A porcine study of the area of heated tissue during hot-balloon ablation: Implications for the clinical efficacy and safety.

INTRODUCTION: Hot-balloon ablation depends solely on thermal conduction, and myocardial tissue is ablated by only conductive heating from the balloon surface. Despite growing clinical evidence of the efficacy and safety of hot-balloon ablation for atrial fibrillation (AF), the actual tissue temperature and the mechanism of heating during such ablation has not been clarified. To determine, by means of a porcine study, the temperatures of tissues targeted during hot-balloon ablation of AF performed with hot-balloon set temperatures of 73°C or 70°C, in accordance with the temperatures now used clinically. METHODS: After a right thoracotomy, thermocouples with markers were implanted epicardially on the superior vena cava (SVC) and pulmonary veins (PVs) in six pigs. The tissue temperatures during hot-balloon ablation (balloon set temperatures of 73°C and 70°C, 180 s/PV) were recorded, and the maximum tissue temperatures and fluoroscopically measured distance from the balloon surface to the target tissues were assessed. RESULTS: Sixteen SVC- and 18 PV-targeted energy deliveries were performed. Full-thickness circumferential PV lesions were created with all hot-balloon applications. A significant inverse relation was found between the recorded tissue temperatures and distance (r = -.67; p < .001) from the balloon surface. No tissue temperature exceeded either of the balloon set temperatures. The best distance cutoff value for achieving lethal tissue temperatures more than 50°C was 3.6 mm. CONCLUSION: The hot-balloon set temperature, energy delivery time, and tissue temperature data obtained in this porcine study supported the clinical efficacy and safety of the hot-balloon ablation as currently practiced in patients with AF.

Optimization of the hot balloon ablation strategy using real-time pulmonary vein potential monitoring.

INTRODUCTION: Optimal radiofrequency-generated thermal energy applications have not been established for hot balloon ablation (HBA) systems. We investigated the feasibility of real-time monitoring of pulmonary vein (PV) potentials and optimal time-to-isolation (TTI)-guided application strategies in HBAs. METHODS AND RESULTS: Real-time monitoring of PV potentials was performed using a four-electrode unidirectional catheter in 34 consecutive patients. Acute isolation was achieved when PV potentials disappeared during HBAs and were undetected by high-resolution mapping. The TTI, the difference between TTI and the time to reach target temperature (TTRT), and ablation time after isolation were examined for 177 applications in 136 PVs. Real-time monitoring of PV activity was obtained in 167 out of 177 applications (94.3%) and acute isolation was achieved in 97 out of 177 (54.8%) applications. TTI-TTRT was significantly shorter, and ablation times after isolation were significantly longer in the acute isolation group than in the other groups. TTI-TTRT <4.5 seconds and TTIs <33.5 seconds predicted acute isolation (sensitivity 74.2%, specificity 88.4%; sensitivity 76.3%, specificity 76.7%, respectively). Ablation time after isolation >148.5 seconds (sensitivity 93.6%, specificity 51.7%) and >120.5 seconds (sensitivity 84.0%, specificity 78.6%) predicted acute isolation in superior PVs and inferior PVs, respectively. CONCLUSIONS: Real-time assessment of PV isolation can be achieved during HBAs with single-shot techniques. (TTI-TTRT)s <4.5 seconds and TTIs <33.5 seconds predicted for acute isolation. Ablation time after isolation >148.5 seconds in superior PVs and >120.5 seconds in inferior PVs were effective application durations.

Development of a new HotBalloonTM ablation catheter equipped with a balloon surface temperature monitoring sensor for pulmonary vein isolation.

The balloon surface temperature (BST) should be monitored to ensure the success of the ablation procedure using the HotBalloonTM ablation catheter (HBC) in clinical settings. Therefore, we sought to develop a new HBC equipped with a surface temperature monitoring sensor. The BST was evaluated using a pseudo-tissue model and a thermocouple to imitate catheter insertion into the pulmonary vein. Thermo-fluid analysis with computer-aided engineering (CAE) was performed to analyse the temperature distribution in the catheter and the balloon. The CAE analysis reproduced the results from a pseudo-tissue model experiment and demonstrated that some fluid zones inside the catheter shaft had a nearly identical temperature as the BST during the liquid suction period. The pseudo-tissue model experiment confirmed that the temperature was almost the same between the balloon surface and the position of 5 mm inside the catheter shaft from the proximal end of the balloon. A thermocouple placed at 5 mm or 25 mm from the proximal end of the balloon within the catheter shaft showed an equivalent temperature result. This 5-25-mm distance is acceptable to set the BST monitoring sensor inside the catheter shaft, since the sensor can help accurately estimate the BST.