The terminal segment of the human phrenic nerve as a novel implantation site for diaphragm pacing electrodes: anatomical and clinical description.

Abstract

BACKGROUND\nDiaphragm pacing allows certain ventilator-dependent patients to achieve weaning from mechanical ventilation. The reference method consists in implanting intrathoracic contact electrodes around the phrenic nerve during video-assisted thoracic surgery, which involves time-consuming phrenic nerve dissection with a risk of nerve damage. Identifying a phrenic segment suitable for dissection-free implantation of electrodes would constitute progress.\n\n\nSTUDY DESIGN\nThis study characterizes a free terminal phrenic segment previously never fully described before. We conducted a cadaver study (n=14) and a clinical observational study during thoracic procedures (n=54).\n\n\nRESULTS\nA free terminal phrenic segment was observed on both sides in 100% of cases, jumping from the pericardium to the diaphragm and measuring 60mm [95% confidence interval; 48-63] and 72.5mm [65-82] (right left, respectively; p=0.0038; cadaver study). This segment rolled up on itself at end-expiration and became unravelled and elongated with diaphragm descent (clinical study). Three categories of fat pads were defined (type 1: pericardiophrenic bundle free of surrounding fat; type 2: single fatty fringe leaving the phrenic nerve visible until diaphragmatic entry; type 3: multiple fatty fringes masking the site of penetration of the phrenic nerve) that depended on body mass index (p=0.001, clinical study). Hematoxylin-eosin and toluidine blue staining (cadaver study) showed that all of the phrenic fibers in the distal, pre-branching part of the terminal segment were contained within a single epineurium containing a variable number of fascicles (right: 1 [95%CI 0.65-4.01]; left 5 [3.37-7.63]; p=0.03).\n\n\nCONCLUSION\nDiaphragm pacing through periphrenic electrodes positioned on the terminal phrenic segment should be tested.