Abstract
This case series describes four obstructive sleep apnea patients who underwent hypoglossal nerve stimulation implant surgery. After a period of OSA resolution with therapy, these patients presented with symptoms of increased snoring and reduced tongue sensation with implant activation. Impedance testing showed abnormally elevated values on bipolar electrode settings, and electrode reprogramming led to restored therapeutic benefit.
Keywords: obstructive sleep apnea, sleep medicine, surgical treatment of obstructive sleep apnea
1. Introduction
Hypoglossal nerve stimulation (HNS) is a therapy offered to select patients with obstructive sleep apnea (OSA) who cannot tolerate continuous positive airway pressure (CPAP). HNS devices with Inspire IV systems (Inspire Medical Systems, Golden Valley, MN) are composed of an implantable pulse generator, a sensing lead, and a stimulation lead to stimulate the hypoglossal nerve distally. HNS decreases OSA severity and snoring [1]. Device failure through malrotation of the implantable pulse generator and tangled leads from Twiddler's Syndrome has been described [2]. Sensing lead migration or fractures have also been documented with Inspire IV [3]. However, the clinical presentation of malfunction of the stimulation lead has not been described. In this case series we describe four patients who presented with stimulation lead malfunction.
Alongside HNS devices, consumer sleep technology apps are tools to track sleep. Understanding HNS lead malfunctions and how sleep apps can monitor OSA‐related symptom changes may guide management of complications. SnoreLab (Reviva Softworks Ltd) app data, recording snoring duration and severity, was analyzed for one patient.
2. Case Series
This case series was approved by the UCSF IRB (#24‐41465). The first patient is a 65‐year‐old woman with a preoperative AHI of 64 events/h. The patient completed a successful Inspire IV HNS implant surgery via 2‐incision approach with no complications. For 2 years after surgery, the patient completed regular follow‐up and reported no major problems with a therapeutic AHI of 11 events/h on a home sleep study (HSAT) at a chronic HNS stimulation setting of 1.2 V (+‐+). Two years after implantation, the patient reported increased snoring and the absence of tongue motion sensation upon implant activation. The patient utilized the SnoreLab app to track her snoring intermittently and reported increased snoring duration and severity (Figure 1). Upon evaluation of the implant with impedance testing, there was limited tongue motion across voltage ranges 1.2–3.0 V at the bipolar (+‐+) electrode setting. Impedance testing revealed the center stimulating electrode was nonfunctional with high impedances on bipolar (+‐+) and unipolar (0‐0) center electrode dependent settings (Table 1). HNS was reprogrammed to a lateral electrode configuration at 1.0 V (‐0‐), which resulted in improved tongue motion. The patient uptitrated stimulation at home to 1.2 V (‐0‐). After 1 month, this resulted in improved snoring and a therapeutic AHI of 5 events/h on HSAT, with optimal (83%) adherence, defined as device usage for ≥ 70% of nights during the 30 days of available data preceding the sleep study [4].
FIGURE 1.
SnoreLab based snoring percentage for Patient 1. Asterisk denotes significant difference compared to snoring percentage at baseline. During the phase with reported symptom changes, the patient displayed a significantly higher snoring percentage which resolved with re‐programming her implant. [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com]
TABLE 1.
Impedance testing results for first, second, and third patients. Impedance values > 7000 Ω for +‐+ and 0‐0 electrode configurations imply center electrode malfunction.
