Effects of internal mammary artery dissection on phrenic nerve perfusion and function

Abstract

The effects of left internal mammary artery (LIMA) dissection and distal division on phrenic nerve perfusion and function were examined in an adult swine model. Phrenic nerve perfusion was determined by left atrial injection of radioactively labeled microspheres. Phrenic nerve function was determined by measuring nerve and diaphragm potentials evoked by bilateral phrenic nerve stimulation. In the first group of animals (n = 9), the LIMA was dissected with ligation of all its branches. Left phrenic nerve perfusion and function decreased after LIMA dissection in every animal studied, whereas only minimal changes were observed on the right. Sixty minutes after LIMA dissection, left phrenic nerve mean perfusion decreased 71%. Left phrenic nerve and left diaphragm mean action potential amplitudes decreased 54% and 80%, respectively. In the second group of animals (n = 4), the LIMA dissection was performed without division of the pericardiacophrenic artery, a small proximal branch of the internal mammary artery that supplies the phrenic nerve. Sixty minutes after LIMA dissection, left phrenic nerve perfusion had decreased by 21% from control values, with a corresponding decrease in left phrenic nerve and diaphragm mean action potential amplitudes of 19% and 23%, respectively. These results indicate that LIMA dissection with division of all its branches in this model is associated with a significant impairment in left phrenic nerve perfusion and function and suggests a causal relationship. These results may also explain the apparent increased phrenic nerve cold sensitivity and increased incidence of phrenic nerve dysfunction associated with LIMA grafting. Compared with the universally advocated method of complete LIMA dissection, sparing the pericardiacophrenic artery during the LIMA dissection significantly improves left phrenic nerve perfusion and function.