ELECTROPHYSIOLOGIC SIGNIFICANCE OF LEFTWARD QRS AXIS DEVIATION IN BIFASCICULAR AND TRIFASCICULAR BLOCKS

Background: Intraventricular conduction disturbances determine complet e impairment of impulse propagation along the right or left bundle bra nch or the two left fascicles. Hypothesis: This study was undertaken t o investigate the electrophysiologic significance of QRS axis (QRSA) o rientation in bifascicular and trifascicular blocks. Methods: A group of 76 subjects, 43 with right bundle-branch block (RBBB) and left ante rior hemiblock (LAH) (Group A), and 33 with left bundle-branch block ( LBBB) (Group B) was submitted to electrophysiologic evaluation. Result s: In Group A, QRSA was inversely related only to intraventricular con duction, while in Group B, QRSA inversely related to infrahisal conduc tion times, A value of <-60 degrees was considered the cut-off point f or determining subjects with a considerable leftward QRSA deviation. O f the 27 Group A patients with a QRSA <-60 degrees, 38.5% developed an infrahisal second-degree atrioventricular (AV) block during increment al atrial stimulation (IAS) in comparison with 11.1% of those with QRS A >-60 degrees. Of the 9 Group B patients with a QRSA <-60 degrees, 44 .4% exhibited severe impairment of infrahisal conduction at baseline a nd 66.6% developed an infrahisal second-degree AV block during IAS, wh ereas among the remaining 24 with a QRSA >-60 degrees, in only 8.3% we re both infrahisal (HV1 and HV2) intervals dangerously prolonged, and 23.8% encountered an infrahisal second-degree AV block during IAS. In Group A, atrioventricular conduction time >200 ms exhibited a better p redictive accuracy than QRSA <-60 degrees for the development of an in frahisal second-degree AV block during IAS, whereas the latter appeare d the best noninvasive predictor in Group B with a slightly lesser pre dictive accuracy than HV >80 ms. Conclusion: The degree of leftward QR SA deviation seems to reflect the entity of intraventricular conductio n delay in patients with RBBB + LAH, while it appears to be directly r elated to infrahisal conduction prolongation in those with LBBB.