| Popis: |
Summary A case of paroxystic atrio-ventricular (A-V) block is presented. Attacks of A-V block were elicited by either atrial or ventricular induced premature beats, and normal A-V conduction was resumed through appropriately-timed junctional escape beats. Thus, a “zone of opportunity” for A-V conduction was evidenced during a stimulation procedure. The underlying mechanism of such rarely observed “bradycardia-dependent A-V blocks” is not known. The spontaneous depolarization of specialized conducting fibers in late stages of diastole appears to be the most plausible explanation. Such a form of block must be considered as an A-V dissociation rather than an A-V block, due to the slowing down of the primary pacemaker, associated with a “concealed” subsidiary pacemaker. This phenomenon is not proper to the A-V node, and another case is presented, involving a bilateral bundle-branch block, as shown by means of His bundle recordings. |
