Left Phrenic Nerve Displacement Using a Sizing Balloon During Epicardial Ventricular Tachycardia Ablation

The phrenic nerve (PN) can be an obstacle for catheter ablation of ventricular arrhythmias, and PN injury is a potential complication of epicardial ventricular tachycardia (VT) ablation.^1-3 A close anatomic relationship between the left PN and lateral aspect of the left ventricular epicardium should be kept in mind during epicardial VT ablation. PN stimulation and protective measures such as the sheath/catheter, balloon displacement, or saline/air infusion before ablation can be performed to avoid PN injury.^2-5

In this article, we describe a case requiring left lateral epicardial VT ablation and left PN displacement using a sizing balloon to prevent PN injury.

Case Presentation

A 54-year-old male with non-ischemic cardiomyopathy and recurrent fast VTs (CL 270 to 250 ms) requiring multiple ICD shocks was referred to our center for catheter ablation. After preprocedural optimal patient preparation, conventional epicardial access was obtained using a subxiphoid posterior   approach. The preferred approach of our center is substrate-based VT ablation, especially in patients with fast VTs and hemodynamic instability, as in our case. In addition, anesthesia frequently renders VT noninducible, and hemodynamically tolerable clinical VTs can degenerate into faster VTs and even ventricular fibrillation when performing entrainment mapping. An endocardial-first mapping strategy revealed normal bipolar voltages without local abnormal ventricular activities (LAVAs). The unipolar voltage map demonstrated epicardial low-voltage areas in the inferolateral wall of the left ventricle. Through a previously accessed route, epicardial high-density voltage mapping was performed using a deflectable sheath (MOBICATH, Biosense Webster, Inc., a Johnson & Johnson company) and a multipolar mapping catheter (PENTARAY 2-6-2 catheter, Biosense Webster) (Figure 1A). The epicardial voltage map showed a large low-voltage area (<1 mV) with extensive scar (<0.5 mV) and widespread LAVAs on the entire inferolateral wall of the epicardium (Figure 1B). A high-output (10 mA, 2 ms) pacing maneuver on the mid-basal inferolateral wall of the left ventricular epicardium containing ablation targets revealed PN capture. Virtual PN course was tagged on the 3D map (CARTO 3, Biosense Webster) (Figure 1B). Extensive ablation points using a radiofrequency catheter (THERMOCOOL SMARTTOUCH SF, Biosense Webster) were delivered throughout the entire low-voltage area and LAVAs in it except PN course (Figure 1C). After that point, withdrawal of the ablation catheter and re-wiring of the steerable sheath with 2 separate standard 0.035˝ J-tip guidewires were performed (Figure 1D). Withdrawal of the steerable sheath then resulted in 2 guidewires through a common subxiphoid access without performing a second pericardial puncture. From one of the wires, a sizing balloon (24 mm x 45 mm with 20 cc inflation volume of half contrast) designed for atrial septal defect procedures (Cocoon Sizing Balloon, Vascular Innovations) was advanced and located on the lateral wall of the epicardium (Figure 1E). With the help of the second wire, the previously used steerable sheath was introduced (Figure 1F). An inflated balloon separated the left PN from the target sites and high-output pacing resulted in no capture of the PN along its course. Low-voltage areas with LAVAs that could not be ablated before were ablated and scar homogenization with elimination of all LAVAs was achieved (Figures 1C, 1G, and 1H, Videos 1 and 2). After ablation of all targeted sites, PN patency was checked using repeat high-output pacing. Deflation and re-inflation of the balloon over multiple sites along the left PN course were performed before and after each ablation point. No PN palsy was detected during peri- and post-procedural periods.

Discussion

To the best of our knowledge, this is the first report of epicardial left PN displacement using a sizing balloon to prevent PN injury during an epicardial VT ablation procedure.

The aim of the VT ablation is to prevent recurrences that can be related with mortality. Also, peri-procedural complications can result in significant morbidity and mortality. One of the complications specific to epicardial VT ablation is the PN palsy that can be varied in symptom presentation from asymptomatic finding to significant dyspnea.^4,6 Especially in non-ischemic cardiomyopathy, mid-basal lateral aspect of the left ventricular epicardium contains low-voltage areas and LAVAs and close anatomic relationship between the left PN and the targeted epicardium could limit the epicardial ablation.⁷ No ablation points over the PN course can cause incomplete substrate ablation that can be related with VT recurrence. To overcome this anatomic obstacle, mechanical displacement of the left PN from the adjacent epicardium using a large balloon has been demonstrated as an effective method for ablation of targeted abnormal voltage areas containing abnormal electrograms that generally related with clinical VTs.^3,4 Although effective, some inherent limitations of the current technique are difficulties in maneuverability of the balloon during repositioning, longer procedural and fluoroscopy times, and difficulties in orienting of the force vector to the visceral pericardium for successful lesion formation. In addition, some safety concerns that may be specific to this technique are pleuro-pericardial fistula formation, external compression of epicardial coronary arteries, and tamponade-like hemodynamic changes, especially with large balloons.

Summary

In this article, we presented a case requiring left PN displacement due to a close anatomic relationship with the adjacent epicardium with low-voltage areas and LAVAs requiring epicardial ablation. A large sizing balloon designed for congenital heart defects was used to separate the visceral pericardium/epicardium overlying abnormal areas from the parietal/fibrous pericardium closely related with the left PN. 

Video 1:

Video 2:

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Disclosures: The authors have no conflicts of interest to report regarding the content herein.

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