Background
The history of pacing the diaphragm is not new. The earliest record of phrenic stimulation for the treatment of asphyxia was reported in 1783. In the mid-1850s, French neurologists also proposed such an idea, but it was Hugo Wilhelm von Ziemssen who performed the first diaphragmatic pacing on a young female patient who had asphyxiated on charcoal vapor. Several decades later, Duchenne also commended the benefits of diaphragmatic stimulation. Diaphragmatic stimulation did not gain any momentum because of the crude nature of surgery and lack of appropriate anesthesia. The technique was revived about a century later by Sarnoff and colleagues at Harvard, where they paced the phrenic nerve in dogs. Later, they applied the technique to a young child with complete respiratory paralysis following an intracranial aneurysm rupture. However, the true beginnings of diaphragmatic pacing started in the 1860s and 70s. The father of modern diaphragm pacing is Dr William W L Glenn from Yale University, who showed that the technique was not only practical but could be used clinically for the treatment for several medical disorders. With advances in technology, more refined and flexible electrodes were developed, and the thoracoscopic method of implantation became practical. [1, 2, 3, 4, 5]
There are 3 commercially available devices that can stimulate the diaphragm—namely, the Synapse Biomedical NeuRx; the Mark IV Breathing Pacemaker, made by Avery Biomedical Devices; and the Atrotech OY's Atrostim PNS. The Avery and the Synapse devices are available in the United States, and the Atrotech device is available only in Europe. The Synapse NeuRx DPS received FDA approval in 2011 for humanitarian use in patients 21 years or older with amyotrophic lateral sclerosis (ALS), and the cost may not be reimbursed by Medicaid or Medicare services. The Avery Mark IV Breathing Pacemaker received full premarket approval by the FDA in 1987 and is reimbursed by Medicaid and Medicare services. A key difference between the two is that the Mark IV Breathing Pacemaker stimulates the phrenic nerve and the NeuRx DPS stimulates the diaphragm. [6, 7]
Currently, several clinical centers offer diaphragm pacing for selected patients. [1, 2, 8, 9, 3, 4]
All currently available systems involve an external transmitter and an implanted receiver, but fully implantable diaphragmatic pacing systems are being developed. The current pacing systems are more affordable and easier to place than the earlier systems. [5, 10]
Diaphragmatic pacing should be considered in the following patients:
-
Those with apnea from a central cause (the CNS lesion must be higher than C2,C3 because the phrenic nerve originates from the anterior horns of C3-5.
-
Patients with amyotrophic lateral sclerosis and polio
-
Patients with upper cervical spine injury
-
Patients with basilar meningitis or brainstem infarction
-
Patients with central sleep apnea
Indications and Contraindications
Diaphragm pacing is performed to provide ventilatory support in 2 main clinical scenarios:
-
Central alveolar ventilation, or what is better known as sleep apnea
-
High spinal cord paralysis in which the drive for respiration is still present but the injury to the spinal cord prevents stimulation from the phrenic nerves
These 2 conditions account for most cases of diaphragm pacing. [11, 12, 13]
Another, albeit rare, use of diaphragm pacing is to treat patients with intractable hiccups. [14] The remaining group of patients in whom diaphragm pacing has been used consists of those with severe COPD. In these individuals, the hypoxic stimulation is diminished by administration of any amount of oxygen. [15]
Diaphragm pacing is contraindicated for patients in whom the phrenic nerve is not functional. Such patients include those with severe traumatic injury to the nerve, those with nerve tumors, and most of those with neuropathies. In addition, diaphragm pacing is contraindicated for patients with conditions in which the diaphragm itself is not functional.
Technical Considerations
Compared with positive-pressure ventilation, diaphragm pacing has a number of advantages. One major advantage is that it allows a greater degree of independence. With diaphragm pacing, the patient is no longer isolated in a room, attached to a mechanical ventilator with an uncomfortable tube down the upper airways. Patients with central hypoventilation may be able to ambulate, go to work, travel, and perform most daily living activities. Portable diaphragmatic pacemakers are available that can be used for ambulatory monitoring of heart rate and rhythm.
Another major advantage is that diaphragm pacing affords the patient the ability to speak, which is impossible with an endotracheal tube in place. Once diaphragm pacing has been performed, the tracheostomy stoma can be plugged and speech resumed. Speech capability made possible by diaphragm pacing is particularly important to patients who are quadriplegic and on a ventilator. [16, 17, 18, 19] In addition, diaphragm pacing does not result in tracheal injury, tracheomalacia, tracheal stenosis, subglottic stenosis, tracheoesophageal fistula, or tracheitis.
Furthermore, the extremely irritating copious secretions seen during mechanical ventilation are avoided. Patients on a ventilator are always at risk for death. The tubing may become kinked, coiled, obstructed, or even disconnected, and the tracheostomy site may become plugged. [20]
Outcomes
Studies have shown that diaphragm pacing is effective and helps support ventilation in specific patient populations. Diaphragmatic pacing can provide independence from a mechanical ventilator and can help patients communicate and have a better quality of life. However, long-term studies are still needed; the majority of studies published are retrospective studies or case reports. [21, 22] Some studies have reported that patients can be paced for up to 20 years without much negative sequelae; however, the data have been difficult to interpret because of heterogeneity of methodology for follow-up. It should also be mentioned that a trial involving the NeuTx DPS system pacer for patients with ALS was halted and there is concern that this device may actually be causing harm. [4, 5, 13, 17, 18, 19, 23, 24, 25, 26, 27, 28, 29, 30]
-
The newest approach to diaphragmatic pacing; the pacing electrodes are introduced via laparoscopy from the left chest.
-
The older method of phrenic nerve stimulation for diaphragmatic pacing.
-
Pacing of the diaphragm.
