Fehmi Keçe

Chapter 6 136 6.4 Discussion 6.4.1 Main Findings The major finding of this study is that an additional ablation with 90, 120 or 150s after time- to-isolation showed a stepwise decrease in reconnection/DC. Consequently, additional ablations for the treatment of reconnection/DC decreased similarly while the success rates at one-year off AAD were not significantly different. During follow-up the rate of repeated procedures decreased with increasing additional ablation. To the best of our knowledge, this is the first trial studying single cryoballoon applications with the ablation duration based on time-to-isolation. 6.4.2 Decreasing ablation duration with the second-generation cryoballoon The second-generation cryoballoon with more injection ports for more homogenous and faster cooling was introduced to achieve more durable PVI. At the cost of a higher success rate, more transient and persistent phrenic nerve palsies were described (11). Instead of a double 300s fixed ablation duration, a double 240s fixed duration was proposed by the manufacturer. Subsequently, studies showed that a single ablation per vein is sufficient (12). In addition, shortening the ablation duration from 4 to 3 minutes did not increase AF recurrence (2, 13). 6.4.3 Making ablation duration dependent on time-to-isolation Cryothermal energy delivery does not only depend on ablation duration, but also on adequate balloon-tissue contact (14). As balloon gas flow is constant, time to PVI is related to balloon-tissue contact, with a shorter time-to-isolation indicating a better contact (15). Indeed, time-to-isolation predicted durable PVI in several studies with significantly lower PV reconnections at 1 year follow up (4, 16). In a canine model, a 60s additional ablation after time-to-isolation showed 100% durable PVI on histology (17). In addition, extending ablation duration based on a longer time-to-isolation was not associated with durable PVI. Furthermore, a perfect score for the assessment of occlusion was more relevant than total ablation duration in predicting gaps. Therefore, balloon-tissue contact remains the most important factor for durable PVI. Moreover, making ablation dependent on time- to-isolation is feasible, since in a majority of the veins (88%) time-to-isolation could be observed, while other researchers report 72-81% (18, 19). This percentage may become even higher with the future introduction of the third-generation cryoballoon with a shorter- tip, which facilitates PV electrogram registration.