EComment. Hybrid treatment of lone-standing atrial fibrillation

Abstract

We read with interest the article by La Meir and colleagues about minimally invasive thoracoscopic hybrid treatment of lone atrial fibrillation, via the use of either a monopolar or bipolar radiofrequency device [1]. Following their early institutional experience, they conclude that the use of a bipolar device is associated with a better outcome compared to a unipolar device, especially in patients with persistent and long-standing persistent AF. Although the study deals with a topic of vivid interest and controversial debate, the article has several major limitations. First, the authors claim that the described approach is a hybrid technique. However, the paper does not define any true hybrid approach, merging surgical and electrophysiological (EP) techniques as previously proposed by several other groups, including ours [2]. In fact, no systematic protocol was described and from the paper it is possible only to infer that patients underwent a surgical ablation and a concomitant EP evaluation which was targeted at addressing potential gaps or additional right-sided lesions (IVC, SVC, intercaval). However, those right-sided lesions were almost exclusively delivered in the group undergoing bipolar RF ablation and patients with persistent and long-standing AF could have robust benefits from such additional ablations on the right atrium. Of note, it is important to stress that there was a major difference, almost significant (p = 0.054), among the two groups with respect to the presence of paroxysmal AF preoperatively (unipolar RF= 26.3% vs bipolar RF = 45.7%). Ablation for paroxysmal AF is obviously associated with a significantly better outcome regardless of the type of lesion set and energy source. This bias is even more significant given the small sample size (unipolar = 19 vs bipolar = 35) which are further divided into even smaller subgroups (paroxysmal, persistent, long-standing persistent). Furthermore, the authors evidenced the need for endocardial touch-up due to gaps, in particular following unipolar RF ablation (with the site of such gaps not being disclosed). Nevertheless, they report (as outlined in the Discussion section) a device setting of 60°C and 120 s which is clearly not the recommended one. In fact, the proper settings of the monopolar device used in the study should be 75°C and 120 s with at least a double application per segment (the device has 2 segments, proximal and distal) which means that ablations must be delivered at least 4 times, and not 2.8 as reported by the authors themselves. This implies that the monopolar device may have been used improperly in terms of inadequacy of either temperature or number of applications, therefore leading to absence of conduction block in the whole series of patients undergoing ablation with the monopolar device. Moreover, the timing between the surgical and electrophysiological procedures is a matter of utmost importance. In fact, simultaneous surgical/EP procedures may be associated with false negative results (such as acute demonstration of a bidirectional block which could be only transient and not potentially confirmed in the chronic setting), as well as with false positive results in terms of early inducible arrhythmias, which usually require further “maturation” of the ablative lesions [3]. It is also debatable whether the excision of the left atrial appendage (which occurred once again exclusively in the group undergoing bipolar RF ablation) could have contributed to a significant volume reduction or potentially to different rhythm outcome as well. In conclusion, besides specific technical issues, such as incorrect device settings for the monopolar device or an extensive lesion set with right-sided lesions only in the bipolar group, the current study deals with a limited number of patients, therefore leading to consistent statistical quirks which can severely jeopardize the reliability and the interpretation of the results. Further studies, enrolling larger and comparable populations receiving similar left and right atrial lesion sets, are warranted in order to further elucidate the real impact of different types of energy sources in the clinical outcome of patients undergoing minimally invasive AF surgical ablation. Conflict of Interest: Claudio Muneretto and Gianluigi Bisleri disclose a financial interest with Estech.