Introduction:
Success of cryoablation for atrial fibrillation (AF) requires creation of continuous, circumferential lesions around the pulmonary veins (PVs). The depth of these cryo-lesions depends on tissue contact, balloon location, ablation duration and nadir temperature. An optimum lesion depth must be achieved such that effective isolation occurs without collateral cryothermal damage to surrounding structures eg, phrenic nerve injury (PNI).
Hypothesis:
Increased RSPV ovality results in poor pairing between the balloon and PV, which may cause deeper freezing at the lateral circumference of the PV antrum, near the course of the phrenic nerve, resulting in PNI.
Methods:
Consecutive patients undergoing cryoablation for paroxysmal/persistent AF were included. Pre-procedural cardiac CT scans were analyzed to evaluate PV size (diameters, cross-sectional area, circumference) and ovality (ratio of maximum:minimum diameter (d
max
:d
min
), shape). Effects of these anatomic characteristics on rates of complications were analyzed.
Results:
RSPVs from 310 patients (age 65.2 years, 38.1% female, 43.2% persAF) were studied. RSPVs were the largest of the 4 normal PVs (d
max
21.5±4 mm; d
min
17.8±3.8 mm; area 309±113 mm
2
; circumference 124.2±22.8 mm). A majority of RSPVs were round (57.3% round, 26.9% oval and 15.9% flat), with median d
max
:d
min
= 1.18 [1.1-1.32].
PNI was the 2nd most common complication (after access-site complications). Transient diaphragmatic palsy occurred in 2.9% of patients; there were no cases of complete or persistent diaphragmatic paralysis.
Patients in whom diaphragmatic palsy occurred had more oval veins (median d
max
:d
min
1.35 [1.23-1.5] vs 1.18 [1.1-1.31]; p=0.015). Additionally, there was a significant difference in the proportion of patients with round RSPVs who had diaphragmatic palsy (1.1%) compared to those with oval or flat RSPVs (5.3%) (p=0.029) (Fig).
Conclusion:
Increased RSPV ovality is associated with phrenic nerve injury.
Left phrenic nerve injury after cryoballoon ablation of the pulmonary veins
