How close are the phrenic nerves to cardiac structures?: Implications for cardiac interventionalists

Background: Phrenic nerve injury is a recognized complication following cardiac intervention or surgery. With increasing use of transcatheter procedures to treat drug-refractory arrhythmias, clarification of the spatial relationships between the phrenic nerves and important cardiac structures is essential to reduce risks. Methods and Results: We examined by gross dissection the courses of the right and left phrenic nerves in 19 cadavers. Measurements were made of the minimal and maximal distances of the nerves to the superior caval vein, superior cavoatrial junction, right pulmonary veins, and coronary veins. Histologic studies were carried out on tissues from six cavaders. Tracing the course of the right phrenic nerve revealed its close proximity to the superior caval vein (minimum 0.3 +/- 0.5 mm) and the right superior pulmonary vein (minimum 2.1 +/- 0.4 mm). The anterior wall of the right superior pulmonary vein was < 2 mm from the right phrenic nerve in 32% of specimens. The left phrenic nerve passed over the obtuse cardiac margin and the left obtuse marginal vein and artery in 79% of specimens. In the remaining specimens, its course was anterosuperior, passing over the main stem of the left coronary artery or the anterior descending artery and great cardiac vein. Conclusions: The right phrenic nerve is at risk when ablations are carried out in the superior caval vein and the right superior pulmonary vein. The left phrenic nerve is vulnerable during lead implantation into the great cardiac and left obtuse marginal veins.