Evaluation of frontal plane QRS loop rotation in vectorcardiographic diagnosis

Abstract

The diagnostic usefulness of frontal plane QRS loop rotation in the Frank vectorcardiogram (VCG) was evaluated in a series of 598 normal subjects, 301 patients with postero-diaphragmatic myocardial infarction (PDMI), 84 with lateral myocardial infarction (LMI), 844 with left ventricular hypertrophy (LVH), and 190 with right ventricular hypertrophy (RVH). In normals 62% showed clockwise (CW) rotation of the QRS loops; 28%, figure-of-eight; and 10%, counterclockwise (CCW). The respective distributions were 68%, 23%, and 9% in PDMI; and 23%, 40%, and 37% in LMI. In normals the superior and inferior limits (96% range) of the maximal QRS vector angles were +15° and +79° in VCGs with CW rotation, +12° and +62° in VCGs with figure-of-eight, and −4° and +58° in VCGs with CCW rotation. Based on these limits, approximately half of PDMI cases (with 2% false positives) and a little over two-thirds of LMI cases (with 4% false positives) could be separated from normal. In LVH and RVH groups without clinical evidence of ischemic heart disease, the superior and inferior limits (96% range) of the maximal QRS vector angles differed from those of normal. In LVH such limits were +1° and +86° in VCGs with CW rotation, +12° and +62° in VCGs with figure-of-eight, and −86° and +48° in VCGs with CCW rotation. The respective limits in RVH were +13° and −160°, −3° and +76°, and −30° and +65°. Thus, when LVH or RVH is present, the foregoing limits separating PDMI or LMI from normal need to be modified accordingly. Results of the study demonstrate the diagnostic significance of QRS rotation analysis in the frontal plane VCG. These findings should prove useful as the standard of reference for clinical interpretation of the Frank VCG.