The Significance of Diagnostic Q Waves in the Presence of Bundle Branch Block

We have examined the hearts of 192 subjects in whom complete right bundle branch block (RBBB) and complete or incomplete left bundle branch block (LBBB) had been demonstrated electrocardiographically during life. The exact anatomic sites of infarction were carefully tabulated and the morphologic patterns of the QRS complexes were grouped according to the leads showing abnormal Q waves or Q-equivalents. RBBB did not interfere with the diagnosis of myocardial infarction (MI); diagnostic Q waves were present in the electrocardiograms of 26 of 36 subjects with infarction. False Q waves were recorded in ten of 40 subjects without infarction but were associated with clinical evidence of right ventricular loading and appeared in the leads usually associated with the Q waves of cor pulmonale. In the known presence of infarction, certain patterns of incomplete and complete LBBB provided rough clues as to the general site of myocardial lesions. When the presence of infarction was not known, the finding of Q waves or Q-equivalents anteriorly or laterally in the LBBB pattern was not diagnostic of infarction. (This occurred in 24 of 68 patients with infarction and in 19 of 48 without.) The finding of Q waves inferiorly strongly suggested concomitant MI; there were no false positives in the complete LBBB group and only two in the incomplete LBBB group.