Natural history of neuromodulation devices and therapies: a patient-centered survival analysis

Zoe E. Teton Department of Neurological Surgery, Oregon Health & Science University, Portland, Oregon

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Daniel Blatt Department of Neurological Surgery, Oregon Health & Science University, Portland, Oregon

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Amr AlBakry Department of Neurological Surgery, Oregon Health & Science University, Portland, Oregon

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James Obayashi Department of Neurological Surgery, Oregon Health & Science University, Portland, Oregon

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Gulsah Ozturk Department of Neurological Surgery, Oregon Health & Science University, Portland, Oregon

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Vural Hamzaoglu Department of Neurological Surgery, Oregon Health & Science University, Portland, Oregon

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Philippe Magown Department of Neurological Surgery, Oregon Health & Science University, Portland, Oregon

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Nathan R. Selden Department of Neurological Surgery, Oregon Health & Science University, Portland, Oregon

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Kim J. Burchiel Department of Neurological Surgery, Oregon Health & Science University, Portland, Oregon

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Ahmed M. Raslan Department of Neurological Surgery, Oregon Health & Science University, Portland, Oregon

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OBJECTIVE

Despite rapid development and expansion of neuromodulation technologies, knowledge about device and/or therapy durability remains limited. The aim of this study was to evaluate the long-term rate of hardware and therapeutic failure of implanted devices for several neuromodulation therapies.

METHODS

The authors performed a retrospective analysis of patients’ device and therapy survival data (Kaplan-Meier survival analysis) for deep brain stimulation (DBS), vagus nerve stimulation (VNS), and spinal cord stimulation (SCS) at a single institution (years 1994–2015).

RESULTS

During the study period, 450 patients underwent DBS, 383 VNS, and 128 SCS. For DBS, the 5- and 10-year initial device survival was 87% and 73%, respectively, and therapy survival was 96% and 91%, respectively. For VNS, the 5- and 10-year initial device survival was 90% and 70%, respectively, and therapy survival was 99% and 97%, respectively. For SCS, the 5- and 10-year initial device survival was 50% and 34%, respectively, and therapy survival was 74% and 56%, respectively. The average initial device survival for DBS, VNS, and SCS was 14 years, 14 years, and 8 years while mean therapy survival was 18 years, 18 years, and 12.5 years, respectively.

CONCLUSIONS

The authors report, for the first time, comparative device and therapy survival rates out to 15 years for large cohorts of DBS, VNS, and SCS patients. Their results demonstrate higher device and therapy survival rates for DBS and VNS than for SCS. Hardware failures were more common among SCS patients, which may have played a role in the discontinuation of therapy. Higher therapy survival than device survival across all modalities indicates continued therapeutic benefit beyond initial device failures, which is important to emphasize when counseling patients.

ABBREVIATIONS

DBS = deep brain stimulation; ET = essential tremor; GPi = internal globus pallidus; PD = Parkinson’s disease; SCS = spinal cord stimulation; STN = subthalamic nucleus; Vim = ventral intermediate nucleus; VNS = vagus nerve stimulation.

OBJECTIVE

Despite rapid development and expansion of neuromodulation technologies, knowledge about device and/or therapy durability remains limited. The aim of this study was to evaluate the long-term rate of hardware and therapeutic failure of implanted devices for several neuromodulation therapies.

METHODS

The authors performed a retrospective analysis of patients’ device and therapy survival data (Kaplan-Meier survival analysis) for deep brain stimulation (DBS), vagus nerve stimulation (VNS), and spinal cord stimulation (SCS) at a single institution (years 1994–2015).

RESULTS

During the study period, 450 patients underwent DBS, 383 VNS, and 128 SCS. For DBS, the 5- and 10-year initial device survival was 87% and 73%, respectively, and therapy survival was 96% and 91%, respectively. For VNS, the 5- and 10-year initial device survival was 90% and 70%, respectively, and therapy survival was 99% and 97%, respectively. For SCS, the 5- and 10-year initial device survival was 50% and 34%, respectively, and therapy survival was 74% and 56%, respectively. The average initial device survival for DBS, VNS, and SCS was 14 years, 14 years, and 8 years while mean therapy survival was 18 years, 18 years, and 12.5 years, respectively.

