Dual-Modality Focal Ablation for Refractory Ventricular Summit Ectopy

Abstract

Background

Catheter ablation at the left ventricular (LV) summit area has posed several challenges because of the complex architecture, the variable depths of the arrhythmia foci, and the proximity to the coronary vasculature. Several ablation methods have been proposed such as epicardial access, coronary venous alcohol infusion, or even hybrid surgical ablation, but the outcomes remain ill-defined.

Case Summary

A 53-year-old woman with frequent LV summit premature ventricular contractions (PVCs) presented to our institute for redo ablation due to PVC-induced cardiomyopathy. She had previously failed 2 prior ablations, including the epicardial approach during the second attempt. Due to the lack of other reasonable options, compassionate use of a novel dual-modality ablation catheter was pursued, which resulted in successful PVC suppression both acute and at short-term follow-up.

Discussion

The case highlights the feasibility of the novel TactiFlex Duo catheter for treatment of refractory PVCs. This catheter enables dual-modality ablation including both radiofrequency and pulse field ablation. Energy delivery achieved adequate lesion penetration without any acute collateral damage, including coronary vasculature.

Take-Home Messages

Our case presents the first-in-human use of the novel TactiFlex Duo catheter combining, and underscoring the potential benefit of, radiofrequency/pulsed field ablation in ventricular ablation.

Graphical Abstract

Background

Ventricular arrhythmia from the left ventricular (LV) summit is recognized as one of the most difficult-to-treat arrhythmias because of the complex anatomy and proximity to the epicardial coronary arterial system. Although ablation below the left sinus of Valsalva as a vantage point has helped improve success, deeper intramyocardial or epicardial foci remain problematic even with more advanced ablation techniques including venous alcohol and surgical ablation.1, 2, 3 Pulse field ablation (PFA) has been widely accepted as a primary modality for atrial fibrillation ablation given its minimal thermal effect and unique ablative methodology. As such, interest has naturally pivoted to its use in the ventricle, especially as a bailout strategy. However, there remains significant uncertainty regarding its safety and efficacy, the latter related to the depth of ablation lesions. Here, we present the first ever use of the TactiFlex Duo (Abbott) contact force-sensing, dual-modality radiofrequency ablation (RFA)/PFA catheter for ventricular ablation through a compassionate use pathway in a patient with 2 failed previous ablations.

Case

A 53-year-old woman with pertinent history of frequent premature ventricular contractions (PVCs) and presumptive PVC-induced cardiomyopathy (35% PVC burden, ejection fraction: 25%) presented to our institute for consideration of a repeat PVC ablation after failing 2 previous attempts. The clinical PVCs showed a left bundle branch block pattern, with right inferior axis and a V₂ transition ratio of >0.6, suggesting a left ventricular outflow tract (LVOT) focus (Figure 1).⁴ The QRS width was 216 milliseconds, with a maximal deflection index of 0.66 and a variable coupling interval. Given failed PVC suppression with beta-blocker and calcium channel blocker, and the desire to avoid long-term antiarrhythmic therapy, she elected to proceed with catheter ablation. During the first procedure, the initial earliest activation was first mapped to the anterior and septal aspect of the right ventricular outflow tract (RVOT). Ablation resulted in marked suppression of the PVCs; however, some rare, residual PVCs were still present. Additional mapping was performed in the coronary sinus and LVOT to target the remaining PVCs. The earliest site was noted near the proximal anterior interventricular vein (AIV). However, due to the proximity to the left anterior descending (LAD) coronary artery, no ablation was performed. Additional ablation was performed from the endocardial LVOT but did not result in further PVC suppression. During follow-up, PVCs recurred with similar burden, and the patient elected to undergo a repeat ablation, including an epicardial approach given that the earliest site during the first procedure was epicardial. The earliest activation was again mapped epicardially. However, during additional high-density mapping at the site of earliest activation, clinical PVCs were suppressed by mechanical bump from catheter manipulation. Empirical ablation was then performed epicardially near the earliest site, about 1 cm away from the LAD. Additional consolidative ablation was performed from the RVOT site that previously resulted in suppression of clinical PVCs. No PVC recurrence was seen acutely, but the clinical PVCs recurred within a few hours postprocedure. The patient continued to have NYHA functional class II/III heart failure symptoms and a persistently low ejection fraction despite optimal goal-directed medical therapy. After a shared decision-making process, the patient elected to proceed with the third time redo ablation instead of attempting long-term amiodarone therapy due to the potential long-term side effects and toxicity. Informed consent was obtained for compassionate use of the TactiFlex Duo catheter. Institutional review board and Food and Drug Administration approval was obtained.

