Second-Degree AV Block Type I

The clinician must understand the electrophysiologic substrate of Wenckebach block and apply advanced diagnostic and management strategies. On intracardiac electrogram during electrophysiology study, Wenckebach block shows progressive prolongation of the AH interval (atrium to His bundle, representing AV nodal conduction time) with constant HV interval (His bundle to ventricle, representing His-Purkinje conduction time), confirming AV nodal level block. The AH interval normally measures 50-120 ms; prolongation above 200 ms indicates significant AV nodal conduction delay. Autonomic maneuvers help localize the block: carotid sinus massage (increases vagal tone) worsens AV nodal block; atropine or isoproterenol improves it. Conversely, these maneuvers do not improve infranodal block and may worsen it. The clinician must also recognize atypical Wenckebach patterns: in up to 30% of cases, the PR increment is not strictly progressive (the second PR interval may show the greatest increment, with subsequent increments being smaller -- the classic description of progressively increasing increments is actually the exception). The clinician determines the need for electrophysiology study, manages complex presentations (2:1 block, Wenckebach with bundle branch block), and decides on pacemaker implantation for the...