Anatomical interrelation between the phrenic nerve and the internal mammary artery as seen by the surgeon

Paresis of the diaphragm (especially left-side paresis) is a relatively frequent finding following cardiac surgery. While, usually, it is a rather benign condition, in exceptional cases it may lead to severe impairment to death of the patient. The supposed causes of damage to the phrenic nerve include: local myocardial cooling by ice slush; opening of the pleural cavity in connection with local cooling; cross clamp length; total hypothermia; central venous cannulation; traction-related damage; mammary artery harvesting. Perhaps the commonest cause of damage to the phrenic nerve, i.e., the effect of local myocardial cooling by ice slush, and the mode of phrenic nerve protection have been studied in considerable detail. The authors focused their attention on the interrelation between the phrenic nerve and the proximal segment of the mammary artery. Using anatomical preparations, the authors demonstrate the very intimate relationship of the above entities. The interrelation of the two anatomical structures basically differs depending on whether the left or right side is concerned. 1) On the left: The phrenic nerve, on entering the thorax, runs between the subclavian artery and vein laterally from the mammary artery crossing it medially; it parts the latter and continues in mediastinal adipose tissue to run on the pericardium toward the diaphragm. 2) On the right: The phrenic nerve passes between the subclavian vein and artery medially from the mammary artery. For another 3-4 cm, it runs along the medial and dorsal edges of the mammary artery.(ABSTRACT TRUNCATED AT 250 WORDS)