Elevated Right Hemidiaphragm After Right Atrial Catheter Ablation
This represents a complication of the ablation procedure—specifically, right phrenic nerve palsy (Answer D).
Mechanism and Pathophysiology
The right phrenic nerve courses along the lateral right atrium and superior vena cava, making it vulnerable to thermal injury during right atrial ablation procedures. When the phrenic nerve is damaged, the ipsilateral hemidiaphragm becomes paralyzed and appears elevated on chest X-ray due to loss of its normal downward contractile force 1.
Key anatomical relationship: During catheter ablation in the right atrium for supraventricular tachycardia, radiofrequency energy delivery near the crista terminalis or lateral right atrial wall can inadvertently injure the adjacent right phrenic nerve, resulting in hemidiaphragm paralysis 1.
Why Other Options Are Incorrect
Option A (chronic left phrenic nerve injury): This is anatomically incorrect—the procedure was performed in the RIGHT atrium, and the finding is RIGHT hemidiaphragm elevation. Left phrenic nerve injury would cause left hemidiaphragm elevation.
Option B (vagus and accessory nerve injury): These nerves do not control diaphragmatic function. The vagus nerve affects heart rate and gastrointestinal function, while the accessory nerve (CN XI) innervates the trapezius and sternocleidomastoid muscles.
Option C (incidental finding): The temporal relationship—appearing on postoperative imaging immediately after the procedure—strongly suggests a procedural complication rather than a coincidental finding.
Clinical Context from Guidelines
While the most recent 2025 guidelines on pulsed field ablation report 0% persistent phrenic nerve palsy with newer PFA technology 2, traditional radiofrequency ablation carries a recognized risk of this complication. The guidelines specifically mention phrenic nerve injury as a known complication of right atrial procedures 3.
Important distinction: The 2025 guidelines note that phrenic nerve stunning from PFA is "usually temporary and self-resolved" and "usually managed by monitoring without needing specific intervention" 2. However, radiofrequency ablation can cause permanent injury, as documented in the case literature 1.
Clinical Implications
Immediate recognition is critical because:
- Phrenic nerve palsy can severely affect respiratory function
- Patients may develop paradoxical breathing and dyspnea on exertion 4
- Most cases from radiofrequency ablation are persistent rather than transient 1
Management approach:
- Serial chest X-rays to document persistence
- Pulmonary function testing to assess respiratory impact
- If symptomatic and persistent beyond 12-14 months, consider video-assisted thoracoscopic diaphragm plication 4
Common Pitfall
Do not dismiss an elevated hemidiaphragm as an incidental finding when it appears on immediate postoperative imaging after cardiac ablation. The temporal relationship to the procedure makes iatrogenic injury the most likely diagnosis until proven otherwise.