Abstract 2653: Characterization of the Pulmonary Vein Tissue Temperature Response to Cryo Therapy: Threshold of Irreversible Cryothermal Injury
Background: Cryoballoon ablation has been developed as an alternative to radiofrequency interventions to achieve pulmonary vein isolation (PVI) in the treatment of AF. Nevertheless the actual degree of cryothermal energy penetration required for successful PV isolation has never been evaluated.
Methods: To characterize the actual tissue temperatures achieved with cryoballoon ablation, 16 dogs were studied. The relationship between cryoballoon internal and surface temperatures, and PV tissue temperatures were established using embedded thermocouples during 4 to 8 minute energy.
Results: Sixty-five cryoballoon ablations were performed at the PV ostia including 13 in the LIPV, 9 in LSPV, 5 in RIPV, and 38 in RSPV. The minimum internal temperature of the balloon ranged from -75 to -24 oC, (-50.5 ± 13.7 oC), the balloon surface from -70 to -21 oC, (-52.2 ± 11.5 oC). Target tissue epicardial temperatures ranged from -50 to v8.5 oC, (-23.5 ± 9.5 oC), demonstrating a cryoballoon to epicardium temperature gradient of 28.7 ± 11.2 oC. The internal balloon temperature and epicardial tissue temperatures tended to be colder with balloon occlusion of PV blood flow than with periballoon leak: inner balloon -48.4 ± 13 vs. -43.6 ± 12.3 oC and tissue -22.4 ± 8.8 vs. -18.4 ± 9.2 oC, respectively. During distal CS and RA pacing, tissue temperatures of -27 ± 5.4 oC were correlated with entrance block, compared to -15 ± 3.5 oC, in the absence of block (p=0.005). The freeze/thaw cycle showed a predictable profile when block was achieved with a rapid cooling/freezing phase followed by a 2-stage thawing process.
Conclusion: These data characterize the temperature required for PV isolation and the relationship between tissue temperatures achieved and those generated by a cryoballoon. Tissue temperatures colder than -22 oC are required to achieve conduction block. This information is critical for successful ablation and for understanding the biophysics of mechanistic tissue changes needed for successful cryoablation.