| Voltage | Patient 1 | Patient 2 | Patient 3 | ||||||
|---|---|---|---|---|---|---|---|---|---|
| +‐+ | 0‐0 | ‐0‐ | +‐+ | 0‐0 | ‐0‐ | +‐+ | 0‐0 | ‐0‐ | |
| 1.5 | > 7000 | > 7000 | 1236 | > 7000 | > 7000 | 1220 | > 7000 | > 7000 | 3905 |
| 2.0 | > 7000 | > 7000 | 1231 | > 7000 | > 7000 | 1274 | > 7000 | > 7000 | 1673 |
| 2.5 | > 7000 | > 7000 | 1326 | > 7000 | > 7000 | 1022 | > 7000 | 5067 | 1917 |
| 3.0 | > 7000 | > 7000 | 1138 | > 7000 | > 7000 | 1123 | 3814 | 4207 | 2069 |
The second patient is a 72‐year‐old woman with a preoperative AHI of 24 events/h who underwent a successful Inspire IV HNS implant surgery via 3‐incision approach with no complications. For 6 years, the patient completed regular follow‐up and reported no major problems with a therapeutic AHI of 12 events/h on HSAT at 2.5 V (+‐+) HNS electrode setting. 7 years after implantation, the patient reported irregular pulsing with intermittent lack of tongue sensation and abnormally strong pulses on implant activation. Device testing revealed high impedances and central electrode malfunction at (+‐+) and (0‐0) configurations (Table 1). Implant reprogramming with a change in electrode configuration to (‐0‐) at 0.5 V led to improved tongue motion. The patient uptitrated the new setting to 0.6 V (‐0‐) and HSAT showed a therapeutic AHI of 9 events/h, with 100% nightly adherence.
The third patient is an 84‐year‐old woman with a preoperative AHI of 33 events/h who underwent a successful Inspire IV HNS implant surgery via a 2‐incision approach with no complications. For 3 years, the patient completed regular follow‐up and reported no major problems. A postoperative HSAT at 1.9 V (+‐+) showed a therapeutic AHI of 13 events/h. Three years after implantation, the patient noted increased daytime sleepiness and snoring. An HSAT showed an elevated AHI of 36 events/h with HNS on at 2.0 V (+‐+). Query of the implant demonstrated center electrode malfunction with high impedances at 1.5 and 2.0 V at (+‐+) and (0‐0) configurations (Table 1). Compared to her initial HNS activation appointment which showed a functional threshold of 0.2 V (+‐+), the patient's functional threshold was elevated at 1.4 V (+‐+). The implant was then reprogrammed to a lateral electrode configuration at 1.3 V (‐0‐) resulting in improved tongue motion. The patient uptitrated the new setting to 1.8 V (‐0‐) and HSAT showed an AHI of 16 events/h, with 97% nightly adherence. The patient was asked to uptitrate her stimulation further and will be retested.
The fourth patient is a 43‐year‐old man with a preoperative AHI of 91 events/h who underwent a successful Inspire IV implant surgery via 2‐incision approach with no complications. For 4 years, the patient completed regular follow‐up with no major problems. A postoperative HSAT showed a therapeutic AHI of 15 events/h at 1.6 V (+‐+). Four years after implantation, the patient reported significant weight gain with return of daytime sleepiness and inconsistent tongue sensation during implant activation. An updated HSAT with HNS on at 1.9 V (+‐+) showed an AHI of 36 events/h. There was no tongue motion on activation across voltage ranges 1.8–3.0 V (+‐+), in contrast to his prior visits which showed strong tongue protrusion at similar stimulation levels. Impedance testing showed center electrode malfunction with high impedances across voltage ranges of 1.5–4.0 V for (+‐+) and (0‐0) configurations. His implant was reprogrammed to the lateral electrode configuration (‐0‐) at 0.8 V, which restored strong tongue motion. The patient uptitrated the new setting to 1.2 V (‐0‐) and HSAT showed a therapeutic AHI of 7 events/h, with 72% nightly adherence.
3. Discussion
We describe four cases of stimulation lead malfunction presenting as return of sleep apnea‐related symptoms and changes in tongue sensation during implant activation.
Impedance refers to the total electrical resistance encountered by the current as it travels from the stimulation leads to the nerve tissue. Elevated impedance indicates excessive resistance, suggesting ineffective electric transmission to the nerve [5]. Impedance values < 200 Ω may indicate a short between conductors, > 2000 Ω should be interpreted as informational, and values > 7000 Ω suggest an open circuit, in which the current does not effectively enter the tissue [6]. Lack of appropriate stimulation can lead to reduction of tongue movement with stimulation. High impedance values can indicate lead disconnection, lead fracture, or scar tissue or lack of contact with tissue near the electrode. Clinical evaluation with impedance testing should be performed if implant activation does not produce typical tongue motion. Updated home sleep study testing clarifies OSA severity changes. Abnormally high impedances on specific electrode settings suggest malfunction of a stimulation electrode. Reconfiguration of the electrode settings based on the impedance profile can be achieved if center electrode malfunction is recognized. Afterwards, uptitration, updated sleep study testing, and follow up on sleep‐related symptoms should be accomplished to understand new therapeutic treatment levels (Figure 2).