CONCLUSIONS

The authors report, for the first time, comparative device and therapy survival rates out to 15 years for large cohorts of DBS, VNS, and SCS patients. Their results demonstrate higher device and therapy survival rates for DBS and VNS than for SCS. Hardware failures were more common among SCS patients, which may have played a role in the discontinuation of therapy. Higher therapy survival than device survival across all modalities indicates continued therapeutic benefit beyond initial device failures, which is important to emphasize when counseling patients.

In Brief

For the first time, researchers have reported comparative device and therapy failure rates out to 15 years for hundreds of DBS, SCS, and VNS patients at a single institution over 22 years. These results provide the fundamental statistics necessary for clinicians to answer patients when asked how long they can expect to utilize both their device and therapy and, by analyzing these aspects separately, the authors have demonstrated that all three therapies maintain therapeutic efficacy beyond initial device failures - an important distinction to emphasize when counseling patients in light of the well-established complication rates associated with these devices.

Level 1 evidence supports the use of neuromodulation technology for multiple indications: deep brain stimulation (DBS) for Parkinson’s disease (PD),2,12,23,24,35 essential tremor (ET),25 and dystonia;34 vagus nerve stimulation (VNS) for refractory epilepsy;17,21,33 and spinal cord stimulation (SCS) for chronic pain.18,19,22

Neuromodulatory interventions may be difficult to sustain for some patients, in part because they depend on the ongoing function of implanted medical devices. The length of survival for various neuromodulatory therapies depends on the particular technology used, the indication for therapy, and the practical difficulties of maintaining a working system that sustains therapeutic benefit. Analysis of device survival and therapy survival together, therefore, presents an opportunity to evaluate treatment effectiveness in a novel way. Device and therapy survival data are necessary to guide accurate, patient-centered counseling when deciding whether or not to institute neuromodulatory therapy. Presenting this information side by side in language that patients can understand is something that has not been done previously, but it is of significant practical importance. Therefore, we investigated neuromodulatory device and therapy survival using Kaplan-Meier analysis of a 22-year, single-institution experience with DBS, VNS, and SCS.

Methods

Definitions

Device survival was defined as the time in months between device implantation and device failure due to infection, hardware malfunction, lack of therapeutic efficacy, and lead or catheter migration. Therapy survival was defined as time in months between therapy initiation and the time when therapy was deemed to be ineffective or therapeutic value did not outweigh the complications associated with device maintenance (Fig. 1).

FIG. 1.
FIG. 1.

Visual representation of how we defined device survival versus therapy survival.

Thus, device failure sometimes results in a therapy failure as well. For example, if a device failed and it was not repaired or replaced to reinstitute continuous therapy, then this would also constitute a therapy failure, as the effort required to fix the device clearly did not outweigh the benefit of the therapy itself. In other cases, therapy failure will result in a device failure if the patient terminates use of their device due to a lack of therapeutic efficacy. While these examples illustrate the inherent overlap in these measurements, they represent a minority of the cases, and therefore we determined that there is still significant utility in examining them separately. Device replacement for battery end of life was considered to be normal device maintenance. However, if a patient’s battery reached end of life prematurely due to faulty manufacturing, this was deemed a device failure due to hardware malfunction. Survival analyses were performed to determine the percentage of patients still utilizing their therapy and their initial device at 5, 10, and 15 years.

Patients and Neuromodulation Therapies

This is a retrospective chart review of all patients who initiated neuromodulatory therapy with DBS, VNS, or SCS at our institution between 1994 and 2015. The search was performed on our billing database, utilizing both diagnosis and procedure codes to ensure that all patients were captured. The study was approved by the institutional review board with a waiver of patient consent.

For each patient, demographic data; diagnosis; neuromodulation modality; smoking status; and diagnoses of diabetes, autoimmune conditions, and immune deficiencies were collected. For SCS, the principal presenting symptom (back pain, leg pain, both, or other) was also noted. For DBS, the electrode target (subthalamic nucleus [STN], internal globus pallidus [GPi], or ventral intermediate nucleus [Vim]) was documented.

