Diaphragm pacing

Introduction
Diaphragm Pacing, also known as phrenic nerve pacing, is the rhythmic application of electrical impulses to the diaphragm, resulting in respiration for patients who would otherwise be dependent on a mechanical ventilator.

This concept was originally referred to as electrophrenic respiration, although the Food and Drug Administration identifies the device as a “diaphragmatic/phrenic nerve stimulator”. A phrenic nerve pacemaker, with electrodes placed around the phrenic nerve, is a Class III medical device, which requires premarket approval. An newer approach has been developed and approved by the FDA (see “diaphragmatic pacemaker”) at Case Western Reserve University which places the electrode in the diaphragm using minimally invasive surgical technique.

Indications for Use
According to Medicare, phrenic nerve stimulators are indicated for “selected patients with partial or complete respiratory insufficiency” and “can only be effective if the patient has an intact phrenic nerve and diaphragm.” (Medicare National Coverage Determinations Manual, Chapter 1, Part 2, Section 160.19) Common patient diagnoses for phrenic nerve pacing include patients with spinal cord injury, central sleep apnea (ie, Ondine's curse), and diaphragm paralysis.

Surgery
The surgery is performed by placing an electrode around the phrenic nerve, either in the neck (ie, cervically), or in the chest (ie, thoracically). This electrode is connected to a radiofrequency receiver which is implanted just under the skin. An external transmitter sends radio signals to the device by an antenna which is worn over the receiver.

For the cervical surgical technique, the phrenic nerve is approached via a small (~5 cm) incision slightly above, and midline to, the clavic. The phrenic nerve is then isolated under the scalenus anticus muscle.

For the thoracic surgical technique, a small (~5 cm) incisions over the 2nd or 3rd intercostal space. The electrodes are placed around the phrenic nerves alongside the pericardium. Use of a thorascope allows for this technique to be performed in a minimally-invasive manner.

Patients are usually hospitalized for 1-3 days post-operatively, although some implantations can be performed on an outpatient basis.

Availability
There are currently three commercially distributed diaphragmatic / phrenic nerve stimulators made by Synapse Biomedical, Inc. (USA), Avery Biomedical Devices, Inc. (USA), and Atrotech OY (Finland). The Synapse (NeuRx DPS(TM)) and Avery (“Mark IV Breathing Pacemaker”) devices are distributed worldwide. The Atrotech device (“Atrostim Jukka”) is not available in the United States.

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