title: The time course of exit and entrance block during cryoballoon pulmonary vein isolation.
abstract: OBJECTIVE
  The dynamic time course of entrance and exit block during pulmonary vein isolation (PVI) is unknown. The purpose of this series was to dynamically evaluate the manifestation of entrance and exit conduction block during simultaneous circumferential PVI.
  
  
  RESULTS
  Pacing manoeuvres were performed during cryoballoon ablation of left-sided pulmonary veins (PVs) in 30 consecutive patients with a history of drug-refractory paroxysmal atrial fibrillation. At the onset of ablation continuous pacing was performed from the PV at a cycle length of 600 ms until the appearance of exit block. Once exit block was demonstrated, uninterrupted pacing was immediately transitioned to the distal coronary sinus (CS) catheter and continued at 600 ms throughout the rest of the cryoapplication. The timing of exit block, entrance block, and corresponding cryoballoon temperature were noted for all patients. In the 45 PVs when real-time PV recordings were available during cryothermal ablation, the presence of exit block was reliably demonstrated to precede entrance block (P < 0.0001) by a median of 5 s [interquartile range (IQR) 3, 12; median temperature at isolation -39°C (IQR -30, -45); nadir ablation temperature -53°C (IQR -48, -59)]. In all cases, when uninterrupted pacing was transitioned from the PV to the distal CS, entrance conduction from the left atrium to PV remained intact.
  
  
  CONCLUSIONS
  Circumferential PV ablation results in progressive PVI, beginning with unidirectional exit block, and followed by entrance block. As exit block reliably precedes entrance block, we are able to provide justification for the exclusive use of entrance conduction block as the endpoint of cryoballoon-based PVI.
authors.affiliation: Electrophysiology Service, Montreal Heart Institute, Department of Medicine, Université de Montréal 5000 Belanger Street E., Montreal, QC, Canada H1T 1C8.
authors.forename: Jason
authors.initials: J
authors.lastname: Andrade
authors.forename: Paul
authors.initials: P
authors.lastname: Khairy
authors.forename: Marc
authors.initials: M
authors.lastname: Dubuc
authors.forename: Marc W
authors.initials: MW
authors.lastname: Deyell
authors.forename: Denis
authors.initials: D
authors.lastname: Roy
authors.forename: Mario
authors.initials: M
authors.lastname: Talajic
authors.forename: Bernard
authors.initials: B
authors.lastname: Thibault
authors.forename: Peter G
authors.initials: PG
authors.lastname: Guerra
authors.forename: Léna
authors.initials: L
authors.lastname: Rivard
authors.forename: Laurent
authors.initials: L
authors.lastname: Macle
mesh_terms: D000200:Action Potentials; D000368:Aged; D001281:Atrial Fibrillation / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery*; D062906:Cardiac Catheters; D002304:Cardiac Pacing, Artificial; D003452:Cryosurgery / Q000295:instrumentation* / Q000379:methods; D022062:Electrophysiologic Techniques, Cardiac; D004867:Equipment Design; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011667:Pulmonary Veins / Q000503:physiopathology / Q000601:surgery*; D013997:Time Factors; D016896:Treatment Outcome
keywords: Atrial fibrillation; Cryoballoon ablation; Pulmonary vein electrophysiology; Pulmonary vein isolation