The diagnosis of myocardial infarction in the presence of left bundle branch block.

Our analysis confirms the limited value of the electrocardiogram for the diagnosis of acute myocardial infarction in the presence of complete left bundle branch block. The various electrocardiographic criteria that have been proposed in the past as indicators of myocardial infarction lack sensitivity and predictive accuracy. In addition, they are subject to considerable inter-observer variability. In order of decreasing sensitivity, the following electrocardiographic criteria may be of diagnostic value: (1) serial changes of QRS complex or ST segment (sensitivity, 67 per cent); (2) ST segment elevation (sensitivity, 54 per cent; for anteroseptal infarction, 76 per cent); (3) abnormal Q waves (sensitivity, 31 per cent; for anteroseptal infarction, 53 per cent; highly specific: appearance of RV1, Qv6); and (4) sign of Cabrera (sensitivity, 27 per cent, for anteroseptal infarction, 47 per cent).