Statistical Analysis

Kaplan-Meier survival curves were plotted for each neuromodulation device (initial devices only) and therapy. Kaplan-Meier curves are presented without censored data. Censored data can be found in Supplementary Table 1. A Cox regression was performed using the following variables to see if any were predictive of device or therapy failure: age, sex, location of the electrode or catheter, diabetes mellitus status, immunodeficiency status, smoking status, and reason for device compromise. A p value ≤ 0.05 was considered statistically significant.

Results

Patient Cohort

In the 22-year time period reviewed, 961 patients were included for analysis: 450 DBS patients, 383 VNS, and 128 SCS (Table 1). Among patients who underwent DBS implantation, 300 (67%) patients had PD, 136 (30%) had ET, 9 (2%) had dystonia, and 1 (0.2%) had central tremor and 1 (0.2%) patient suffered from Gilles de la Tourette syndrome. DBS electrodes targeted the Vim in 149 (33%) patients, the GPi in 159 (35%) patients, and the STN in 142 (32%) patients. All VNS devices were implanted for drug-resistant epilepsy. Patients who underwent SCS were being treated for either refractory leg-predominant back and leg pain or neuropathic leg pain. Cox regression analyses were conducted for sex; smoking status; type of insurance; and diagnosis of diabetes, autoimmune condition, or immunodeficiency. None of these variables was found to be a statistically significant predictor of device or therapy survival, across all neuromodulation modalities. Cox regression analyses were conducted to determine if age or obesity were predictive of device or therapy survival in both DBS and SCS patients, and neither was found to be statistically significant predictors in either patient cohort.

TABLE 1.

Patient characteristics by neuromodulation modality

DBSVNSSCSTotal
No. of patients450383128961
Median age, yrs (range)65 (14–86)18 (2–74)50 (15–83)
Sex, n (%)
 Female160 (35)204 (53)75 (59)
 Male290 (64)179 (47)53 (41)
Diabetes mellitus, n (%)59 (13)3 (0.7)14 (11)

Therapy and Device Survival by Neuromodulation Modality

Deep Brain Stimulation

The mean DBS therapy survival was 18 years ± 15.9 months, and the mean device survival was 14 years ± 20.5 months (Table 2). The percentage of patients still utilizing DBS therapy at 5, 10, and 15 years was 96%, 91%, and 85%, respectively (Fig. 2A solid line and Table 3). The percentage of patients still utilizing their initial DBS device at 5, 10, and 15 years was 87%, 73%, and 32%, respectively (Fig. 2A dotted line and Table 3). Among the 450 patients who underwent DBS, 50 (11%) patients experienced a failure of their initial device; 52% of these failures were due to infection, 22% were due to hardware failure, 6% were due to migration of an electrode, and 20% of these failures were due to therapy ineffectiveness (Table 4). Together, these complications led to device revision in 4% and device removal in 7% of patients. A Cox regression analysis for indication for DBS was performed, and there was no statistically significant difference between PD and ET patients in either device or therapy survival.

TABLE 2.

Mean device and therapy survival

Mean Device Survival (yrs)Mean Therapy Survival (yrs)
DBS1418
VNS1418
SCS812.5
FIG. 2.
FIG. 2.

Kaplan-Meier analyses of therapy survival (solid lines) versus device survival (dotted lines) for DBS (A), VNS (B), and SCS (C).

TABLE 3.

Therapy and initial device survival percentage over time by neuromodulation modality

DBSVNSSCS
Initial device survival (%)
 5 yrs879050
 10 yrs737034
 15 yrs325416
Therapy survival (%)
 5 yrs969974
 10 yrs919756
 15 yrs859145
TABLE 4.

Causes of initial device failure

No. of Failures (%)
DBSVNSSCS
Infection26 (52)9 (15)6 (15)
Hardware failure11 (22)49 (80)14 (36)
Device migration3 (6)1 (2)3 (8)
Device ineffective10 (20)2 (3)16 (41)
Total50 (100)61 (100)39 (100)

Vagus Nerve Stimulation

The mean VNS therapy survival was 18 years ± 15.9 months, and the mean device survival was 14 years ± 6 months (Table 2). The percentage of patients still utilizing VNS therapy at 5, 10, and 15 years was 99%, 97%, and 91%, respectively (Fig. 2B solid line and Table 3). The percentage of patients still utilizing their initial VNS device at 5, 10, and 15 years was 90%, 70%, and 54%, respectively (Fig. 2B dotted line and Table 3). In the 383 patients who underwent VNS, 61 (16%) experienced a failure of their initial device: 15% of these failures were due to infection, 80% were due to hardware failure, 2% were due to device migration, and 3% were due to a lack of therapeutic effectiveness (Table 4). Device revision was performed in 13% (all electrode revisions), while the device was removed in 3% of patients.

