New electrocardiographic criteria for inferior myocardial infarction.

The sensitivity of existing electrocardiographic (ECG) Q-wave criteria for inferior myocardial infarction (IMI) is poor. New criteria were developed after prospective analysis of the ECGs of 300 consecutive subjects undergoing cardiac catheterization (group 1). These criteria were then prospectively tested in a second group of 300 consecutive subjects undergoing cardiac catheterization (group 2). Only patients with left bundle branch block were excluded from both groups. In each group, IMI subgroups were defined on the basis of angiographic inferior wall motion abnormalities associated with a 70% or greater stenosis of the supplying coronary artery. All subjects who did not satisfy these angiographic criteria were included in the non-IMI subgroups. The new ECG criteria defined in the group 1 subjects were: 'Q' waves in one or more of the ECG leads 2, 3, or a VF, where 'Q' waves are those at least 30 ms in duration (onset to nadir) or those with a Q:R ratio at least 1:4, provided the QRS amplitude is greater than or equal to 0.5 mV. The ECG pattern 'Q3qF', where 'q' waves are those not satisfying either of the above, is excluded from these criteria. When tested in the group 2 subjects, the proposed criteria were significantly (P less than 0.001) more sensitive (68%) than those of the New York Heart Association (28%), though less specific (84% versus 97%, P less than 0.001). Of 300 ECGs analysed by two independent observers, disagreements as to the diagnosis by the proposed criteria were encountered in 19 cases (6%).