The ST injury vector: electrocardiogram-based estimation of location and extent of myocardial ischemia

Analysis of ST deviations from the 12-lead electrocardiogram allows for estimation of a spatial ST injury vector. The goal of the present study was to compare the location and extent of transmural myocardial ischemia evaluated by myocardial perfusion imaging with the direction and magnitude of the ST injury vector.

Twelve-lead electrocardiograms were recorded from 75 acute myocardial infarction patients with single-vessel disease and thrombolysis in myocardial infarction (TIMI) flow 0/1 (30 left anterior descending [LAD], 28 right coronary artery [RCA], 17 left circumflex artery [LCX]). ST deviations were measured in the J point in all leads and used to estimate ST injury vectors for each patient. Myocardial perfusion imaging was performed to evaluate the extent and location of myocardial ischemia at the time of coronary intervention.

Ninety-two percent of the patients showed ST injury vectors within the expected directional range for the identified anatomic segment of ischemia by myocardial perfusion imaging. ST injury vector direction separated LAD, RCA, and LCX occlusion patients; 90% of the LAD patients showed anterior vectors, 82% of the RCA patients showed posteroinferoseptal vectors, and 59% of the LCX patients showed posteroinferolateral vectors. Eight patients did not fulfill the ST elevation criteria for ST elevation myocardial infarction but showed anterior ST depression and prominent ST injury vectors in the posterior torso direction. There was a moderate correlation between the extent of ischemia and ST injury vector magnitude for the ischemic patients, r = 0.29.

We found strong agreement between the direction of the ST injury vector and the location of myocardial ischemia. The ST injury vector may be the key to higher diagnostic accuracy for inferobasal transmural ischemia and may help distinguishing between RCA and LCX occlusions in the acute phase.