Portal de Periódicos da CAPES

Paroxysmal Atrioventricular Block Related to Hypopolarization and Spontaneous Diastolic Depolarization

1973; Elsevier BV; Volume: 63; Issue: 5 Linguagem: Inglês

10.1378/chest.63.5.678

1931-3543

Mauricio B. Rosenbaum, Marcelo V. Elizari, Raúl J. Levi, Gerardo Nau,

Cardiac electrophysiology and arrhythmias

Eight cases of paroxysmal atrioventricular block (PAVB), and ten similar cases from the literature were analyzed. Atrioventricular block was shown to occur both at rapid and slow rates, with an intermediate normal conduction range. The tachycardia-dependent AY block was related to prolonged recovery and was termed "phase-3 block;" the bradycardia-dependent AV block was related to hypopolarization plus spontaneous diastolic depolarization and was termed "phase-4 block." However, the PAVB truly began and was maintained when a single P wave fell on the phase-4 block range. Therefore, this form of PAVB can be termed "phase-4 PAVB." Normal AV conduction was reestablished only after a ventricular escape beat, when a subsequent P wave fell on the normal conduction range. This indicated that the escape beat activated the injured region, starting the whole process anew. In phase-4 block, as well as in phase-3 block, retrograde conduction tends to be preserved at a time when orthograde conduction has already failed. Diffuse involvement of the intraventricular conduction system was documented in most cases. The critically injured region was most likely intranodal in location. Other explanations, such as supernormal conduction, vagal effects, and Wedensky effect and facilitation, are discussed. Eight cases of paroxysmal atrioventricular block (PAVB), and ten similar cases from the literature were analyzed. Atrioventricular block was shown to occur both at rapid and slow rates, with an intermediate normal conduction range. The tachycardia-dependent AY block was related to prolonged recovery and was termed "phase-3 block;" the bradycardia-dependent AV block was related to hypopolarization plus spontaneous diastolic depolarization and was termed "phase-4 block." However, the PAVB truly began and was maintained when a single P wave fell on the phase-4 block range. Therefore, this form of PAVB can be termed "phase-4 PAVB." Normal AV conduction was reestablished only after a ventricular escape beat, when a subsequent P wave fell on the normal conduction range. This indicated that the escape beat activated the injured region, starting the whole process anew. In phase-4 block, as well as in phase-3 block, retrograde conduction tends to be preserved at a time when orthograde conduction has already failed. Diffuse involvement of the intraventricular conduction system was documented in most cases. The critically injured region was most likely intranodal in location. Other explanations, such as supernormal conduction, vagal effects, and Wedensky effect and facilitation, are discussed. The Role of Spontaneous Diastolic Depolarization in Second Degree A-V Block: The Mechanism of "Paroxysmal" A-V Block and of a New Form of Pseudo-supernormal A-V ConductionCHESTVol. 63Issue 5PreviewDr. Mauricio Rosenbaum and his coworkers describe (see page 678 ) the mechanism of an unusual type of A-V block which, in most instances, represents a special form of bradycardia-dependent bundle branch block. The failure of transmission of the atrial impulse to the ventricle is ascribed to hypopolarization and spontaneous depolarization in an injured region of one bundle branch with concomitant complete conduction block in the contralateral bundle branch. Full-Text PDF