The anatomical location of the right phrenic nerve (RPN) in close proximity to the right pulmonary veins has become a critical consideration for electrophysiologists performing pulmonary vein isolation, the cornerstone treatment for atrial fibrillation. Although radiofrequency ablation in this region is rarely associated with complications-unlike cryoballoon ablation-the proximity of the RPN to the ablation site is considered the most widely accepted mechanism of nerve injury. Therefore, accurately defining its anatomical course is essential to prevent complications.

This concern extends to any ablation procedure performed near the RPN, including those targeting the lateral-posterior region of the right atrium, particularly during atrial tachycardia ablation or cardioneuroablation. Several methods have been used to precisely localize the RPN. The most commonly employed technique is phrenic nerve stimulation; however, there is growing interest in the use of computed tomography (CT) to identify structures running parallel to the nerve-such as the pericardiophrenic artery and vein-enhanced with contrast. Three-dimensional reconstruction through image segmentation has proven useful in defining the anatomy of cardiac chambers and adjacent extracardiac structures.

This study aims to compare two approaches for visualizing the course of the right phrenic nerve: one based on computed tomography imaging and the other on the nerve's response to stimulation during the procedure. This comparison will allow us to assess the concordance between imaging findings and intra-procedural observations, ultimately contributing to improved procedural safety.

Inclusion Criteria:

• Ability to provide informed consent
• Patients who have undergone or will undergo transcatheter AF ablation or CNA
• Availability of 64-slice contrast-enhanced MDCT with RPN segmentation using ADAS® software prior to ablation
• Age ≥ 18 years

Exclusion Criteria:

• Inability to provide informed consent
• Inability to perform contrast-enhanced CT before transcatheter AF ablation or CNA
• Age < 18 years

All patients underwent an electrocardiography-gated cardiovascular CT using a 64-slice multidetector row CT scanner (Revolution CT, GE Healthcare Global Diagnostic Imaging) prior to the ablation procedure. The position line was set at 0.5 cm below the tracheal bifurcation to the cardiac diaphragmatic surface. The acquisition was performed within a single breath- hold. The gantry rotation time was 0.35 s, and the tube current was 350-750 mA at 120 kV. Iodinated contrast material (60 mL; Omnipaque 300 mg/mL), was injected at a rate of 4-5 mL/s, followed by 20 mL of saline solution. A second acquisition immediately after is performed to study the venous phase. Original images at 75% or 45% R-R intervals were transferred to post-processing Workstation, with a section thickness of 0.625 mm. If motion artifacts appeared, the electrocardiographic editing technique was used and the reconstructed window was moved forward or backward for 5% R-R interval until the motion artifacts disappeared.