Electrophysiologic significance of leftward QRS axis deviation in bifascicular and trifascicular blocks.
BACKGROUND
Intraventricular conduction disturbances determine complete impairment of impulse propagation along the right or left bundle branch or the two left fascicles.


OBJECTIVE
This study was undertaken to investigate the electrophysiologic significance of QRS axis (QRSA) orientation in bifascicular and trifascicular blocks.


METHODS
A group of 76 subjects, 43 with right bundle-branch block (RBBB) and left anterior hemiblock (LAH) (Group A), and 33 with left bundle-branch block (LBBB) (Group B), was submitted to electrophysiologic evaluation.


RESULTS
In Group A, QRSA was inversely related only to intraventricular conduction, while in Group B, QRSA inversely related to infrahisal conduction times. A value of < -60 degrees was considered the cut-off point for determining subjects with a considerable leftward QRSA deviation. Of the 27 Group A patients with a QRSA < -60 degrees, 38.5% developed an infrahisal second-degree atrioventricular (AV) block during incremental atrial stimulation (IAS) in comparison with 11.1% of those with QRSA > -60 degrees. Of the 9 Group B patients with a QRSA < -60 degrees, 44.4% exhibited severe impairment of infrahisal conduction at baseline and 66.6% developed an infrahisal second-degree AV block during IAS, whereas among the remaining 24 with a QRSA > -60 degrees, in only 8.3% were 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 predictive accuracy than QRSA < -60 degrees for the development of an infrahisal second-degree AV block during IAS, whereas the latter appeared the best noninvasive predictor in Group B with a slightly lesser predictive accuracy than HV > 80 ms.


CONCLUSIONS
The degree of leftward QRSA deviation seems to reflect the entity of intraventricular conduction delay in patients with RBBB + LAH, while it appears to be directly related to infrahisal conduction prolongation in those with LBBB.
Seconda Università di Napoli, Facoltà di Medicina e Chirurgia, Italy.
V
V
Ducceschi
B
B
Sarubbi
A
A
D'Andrea
B
B
Liccardo
P
P
Lucca
M S
MS
Mayer
A
A
Scialdone
L
L
Santangelo
A
A
Iacono
D000368:Aged; D002037:Bundle-Branch Block / Q000175:diagnosis / Q000503:physiopathology; D002304:Cardiac Pacing, Artificial; D016022:Case-Control Studies; D004562:Electrocardiography; D005260:Female; D006327:Heart Block / Q000175:diagnosis* / Q000503:physiopathology; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008297:Male