Spinal Cord Stimulation

Every patient who received a permanent SCS implant first received a trial implant that demonstrated at least a 50% reduction in pain, as is standard of care at our institution. The mean survival for SCS therapy was 12.5 years ± 16 months, and the mean survival for SCS devices was 8 years ± 13.6 months (Table 2). The percentage of patients still using SCS therapy at 5, 10, and 15 years was 74%, 56%, and 45%, respectively (Fig. 2C solid line and Table 3). The percentage of patients still using their initial SCS device at 5, 10, and 15 years was 50%, 34%, and 16%, respectively (Fig. 2C dotted line and Table 3). Among the 128 patients who underwent SCS, 39 (30%) experienced a failure of their initial device: 15% of these cases were due to surgical site infection, 36% of these were due to hardware failure, 8% were due to lead migration, and 41% of these cases were due to lack of therapeutic efficacy (Table 4). The majority of patients had paddle electrodes implanted, with only 35 (27%) receiving percutaneous leads. Half of the lead migrations were in patients who had received paddles (2/4) and half were in patients who had received percutaneous leads (2/4). Devices were revised in 17% of these patients, and 14% of patients had their devices explanted.

Discussion

An analysis of initial device and overall therapy survival rates for 3 commonly used neuromodulatory treatments, DBS, VNS, and SCS, is presented. Device survival is directly related to adequate device functioning and continuing therapeutic effectiveness, while inversely related to the occurrence of device infection, malfunction, or migration. In contrast, therapy survival reflects an interaction between device survival and patient willingness to undergo additional surgical procedures to repair or replace a nonfunctioning device in order to maintain therapy, a willingness that is highly dependent on overall benefit obtained from the therapy. Thus, the difference between device and therapy survival represents an objective measure of perceived therapeutic value. For example, a patient who has experienced a significant reduction in seizures since having a VNS system implanted may be more willing to undergo a subsequent operation to have a replacement device implanted in the event of a hardware malfunction as opposed to a patient who had only marginal therapeutic benefit to begin with.

The statistical data presented here are of particular value to clinicians counseling patients on the potential benefit of neuromodulatory therapy. By examining both device and therapy survival separately, statements can be made to assist in managing patient expectations for the treatment they are considering (e.g., “In 5 years, there is a 96% chance that DBS therapy will still be effective in treating your tremor, and an 87% chance that your initial DBS implant will still be in place”).

While these survival analyses confer significant practical benefit, the device data presented in aggregate also allow for intriguing comparisons between the various modalities. For instance, DBS and VNS therapies have a natural history that is very different from that of SCS, with higher device and therapy survival rates in the former group (Fig. 2). It is possible that the limited device survival in SCS discourages patients from pursuing the therapy for a longer period of time. Of note, SCS is directed at pain management, a subjective outcome, while DBS and VNS are directed at objective conditions of movement disorders and medically refractory epilepsy, respectively. This is especially apparent when comparing the relative causes of device failure; 41% of SCS failures were due to lack of therapeutic efficacy while this accounted for 20% of DBS device failures and just 3% of VNS failures. The complex psychosocial aspects of pain management may contribute to these varied rates of efficacy. Additionally, DBS and VNS devices are implanted in the head and neck, while the SCS device is implanted around the torso. Whether the observed lower device survival is related to anatomical location of implantation is not clear but could conceivably play a role.

Another intriguing benefit to examining therapy and device survival in the same context is that across all modalities, therapy survival was significantly higher than device survival (Fig. 3). This could be indicative of a greater willingness of patients to undergo revisions and replacements to maintain therapy and that this benefit is maintained out to 15 years. This is an important factor to emphasize when counseling patients in that, despite potential complications with the hardware itself, the overall benefit obtained is often significant enough that patients will undergo additional surgical procedures to maintain it.

