New Criteri for the Diagnosis of Inferior Infarction in Patients with Left Bundle Branch Block

The ability to diagnose inferior infarction in patients with left bundle branch block (LBBB) is limited by the lack of established criteria. To develop criteria, the ECGs of 187 patients with LBBB who had either normal results (Normals) or an isolated, unequivocal inferior infarct (IMI) on stress thallium testing were examined. Patients with acute IMI within 30 days of the thallium were excluded. LBBB was defined as QRS duration ≥ 120 msec with the classic patterns of changes in leads I, aVL, V5, and V6. Q-waves were significant if they were ≥ 30 msec in duration and 25% the height of the R-wave; T-waves were considered inverted if they were either totally negative or biphasic with initial negative deflection. Results: The presence of diagnostic Q-waves or T-inversion in VF was found to be predictive of IMI in patients with LBBB with 85% sensitivity and 86% specificity. The presence of both Q-waves and T-inversion in aVF was diagnostic with specificity of 100% though low sensitivity of 13%. Conclusion. The presence of either Q-wave or T-inversion in aVF appears to be useful in predicting past inferior infarction in patients with LBBB. The combination of the two, though rare, has high positive predictive value.