False-positive posterior myocardial infarct criteria during left anterior descending coronary angioplasty

Abstract

In reviewing ECG change during acute anterior myocardial infarction (AMI) and during transluminal coronary angioplasty of the left anterior descending (LAD) coronary artery, QRS changes mimicking posterior myocardial infarct (PMI) and false-positive points for PMI using the QRS infarct size scoring system were observed in about 20% of patients. Nineteen patients in whom a three-lead electrocardiogram (ECG) was continuously recorded during transluminal coronary angioplasty of a proximal left anterior descending (LAD) coronary artery were reviewed. All but two had significant ST-segment shifts in V 2 within a few seconds of balloon occlusion of a proximal LAD. In many such patients the R wave amplitude in V 2 measured from the PR segment baseline remained relatively stable and the S amplitude tracked with the J point. However, of the 19 patients studied, 11 had transient QRS changes greater than could be accounted for by baseline shift alone and 4 had transient false-positive PMI points by QRS MI size score. Transient QRS changes were observed as follows: (1) significant increase in R waves and/or decrease in S waves in V 2 due to right septal block (or conduction delay) occurred in 3 of 11 patients and was the cause of the falsepositive criteria for PMI; (2) 5 of 11 patients had a major decrease in R waves in V 2 due to left septal block; (3) 2 of 11 patients had both (1) and (2); and (4) 1 of 11 had transient frontal plane axis shifts with the QRS configuration of anterosuperior fascicular block plus right and left septal block. This occurred in one of six patients with balloon occlusion proximal to the main diagonal branch of the LAD. None of the three conduction abnormalities, alone or in combination, significantly prolonged the QRS, and all promptly disappeared within seconds of balloon deflation. This report defines a proposed anatomic and electrophysiologic basis for the changes.