FIG. 3.
FIG. 3.

Kaplan-Meier analyses of all modalities. Survival analyses of devices (A) and therapy (B) are depicted for DBS (black solid line), VNS (black dotted line), and SCS (gray solid line).

Survival of neuromodulation devices and therapies that employ open-loop technologies and mostly nonrechargeable systems is described. Newer, more innovative systems such as high-frequency SCS, burst stimulation SCS, directional stimulation DBS, and responsive VNS are currently being implemented and will likely warrant their own independent analyses once adequate follow-up data are available.

Deep Brain Stimulation

Randomized controlled trials have confirmed that neurostimulation for PD increases overall mobility and daily hours spent mobile without dyskinesia.12,29,35–37 Quality-of-life measures are also improved with DBS for PD.11,15,35 Electrode location in either the GPi or STN has largely shown equivalent clinical improvements in randomized controlled trials2,16,23,24 and in a large 2014 meta-analysis.20 Traditionally, complications associated with DBS are specific to the procedure, discussed in comparison to medication regimens, and tend to focus on surgical site infections, with hardware malfunction and lead migration reported infrequently.12,35,37 One recent case series presented 10-year follow-up data on nearly 80 DBS patients but only reported adverse event data for specific complications with no mention of overall device and therapy survival.5 While this may be important information for clinicians, it does not always translate to utility when counseling patients. A 2012 retrospective analysis by Falowski et al. examined hardware and surgical complications in devices at one institution over 10 years.14 The authors found that 5.7% of their total cohort required revision, but they did not differentiate between loss of efficacy and lead migration and did not report on total number of device removals. Despite this ambiguity surrounding the cause for revisions, their revision rate was similar to our overall revision rate of 4% for DBS devices.

Essential tremor responds very well to thalamic DBS with tremor control in up to 80% of patients, but, unfortunately, the majority of responders (up to 70%) will eventually show loss of benefit to some degree.9,30 Devices implanted for ET reportedly have higher hardware complication rates than those for PD, but most of these studies did not comment on overall revision and replacement rates as a result of these complications.4,9 Multiple studies with follow-up of longer than 5 years reported hardware complications slightly above 20%, but these are difficult to compare due to heterogeneity in follow-up times and variable complication categories.3,9,26,31,38 Despite these reported increased rates of hardware malfunction in ET patients, we found no difference in device survival between PD and ET patients.

Vagus Nerve Stimulation

VNS therapy has been shown to produce a 50% seizure reduction in 24% to 46% of patients.6,7,33 A 2011 meta-analysis evaluating VNS efficacy showed an average seizure reduction of 51% with an odds ratio of 1.83 for ≥ 50% seizure reduction.13 Similar benefits have been reported in both children and adolescents.32 Among class 1 and 2 evidence trials for VNS, the rate of therapy discontinuation without device failure ranges from 12% to 17% within 5 years.1,6 This is notably higher than our findings in which 1% of patients discontinued therapy within the first 5 years. Couch et al. recently published a 14-year, single-center, single-surgeon examination of VNS revision surgeries and found an all-cause revision rate of 19%, similar to that in our cohort.10 In a recent longitudinal retrospective study examining 247 patients over a mean follow-up time of 12 years, relevant data on causes of complications and reoperations were provided; however, rates of overall device failure or therapy discontinuation were not discussed.27 While we note that our infection and hardware complication rates were similar to those of Couch et al., it is difficult to translate into a patient-centered context given the lack of statistics demonstrating overall device and therapy survival. It is likely that these rates are of more importance to patients when considering a new therapy. However, the data are lacking, with no Kaplan-Meier analyses included in the abovementioned studies for device or therapy survival.

Spinal Cord Stimulation

In 2016, Bir et al. published a study examining revision-free survival of SCS devices from a single center over a 15-year period.8 Nearly one-third (32.6%) of patients required revision and almost 10% of devices were removed. Revision-free survival was 75% at 1 year, 65% at 3 years, and 45% at 5 years. While revision-free survival was similar to our findings at 5 years (45% vs 50%), rates of revision were significantly higher in the Bir et al. study than in ours (32.6% vs 17%), with lower rates of removal (10% vs 14%). Despite both studies being conducted over roughly the same length of time (20 years vs 22 years in our study), the Bir et al. study did not report on device survival beyond 5 years, and there was no comment on therapy survival.

