Safety and preliminary efficacy of functional electrical stimulation cycling in an individual with cervical cord injury, autonomic dysreflexia, and a pacemaker: Case report

Abstract

Context: Functional electric stimulation (FES) cycling is a commonly used therapeutic exercise modality after spinal cord injury (SCI); however, additional precautions must be taken in certain situations. The purpose of this study was to develop and apply a safety monitoring protocol for autonomic dysreflexia (AD) during FES cycling and to determine if an interval-FES cycling program can be safe and beneficial to an individual with cervical SCI, a history of AD, and a non-dependent cardiac pacemaker.

The participant was a 36-year-old male with C6 AIS-C SCI sustained 9 years earlier, intermittent AD, and implanted cardiac pacemaker. Ten sessions of interval-FES cycling were performed twice weekly for 5 weeks. Rating of perceived exertion (RPE), blood pressure (BP), oxygen saturation (O2sat), and heart rate (HR) were monitored before, after, and every 5 min during cycling. ECG and cardiac pacemaker were evaluated by a cardiologist after ending the program.

Findings: The participant reported self-limited chills 27 times over 10 sessions (19 “light”, 3 “moderate”, 5 “sharp”). Chills coincided with BP increases 59% of the time and their magnitudes moderately correlated (r = 0.32). The ECG was determined to be normal and the pacemaker fully functional at the end of the study, while blood glucose decreased (111–105 mg/dl), HbA1c levels increased (5.5–5.9%), and resting BP decreased (118/84–108/66 mmHg).

Conclusion/Clinical Relevance: A person with cervical SCI, symptomatic AD, and a non-dependent pacemaker can safely participate and benefit from the interval-FES cycling program provided adequate monitoring of symptoms and vital signs.

Introduction

Functional electrical stimulation (FES) cycling has become a popular therapeutic modality after spinal cord injury (SCI). Most commonly reported benefits of FES cycling are increased lean-to-fat-mass ratio, enhanced bone mineral density, improved blood flow and vasoreactivity in paralyzed legs, increased HDL, improvement in glucose disposal, and improved perception of the quality of life.^1–5

The general safety of FES cycling is exemplified by increased use in rehabilitation settings, research laboratories, and home exercise programs.^6–11 However, individuals with SCI at T6 and above are often disqualified from FES cycling due to the possibility of provoking autonomic dysreflexia (AD). This puts them in a disadvantaged position and precludes access to this potentially beneficial therapeutic modality. AD is a condition of uncontrolled sympathetic responses and can be life-threatening.^12,13 Classically, AD presents with headache, redness and sweating above the level of SCI, anxiety, and paroxysmal hypertension and bradycardia.¹⁴ The most common precipitants are a full bladder, urinary infection, severe constipation, pressure sores, or other conditions causing discomfort or pain below the level of SCI,¹⁵ as could be provoked by the FES cycling. The reported prevalence of AD in those with T6 or higher SCI is 48% to 91%.¹² Popok et al.¹⁶ defined AD as an increase in systolic blood pressure (BP) of 20 mmHg above the baseline.

Another typical disqualifier for FES cycling is the implanted pacemaker. Applying neuromuscular electrical stimulation (NMES) to lower extremity muscles at frequencies 20–200 Hz (pulse width 400 µs) is deemed safe based on no excessive changes in BP, heart rate (HR), and incidence of pacemaker malfunction in 61 cardiovascular surgery patients.¹⁷ Wiesinger et al.¹⁸ performed a similar study using NMES (frequency 50 Hz, pulse width 700 µs) over the knee extensors in four men with chronic heart failure and implanted bipolar dual-chamber pacemakers. They performed 20 min of stimulation under continuous electrocardiogram (ECG) and reported no adverse effects or pacemaker malfunction. A recent systematic review of the safety of electrical stimulation targeting lower extremity muscles concluded that FES should be used with caution in patients with pacemakers and defibrillators and monitored for electromagnetic interference.¹⁹ However, information specific to individuals with SCI is currently missing.

During the screening for eligibility in our ongoing study of interval-FES cycling, a prospective participant reported occasional episodes of AD and history of pacemaker implantation. Although formally disqualified from that study, we invited this person to enroll in an ad-hoc developed single-subject study to examine both safety and preliminary efficacy of FES cycling in the situation of relative contraindication for FES cycling. Thus, the purpose of this single-subject study was twofold, (1) to develop a safety protocol for monitoring AD and the implanted pacemaker, and to determine the relationship between self-reported symptoms of AD and BP, HR, oxygen saturation (O2sat), and rating of perceived exertion (RPE), and (2) to determine if 10 sessions of interval-FES cycling could safely provide benefits to this individual with cervical SCI, symptomatic AD, and a non-dependent cardiac pacemaker.

Case report

Participant

The participant was a 36-year-old male with C6 incomplete SCI (American Spinal Injury Association Impairment Scale C, lower extremity motor score 0). He was 9 years post-injury at the time of enrollment, 1.71 m tall, and weighed 94.4 kg.

The participant was cleared for participation by his personal physician and completed an informed consent process prior to enrollment. This study was approved by the institutional review boards of two southeastern universities as the pre- and post-testing was performed at one university and the FES cycling was performed at the other.

