Hidden Heart Pathway Behind Failed Pulsed Field Ablation Revealed in Rare Case

A single remarkable case from Japan is forcing electrophysiologists to rethink one of the most celebrated technologies in modern cardiology. Pulsed field ablation, a technique that destroys rogue heart tissue with bursts of electricity rather than heat, has been hailed for its precision and safety. Yet a 55-year-old man whose atrial fibrillation returned just three months after an apparently successful procedure has shown clinicians exactly how the technology can be outmaneuvered by the heart’s own hidden wiring. The culprit, his physicians discovered, was an epicardial connection: a muscular bridge running along the outside of the heart that allowed electrical signals to slip past the ablation scars entirely. The case, published in Clinical Case Reports, offers a rare and technically detailed window into why some patients relapse despite flawless-looking procedures, and why the anatomy of the pulmonary veins may hold the key to predicting who is at risk.

The patient’s story began with two years of troubling palpitations. When his heart raced, an electrocardiogram captured an irregular narrow-complex tachycardia at 111 beats per minute, complete with right bundle branch block morphology and a leftward axis deviation of minus 21 degrees. Yet his heart was structurally sound: transthoracic echocardiography showed preserved left ventricular function and no abnormalities, and his thyroid function was normal. High-resolution, contrast-enhanced computed tomography revealed a crucial anatomical detail that would later prove decisive. His left superior and left inferior pulmonary veins did not drain into the left atrium separately, as they do in most people. Instead, they formed a single left common pulmonary vein, a variant present in a minority of the population that creates a wider, more complex target for any ablation strategy.

His first procedure was, by every conventional measure, a textbook success. Under general anesthesia with propofol and fentanyl, ventilated through a supraglottic i-gel airway, he underwent pulsed field ablation using the FARAPULSE system from Boston Scientific. The team delivered twenty-two applications to the left common pulmonary vein, ten to the right superior vein, and eight to the right inferior vein, alternating between the device’s basket and flower electrode configurations. Each application used a 2.0 kilovolt biphasic waveform with four pulse trains, and catheter contact was verified before every delivery using fluoroscopy and intracardiac echocardiography. When the team finished, electro-anatomical mapping with the EnSite NavX system confirmed that all the pulmonary veins had been acutely isolated from the left atrium. The electrical triggers responsible for his arrhythmia appeared, on the maps, to be sealed off for good.

Three months later, an external event monitor told a different story. Atrial fibrillation had returned. The team brought him back for a second procedure, this time with an esophageal temperature probe in place and access gained through the right internal jugular and right femoral veins. Using the OctaRay mapping catheter and the CARTO3 v8 system from Biosense Webster, they began reconstructing the arrhythmia in three dimensions. Almost immediately, they caught something valuable in the act: spontaneous premature atrial contractions, the stray beats that ignite atrial fibrillation, firing on the monitor in real time. Mapping placed their origin just beneath the ostium of the left common pulmonary vein on the posterior wall of the left atrium, slightly apart from the isolation line created during the first procedure.

What followed was a genuine detective story played out with millimeter precision and millisecond timing. Radiofrequency applications with a QDOT Micro catheter at 35 watts and a target ablation index of 400 transiently suppressed the premature beats but could not eliminate them permanently. Meanwhile, voltage mapping during right atrial pacing revealed that the left pulmonary vein had electrically reconnected to the atrium, with ripple mapping pinpointing the anterior carina, the ridge between the vein branches, as the earliest site of reconduction. The puzzle was this: the recurring trigger sat on the posterior wall, far from the isolation line, yet the reconnected vein was waking up first at the anterior carina. The two findings only made sense together if electricity was traveling along a concealed route outside the endocardial surface.

To test that hypothesis, the team paced from four distinct sites inside the left common pulmonary vein and measured how long each impulse took to reach the distal coronary sinus electrode. The numbers were striking. Pacing from the posterior bottom of the vein produced a conduction time of 140 milliseconds, and from the posterior roof 138 milliseconds, while pacing from the anterior ostium produced just 30 milliseconds. When the map was reconstructed with pacing from the vein, the earliest activation site matched the uneliminated trigger exactly. The pattern pointed to an epicardial connection, a subepicardial muscular bundle linking the anterior carina of the left pulmonary vein to the posterior atrial wall near the vein’s ostium, rather than a simple endocardial gap in the ablation line. The team targeted this presumed pathway at the inferior portion of the anterior carina with 35 watts and a target ablation index of 500, completed the pulmonary vein isolation, and rendered the arrhythmia non-inducible.

