Delayed Recovery of Cryoballoon Ablation-Induced Phrenic Nerve Palsy: A Case Report

Abbreviations

AF, Atrial fibrillation

CBA, Cryoballoon ablation

HFpEF, Heart failure with preserved ejection fraction

PNP, Phrenic nerve palsy

PV, Pulmonary vein

RSPV, Right superior pulmonary vein

SSS, Sick sinus syndrome

INTRODUCTION

Atrial fibrillation (AF) is a global health challenge associated with increased risks of stroke and heart failure. Cryoballoon ablation (CBA) has emerged as a highly effective and standardized therapeutic intervention for AF, offering comparable outcomes to radiofrequency ablation.¹ However, despite its efficacy and favorable safety profile, CBA is uniquely associated with phrenic nerve palsy (PNP) due to the anatomical proximity of the right phrenic nerve to the superior pulmonary veins (PVs).²

PNP remains the most frequent complication of CBA, with a reported incidence ranging from 2% to 3%. In the majority of clinical scenarios, diaphragmatic function recovers spontaneously, often during the procedure itself or within the first 6 to 12 months post-ablation. Cases of "ultra-prolonged" PNP — defined as paralysis persisting beyond one year — are exceedingly rare and poorly documented in current literature. Furthermore, the clinical burden of prolonged PNP on elderly patients with multiple cardiopulmonary comorbidities, such as heart failure and asthma, can be severe, potentially leading to a cascade of respiratory complications.

In this report, we present a complex case of a 75-year-old female who developed right-sided PNP during CBA for persistent AF. Her clinical course was uniquely challenging, involving the development of sick sinus syndrome (SSS) and recurrent pneumonia. Most notably, her diaphragmatic function achieved full recovery only after 13 months, providing significant clinical evidence that long-term patience and supportive care can lead to successful outcomes even in protracted cases of nerve injury.

CASE PRESENTATION

A 75-year-old female with a medical history of persistent AF (CHA₂DS₂-VASc score of 6, managed with Edoxaban), heart failure with preserved ejection fraction (HFpEF, New York Heart Association Class II), hypothyroidism (on Levothyroxine), type 2 diabetes mellitus (on Dapagliflozin), and asthma, was followed regularly at our cardiovascular outpatient department.

Due to worsening symptoms, including occasional palpitations and frequent junctional bradycardia after medication, the patient and her family opted for an electrophysiology study and catheter ablation. The procedure was performed using a PolarFit CBA. At the beginning of the ablation, the patient’s electrocardiography showed sinus rhythm. Circumferential isolation of the left pulmonary veins (left superior pulmonary vein and left inferior pulmonary vein) was achieved successfully. However, during the first ablation shot of the right superior pulmonary vein (RSPV) (Figure 1A), the procedure was abruptly terminated at 47 seconds (minimum temperature -57 °C) (Figure 1B) due to the sudden onset of PNP. At that time, abdominal palpation showed decreased diaphragmatic contraction, and the minimal Diaphragm Movement Sensor signal on the PolarFit system was 55%. We subsequently used an Orion mapping catheter to identify residual PV potentials in the RSPV and right inferior pulmonary vein. Segmental ablation was then performed using an IntellaNav MiFi 4 mm open-irrigation catheter to bridge the isolation gaps and target the RSPV trigger site. Following ablation, PV potentials were confirmed to be eliminated in all four PVs. Unfortunately, the phrenic nerve palsy did not recover by the end of the procedure, despite the immediate cessation of energy delivery.

Figure 1.

Under fluoroscopy guidance, the cryoballoon was inserted into the right superior pulmonary vein (RSPV) and inflation was done then with cryoablation, as demonstrated by the contrast injection (A). The minimal temperature was -57 °C, the time to target was 25 seconds and the time to isolation was 22 seconds, whereas the total duration was 47seconds (B).

Within 24 hours, the patient developed weakness, dizziness, and dyspnea. A post-procedural chest X-ray confirmed an elevated right hemidiaphragm, leading to a diagnosis of CBA-related right PNP (Figure 2B). Subsequently, some choking episodes were complained and aspiration pneumonia developed after the ablation procedure. Antibiotics were prescribed as well as O2 supply. As she finished the course of infection control and slowly weaned off from oxygen, she was discharged 12 days after the ablation.

