Vectorcardiographic differentiation between right ventricular hypertrophy and posterobasal myocardial infarction.

Vectorcardiograms were recorded by the Frank lead system in 203 cases of right ventricular hypertrophy (RVH) and 85 cases of posterobasal myocardial infarction (PBMI). Of the RVH cases, 33 were confirmed by autopsy and 135 by cardiac catheterization or surgery. Of the cases of PBMI, 12 were confirmed by autopsy and 48 had definite clinical episodes associated with enzymatic or serial electrocardiographic changes or both. Of several measurements made, the following proved most helpful: (1) location of mean frontal plane QRS axis between 750 and 220° in 64% of the cases of RVH and between 350° and 74° in 78% of the cases of PBMI; (2) location of mean horizontal plane QRS axis between 350° and 90° in 85% of the cases of PBMI but in only 11% of the cases of RVH; (3) location of the 0.04-sec instantaneous vector in the horizontal plane between 35Q0 and 60° in 76% of the cases of PBMI but in only 22% of the cases of RVH; (4) magnitude of terminal rightward voltage of less than 1.0 mv in 88% of the cases of PBMI and equal to or greater than 1.0 mv in 80% of the cases of RVH; and (5) clockwise inscription of the horizontal plane loop favored RVH, but counterclockwise rotation in the horizontal plane was not helpful. Synthesis of criteria 2 and 4 provided the best combination for the separation of RVH from PBMI. If both these criteria were fulfilled, a correct diagnosis could be made with 95% certainty.