Ablation of Paroxysmal Atrial Fibrillation in a Patient with an Unusual Anatomic Variant

Introduction

Atrial fibrillation (AF) is the most common sustained arrhythmia, affecting as many as 5 million people in the United States. By 2050, up to 15 million people may suffer from this often debilitating condition.¹ Over the past 15 years, catheter ablation has become an effective therapy for AF. More specifically, pulmonary vein isolation (PVI) is an accepted treatment for paroxysmal atrial fibrillation (PAF).^2,3 Recent trials demonstrate that ablation success at 12 months is in the 65–75% range.^4,5 We present a case of a patient with PAF with an unusual anatomic variant, which presented some challenges regarding ablation treatment.

Case Description

A 56-year-old man initially presented with severely symptomatic PAF with multiple ED visits for dyspnea and palpitations. His cardiac evaluation was unremarkable otherwise with normal coronary arteries and preserved systolic LV function. During his course of therapy over months, multiple drugs were administered, including antiarrhythmic drugs, with little efficacy. He remained symptomatic and arrived to our clinic to be evaluated for possible ablation therapy. Echocardiogram revealed normal left atrial size (3.8 cm). In addition, the patient was asymptomatic in sinus rhythm and remained very active. 

After a comprehensive discussion with the patient regarding the ablation procedure, he decided to proceed to PVI for PAF using radiofrequency (RF) ablation. In our practice, we obtain a high-resolution CT scan of the left atrium (LA) about 2 to 3 days prior to the procedure to evaluate the anatomic feature of the LA including the location of the pulmonary veins. This scan helps us design a safe and effective strategy for ablation. We also merge this scan into our 3D electroanatomic mapping system (Carto, Biosense Webster, Inc., a Johnson & Johnson company), so we may improve the accuracy of RF lesion placement. Interestingly, the initial CT scan revealed what appeared to be left superior (LSPV) and inferior (LIPV) pulmonary vein stenosis. Figure 1 demonstrates some compression of the LIPV in a caudal view. We initially thought the patient might have had a prior ablation leading to pulmonary vein stenosis, which is a known but rather uncommon complication of PVI.⁶ As this was not the case, the cause of the stenosis was obvious after superimposing the descending aorta onto the scan. Figure 2 shows external compression of the LSPV and LIPV by the descending aorta. The descending aorta was normal in diameter as well (Figure 3). It is also important to note that the patient never exhibited any symptoms of pulmonary vein stenosis. 

We proceeded with the ablation by performing a double transseptal puncture planning to perform PVI using a wide circumferential ablation technique, remaining safely away from the pulmonary veins. For this particular case, we employed intracardiac echocardiography (ICE) to specifically determine pulmonary vein flow velocities in the LSPV and LIPV. The flow velocities of both veins were approximately 0.75 m/s or slightly above normal mean PV flow velocities corrected for age (mean 0.53 m/s).⁷  By placing a Lasso catheter into each of the left PVs, the patient exhibited significant atrial ectopy, leading to sustained AF on multiple occasions. Of note, a steerable sheath was used to place the Lasso in the left veins due to the distorted anatomy. Our ablation of the right pulmonary veins using the aforementioned technique was routine. However, our ablation technique was more challenging for the left veins. Given the posterior location of the aorta compressing the left pulmonary veins, we limited our posterior LA ablation line more medially than we would have if the aorta was not in its present location. We felt that this method would provide the least chance of progressive PV stenosis as well as theoretical damage to the great vessels. We used 3D electroanatomic mapping for accurate ablation lesion placement (Figure 4). During RF application, ICE was used to monitor left PV flow velocities. We were able to isolate both left veins without any significant rise in velocities using low power (20W) on the posterior LA wall with an irrigated tip catheter (Biosense Webster’s ThermoCool^® SF). Figure 5 demonstrates isolation of the LIPV. Of note, after isolation of the left veins, no atrial ectopy could be produced by Lasso manipulation in those veins as previously noted. In addition, rapid atrial pacing failed to induce further AF. The patient has returned without any sequelae after his procedure. 

Discussion

Catheter ablation has become one of the primary and most effective treatments for AF. The patient in this case appeared to be an ideal candidate for AF ablation; he had failed medical therapy and remained highly symptomatic. Given the general ease by which we may obtain LA imaging for ablation, we suspect those who ablate AF will recognize more variant anatomy that will alter the general strategies used for PVI. The compression of the pulmonary veins by a nonaneurysmal aorta appears to be a rather uncommon entity. Ho et al described 4 out of 200 AF ablation patients who had similar anatomy to our patient via pre-procedural imaging.⁸ Detailed MRI imaging was used to aid in ablation in this series, but not all pulmonary veins could be isolated due to the anatomic constraints. With the small number of patients, the authors could not draw any meaningful conclusions regarding clinical outcome of these patients compared with those with normal PV-LA anatomy.⁹ In our patient’s case, we were able to isolate the four pulmonary veins acutely with low-power RF application. However, a standard way to approach such patients is still highly debatable. Furthermore, the durability of the PV isolation has yet to be determined as we currently lack long-term data for our patient.

Pre-procedural imaging is becoming a common part of the evaluation of an AF patient prior to ablation. High-resolution imaging may provide very valuable information regarding specific LA anatomy, which may provide the operator a means by which to alter his or her strategy when the time comes to ablate. A standard approach by which to ablate these patients has yet to be defined.

Disclosures: Dr. Gururaj has no conflicts of interest to report regarding the content herein. Mr. Gantos and Mr. Jones report employment with Biosense Webster, Inc.  

References

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