The participant first underwent a screening session to ensure he could safely tolerate FES cycling (RT300, Restorative Therapies Inc, Baltimore, MD) and to obtain baseline cycling parameters (speed and resistance, electrical stimulation intensity, frequency, and pulse width). As a preventive measure, the participant emptied bowel and bladder prior to each session.²⁰ Due to a history of AD and an implanted pacemaker, a physician (Doctor of Osteopathic Medicine) was on-site during all FES sessions, as advised by Cenik et al.²¹ The FES cycling was performed in a university exercise laboratory for 30 min twice weekly for 5 weeks.

Surface electrodes were placed on the quadriceps, hamstrings and gluteal muscles. Stimulation intensity was set based on the visual appearance and palpation of a strong muscle contraction while maintaining participant comfort (range for the quadriceps, hamstrings and gluteal muscles of 50–48 mA, 45–43 mA, and 40–38 mA, respectively). The frequency was maintained at 40 Hz and pulse width at 350 µs. Per the interval protocol, the stimulation was set to 100% of the selected intensity for the high-intensity phase (e.g. 48–50 mA for quadriceps) and to 50% for the low-intensity phase (e.g. 24–25 mA for quadriceps). The phases alternated every 30 s with a 10-second ramp-up/down transition time between the phases. The cycling speed was maintained at 35 rpm while the resistance was 0.64 Nm during the high-intensity phase and 0.50 Nm during the low-intensity phase (lowest resistance allowed by the device). The entire session lasted 30 min with a 2-minute passive cycling warm-up and cool-down.

The safety protocol included an intermittent monitoring of RPE (6–20 Borg scale), BP, O2sat, and HR during each training session; before cycling, 6 times at five minute intervals during cycling (excluding ramp-up/down periods), and again after cycling (total of 60 during active cycling over 10 sessions). In the case of an AD episode (>20 mmHg increase in systolic BP, symptoms/signs of AD), the stimulation intensities were decreased. All sessions were monitored by a physician, physical therapist, and other laboratory technicians. For the efficacy assessment, weight, pulse wave velocity, BP, blood glucose, and HbA1c measures were collected before and at the end of the FES cycling program. A 3-lead ECG was recorded continuously during both assessment sessions whereas the pacemaker was interrogated at a local medical center on the day of the post-assessment. Both were reviewed by a cardiologist.

Results

During the 10 sessions, the participant reported symptoms 27 times. They were always reported during FES cycling and never before or after. The frequency of reported symptoms (AD events) ranged from 0–5 times during a single session. The symptoms were self-limited and none required medical attention or premature termination of the FES cycling. The participant left the facility asymptomatic each time.

All 27 symptoms were described as “chills” and rated “light” 19 times, “moderate” 3 times, and “sharp” 5 times. On 6 of 8 occasions when chills were reported as moderate or sharp, increased BP was subsequently recorded (range 133/102-165/110 vs. baseline 113/73-145/96). Systolic BP elevations of 20 mmHg or more coincided with subjective symptoms 59% of the time. There was a moderate correlation (Spearman’s rho r = 0.32) between the ratings of reported symptoms (chills) and increases in BP.

HR, O2sat, and RPE were largely unchanged during the sessions (HR 48–63 bpm, O2sat 93%-97%, RPE 7–9 corresponding to very light exertion). ECG was normal with the exception of ST-segment elevation during post-assessment, which the participant's cardiologist interpreted as a pacemaker artifact, not cardiac ischemia. The pacemaker was determined to be fully functional (in use 1.7% of the time, remaining battery life of 6–10 years as before entering the study).

In terms of the efficacy, body weight decreased slightly from 94.4–93.9 kg, blood glucose levels decreased from 111 to 105 mg/dl, HbA1c levels increased from 5.5–5.9%, and resting BP decreased from 118/84–108/66 mmHg. Pulse wave velocity was essentially unchanged, 5.3–5.4 m/s.

Discussion

While the results of this single-case study cannot be generalized to the overall SCI population, it appears that an interval-FES cycling program could be safely administered to an individual with cervical SCI, sporadic AD, and a non-dependent pacemaker. Furthermore, the results of this study may inform further refinement of a safety protocol for monitoring AD since a moderate correlation was found between the ratings of self-perceived symptoms and elevations in systolic BP. Also, because symptom reporting and BP increases did not always coincide, it is important to use a combination of both for more thorough safety monitoring.

Concerning the efficacy of interval-FES cycling, the outcomes were mixed but generally encouraging as body weight, BP, and blood glucose modestly decreased, although HbA1c levels increased. Not attaining more substantial results could be attributed to limited number of sessions or inadequate muscle stimulation to produce work sufficient for inducing physiological changes.

Conclusion

An individual with incomplete cervical SCI, a history of intermittent AD, and a non-dependent pacemaker can safely participate in a low-intensity FES cycling program, which may result in some clinical benefit. To reduce the risk of complications from AD or electromagnetic interference of the pacemaker, the results support recommendations for vital sign monitoring, physician supervision, ECG recordings during FES cycling sessions, and regular periodic pacemaker interrogation.

Disclaimer statements

Contributors None.

Funding The research reported in this publication was supported by the National Institute of General Medical Sciences of the National Institutes of Health via the Center for Clinical and Translational Research [grant number U54GM115428].

Conflicts of interest Authors have no conflicts of interest to declare.