Dosing of the second-generation cryoballoon using acute time-to-pulmonary vein isolation as an indicator of durable ablation in a canine model.

BACKGROUND: Rigid time-based dosing protocol(s) currently used in the clinic for cryoballoon ablation of atrial fibrillation may be inadequate to guide the circumferential and transmural cryothermal energy transfer across the pulmonary vein (PV) and may result in injury to collateral tissues or electrical gaps between the PV and left atrium (LA). OBJECTIVE: A physiologic endpoint (e.g., acute time-to-PV isolation a.k.a. time-to-effect; TTE) may be effective in the determination of a transmural lesion formation and may allow for individualized ablation dosing across each PV. METHODS: Thirty PVs from 15 dogs were randomized into five dosing protocols, including (1) TTE + 60 s, (2) TTE + 90 s, (3) TTE + 120 s, (4) TTE + 150 s, and (5) 2 × 180 s. Ablations were conducted with a 23-mm second-generation cryoballoon, and TTE was assessed during a freeze by pacing from an inner balloon-lumen circular diagnostic catheter to a quadripolar diagnostic catheter in the coronary sinus. After ablation, animals were survived for 30 to 34 days, and repeat electrophysiology assessment of PV isolation was conducted after which animals were euthanized for gross anatomy and histological examination. RESULTS: At study termination, efficacy endpoint evaluations were based on maintenance of PV electrical isolation, gross anatomy assessment of PV lesions, and histological examination of PVs. Five efficacy endpoint failures were noted, including the following: 1 PV in the TTE + 90 sec group; 2 PVs in the TTE + 120 sec group; 1 PV in the TTE + 150 s group; and 1 PV in the 2 × 180 s group. Regarding safety, one phrenic nerve injury was observed in the 2 × 180 s cohort. No other complications were observed. CONCLUSIONS: In a canine model, effective PV isolation could be found even in the shortest duration dosing cohort (TTE + 60 s). One complication (phrenic nerve injury) was observed in the longest duration dosing group (2 × 180 s). Further studies will be required to correlate these results to a 28-mm cryoballoon (more commonly used in the cryoablation of a human LA); however, to date, this is the first reporting of a successful cryoablation using TTE + 60 s dosing (approximately 90 s total duration of freezing).

Novel utility of cryoablation for ventricular arrhythmias arising from the left aortic cusp near the left main coronary artery: a case series.

BACKGROUND: Ablation of ventricular tachycardia and premature ventricular contraction arising at the aortic root has been described. The use of radiofrequency ablation energy has been associated with life-threatening collateral damage. The use of cryoablation as a safer alternative energy source at the aortic root has not been previously described. OBJECTIVE: To demonstrate that cautious cryoablation near the ostia of the left main coronary artery is technically feasible and is a safe, effective alternative energy source for ablation at the aortic root. METHODS: Six patients (mean age 36 years; 4 women) with refractory frequent premature ventricular contractions or ventricular tachycardia underwent electrophysiological study and ablation. Two patients had associated nonischemic cardiomyopathy. Patients' ventricular arrhythmias were localized by using 3D mapping, with arrhythmia foci being mapped to the left aortic cusp near the left main coronary artery. The proximity to the ostium of the left main coronary artery was confirmed by using intracardiac ultrasound and coronary angiogram. Focal ablation, up to 240 seconds with freeze-thaw-freeze cycles, was performed by using an 8-mm cryoablation catheter via a retrograde aortic approach. RESULTS: Termination of ventricular arrhythmia during ablation was observed in all 6 patients. All patients were followed for greater than 6-month postablation. One patient had acute ST-segment elevation during ablation below the left main ostium that resolved within 30 seconds of termination of ablation. There were no postprocedure complications and no significant arrhythmia recurrences. CONCLUSIONS: Aortic root ventricular arrhythmia ablation carries an increased risk for collateral damages. This case series demonstrates that cautious cryoablation near the ostia of the left main coronary artery can be performed and is a safe, effective alternative energy source for ablation at the aortic root.