Figure 2.

The patient’s baseline chest-X-ray suggested borderline heart size with mild lung congestion (A). Soon after the cryoballoon ablation, elevation of right side diaphragm was noted (B). Evidence of right phrenic nerve palsy persisted 4 months after the ablation (C). More than 13 months later, the phrenic nerve palsy resolved as her right diaphragm returned to baseline level (D).

During outpatient follow-up, the patient experienced recurrent cough and dyspnea, leading to readmission for intravenous antibiotics and oxygen therapy to treat pneumonia. Additionally, persistent general malaise was attributed to SSS. Consequently, she was admitted for the implantation of a permanent pacemaker. Following the procedure, her clinical condition and quality of life significantly improved. Regular follow-up chest X-rays were performed. Finally, more than 13 months post-ablation, a chest X-ray demonstrated that the right diaphragm had returned to its normal position, signifying the full resolution of the PNP (Figure 2D). Her symptoms of cough and dyspnea resolved as well.

DISCUSSION

The presented case illustrates a remarkably prolonged recovery of PNP following CBA, extending beyond the typical 12-month window. It also highlights the complex clinical trajectory of a patient who suffered from both mechanical (PNP) and electrical (SSS) complications post-procedure.

PNP is the most common complication of CBA, occurring in approximately 2-3% of procedures,² with RSPV being the riskiest ablation site, primarily due to the proximity of the right phrenic nerve to the RSPV. Fewer cases of left PNP were reported during CBA of the left superior PV, as compared with the right side.^3,4 While the "Fire and Ice" trial and other major registries suggest that the vast majority of PNP cases resolve within 6 to 12 months,¹ another research still reported a 4-year time for complete recovery in 3 patients, all happened during ablation of RSPV.⁵ Among them, the age ranged from 47 to 75 years old, whereas the nadir temperature ranged from -48 °C to -57 °C. In our patient, both her age (75 years old) and the nadir temperature (-57 °C) were relatively risky compared to the reported research, even though our total freezing time (47 seconds) was not long compared to theirs (from 83 to 171 seconds). For our patient, she required 13 months to achieve full recovery. This occurs even with modern safety protocols,^6,7 as seen in this case where pre-procedural computed tomography of PV was done and where ablation was stopped at 47 seconds upon detection of nerve injury. The severity of injury, despite the rapid termination of energy, may be related to the low nadir temperature reached (-57 °C), which can cause more profound axonal damage.

The clinical significance of PNP was particularly pronounced in this patient due to her underlying HFpEF and asthma. The diaphragmatic paralysis led to impaired pulmonary ventilation and clearance, directly contributing to recurrent pneumonia and necessitating readmissions for intravenous antibiotics and oxygen therapy. This underscores that in high-risk populations, PNP is not merely an incidental radiographic finding but a significant driver of morbidity that can lead to a cascade of respiratory complications.

Additionally, the management of this patient was complicated by the development of symptomatic SSS. While the patient had a history of junctional bradycardia after medication, the persistent malaise and electrical disturbances post-ablation necessitated the implantation of a permanent pacemaker. The interplay between respiratory compromise from PNP and chronotropic incompetence from SSS created a challenging management scenario, which only stabilized after both pacemaker implantation and the eventual resolution of the PNP.

LEARNING POINTS

1. This case serves as a reminder that the recovery of cryoballoon-induced PNP can exceed 13 months. Physicians should maintain long-term follow-up and aggressive management of pulmonary complications, especially in elderly patients with pre-existing heart failure and lung disease.

DECLARATION OF CONFLICT OF INTEREST

The authors have no financial interest or relationship to disclose.

INFORMED CONSENT

Informed consent was obtained from the patient for publication of this case report and any accompanying images. Efforts have been made to ensure the patient’s privacy and confidentiality, including the removal of identifying details.

FUNDING STATEMENT

This work was supported by the Biosense Webster IIS (C2304900), Ministry of Science and Technology (NSTC 113-2628-B-075-003-MY3); and Taipei Veterans General Hospital (grant no. V115C-029), Veterans General Hospitals and University System of Taiwan Joint Research Program Joint Research Program (VGHUST114-G1-4-1).

The funders were not involved the design of this study.