Unexpected ventricular fibrillation triggered by pulsed field ablation for atrial fibrillation

Key Teaching Points.

• •This case describes the sudden occurrence of ventricular fibrillation during pulsed field energy application at the mitral isthmus using a dual-energy lattice-tip catheter.
• •Given the absence of ischemic signs, pacemaker interference—such as noise reversion mode—and the characteristics of the energy delivery system may have contributed to this arrhythmic event.
• •This case raises concerns about the potential arrhythmogenicity of pulsed field ablation and underscores the need for further investigation into its safety profile.

Introduction

Pulsed field ablation (PFA) is a novel energy modality increasingly used in atrial fibrillation catheter ablation, characterized by its selectivity for cardiomyocytes and reduced risk of collateral damage. Here we describe and discuss a case of unexpected ventricular fibrillation (VF) during PFA with the dual-energy lattice-tip focal catheter, Sphere-9^TM catheter (Affera^TM Mapping and Ablation system, Medtronic, Minneapolis, MN).

Case report

A 72-year-old man was admitted for catheter ablation of a symptomatic atypical flutter of 4 weeks’ duration. The patient had a history of persistent atrial fibrillation treated 2 years earlier by PFA using the pentaspline PFA catheter (FARAPULSE, Boston Scientific Inc, Marlborough, MA). Pulmonary vein isolation, posterior wall isolation, and endocardial mitral isthmus ablation were performed. The medical history included dual-chamber pacemaker implantation 12 years earlier for sick sinus syndrome and typical flutter ablation 11 years earlier. He was on rivaroxaban and sotalol.

The procedure was performed under general anesthesia. The baseline rhythm was atypical flutter. Transseptal puncture was uneventful, and a 3-dimensional mapping system (Prism-1 Mapping software, Medtronic) confirmed a perimitral flutter with endocardial reconnection at the mitral isthmus. Pulsed field energy was applied to create a posterior mitral line between the left inferior pulmonary vein and the mitral valve (Figure 1A and 1B). During the first application, the patient returned to sinus rhythm. However, during subsequent applications to complete the mitral line, VF suddenly occurred during energy delivery (Figure 1C). Defibrillation was immediately performed, restoring sinus rhythm. Pacemaker interrogation revealed no abnormalities or recordings. Electrocardiogram (ECG) analyses before and after VF showed unchanged, known T-wave abnormalities attributed to pacemaker-related T-wave memory, without signs of ischemia (Figure 2). Given the patient’s hemodynamic stability, mitral isthmus ablation was completed without further incident, and bidirectional block of the mitral isthmus was achieved.

Figure 1.

A: Activation map showing the perimitral flutter and the posterior mitral line performed. B: Activation map and the catheter position during the application inducing ventricular fibrillation. C: Ventricular fibrillation occurrence during delivery of pulsed field energy.

Figure 2.

A: Electrocardiogram (ECG) in sinus rhythm, 6 months prior ablation, showing T-wave abnormalities attributed to pacemaker-related T-wave memory. B: ECG the day before ablation showing atypical flutter. C: ECG before ventricular fibrillation occurrence, showing similar pacemaker-related T-wave memory changes. D: ECG after defibrillation, showing similar T-wave abnormalities.

Postprocedure coronary angiography identified a 70% calcified proximal stenosis in the circumflex artery (Figure 3A), deemed hemodynamically stable, with no immediate need for angioplasty. The ECG on the following day revealed unchanged, known T-wave abnormalities. Echocardiography showed a left ventricular ejection fraction of 50% and biatrial dilation. The patient remained stable and asymptomatic and was discharged 24 hours after the ablation.

Figure 3.

A: Coronary angiography showing stenosis in the proximal circumflex artery (red arrow). B: Fusion image of coronary angiography and electroanatomic mapping (right anterior oblique 14°, caudal 13° projection), indicating the ablation site located remotely from the circumflex stenosis (red arrow). C: Fusion image of coronary angiography and electroanatomic mapping in another projection (left anterior oblique 36°, cranial 30° projection), showing the mitral isthmus located remotely from the circumflex stenosis (red arrow).