Figure 1.

Baseline Electrocardiogram Demonstrate the Clinical Premature Ventricular Contraction Morphology

(A) Sinus rhythm with the clinical premature ventricular contraction in bigeminy fashion. (B) Maximum deflection index calculation which was suggestive of intramyocardial/epicardial exit. (A) Maximum peak deflection measurement. (B) QRS width. A/B = maximum deflection index.

The third procedure was performed under general anesthesia given disinhibition and discomfort with light sedation. Paralysis was maintained throughout the procedure. Arterial and venous vascular access was achieved under ultrasound guidance. Subsequently, an activated clotting time of 300 to 350 seconds was maintained with heparin bolus and infusion. Intraprocedurally, intracardiac echocardiography was used (ViewFlex, Abbott). Detailed activation and pace mapping was performed within both the RVOT and LVOT using the Advisor HD Grid catheter and EnSite mapping system (Abbott). Detailed mapping within the coronary venous system was performed using a dedicated 4-F 20-electrode catheter (Map-iT). The earliest mapped site was again confirmed to be within the AIV (54 milliseconds pre-QRS, with an rS morphology on unipolar electrogram). Mapping of the intraseptal venous tributaries was attempted. However, extensive mapping was limited due to difficulty in wire engagement. Otherwise, the earliest endocardial sites were on the septal RVOT and just beneath the left sinus of Valsalva (10 milliseconds pre-QRS, with rS morphology on unipolar EGM). The Map-iT catheter was exchanged for the ablation catheter. The best pace map match was 89%. The local unipolar electrogram also had an rS configuration (Figures 2 and 3). Before commencing ablation, selective left coronary angiogram was performed, which demonstrated that the ablation catheter was directly on top of the LAD coronary artery. There was no suitable branch for alcohol ablation given that the earliest site was in the AIV itself, and we elected against double-balloon technique. At the earliest site, we proceeded with PFA delivery using a nominal setting of 2,400 V/5 bursts. Vasospasm prophylaxis was implemented with intracoronary nitroglycerin (200 μg) before each PFA delivery. Of note, there was no coronary vasospasm with PFA delivery and no skeletal muscle stimulation (Video 1). This ablation resulted in transient suppression of the PVCs, but they recurred within 1 minute. Despite additional ablation, PVCs recurred after 5 minutes. Subsequent ablation was performed from the earliest RVOT site with RFA (30 W, 90 seconds) and then PFA. This resulted in a more durable suppression; however, PVCs would recur after 15 minutes. Finally, the ablation catheter was advanced through the retroaortic approach to the earliest LVOT site where further ablation was performed. The area that showed the earliest activation in the LVOT was preconditioned with long durations of RFA (longest of 2 minutes) and later consolidated with PFA delivery. After this combined approach (Figures 3 and 4), the clinical PVC was completely suppressed throughout the remainder of the case. No recurrence was observed after a 1-hour period of observation in the laboratory. Final coronary angiography showed no change in coronary artery anatomy. The procedure was then concluded, and there were no acute complications. After the procedure, the patient was observed over 24 hours in hospital without recurrence of PVCs. A postprocedural cardiac magnetic resonance was performed and showed focal new delayed enhancement consistent within the ablation site (Figure 5). At 2-month follow-up, the patient was feeling well without symptomatic PVC recurrence.

Figure 2.

Site of Earliest Activation for the Premature Ventricular Contraction

(A and B) Location of the earliest signal on right anterior oblique (RAO) and left anterior oblique (LAO) fluoroscopy. (C) Local electrogram at the site of the earliest activation. Note that the unipolar signal has an rS configuration, which was suggestive of deeper foci. Please see Figure 3 for signal with Map-iT catheter and sites of ablation.

Figure 3.

Sites of Ablation

(A) Left anterior oblique cranial. (B) Left lateral. The CS, GCV, AIV, RVOT, LVOT, and AV/aorta are shown. Blue, orange, and white dots: lesions from pulsed field ablation, with colors varying based on contact force algorithms. Red dots: radiofrequency ablation lesions. The green electrode and circle highlight the earliest signal on the Map-iT catheter. (C) Local electrogram from the Map-iT catheter. AIV = anterior interventricular vein; AV = aortic valve; CS = coronary sinus; GCV = great cardiac vein; LVOT = left ventricular outflow tract; RVOT = right ventricular outflow tract.

Figure 4.

