Discussion
This retrospective study showed that despite a longer duration of AF and a more frequent prevalence of prior AF ablation, prior cardioversions, and persistent/LSPAF, the hybrid convergent cohort demonstrated success similar to the results seen in a much less complex cohort of primarily PAF treated with early, stand-alone cryoballoon ablation. This was not at the expense of more frequent perioperative complications. Moreover, the hybrid cohort received significantly less class I AAD prescriptions at 12 months when compared to the cryoballoon group.
At the time of study initiation, there were no efficacy data from large, randomized, multicenter clinical trials using cryoablation in AF. Many of the non-randomized clinical trials using radiofrequency or cryo-energy in patients with PAF reported outcomes between 38% to 78% for a single ablation and one-year success rates of 54% to 80% for multiple ablations7. The experience at our center using first generation cryoablation catheters for PAF was similar, with success rates of greater than 70%. We found recurrence of PAF was generally due to difficult pulmonary vein anatomy (i.e., large common PV on the left or large ovoid PV ostium) or more likely extrapulmonary vein triggers (i.e., posterior wall or carina). To minimize multiple procedures, we collaborated with our cardiovascular surgical colleagues on the hybrid convergent ablation technique to address extrapulmonary vein triggers and substrate modification to improve efficacy after a second ablation procedure.
On the contrary, non-randomized persistent AF trials from that time demonstrated single procedure efficacy of 22 to 45%. The majority of centers reported efficacy rates of less than 30%7. In line with these results, our single procedure success rate for persistent AF using a first generation cryoballoon catheter to only isolate the pulmonary veins was also approximately less than 50% at one year. Consequently, to minimize repeat ablations and maximize outcomes in this patient population, we collaborated with our surgeons on the hybrid/convergent ablation technique as an initial approach.
While an atrial fibrosis-guided AF ablation approach showed theoretical promise, the negative DECAAF2 trial illuminates the importance of PVI.8 Despite different explored ablation strategies for persistent AF, none have previously proven superior effectiveness over PVI.9–11 Recently however, in patients with persistent and LSPAF, DeLurgio et al showed superior effectiveness over endocardial ablation with the convergent approach.3Moreover, Makati and colleagues summarize these techniques, describing “best practices.5” Nevertheless, there is still a lack of real-world, long-term evidence on the convergent approach; especially with the utilization of cryotherapy ablation. In fact, many of the long-term follow-up data in “real-world,” community settings, are either for PVI in early AF disease or demonstrate PVI in advanced AF disease with room for efficacy improvement.
In comparison to a meta-analysis which included 551 patients across six studies, our cohort was noted to have a similar rate of freedom from atrial arrhythmia occurrence (67% vs 69%) but less class I/Class III AAD utilization at one year (39% vs 50%). In alignment with the six major studies, we shifted from a transdiaphragmatic surgical approach to a subxiphoid, pericardial approach early in our study. Similarly, our hybrid ablation was performed in the same setting as opposed to two separate visits. Importantly, only three studies specify inclusion of patients with prior PVI, whereas in our study, these patients composed the majority of the hybrid cohort. Our hybrid patients notably had a longer preprocedural mean duration of AF (9.4 years vs 2-5.1 years). Monitoring methods for arrhythmia detection such as serial EKGs and continuous monitoring were comparable to the majority of previously published studies4. A key distinguishing factor is that we present a study with two intentionally different cohorts with different complexities across the AF spectrum.
Isolating comparison to the only study which utilized cryoballoon exclusively (Makati et al), our hybrid group included much more PAF patients (41.8% vs 1.5%), a similar amount of persistent AF patients (45.5% vs 38.1%) and less LSPAF patients (12.7% vs 60.4%). Age, sex, and CHADS2VASc scores were comparable (table 1). Our hybrid cohort had a higher prevalence of prior cardioversions (83.5% vs 58%) and we reported similar periprocedural complication rates (3.7 % vs 6%). Notably, our study provides longer follow up (up to 48 months vs up to 24 months). Freedom from atrial arrhythmia at designated follow up intervals is compared between our study and the study performed by Makati et al as follows: 6 month (85.1% vs 91.1); 12 month (66.5% vs 82.4%); 24 months (61.4% vs 51.7% ).12
A major limitation to our study includes selection bias. The high prevalence of PAF in the hybrid cohort may lead to possible improved outcomes given a lower complexity of AF. However, patients selected for study needed to have previously failed both class I/III AAD and CB PVI ablation. This study intentionally evaluated cohorts with different complexities of AF and therefore should not be seen as a traditional, “standard of care vs novel intervention” study. The retention rate in this longitudinal cohort study gradually declined over the course of 48 months however this pattern has also been appreciated in previously published projects. Future studies in this field would be those designed to elucidate the differences in patient characteristics and clinical outcomes in patients undergoing hybrid ablation who have had prior PVI ablation vs not. Findings would likely uncover additional insight into the reasons for AF recurrence therefore add clinical utility to the provider.