Diaphragm Pacemaker System for Acquired Central Hypoventilation Syndrome
Critical Limitation of Available Evidence
The available evidence addresses diaphragm pacing exclusively in congenital central hypoventilation syndrome (CCHS), not acquired central hypoventilation syndrome (ACHS). While the physiologic principles of diaphragm pacing may apply to both conditions, the specific patient selection criteria, outcomes, and management protocols have only been formally studied and validated in CCHS populations 1, 2.
Extrapolating from CCHS Evidence to ACHS
When Diaphragm Pacing May Be Considered
Diaphragm pacing can serve as an optimal form of ventilatory support during wakefulness in carefully selected ACHS patients who meet strict candidacy criteria: no or mild intrinsic lung disease, non-obese status, intact phrenic nerve-diaphragm axis integrity, and presence of a tracheostomy at least initially 1, 3.
Key patient selection requirements include:
- Intact phrenic nerve function bilaterally - must be confirmed via phrenic nerve stimulation studies prior to implantation 3, 4
- Absence of significant intrinsic lung disease - patients with restrictive or obstructive lung pathology are poor candidates 1
- Non-obese body habitus - obesity impairs diaphragmatic function and pacing efficacy 1
- Stable underlying condition - the etiology of ACHS should be stable rather than progressive 5
Practical Implementation Strategy
Bilateral implantation of phrenic nerve electrodes and receivers is mandatory to achieve optimal ventilation 1, 3. The system consists of:
- Battery-operated external transmitters generating electrical pulses 1
- External antennae transmitting radio frequency signals 1
- Subcutaneously implanted receivers bilaterally 1
- Monopolar platinum electrodes on each phrenic nerve 1
Conservative use of 12-15 hours per day is recommended for ambulatory patients, typically during waking hours 1, 3. This provides:
- Freedom from mechanical ventilator during daytime activities 1
- Improved mobility and quality of life 5
- Enhanced speech and olfaction compared to tracheostomy ventilation 5
Critical Safety Requirements
Patients using diaphragm pacing require continuous monitoring with pulse oximetry and end-tidal CO2, plus continuous care by a highly trained registered nurse 1. This is non-negotiable.
Patients requiring 24-hour ventilatory support must have an alternate form of ventilation for part of the day 1. Diaphragm pacing alone cannot serve as sole support for continuous ventilation needs. The typical approach combines:
- Diaphragm pacing during waking hours (if criteria met) 1
- Positive pressure ventilation via tracheostomy during sleep 1
Essential Backup Equipment
All patients must have spare antennae at home, as these components most frequently break 1. Additionally:
- A backup diaphragm pacer transmitter is mandatory, already programmed based on physiologic testing 1
- Settings should be established at a center with extensive expertise in diaphragm pacing 1
Surgical Considerations
Implantation should only be performed by cardiovascular-thoracic surgeons with extensive expertise in diaphragm pacing, ideally using thoracoscopic approach 1. The procedure requires:
- Thoracic surgery and hospitalization for internal component placement 1
- Biannual then annual comprehensive in-hospital evaluations 1, 3
- Digital oscilloscope and surface electromyogram recordings for optimal settings 1
Common Complications and Management
Obstructive apnea can occur during sleep in decannulated patients because synchronous upper airway muscle contraction does not occur with paced inspiration 1, 3. Management strategies include:
- Lengthening inspiratory time on pacer settings 1, 3
- Decreasing force of inspiration 1, 3
- Maintaining tracheostomy if obstructive events persist 1
Other potential complications include:
- Wire breakage requiring surgical revision 5
- Radiofrequency failure 5
- Infection at implant sites 5
- Shoulder pain requiring chronic analgesics (reported in one case) 6
Cardiac Pacemaker Compatibility
Patients requiring both cardiac and diaphragm pacemakers can use both simultaneously without interference, provided the cardiac pacemaker is bipolar 1, 3. This minimizes electromagnetic interference with the monopolar phrenic nerve electrodes 1, 3.
Evidence from ACHS-Specific Studies
Limited research demonstrates feasibility in acquired conditions:
- A 2007 study using spinal cord stimulators for phrenic nerve stimulation showed stable ventilation in 6 patients with brainstem or high cervical cord dysfunction over 4 years 4
- A 2013 case report documented reversal of life-threatening pulmonary hypertension (systolic PAP from 80 to <40 mmHg) in an adult CCHS patient using diaphragm pacing 6
- Historical data from 1979 showed successful management of chronic ventilatory failure in patients with upper cervical cord lesions and primary alveolar hypoventilation 7
Critical Pitfalls to Avoid
- Never use diaphragm pacing as sole support in patients requiring 24-hour ventilation - always maintain alternate ventilation for part of the day 1
- Never proceed without confirming intact phrenic nerve function bilaterally - this is an absolute prerequisite 1, 3
- Never rely on apnea/bradycardia monitors - these will not detect hypoventilation or obstructed breaths, and pacer artifact falsely elevates recorded heart rate 1
- Never implant without access to a center with extensive diaphragm pacing expertise - ongoing management requires specialized knowledge and equipment 1
Comparison to Alternative Ventilation Modalities
For ACHS patients who are not candidates for diaphragm pacing:
- Positive pressure ventilation via tracheostomy remains the most reliable method 1, 2
- BiPAP should only be considered in older patients (≥6-8 years) with milder phenotypes requiring support only during sleep 2
- Negative pressure ventilation has significant limitations including lack of portability and patient discomfort 1