Signal From the Endocardial Left Ventricular Outflow Tract Site Where Durable Suppression Was Achieved

As illustrated, the bipolar signal was marginally ahead of the QRS, with an rS on the unipolar electrogram (ABL uni d), suggesting a deeper focus.

Figure 5.

2-Chamber Myocardial Delayed Enhancement Sequence Demonstrated New Changes Corresponding to the Targeted Areas Consistent With Ablation (Encircled Area)

Discussion

The LV summit poses significant challenges for catheter ablation because of its complex architecture, proximity to coronary vascular structures, and often deep arrhythmic foci with broad exits.⁵ As described in our case, exhaustive prior attempts with RFA from various vantage points around the earliest activation site were performed without significant PVC suppression with ablation at the earliest site identified precluded by proximity to the LAD. Although chemical ablation with alcohol is a potential option, inability to cannulate the areas of interest because of restricted anatomy and uncontrolled lesion depth may unbalance the risk-benefit ratio. Although hybrid surgical ablation can be considered, this more invasive approach is associated with greater morbidity. Currently, radiofrequency ablation has remained a cornerstone modality in PVC treatment, along with medical options. Nevertheless, the efficacy of this utility has varied, from 80% to 95%, depending on the foci location.⁶ Several explanations can be rationally deduced for such limitations, such as deep-lying substrate (electrocardiogram morphology and procedural findings suggested this to be the case), limited penetration from RF itself, and inability to ablate at the actual site of activation due to proximity to the coronary vasculature. With the prevailing use of PFA in atrial tachyarrhythmias, there have been more reports on the utility of PFA in ventricular arrhythmias. However, there remains uncertainty regarding efficacy, safety, and the consistency in settings.

This is the first-in-human experience of the use of the TactiFlex Duo ablation catheter for ventricular ablation, permitting both RF and PFA. The catheter has identical footprint and maneuverability to the TactiFlex catheter. In PFA mode, it is configured to deliver energy in a monopolar manner. In our case, the return electrode for PFA was varied between the anterior chest and back depending on the catheter ablation site (endocardial aspect and AIV, respectively) in an attempt to enhance lesion depth in the summit area.

With its dual-modality capability, the catheter provides flexibility in both ablation modes and target selection. We believe this versatility contributed to procedural success by permitting ablation from multiple vantage points, with the final effective site located in a region lacking presystolic activation.⁷ Although some of this benefit may be attributable to the ability to ablate in proximity to the LAD—an area inaccessible with RF alone—there is also a theoretical advantage of achieving deeper lesion formation with combined RF/PFA ablation. A preliminary study reported by Verma et al⁸ using a different dual-modality catheter suggested additive effects of preconditioning the lesion with RFA followed by PFA. Preliminary unpublished animal data with the Tactiflex Duo ablation catheter similarly suggests some lesion augmentation with RFA preconditioning; however, the absolute change was not as pronounced, possibly due to larger lesions achieved with either modality alone. Mechanistically, RFA results in lower impedance and tissue edema, which may enhance electrical conductivity. In addition, electroporation is understood as a 2-step pore formation initiated by the application of E-fields. It begins with the formation of small, nonconductive hydrophobic pores. Once a critical radius is exceeded, these initial pores transition into larger, conductive hydrophilic pores. Independently, hydrophilic pores may also arise spontaneously due to thermal energy, which can reduce the energy barrier for pore formation and facilitate the initiation process. As such, electroporation's efficacy may be enhanced by certain protocols that leverage synergistic thermal transfer effects to lower the energy barrier for pore formation. Furthermore, heating could broaden the angular pore formation zone beyond the polar regions, promoting more uniform and widespread pore formation across the cell membrane.⁹

By that means, the effect of electroporation from the subsequent PFA delivery may be potentiated, enabling a deeper penetration to targeted tissues. However, it is important to recognize that lesion formation may reach a point of saturation, beyond which further energy delivery does not yield incremental benefit. PFA may enable the feasibility to perform ablation near the coronary arteries. However, certain precautions, especially given the potential risk of coronary spasm, are warranted.¹⁰ In addition to intracoronary nitroglycerin, we had a coronary guide catheter in place with equipment available for possible emergent percutaneous intervention. Furthermore, although there remain unknown long-term effects of PFA over coronary arteries, we thought the risk-benefit ratio was in favor of ablation given her clinical state. Although we were able to demonstrate safety and efficacy, larger-scale studies are warranted.

Funding Support and Author Disclosures

The authors have reported that they have no relationships relevant to the contents of this paper to disclose.

Appendix

Video 1

Selective Left Main Coronary Angiogram Was Performed While Ablation Was Being Delivered

There was no vasospasm throughout.