Atrial flutter, time to acknowledge its own identity

Atrial flutter and atrial fibrillation are two different arrhythmias whose electrophysiologic mechanisms are the complete opposite to one another. However, both arrhythmias are often considered similar, and what is more dangerous, managed similarly. In this issue of International Journal of Clinical Practice some differences between both arrhythmias are reported and discussed. Atrial flutter and atrial fibrillation are two different arrhythmias whose electrophysiologic mechanisms are the complete opposite to one another: atrial flutter is the paradigm of an organised re-entrant tachycardia, as opposed to the complexity of atrial fibrillation, where multiple rotors and migrant re-entrant circuits can be found throughout both atria, the pulmonary veins, the coronary sinus, or the superior cava vein. However, the clinical presentation, the risk factors, the consequences of uncontrolled tachycardia, and the association with thromboembolic events are akin. As a result of these resemblances, both arrhythmias are often considered similar, and what is more dangerous, managed similarly. Currently, there are no specific guidelines for atrial flutter, and the recommendations for the management of atrial flutter are incorporated into the atrial fibrillation guidelines.1, 2 In this issue of The International Journal of Clinical Practice, Skjøth et al3 presented the results of a retrospective observational study comparing long-term prognosis between patients submitted for an ablation of atrial flutter or atrial fibrillation. Data were drawn from three national Danish databases, and the final sample included a total of 5807 patients. Authors found crude incident events to be more frequent among patients with atrial fibrillation compared with atrial flutter, but after adjustment with a multi-state model analysis, the expected time free of events was lower in patients with atrial flutter. Although atrial flutter patients were more likely to be free of further disease progression or need for renewed ablation, all-cause mortality and heart failure were more frequent among patients with flutter. In this study, data regarding arrhythmias were limited to those that resulted in an intervention, but many arrhythmias are managed with medical treatment, and thus were not considered for the analysis. Recurrences of arrhythmia after an atrial flutter or atrial fibrillation ablation are not uncommon, both arrhythmias may recur as the original type, switch to one another or develop a different atrial tachycardia, but globally are more frequent after a pulmonary vein isolation procedure to treat atrial fibrillation than after the cavotricuspid isthmus ablation for an atrial flutter.4-6 In that respect, the results of the study of Skjøth and colleagues are consistent with the existing literature. Many investigations have studied the stroke incidence in patients with atrial flutter and fibrillation. Those studies are highly conditioned by the anticoagulant treatment prescribed. Both arrhythmias are risk factors for stroke, and thus most patients should receive anticoagulant treatment,7 but controversy exists regarding the therapy maintenance after a successful ablation. In atrial fibrillation, it is generally agreed that long-term anticoagulation should be continued after the ablation according to the CHA2DS2VASc and not to the ablation efficacy, but the decision after a flutter ablation relies more on the subsequent development of atrial fibrillation than on the efficacy of the ablation itself or even the thrombotic risk. The concept of atrial arrhythmias as a marker of stroke risk through factors such as atrial endocardium dysfunction, proinflammatory, and prothrombotic state, rather than the arrhythmia causing a mere mechanical deceleration of the blood flow complicates the decision-making in this scenario.8, 9 Data regarding mortality or heart failure are less dependent on a certain intervention or a physician's decision, and surprisingly the results of the published studies are controversial. In contrast with the findings of Skjøth and colleagues, a large retrospective observational study reported that atrial fibrillation patients had a significantly higher incidence of ischaemic stroke, heart failure hospitalization, and all-cause mortality compared with atrial flutter patients.10 In an earliest publication, no differences in mortality were found between patients with atrial flutter o fibrillation.11 The latter study, like most publications, reports a significant crossover from atrial flutter to atrial fibrillation and vice versa, and often both arrhythmias develop in the same patient over time. Nevertheless, when studies are focused on patients undergoing ablation the results are the opposite: higher all-cause mortality among patients with atrial flutter compared with those with atrial fibrillation.12 These discrepancies may be attributed not only to the arrhythmias but also to the existing differences between both ablation procedures: the risks, efficacy, costs and duration of the intervention are more favourable to cavotricuspid isthmus ablation than pulmonary vein isolation, thus physicians may be more prone to indicate a flutter ablation but more restrictive when considering an atrial fibrillation ablation. A selection bias may explain, at least in part, these findings. Prospective studies are needed to confirm and extend the reported findings. But the available evidence is enough to conclude that atrial flutter is a unique arrhythmia that deserves further investigations to establish its specific recommendations. Authors take responsibility for all aspects of the reliability and freedom from bias of the data presented and their discussed interpretation. The authors report no relationships that could be construed as a conflict of interest. Vicente Bertomeu-Gonzalez contributed in drafting the article and in the final approval of the article. Jesus Castillo-Castillo contributed in drafting and a critical revision of the article.