Case reports of phase 4 paroxysmal atrioventricular block.

Four cases of PAVB were reported, 3 of which manifested third-degree AV block, while one exhibited first-degree AV block, while one exhibited first-degree AV block. The location and mechanism of establishment and disappearance of PAVB was discussed. It was speculated that, in some cases, concealed conduction of P waves could promote depolarization of the injured area which displayed Phase 4 block and thus temporarily restore 1.1 AV conduction.