ROLE OF LEFT-VENTRICULAR CONDUCTION IN THE ELECTROGENESIS OF LEFT-VENTRICULAR HYPERTROPHY - ELECTROPHYSIOLOGIC STUDY IN MAN

Various ECG and vectorcardiographic (ECG-VCG) patterns of ventricular conduction disturbances are inducible by premature right atrial stimulation (PRAS). These patterns are a consequence of different degrees of refractoriness in the specialized ventricular conduction system. Intermediate phases of left bundle branch block (LBBB) induced by PRAS in 20 subjects with normal basal QRS (complexes) were similar to those of left ventricular hypertrophy (LVH). In 18 patients with basal ECG-VCG signs of LVH, right bundle branch block (RBBB) induced by PRAS produced a progressive disappearance of these signs and normalization of the tracings. The initial maximum QRS vector decreased, disappeared or remained absent in the patients with LBBB induced by PRAS and appeared (when absent in the basal VCG) and remained unchanged (when present) in patients with RBBB induced by PRAS. Electrogenic implications of these data are discussed. The ECG-VCG signs of LVH are probably dependent on slowed conduction in the left bundle branch system, while anatomical hypertrophy is probably less important.