eComment. Atrial fibrillation ablation - are we approaching an equivalent standard of cure?

We would like to highlight some important observations in the retrospective observational study by La Meir et al of a minimally invasive hybrid radiofrequency (RF) modified Maze ablation on the beating heart [1]. Common to both groups studied was a left atrial (LA) box ablation as well as a LA isthmus line in 16% to 20% respectively. The bipolar/bilateral group had 46% paroxysmal atrial fibrillation (PAF) patients versus 26% in the monopolar group. Nevertheless, analysis by AF type showed superior results in persistent AF with the bipolar/bilateral technique.

The bipolar/bilateral technique allowed additional excision or closure of the LA appendage in 43% of patients, as well as additional RA lines in 29%, although 20% fewer LA interconnecting lines or complete box lesions were done. Assuming that the secondary hybrid transcatheter endocardial technique ensured that all lesion sets were complete and transmural (by subsequent endocardial gap lesion closure), then one can infer that it was the more extensive ablation pattern used in the bilateral/bipolar approach that was the reason for the superior results. Experimental studies by Cox showed that pulmonary vein isolation (PVI) alone had no effect on the ability to induce or maintain AF, and hence the original Maze procedure was designed to interrupt all potential pathways for atrial macro re-entrant circuits [2].

An important observation though, is the documented higher ‘device related’ incidence of incomplete, non-transmural ‘gap’ lesions with the non-irrigated epicardial monopolar RF device (Cobra Adhere XL; Estech) and unidirectional bipolar device (Coolrail; Atricure) used for the inferior and roof lines. One can therefore conclude that a bipolar bidirectional clamping RF device is a superior tool.

The inability to have guaranteed transmural continuous RF ablation lines is not only a surgical epicardial ablation problem but applies equally to transcatheter endovascular ablation lesions. The Mayo clinic's 5-year freedom from recurrent AF is 87% following the cut-and-sew Maze procedure compared to their poorer 28% 5-year success following catheter ablation [3], which attests to both the validity of both Cox's original concept of interrupting all potential atrial macro re-entrant circuits with the cut-and-sew technique and need for permanent transmurality of ablation lines compared to subsequent concepts and approaches [2]. It is important to note that the patients in La Meir et al's study had lone AF [1] and these results may not be reproducible in patients with underlying structural heart disease, who constitute the current predominant surgical group undergoing concomitant AF ablation, having a 75-80% success rate in maintaining sinus rhythm at 1 year [4].

The cut-and-sew Cox-Maze via a median sternotomy using cardiopulmonary bypass remains the ‘gold standard’ in terms of a 90-95% success without any long-term attrition, but has not been widely accepted because it is a complex open surgical procedure with definite 1-2% perioperative mortality and morbidity risks [5]. La Meir et al's hybrid minimally invasive approach with a 1-year maintenance of sinus rhythm of 95% in lone AF patients appears to have a similar success rate [1].

In the lone AF population, especially if only mildly symptomatic apart from the thromboembolic risk, a hybrid ablation procedure with a mortality risk approaching 0%, minimized surgical incisions, short in-hospital stay, and with similar long-term 95% success rates to the ‘cut-and-sew’ Cox-Maze may well become the future standard of care.

Conflict of Interest: None declared