The electrocardiogram in the presence of myocardial infarction and intraventricular block of the left bundle-branch block type: A clinical pathologic study

Abstract

On the basis of a study of the pathologic, electrocardiographic, and clinical data in 39 cases in which there was a confluent myocardial infarct in the presence of left bundle-branch block, the following observations are made: 1. 1. Substantial evidence of transmural anteroseptal myocardial infarction in the presence of left bundle-branch block would appear to be afforded (a) by a Q deflection in Lead I or (b) by a Q deflection or Q-wave equivalent in Precordial Lead V 6. 2. 2. Supportive evidence of anteroseptal myocardial infarction in the presence of left bundle-branch block would appear to be afforded (a) by an R wave in Lead V 3 or Lead V 4, or both, that is, lower in amplitude than an R wave in Lead V 1 or Lead V 2, or both, or (b) by a notch or slur with a duration of 0.05 second or more in the terminal portion of the QRS complex in precordial leads that shows an rS or QS form. 3. 3. Supportive evidence of infarction involving the posterior wall of the left ventricle in the presence of left bundle-branch block would appear to be afforded by a Q deflection in Standard Leads II and III. 4. 4. Equivocal evidence of anteroseptal infarction in the presence of left bundle-branch block would appear to be afforded by a Q deflection in Lead a V L. 5. 5. In two of three instances in which electrocardiograms showing left bundle-branch block were recorded both before and after myocardial infarction, the height of the R waves in the standard leads decreased markedly. 6. 6. Changes in S-T segments and T waves of a degree to be considered suggestive of myocardial infarction occurred in a minority of cases in which myocardial infarcts were recent. 7. 7. The weight of every heart was more than the weight expected for the height, body weight, and sex of the patient. The mean increase in the weight of the heart over the expected weight was 100 per cent.