Estimation of inferobasal myocardial infarct size by late activation abnormalities of the QRS complex

This report describes the relation of myocardial infarct (MI) size in the left ventricular inferobasal wall, measured at necropsy, to late activation abnormalities of the QRS complex, measured by computerized spatial vectorcardiography. Fifteen patients with single inferobasal MIs and 10 patients with no evidence of heart disease were studied. The percentage of MI in the inferobasal wall was significantly related to the vectorcardiographic abnormalities noted late (i.e., 31 ± 13 ms before the end of the QRS waveform) (r = 0.96, p < 0.00001). The integral of the vector magnitudes during late abnormal activation significantly predicted the amount of MI in the basal inferior wall (r = 0.88) and in the basal inferior wall plus the outer, subepicardial half of the transmural middle inferior, lateral and inferoseptal walls (r = 0.91). The additional information obtained from late activation of the QRS complex contributed more significance to the estimation of the left ventricular inferobasal MI size than the abnormalities commonly noted during early activation (i.e., during the Q wave).