Electrocardiographic identification of the infarct-related artery in acute inferior myocardial infarction.

Introduction: Mortality and morbidity from acute inferior myocardial infarction (MI) are determined, among other factors, by the infarct-related artery (IRA). Several electrocardiographic (ECG) criteria have been proposed to differentiate between the right coronary artery (RCA) and the left circumflex coronary artery (LCx) as the IRA in inferior MI. Recently, a new criterion has been proposed (ST segment depression in lead aVR). It was our objective to evaluate the old and the new ECG criteria in identifying the IRA in patients with inferior MI.

Methods: Patients with inferior MI treated by primary angioplasty were included, following evaluation of the admission ECG. Patients with a previous history of Q-wave myocardial infarction and complete bundle branch block were excluded. The artery with the most severe lesion was considered the IRA. The following ECG criteria were assessed: ST depression in lead DI; ST depression in leads V1 and V2, ST elevation in lead DIII > DII, ST depression in V3/ST elevation in DIII ratio > 1.2 (classical criteria) and ST depression in lead aVR. ST-segment elevation or depression was measured 0.06 sec after the J point.

Results: 53 patients were included (mean age 59.1 +/- 13.9 years, 38 males). The RCA was the IRA in 38 patients and the LCx in 15. Baseline characteristics (age, gender, TIMI flow, Killip class, and pain-to-balloon time) were similar in both groups. All the classical criteria were able to identify the IRA. The new criterion--ST depression in lead aVR--identified the IRA in a small number of patients (sensitivity 33%, specificity 71%, p = NS).

Conclusions: The 4 classical criteria were useful in identifying the IRA in patients with inferior MI. ST depression in lead aVR (a recently proposed new criterion), on the other hand, showed limited utility in differentiating between RCA and LCx.