Retrograde migration of the site of functional block: a mechanism underlying resolution of functional retrograde bundle branch block during AV reentrant tachycardia.
BACKGROUND
Functional bundle branch blocks during supraventricular tachycardia have been described, and their sustainment has been attributed to concealed conduction. Such blocks frequently resolve spontaneously, but the electrophysiologic mechanism of resolution has not been well described. This report describes the resolution of functional bundle branch block through proximal migration of the site of block.


RESULTS
During electrophysiologic study of a patient with reentrant antidromic tachycardia via an atriofascicular accessory pathway, functional retrograde right bundle branch block could be readily induced following tachycardia initiation with right ventricular apical pacing. Resolution of this block was associated with shortening of the tachycardia cycle length. Electrogram recordings along the right bundle branch during tachycardia determined that resolution of the functional retrograde right bundle branch block was associated with migration of the site of block from the distal to the proximal right bundle. When the site of block was directly at the recording site, both anterograde and retrograde activation of the right bundle was demonstrated.


CONCLUSIONS
Migration of the site of block is a mechanism of resolution for functional conduction blocks maintained by concealed conduction.
Tchou
P J
PJ
Department of Cardiology, Cleveland Clinic Foundation, OH 44195, USA.
Trohman
R
R
Kidwell
G
G
Mehdirad
A A
AA
D000328:Adult; D002037:Bundle-Branch Block / Q000503:physiopathology* / Q000628:therapy; D002304:Cardiac Pacing, Artificial; D017115:Catheter Ablation; D004562:Electrocardiography; D004594:Electrophysiology; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology; D006801:Humans; D013611:Tachycardia, Atrioventricular Nodal Reentry / Q000503:physiopathology* / Q000628:therapy; D018879:Ventricular Premature Complexes / Q000503:physiopathology