Other recent SCS studies have reported success and complication rates without discussion of device or therapy survival.18,19,22 Here, we provide device and therapy survival data over 15 years using Kaplan-Meier analysis. Despite a low device survival rate of 16% at 15 years, 45% of patients continued SCS therapy up to that time, indicating continued interest despite the likely need for device revision surgeries.

Interestingly, SCS therapy survival at 1 year is high (85%) (data not shown) and comparable to patient satisfaction rates of 84% at the same time interval.28 This could indicate that subsequent decline in device survival drives a deterioration in patient satisfaction that ultimately supersedes therapeutic benefit and results in therapy discontinuation for half of patients over the subsequent 4 years.

Limitations

This study was limited by retrospective data collection. The definitions used for device and therapy failure do indeed overlap, although we examined them as separate entities. For instance, a patient may still enjoy a limited degree of therapeutic benefit but perceive system repair or replacement as too high of a barrier to the continuation of therapy. In addition, patient selection criteria were not examined in this study, and all procedures were done at a single institution, potentially limiting the generalizability of our findings. We can say that the surgeons at our institution are particularly conservative, which renders patient selection less of an issue. In any case, expanding this investigation across multiple institutions would be a great focus for future study and certainly add to the robustness of the data collected therein.

Despite these limitations, comparative device and therapy survival curves for large cohorts of DBS, VNS, and SCS patient groups, reported here for the first time, provide an opportunity to counsel and inform patients more accurately with regard to the potential duration of successful therapy with these systems.

Conclusions

For the first time, long-term device and therapy survival is analyzed for 3 common neuromodulation devices, DBS, VNS, and SCS, at a single institution over 22 years. While there is a plethora of neuromodulation device literature, it is significantly lacking when it comes to the most fundamental questions concerning the therapies themselves. Initial device survival is infrequently reported, and overall therapy survival is virtually absent. Without basic statistics, clinicians lack a direct way to answer patients when asked how long they can expect to utilize their device and therapy. After examination of hundreds of devices over a span of greater than 2 decades, we provide reliable and accessible data to confidently answer these patient queries out to a 15-year time point. In addition, by analyzing device and therapy survival separately, we have identified a pattern across all neuromodulation modalities in that therapy benefit consistently outlasts device survival. This is an important stipulation that should be emphasized when counseling patients in the utility of these therapies in light of well-established complication rates. Further study of this topic should ideally include prospective documentation of patient and physician factors in decision making at the time of therapy initiation, device revision or replacement, and therapy cessation.

Acknowledgments

We thank Shirley McCartney, PhD, for editorial assistance. We also thank John Marquart, BS, and Ali Ibrahim, MD, for assistance with electronic chart review.

Disclosures

Dr. Raslan: consultant for Abbott.

Author Contributions

Conception and design: Raslan. Acquisition of data: AlBakry, Ozturk. Analysis and interpretation of data: Teton, Blatt, Obayashi, Hamzaoglu. Drafting the article: Raslan, AlBakry. Critically revising the article: Raslan, Teton. Reviewed submitted version of manuscript: all authors. Statistical analysis: Obayashi. Administrative/technical/material support: AlBakry, Obayashi, Ozturk, Hamzaoglu, Magown, Selden, Burchiel. Study supervision: Raslan.

Supplemental Information

Online-Only Content

Supplemental material is available with the online version of the article.

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Supplementary Materials

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Illustration from Ivan et al. (pp 1517–1528). Copyright Kenneth Probst. Published with permission.

  • FIG. 1.

    Visual representation of how we defined device survival versus therapy survival.

  • FIG. 2.

    Kaplan-Meier analyses of therapy survival (solid lines) versus device survival (dotted lines) for DBS (A), VNS (B), and SCS (C).

  • FIG. 3.

    Kaplan-Meier analyses of all modalities. Survival analyses of devices (A) and therapy (B) are depicted for DBS (black solid line), VNS (black dotted line), and SCS (gray solid line).

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