Evaluation of the direction and extent of ice formation during cryoballoon ablation: an experimental study

Impact of wall thickness on the tissue cooling effect of cryoballoon ablation

AIMS

Understanding of the tissue cooling properties of cryoballoon ablation during pulmonary vein (PV) isolation is lacking. The purpose of this study was to delineate the depth of the tissue cooling effect during cryoballoon freezing at the pulmonary venous ostium.

METHODS AND RESULTS

A left atrial-PV model was constructed using a three-dimensional printer with data from a patient to which porcine thigh muscle of various thicknesses could be affixed. The model was placed in a 37°C water tank with a PV water flow at a rate that mimicked biological blood flow. Cryofreezing at the PV ostium was performed five times each for sliced porcine thigh muscle of 2, 4, and 6 mm thickness, and sliced muscle cooling on the side opposite the balloon was monitored. The cooling effect was assessed using the average temperature of 12 evenly distributed thermocouples covering the roof region of the left superior PV. Tissue cooling effects were in the order of the 2, 4, and 6 mm thicknesses, with an average temperature of -41.4 ± 4.2°C for 2 mm, -33.0 ± 4.0°C for 4 mm, and 8.0 ± 8.7°C for 6 mm at 180 s (P for trend <0.0001). In addition, tissue temperature drops were steeper in thin muscle (maximum temperature drop per 5 s: 5.2 ± 0.9°C, 3.9 ± 0.7°C, and 1.3 ± 0.7°C, P for trend <0.0001).

CONCLUSION

The cooling effect of cryoballoon freezing is weaker in the deeper layers. Cryoballoon ablation should be performed with consideration to myocardial thickness.

Association of left atrial wall thickness with recurrence after cryoballoon ablation of paroxysmal atrial fibrillation

BACKGROUND

Transmural injury plays a role in successful atrial fibrillation ablation. The effect of left atrial wall thickness (LAWT) on the efficacy of radiofrequency ablation has been identified, but data on the relationship between LAWT and cryoballoon for paroxysmal atrial fibrillation (PAF) are lacking. We aim to explore the relationship between LAWT and recurrence after cryoballoon ablation (CBA).

METHODS

We studied 364 patients (mean age 62 years) with PAF who underwent a second-generation CBA and pre-procedure cardiac CTA. LAWT and left atrial volume index (LAVI) were obtained based on pre-procedure cardiac CTA measurements. Follow-up was at least 12 months and predictors of atrial tachyarrhythmia recurrence during follow-up were assessed.

RESULTS

Patients were followed up for a median of 19 (12-28) months, with an atrial tachyarrhythmia-free rate of 77.5% after cryoablation. Greater LAVI (50.0 ± 19.6 mL/m2 vs. 44.3 ± 15.4 mL/m2, P = 0.018) and greater LAWT (1.67 ± 0.24 vs. 1.46 ± 0.25 mm, P < 0.001) were associated with atrial tachyarrhythmia recurrence. The mean LAWT of PV antrum correlated with TTI (R = 0.252, P < 0.001). Adding LAWT to the established risk model improved both the discrimination and reclassification effects (IDI: 0.099, 95% CI: 0.065-0.134, P < 0.001; NRI: 0.685, 95% CI: 0.455-0.915, P < 0.001). In a multivariable Cox proportional hazard model, the mean LAWT of PV antrum (hazard ratio [HR]:3.657, 95%CI: 2.319-5.765, P < 0.001) was an independent predictor of atrial tachyarrhythmia recurrence after cryoablation.

CONCLUSIONS

The mean LAWT of PV antrum, obtained from preoperative measurements on CT, was associated with atrial tachyarrhythmia recurrence after cryoablation.

Difference in tissue temperature change between two cryoballoons

BACKGROUND

Cryoballoon ablation, especially Arctic Front Advance Pro (AFA-Pro) (Medtronic, Minneapolis, Minnesota, USA), has been widely recognised as a standard approach to atrial fibrillation (AF). Recently, Boston Scientific has released a novel cryoballoon system (POLARx). Despite comparable acute clinical outcomes of these two cryoballoons, the recent study reported a higher complication rate, especially for phrenic nerve palsy, with POLARx. However, their impact on biological tissue remains unclear.

OBJECTIVE

The purpose of our study is to evaluate temperature change of biological tissue during cryoablation of each cryoballoon using a porcine experimental model.

METHOD

A tissue-based pulmonary vein model was constructed from porcine myocardial tissue and placed on a stage designed to simulate pulmonary vein anatomy and venous flow. Controlled cryoablations of AFA-Pro and POLARx were performed in this model to evaluate the tissue temperature. A temperature sensor was set behind the muscle and cryoballoon ablation was performed after confirming the occlusion of pulmonary vein with cryoballoon.

RESULTS

The mean tissue nadir temperature during cryoablation with AFA-Pro was -41.5°C±4.9°C, while the mean tissue nadir temperature during cryoablation with POLARx was -58.4°C±5.9°C (p<0.001). The mean balloon nadir temperature during cryoablation with AFA-Pro was -54.6°C±2.6°C and the mean balloon nadir temperature during cryoablation with POLARx was -64.7°C±3.8°C (p<0.001).

CONCLUSION

POLARx could freeze the biological tissue more strongly than AFA-Pro.