Pulmonary vein stenosis post cryo AF ablation using single shot 4-minute freeze technique
Authors: Hammouda T , Ali W , Mostafa M , Mahfouz A , Nasr A , Nabil S H , Elnagar R , Kamel O 
Published: May 2023

Abstract

Funding Acknowledgements
Type of funding sources: Foundation. Main funding source(s): Magdi Yacoub foundation

Introduction
Cryo balloon ablation is widely used for AF ablation. Cryo ablation techniques include regular 2 shots per vein Vs single shot freeze technique. Studies showed that the single shot freeze technique is as effective as the double freezing shot, thus becoming the standard technique (1). There is a debate on whether the single shot freeze should be 3 minutes or 4 minutes. Some data suggest similar efficacy while other data suggest more durable PV isolation with the 4-minute technique (2). Severe pulmonary vein (PV) stenosis is a rare but a serious complication. The only available data on iatrogenic PV stenosis are from studies on the single 3-minute freeze technique (3).

Purpose
Assessment of the incidence of PVs stenosis using single shot 4-minute freeze technique.

Methods
We conducted a single center prospective study where we recruited 28 consecutive patients with 102 PVs scheduled for cryo AF ablation using 2nd generation cryo balloon using single shot 4-minute freeze technique as the standard technique. All patients had cardiac CT before ablation and at least 3 months post ablation where each PV’s cross-sectional area was measured. Measurements were validated by a single experienced operator. PV stenosis was classified to minimal, mild, moderate, and severe if the PV’s area decreased by 25%, 25-50%, 50-75% and more than 75% respectively. All patients were assessed regarding the presence of any symptom suggesting PV stenosis or other complications.

Results
Of the studied 102 PVs, only one vein (0.98%) had severe stenosis (asymptomatic) and one vein (0.98%) had moderate stenosis. Both were left superior pulmonary vein (LSPV). 13 veins (12.7%) developed mild stenosis, 74 veins (72%) showed minimal stenosis and 13 veins had no change in area. None of the studied patients developed phrenic nerve palsy or esophageal injury peri-procedure.

Discussion
Our results suggest low risk of developing severe PV stenosis using the 4-minute single shot freeze technique (0.98%). However, minimal, and mild pulmonary vein stenosis occurred in 84.7% of the patients denoting that this change is expected with the procedure. Tokutake et al studied the effect of using the single shot 3-minute freeze technique on PV area 3 months post cryo AF ablation and reported mild, moderate and severe (&gt;75%) PV stenosis in 24.6%, 3.8% and 1.3% of PVs respectively (3). This shows that using the 4-minute freeze technique has a similarly low incidence of severe PV stenosis to the published data on the 3-minute technique. It appears that the LSPV is the most liable for this complication and this goes in line with the previous studies.

Conclusion
Using the 4-minute single shot freeze technique in cryo AF ablation appears to have a comparable low incidence of severe PV stenosis to the published data for the 3-minute freeze technique. The overall risk of severe PV stenosis is low. It appears that the LSPV is the most liable for this complication.