Analysis of discrepancies between VCG and ECG interpretation of inferior wall myocardial infarct

Summary In 247 cases in which an old anteriormyocardial infarction (MI) was suspected and in which SVEC III-lead system vectorcardiograms (VCGs) and matching conventional 12-lead electrocardiograms (ECGs) were available, records were analyzed to investigate the diagnostic agreement or discrepancy between the two techniques. The frequency of agreement (155 cases) exceeded the frequency of disagreement (92 cases), but the frequency of disagreement even with lumped subgroups was high. Eighty percent of this disagreement was between positive VCG and negative ECG diagnostic consensus. The positive MI group by ECG diagnosis showed smaller R waves and larger S waves and larger S waves in leads V2 and V3 and smaller R/S ratios in leads V2 and V4 than the negative MI group by ECG, while small R waves or QS patterns and large S waves in just lead V1 were the only positive finding in the positive MI group by VCG. The important VCG characteristic for positive MI diagnosis was abnormal posterior deviation of the initial QRS vectors. The high incidence of discrepancies shown by positive VCG and negative ECG diagnoses resulted from the fact that, in spite of the presence of a fairly well developed R wave in precordial leads, the initial QRS vectors were displaced posteriorly. In 8 of 18 cases classified into negative VCG and positive ECG diagnostic group, poor R wave progression did not necessarily result in the posterior displacement of the initial QRS vectors. In contrast to the difficulties in applyingECG criteria for anterior MI (variability of QRS patterns in precordial leads), an orthogonal VCG (representing the phasic changes in the depolarization process) seems to clarify the equivocal situation in the ECG diagnosis of MI.