Why the study?
Does left axis shift affect intraventricular conduction time in subjects without other conduction abnormalities or structural heart disease?
Does left axis shift affect intraventricular conduction time in subjects without other conduction abnormalities or structural heart disease?
Leftward shifts in the QRS axis, including left anterior hemiblock, represent a continuous spectrum of intraventricular conduction block characterized by prolonged intraventricular conduction time.
Left axis shift was associated with prolonged IVCT; supports spectrum of conduction delay but should not yet change practice.
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.
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Gladwin S. Das (1976) studied this question.
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