Discussion

We report the occurrence of an unexpected VF as a complication during PFA on the mitral isthmus with the dual-energy lattice-tip ablation catheter. Three hypotheses may explain this event: ischemia, pacemaker interference, or an R-on-T phenomenon with the Affera Mapping and Ablation System.

Ablation at the mitral isthmus has previously been associated with coronary vasospasm, owing to the proximity of the circumflex coronary artery.^1,2 These vasospasms can be effectively prevented with nitrates.^3,4 Because previous reports of vasospasm involved the pentaspline device, nitrates were not administered in our case. A recent case report described vasospasm occurring at the mitral isthmus with the Sphere-9 catheter, suggesting these vasospasms may be more energy mediated than device specific.⁵ However, in our case, pre- and post-VF ECGs showed no ischemic changes (eg, ST-segment elevation). The T-wave abnormalities observed were consistent with pacemaker-related T-wave memory and unchanged from the preablation ECG. Coronary angiography revealed a calcified and stable lesion in the proximal circumflex artery, anatomically distant from the mitral isthmus (Figure 3B and 3C). These findings make vasospasm and ischemia an unlikely cause of VF in this case, although they cannot be entirely excluded.

The patient’s pacemaker (MicroPort) was reprogrammed to VVI mode at 30 beats per minute before ablation and functioned normally both before and after ablation, with no abnormal recordings. However, the possibility of pacemaker interference cannot be entirely excluded. Undersensing or activation of the noise reversion mode during PFA could have resulted in an inappropriate ventricular pacing stimulus coinciding with the T wave, potentially triggering VF. Although speculative, noise reversion alerts have been reported in a patient undergoing PFA.⁶ Although no alerts were recorded on our patient’s device, this does not eliminate the possibility of pacemaker interference. An alternative hypothesis is interaction between the ventricular lead and a malfunctioning ablation catheter; however, in our case, the catheter functioned normally throughout, and the right ventricular lead’s apical position was remote from the mitral isthmus ablation site. This highlights the need for further investigation into the safety of PFA in patients with cardiac devices.

An R-on-T phenomenon related to the Affera System (Medtronic) may be another plausible explanation. The system uses a novel lattice-tip focal catheter, Sphere-9, with a generator toggling between pulsed field energy (HexaPulse, Medtronic) and radiofrequency (HexaGen, Medtronic). Pulsed field energy is delivered through monopolar biphasic pulse trains of microsecond-scale duration, over 3–5.5 seconds, driven with up to ± 2 kV, which is usually below the VF induction threshold: VF induction threshold ranges from 20 V to 60 V at conventional pulse durations from 4 ms to 12 ms and increases exponentially as the pulse width decreases, making microsecond-scale duration pulse well below the VF induction threshold.⁷ However, the pulse train is ungated, meaning it is nonsynchronized with the cardiac cycle. PFA technologies may reduce arrhythmogenesis by synchronizing pulsed field delivery to the cardiac refractory period (ie, ST interval).⁸ Although the ungated biphasic modality was deemed safe and effective in preclinical and early clinical studies,⁹ including for the Affera System,¹⁰ the theoretical risk of an R-on-T phenomenon cannot be excluded. The pentaspline device (FARAPULSE, Boston Scientific Inc) also operates ungated, yet no VF events have been reported despite widespread use.² The difference may lie in the monopolar nature of the Affera System’s energy delivery, even though animal studies showed the safety of unsynchronized biphasic monopolar delivery.¹¹ Given the occurrence of VF during the delivery in our case, we consider it a potentially plausible explanation. To the best of our knowledge, this may represent the first reported case of VF potentially triggered by the ungated and monopolar nature of Affera System energy delivery. This causality remains speculative, given the lack of ischemic changes and normal pacemaker interrogation. This underscores the need for caution and further studies on this topic.

Conclusion

We report an unexpected VF occurrence during pulsed field energy application at the mitral isthmus with the dual-energy lattice-tip catheter, possibly owing to a pacemaker interference or a phenomenon associated with the energy delivery characteristics. This case highlights the need for a deeper understanding of the pulsed field modality and its potential consequences.

Disclosures

The authors have no conflicts of interest to disclose.