The anatomical suspect in this case has a name that cardiologists know well: the ligament of Marshall. This vestigial structure, a remnant of an embryonic vein, carries the Marshall bundle of myocardial fibers from the coronary sinus up the epicardial surface between the left atrial appendage and the left superior pulmonary vein. Its fibers can link the coronary sinus, the posterior and lateral left atrial wall, the ridge of the appendage, and the pulmonary vein antrum into a subepicardial conduction network that no endocardial ablation line can interrupt until lesions become fully transmural. Epicardial connections of this kind are not exotic curiosities. Studies estimate they occur in roughly 11 to 14 percent of patients with atrial fibrillation, and they are more numerous in patients with advanced disease and enlarged left atria. High-density mapping studies have shown that most cluster at the pulmonary vein carina and can extend well beyond the antral ablation line, explaining residual vein potentials and preserved atrial capture even when entrance and exit block appear complete.

Here the left common pulmonary vein becomes more than an anatomical footnote. Research by Kueffer and colleagues has found that this vein variant shows the lowest durability after pulsed field ablation, and the reasoning is anatomically elegant. In patients with a left common trunk, the ligament of Marshall lies closer to the ablation target, increasing the opportunity for epicardial fibers to bypass standard lesion sets. Intriguingly, the picture reverses with radiofrequency energy: lower recurrence rates have been reported for left common pulmonary vein patients treated with point-by-point radiofrequency, while the cryoballoon, another one-shot device like FARAPULSE, has shown reduced durability in the same anatomy. The implication is uncomfortable for the newest technology. One-shot ablation devices, which deliver energy in a fixed geometric pattern, may be inherently more vulnerable to anatomical variants than flexible, point-by-point techniques that an operator can adapt lesion by lesion.

The outcome for the patient, at least so far, is encouraging. After the second procedure he took no anti-arrhythmic drugs or beta-blockers, only a single anticoagulant for six months. Over a full year of follow-up, serial 24-hour Holter monitoring and 12-lead electrocardiography found no recurrence of atrial fibrillation, and he remained entirely asymptomatic, with annual Holter monitoring planned thereafter. The authors are candid about the limits of their evidence. This is a single case that cannot be generalized to everyone with a left common pulmonary vein, and because no electrode catheter was placed within the epicardial pathway and no ethanol was infused into the vein of Marshall, the exact route of the connection was inferred from post-pacing intervals rather than directly proven. The endocardial latency gap, a phenomenon in which conduction recovers with delayed timing, could not be definitively excluded, though the successful ablation at the anterior carina strongly supports the epicardial explanation.

Even with those caveats, the case lands at a consequential moment. Pulsed field ablation is expanding rapidly across the world on the strength of high acute isolation rates and a favorable early safety profile, sparing the esophagus and phrenic nerve from the collateral injury that thermal energy sources can cause. But durability, not acute success, is what determines whether a patient is truly cured, and long-term data relative to conventional treatment remain uncertain. The message from this case is that a perfect-looking lesion set on the inside of the heart can be quietly defeated by conduction running along the outside. For patients with a left common pulmonary vein, the authors argue, careful evaluation and explicit consideration of epicardial reconnection should be part of every ablation plan. As pulsed field technology matures, the hearts it fails to fix may teach clinicians as much as the ones it heals, and the answers may lie in structures no catheter can see from within.

Subject of Research: Epicardial connection as a mechanism of atrial fibrillation recurrence after pulsed field ablation

Article Title: Epicardial Connection as a Resource of Atrial Fibrillation Recurrence After Pulsed Field Ablation: A Case Report

Article References: Lee, K. H., Kitamura, T., Sahashi, S., Sugiyama, H., Izumi, C., & Hayashi, K. (2026). Epicardial Connection as a Resource of Atrial Fibrillation Recurrence After Pulsed Field Ablation: A Case Report. Clinical Case Reports, 14(10), Article e73282. https://doi.org/10.1002/ccr3.73282

Image Credits: AI Generated

DOI: 10.1002/ccr3.73282

Keywords: atrial fibrillation, pulsed field ablation, epicardial connection, pulmonary vein isolation, ligament of Marshall, left common pulmonary vein, electroanatomic mapping, cardiac electrophysiology, FARAPULSE, arrhythmia recurrence, case report, ablation durability