A total of 973 active, deceased, and inactive patients with sufficient data were identified in the Avery Biomedical Company Database, each with their own individual patient file. 331 patients were implanted using the cervical approach, 630 using the thoracic approach, and 12 using cervical for one side and thoracic on the other. Some patients were excluded due to insufficient data contained within their files.
In the 1970s, the Avery Diaphragm Pacemaker was implanted primarily in Spinal Cord Injury patients. The 1980s saw an increase in diversity of diagnoses treated, including central sleep apnea, congenital central hypoventilation syndrome, diaphragm paralysis and others. During the late 1990s and early 2000s, Video Assisted Thoracoscopic Surgery (VATS) became a breakthrough method for implanting the Avery diaphragm pacemaker with Children’s Hospital of Los Angeles popularizing the approach.(1) The Avery data reflects the popularity of VATS in the 2000s.
Figure 1 – Graph of patients implanted per year separated by surgical approach
Figure 2 – Graph of patients implanted per year separated by surgical approach
The vast majority of patients (50%) implanted with the Avery Diaphragm Pacemaker have an indication of high Spinal Cord Injury (SCI). In some cases in which a patient’s phrenic nerve does not pass a Phrenic Nerve Conduction Study, a nerve graft may be considered in order for them to be a candidate for implantation
- Patients with an injury at C1, C2, and higher have little or no movement of their head and neck, and are entirely dependent on ventilatory assistance for breathing.
- Patients with an injury at C3 usually have control of their head and neck and are occasionally weaned from ventilatory assistance.
- Patients with an injury at C4 usually have control of their head and neck, some shoulder movement and are often weaned from ventilatory assistance.
23% of implanted patients have a diagnosis of Congenital Central Hypoventilation (CCHS). CCHS, also historically referred to as “Ondine’s Curse,” is a form of Central Sleep Apnea which studies have shown to be caused by a mutation of the PHOX2b gene. However, more severely affected patients hypoventilate when both asleep and awake.
22% of patients have varying diagnoses that can be grouped together into the broader category of “Acquired Hypoventilation.” These diagnoses include Diaphragm Paralysis, Acute Flaccid Myelitis, Anterior Spinal Artery Syndrome, Arnold Chiari Syndrome, Bacterial Meningitis, Nerve Neuropathy, Antitrypsin Disorder, Encephalitis, ROHHAD Syndrome, and Multiple Sclerosis.
5% of patients treated with the Avery System have a diagnosis of Central Sleep Apnea. It is recommended that prospective patients be diagnosed via a sleep study before being considered for implantation.
Figure 3 – Graph of patient age during surgical implantation separated by approach
Thoracic placement of the electrodes is more common in pediatric cases. This trend is likely due to the small size of the patient in early childhood. Anatomically, it may be more advantageous to implant inside the chest cavity of small children than in the neck as the proximity of the branchial plexus and phrenic nerve are closer in small children increasing the possibility of simultaneously stimulating the branchial plexus with phrenic nerve stimulation. The youngest patient implanted using the cervical approach was 7 months old; 57 days old was the youngest patient implanted thoracically. According to the database statistics, most surgeons using the cervical route wait until the child is 4 or 5 years of age before implantation.
The vast majority of pediatric cervical surgeries occur in patients with the diagnosis of High Spinal Cord Injury (SCI). From the ages of 5 to 19, the number of cervical implantations in SCI patients (63) is nearly double that of all other diagnoses combined (33).
By the time patients reach early adulthood, both surgical approaches are more evenly utilized. In geriatric patients, the cervical approach is favored possibly due to the increased sensitivity geriatric patients have to anesthetic agents.(2) Implanting the Avery Diaphragm Pacemaker via the cervical approach offers the possible use of local or monitored anesthesia.
Figure 4 – Number of years spent using the Diaphragm Pacer as of November 2018
Two patients have been pacing for 40 years. A total of 68 active patients have been using the Avery Diaphragm pacer for over 30 years with an additional 9 patients who paced for over 30 years before death. The average amount of time in between revisions for this group of patients was 15.1 years. Approximately 8% of patients (3 total) in this category required no revisions since their original implantation.
195 revision surgeries were identified in the company database. 37 of 331 patients who were initially implanted cervically and 78 of 630 patients initially implanted thoracically required one or more revision surgeries. Of the 64 cervical implant revisions, 52 had no change of electrode location and 12 had the electrodes moved into the thoracic region. Of the 131 thoracic implant revisions, 126 had no change in the location of their electrode and 5 were moved into the cervical region.
Figure 5 – 44 countries worldwide have implanted the Avery Diaphragm Pacemaker
Company Patient Survey
Avery Biomedical Devices sends a questionnaire every 2 years to each active user of the device. In 2018, a total of 457 patients were sent surveys, 166 responses were recorded. Of those patients, 155 responded to the question “How many hours do you use the pacer per day?” 103 patients responded to the question “Do you have a tracheostomy? If no, was it removed?”
Figure 6 – 155 responses to “How many hours do you pace in a day?”
93% of patients who reported use of the pacer for 24 hours a day have the diagnosis of SCI. The majority of patients (<8 hours and 8-11 hours) reported using the pacer only while sleeping.
Figure 7 – 103 responses to survey for “Presence of Tracheostomy and Removal”
Seventy-six percent of questionnaire responders had a tracheostomy prior to implantation with 24% never requiring one. Roughly one third of patients with a tracheostomy prior to implantation choose to have them removed post-operatively.
- Shaul DB, Danielson PD, McCom JG, Keens TG. Thoracoscopic Placement of Phrenic Nerve Electrodes for Diaphragmatic Pacing in Children J Pediatr Surg 2002 Jul;37(7):974-8
- Kanonidou Z, Karystianou G, Hippokratia. Anesthsesia for the Elderly. Hippokratia. 2007;11(4):175-7.