in both branches of the bundle of His; (b) the right branch is anatomically and especially functionally more vulnerable than the left branch. If the bilateral lesions are not important, right bundle branch block would be produced; if they are severe, complete A-V block would occur. Consequently, an electrocardiographic pattern of left bundle branch block could only appear if the lesions are much more severe in the left than in the right branch. 5. 5. The diagnostic value of each isolated electrocardiographic abnormality is discussed, and the difficulties for a definite diagnosis in some cases are pointed out. 6. 6. Chronic chagasic myocarditis may give place to abnormal QR or QS ventricular complexes, of the same type as observed in myocardial infarction. However, this is a relatively infrequent event. The anatomic reasons for that are explained. More frequent is the presence of abnormal T waves of the “coronary” type, related to the existence of intense subepicardial lesions. 7. 7. Pure cases of chronic chagasic myocarditis may produce a typical pattern of the so-called “left ventricular hypertrophy and strain.” Both dilatation and thickening of the left ventricular wall can cause this electrocardiographic pattern. 8. 8. The electrocardiogram is the best method for the diagnosis of initial forms of chronic chagasic myocarditis.