New criteria for the diagnosis of healed inferior wall myocardial infarction in patients with left bundle branch block.

The diagnosis of healed inferior myocardial infarction (MI) in patients with left bundle branch block (LBBB) is difficult because there are no established criteria. To develop criteria, we retrospectively examined the electrocardiograms of 166 patients with complete LBBB who had either normal images (normals) or an isolated, unequivocal inferior MI on delayed stress thallium imaging. Diagnostic Q waves were defined as a significant Q or QS of at least 30-ms duration. Diagnostic T-wave inversion was defined as complete T inversion or biphasic waves with initial, predominantly negative deflection. The most useful diagnostic findings were in lead aVF, where a Q wave was present in 10 of 35 patients in the MI group compared with only 4 of 131 patients in the normal group (p <0.00001). Diagnostic T-wave inversion was noted in 23 of 35 patients in the MI group compared with 8 of 131 patients in the normal group (p <0.00001). The presence in lead aVF of either a diagnostic Q-wave or T-wave inversion was seen in 30 of 35 patients with inferior MI (sensitivity of 86%) compared with only 12 of 131 patients with uncomplicated LBBB (specificity 91%). Thus, these criteria are potentially useful for the diagnosis of inferior MI in patients with LBBB.