Electrocardiographic differentiation of posterobasal left ventricular hypertrophy from right ventricular hypertrophy.

Increased terminal rightward forces manifested by S waves greater than the 95th percentile (95%) for age in the left chest leads of the ECG can be produced by right ventricular hypertrophy (RVH) and posterobasal left ventricular hypertrophy (LVH). There are no currently available criteria to differentiate these. The S wave in lead V5 exceeded the 95% for age in 445 of 5,240 patients (8.5%). From these, the ECGs of patients with lesions known to produce "isolated" RVH (46 patients) or LVH (38 patients) were chosen for study. Analysis of these ECGs revealed two patterns in each group: 1. Voltage criteria for ventricular hypertrophy other than SV5 & SV6 were present in 26 patients of the RVH group and 15 of the LVH group; 2. The ECGs of the remaining 20 of the RVH and 23 of the LVH group contained no other voltage criteria to diagnose either RVH or LVH. These 43 ECGs were further analyzed. SV5, SV6 and RV5 were similar in both groups (p greater than 0.01). However, SI, R'V4R, R'V1 and the ratio RV2/SV2 were higher (p less than 0.01) and SV2 was lower (p less than 0.01) in the RVH group. Despite significant differences, there was marked overlap of the data. Therefore, discriminant analysis was performed which suggested RVH if SI greater than 5mm, RV2 greater than 10mm and the ratio RV2/SV2 greater than 0.65, and LVH if SI less than 5 mm, RV2 less than 10mm and the ratio RV2/SV2 less than 0.65. In the frontal plane the mean QRS vector was similar; however, in the horizontal plane, it varied between +60 degrees to +200 degrees in the RVH group and between -10 degrees to -130 degrees in the LVH group. The rotation of the QRS loop in the horizontal plane was clockwise (CW) or figure of eight in RVH group and counterclockwise (CCW) in the LVH group. The orthogonal vector data confirm these results. It is concluded that when SV5 is greater than 95% for age and there are no other clear voltage criteria for ventricular hypertrophy the diagnosis of RVH vs LVH may be made on the basis of the following: RVH: RV2 greater than 10mm, SI greater than 5mm and mean horizontal plane QRS vector between +60 degrees to +200 degrees with a CW or a figure of eight loop and LVH: RV2 less than 10mm, SI less than 5mm and mean horizontal plane QRS vector between -10 degrees to -130 degrees with CCW loop.