Navigating the risk of atrial fibrillation after successful ablation of lone typical atrial flutter

Typical atrial flutter (AFL) is a common cardiac arrhythmia for which catheter ablation is highly successful. However, patients who have undergone successful AFL ablation remain at risk for the future development of atrial fibrillation (AF). Previous studies using conventional monitoring (CM) techniques, including intermittent electrocardiograms, Holter monitors, and trans-telephonic monitors, have demonstrated the occurrence of new-onset AF in this population to range from 18% to 50%.1,2 Such a wide range likely reflects the limitations of CM for identifying true occurrence of AF in these patients. Long-term continuous monitoring with implantable loop recorders (ILRs) has been shown to enhance the rate of AF detection in patients undergoing AFL ablation. This has resulted in higher use of long-term oral anticoagulation (OAC) and lower occurrence of cerebrovascular accident (CVA) events in these subjects.3 These observations suggest that improved AF detection post-AFL ablation has significant healthcare implications, and it behoves us to develop a uniform approach for the long-term management of these patients. To do so, we need more rigorous data on the best practices for detecting and treating new-onset AF in this population. The FLUTFIB study published in this issue of the journal addresses some of this knowledge gap. In this three-centre prospective observational study conducted over 7 years (2015–22), 100 patients with lone right atrial cavotricuspid isthmus-dependent AFL who underwent successful ablation received ILR devices (SJM Confirm) during the same hospitalization. Patients were subsequently followed up for a minimum of 1 year. The primary study endpoint was the detection of new AF (any event lasting >30 s), and secondary endpoints included recurrence of AFL, arrhythmia symptoms, and/or CVA events. Over a median follow-up of 24 months (range 3–24 months), new AF was detected in 77 patients and AFL recurred in five patients. Overall, less than half (n = 40) of patients experiencing arrhythmias reported any symptoms. The predominant form of AF was paroxysmal with duration ranging between 30 s and 7 days and most commonly (70%) between 6 min and 24 h. Atrial fibrillation detection resulted in subsequent interventions to achieve rhythm control in 17 that included pulmonary vein isolation (PVI) in 14 and trial of antiarrhythmic drug therapy in 3. None of the participating patients experienced CVA events that may have been due to the continuation of long-term OAC in the majority (70%). Interestingly, the investigators were not able to identify any predictors of future development of AF in this patient cohort. So, how should we interpret these data? The findings of this study align with the existing literature that has reproducibly shown that patients with AFL remain at a high risk for developing AF. This study also supports prior observations on the benefits of long-term continuous monitoring with ILRs for enhancing AF detection in this patient population. The other interesting findings of the FLUTFIB study are that within the study cohort, none of the patients experienced any CVA events and the investigators were not able to identify any variables that could predict future occurrence of AF in this patient population. These warrant further discussion. In a prior observational study of 217 veteran patients with typical flutter and no prior history of AF, we found that after AFL ablation, over a median follow-up of 4 years, 79 patients (36%) developed new-onset AF that was detected by CM in 51 and ILR in 28 (30% vs. 62%, respectively, P < 0.001). Atrial fibrillation detection occurred at 7.7 months after AFL ablation in the ILR group vs. 41 months in the CM group (P < 0.001). Eleven patients (5%) experienced CVA events, and this was exclusively seen in the CM group. Furthermore, only four of these patients (36%) were on long-term anticoagulation (all on warfarin). Median time to occurrence of CVA events post-AFL ablation was 29 months.3 Several reasons were hypothesized for these CVA events in the CM group including higher prevalence of co-morbidities, longer follow-up post-ablation (5.4 vs. 1.3 years for ILR group), poorer AF detection, and suboptimal time in therapeutic range of the international normalised ratios (INRs). With this background knowledge, the absence of CVA events in the current study, with a relatively short median follow-up (2 years, range 3–24 months) and 70% of patients remaining on DOAC therapy after AFL ablation, is not entirely surprising. The high use of OAC post-flutter ablation as observed in this study is consistent with the current guideline recommendations that state that long-term OAC decision in patients with AFL post-successful ablation should follow the same rules as those for AF, i.e. based on CHA2DS2-VAsc scores.4 In this study, the investigators were unable to identify risk factors that could predict future occurrence of AF after successful AFL ablation. Although intriguing, this is not a novel finding. In a previous study of male veteran patients undergoing AFL ablation, we too did not identify any variables that were associated with the development of new-onset AF.2 We also did not find race (African-American vs. Caucasian) to offer any protection from future development of AF in these patients.5 Our prior observations together with the findings of the current study suggest that the traditional factors associated with AF development may not have the same risk predictive power in patients manifesting AFL. The available evidence indicates that both AF and AFL share common electrophysiological triggers and anatomical arrhythmogenic substrate.6 Thus, long-term monitoring for AF in patients presenting with AFL is warranted, and the data favour the use of ILR over CM. However, the ILR platforms are not without flaws. In a previous prospective randomized comparison of ILR vs. CM among AF patients undergoing catheter ablation, we found the overall accuracy of the Medtronic REVEAL platform to be <50%.7 Since we published these data, improvements have been made to the AF diagnostic algorithm of the Medtronic ILR platform. However, there remains lack of comparative data on the AF diagnostics of ILRs made by other vendors. Since only SJM ILRs were used in the current study, it would have been helpful if the investigators had provided data on the sensitivity, specificity, and accuracy of this platform for diagnosing true AF. Despite all the above limitations, the current study is an important step in helping us improve the long-term management of AFL patients who remain at a future risk for developing AF. Within this study, the detection of new AF led to specific rhythm intervention in 17 patients including PVI in 14. This is an interesting observation, and it perhaps reflects changing practices as a result of the EAST-AFNET 4 study that has shown the benefits of an aggressive rhythm control strategy for patients with newly diagnosed AF.8 The high occurrence of AF post-AFL ablation may also be mitigated by performing prophylactic PVI at the time of AFL ablation that has been shown to decrease the future occurrence of AF in these patients.9,10 Finally, the ability of ILR platforms to detect AF relatively soon after AFL ablation suggests that AF may be pre-existing in many of these patients. This begs the question of whether we should contemplate more aggressive screening for AF in patients with lone AFL before subjecting them to ablation. None declared.