FIGURE 2.
Flow chart of recommended workflow to diagnose and manage electrode malfunction.
One patient utilized a snoring phone app which helped provide objective measures of snoring change and triggered presentation to the clinic. Consumer sleep technologies can alert providers to changes in OSA combined with patient‐reported experience [7].
In the bipolar electrode setting, the center electrode acts as an anode, or a site of electron loss, while the lateral electrodes are cathodes, or are sites of electron gain [8]. The center electrode in this setting delivers the current and drives depolarization. As all of our cases involved years of adequate function followed by malfunction of the central electrode alone, we hypothesize that chronic utilization as the active center electrode increased the susceptibility of the center electrode to malfunction. Focal conductor dysfunction may occur from microfracture of the connecting wire. Other potential causes are localized scar tissue formation and mishandling of the electrode on placement. Generator connection can be an issue if all electrodes are not functional. Direct cause requires further investigation after explantation.
4. Conclusion
Understanding the presentation and potential for malfunction of the stimulation lead assists providers in the long‐term management of hypoglossal stimulation devices. Patients with stimulation lead malfunction may report increased snoring and reduced tongue sensation with implant use. Impedance testing helps identify stimulation electrode issues and direct proper re‐programming for return of OSA therapeutic effect.
Funding
The authors have nothing to report.
Conflicts of Interest
M.D. is a consultant for XII Medical. J.C. is a consultant for Inspire Medical Systems and LivaNova.
Data Availability Statement
Research data are not shared.
References
- 1. Zheng Y. J., Cai Y., Ifeagwu K. C., and Chang J. L., “Snoring Patterns During Hypoglossal Nerve Stimulation Therapy Up‐Titration,” Laryngoscope 134, no. 2 (2024): 987–992, 10.1002/lary.30815. [DOI] [PubMed] [Google Scholar]
- 2. Miglani A., Mecham J. C., Hines J. P., Hinni M. L., Miller B. W., and Bansberg S. F., “Hypoglossal Nerve Stimulator Twiddler's Syndrome,” Laryngoscope 131, no. 3 (2021): E1019–E1021, 10.1002/lary.28979. [DOI] [PubMed] [Google Scholar]
- 3. Bestourous D. E., Pasick L. J., Benito D. A., and Zapanta P. E., “Adverse Events Associated With the Inspire Implantable Hypoglossal Nerve Stimulator: A MAUDE Database Review,” American Journal of Otolaryngology 41, no. 6 (2020): 102616, 10.1016/j.amjoto.2020.102616. [DOI] [PubMed] [Google Scholar]
- 4. Soose R. J., Faber K., Greenberg H., Boon M., Woodson T., and Strollo P., “Post‐Implant Care Pathway: Lessons Learned and Recommendations After 5 Years of Clinical Implementation of Hypoglossal Nerve Stimulation Therapy,” Sleep 44, no. Supplement_1 (2021): S4–S10, 10.1093/sleep/zsaa279. [DOI] [PubMed] [Google Scholar]
- 5. Xia F., Li H., Li Y., et al., “Minimally Invasive Hypoglossal Nerve Stimulator Enabled by ECG Sensor and WPT to Manage Obstructive Sleep Apnea,” Sensors (Basel) 23, no. 21 (2023): 8882, 10.3390/s23218882. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6. Inspire Medical Systems , “Inspire Upper Airway Stimulation (UAS) System Model 3028 Generator: Physician Manual,” (2023).
- 7. Cai Y., Zheng Y. J., Cheng C. M., Strohl K. P., Mason A. E., and Chang J. L., “Impact of Hypoglossal Nerve Stimulation on Consumer Sleep Technology Metrics and Patient Symptoms,” Laryngoscope 134, no. 7 (2024): 3406–3411, 10.1002/lary.31398. [DOI] [PubMed] [Google Scholar]
- 8. Strollo P. J., Soose R. J., Maurer J. T., et al., “Upper‐Airway Stimulation for Obstructive Sleep Apnea,” New England Journal of Medicine 370, no. 2 (2014): 139–149, 10.1056/NEJMoa1308659. [DOI] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
Research data are not shared.