Left axis deviation: a spectrum of intraventricular conduction block.
The effects of left axis shift (greater than -30 degrees) on intraventricular conduction time (IVCT) were studied in 63 subjects in whom electrocardiograms before and after appearance of the left axis shift were available. Subjects with electrocardiographic evidence of left or right ventricular hypertrophy, left or right bundle branch block, myocardial infarction, pre-excitation and those receiving antiarrthymic drugs were excluded. The IVCT increased by an average of 25 msec when the QRS axis shifted to -30 degrees or beyond. When the individual AQRS was related to the IVCT a linear correlation (r = -0.8) was observed. It appears that a continuum relation between the AQRS and the IVCT exists throughout the counterclockwise range of +90 degrees to -90 degees. In all leftward shifts in AQRS from from +90 degrees there is a prolongation in IVCT. Our observations indicate that all leftward shifts in AQRS, including the extreme left axis shift (left anterior hemiblock), represent a spectrum of intraventricular conduction block.
D000328:Adult; D000368:Aged; D002036:Bundle of His / Q000503:physiopathology; D002037:Bundle-Branch Block / Q000503:physiopathology*; D002908:Chronic Disease; D003327:Coronary Disease / Q000150:complications; D004562:Electrocardiography; D006349:Heart Valve Diseases / Q000150:complications; D006801:Humans; D006973:Hypertension / Q000150:complications; D008173:Lung Diseases, Obstructive / Q000150:complications; D008875:Middle Aged; D009431:Neural Conduction; D013997:Time Factors