LAUSR

Two decades ago, a landmark paper identified the pulmonary veins (PVs) as the most frequent trigger source for atrial fibrillation (AF) [1]. Subsequently, pulmonary vein isolation (PVI) emerged as a cornerstone of catheter ablation for AF. However, by itself, PVI is not sufficient to treat persistent atrial fibrillation (persAF). Sustained and non-sustained nonPV triggers have been identified in up to 60% of cases of catheter ablation of AF [2–4]. These triggers are localized in the posterior wall (PW), superior vena cava, left atrial appendage, coronary sinus, inter-atrial septum, crista terminalis, and vein ofMarshall [5, 6]. These areas also serve as substrates for perpetuation of AF. The PW is an embryological “sibling” of the pulmonary veins [7] and its ablation has emerged as an attractive conjunctive strategy with PVI for persAF. Progressive remodeling within the PW is believed to enrich the pathological substrate for persAF. This notion of increased arrhythmogenicity is supported by cellular evidence, which indicated that the PW in patients with persAF had higher incidence of delayed afterdepolarizations, larger late sodium currents, calcium currents leading to increased calcium content of sarcoplasmic reticulum, and smaller inward rectifier potassium currents [8]. Microscopically, a higher degree of lymphonuclear and fatty infiltration along with fibrosis has been observed in the PW in persAF patients [9–11]. This underlying substrate leads to spontaneous trigger activity, which then propels fibrillatory impulses to both atria. PW ablation is thought to eliminate potential re-entry and focal triggers for AF, “debulk” the left atrium (LA), re-enforce PVI, and cause autonomic denervation by ablation of ganglionated plexi. Multiple strategies have been attempted in the past to achieve PW isolation (PWI). Surgical Cox maze procedure with creation of a box lesion on the PW [12], a “hybrid approach” [13] with initial thoracoscopic access followed by transvenous catheter ablation to complete endocardial PVI/ PWI were both noted to have significantly lower recurrence rates of atrial arrhythmias. After PVI, creation of linear ablation lines on the roof and floor of LA, connecting the superior and inferior PVs is another approach. A few small retrospective studies have assessed the incremental value of PWI in addition to PVI to reduce recurrence rates of AF. Despite the growing evidence supporting PWI [14], this adjunctive strategy has not been fully adopted worldwide. The long-term clinical outcomes of PWI in patients with non-paroxysmal AF have been controversial. Two randomized controlled trials failed to prove any benefit of PWI in addition to PVI. It is unclear whether these studies were negative simply because the authors performed a single ring or a box in order to isolate the PW [15, 16]. Specifically, there may be concern for recurrence of atrial arrhythmias (i.e., microreentry atrial tachycardia or atrial flutter) from reconnections and gap formation within the ablation site, deterioration of atrial mechanical function, and esophageal heating given its proximity to the ablation lesions. A meta-analysis corroborated that patients who underwent PWI+PVI had lower recurrence of atrial arrhythmias, mainly driven by decrease in AF, than patients who underwent PVI only [17]. The studies included in these meta-analyses had a significant amount of heterogeneity in terms of the technique used for PWI. The most optimal method to successfully accomplish PWI still remains controversial. We currently perform two lines connecting the superior and inferior PVs. Subsequently, high-output pacing (20 mA/2 msec) is performed inside the PW. If myocardial capture is present (i.e., epicardial connections), additional radiofrequency energy is delivered until un-excitability is achieved. A recent multicenter, randomized trial performing PVI demonstrated non-inferiority of cryoballoon to radiofrequency ablation (RFA) [18]. Prior literature for PWI has mostly utilized point-by-point RFA and the use of cryoballoon for this purpose has been limited. Traditionally, the use of cryoballoon * Luigi Di Biase [email protected]