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Prolonged Electrical Muscle Stimulation Exercise Improves Strength, Peak VO2, and Exercise Capacity in Patients With Stable Chronic Heart Failure
Journal of Cardiac Failure Vol. 15 No. 4 2009
Prolonged Electrical Muscle Stimulation Exercise Improves Strength, Peak VO2, and Exercise Capacity in Patients With Stable Chronic Heart Failure PRITHWISH BANERJEE, MD, DIP CARD, MRCP,1 BRIAN CAULFIELD, B.PHYSIO, M.MED.SCI, PhD,2 LOUIS CROWE, MB, BCh, BAO,3 AND ANDREW L. CLARK, MA, MD, MRCP4 Coventry, United Kingdom; Dublin, Ireland; Galway, Ireland; Kingston-upon-Hull, United Kingdom
ABSTRACT Background: Exercise training can help patients with chronic heart failure but may be limited in its applicability due to age and other comorbidities. This investigation evaluated training responses to prolonged electrical muscle stimulation (EMS) in patients with stable chronic heart failure. Methods and Results: In a crossover designed study, 10 patients (age 66 6 6.5 years, 9 male) were randomized to 8 weeks of training or habitual activity before crossing over to the other limb after a washout period of 2 weeks. Training consisted of electrical muscle stimulation of the major leg muscles for a minimum of 1 hour, 5 days a week. Peak oxygen consumption, 6-minute walking distance test, body mass index, and quadriceps muscle strength were the end points. At baseline the mean values for peak oxygen consumption (VO2), 6-minute walking distance, quadriceps strength, and body mass index were 19.5 6 3.5 mL$kg$min, 415.1 6 56.6m, 377.9 6 110.4N, and 27.9 6 3.1kg/m2, respectively. After training, peak VO2 increased to 21.2 6 5.1 mL$kg$min (P ! .05), walking distance increased to 454.9 6 54.5M (P ! .005), quadriceps strength increased to 404.9 6 108.6N (P ! .005), whereas we did not observe a significant effect on body mass index (P O .05). Conclusions: EMS can be used in sedentary adults with stable chronic heart failure to improve physical fitness and functional capacity. It may provide a viable alternative for patients unable to undertake more conventional forms of exercise. (J Cardiac Fail 2009;15:319e326) Key Words: Cardiovascular exercise, physical fitness, muscle stimulation.
The benefits of exercise training in chronic heart failure (CHF) are well established. Recently published guidelines now recommend a regular program of exercise training for many patients with stable chronic heart failure.1e3 In the Exercise Rehabilitation Trial, 3 months of supervised exercise training in addition to usual care in patients with CHF led to significant increases in 6-minute walk distance (6MWT), peak oxygen consumption (VO2), and muscle
strength of the arms and legs as compared with the control group.4 The improvement in peak VO2 was sustained at 1 year.4 In addition to improving exercise capacity, exercise training in CHF patients improves quality of life in both men and women with moderate CHF.5 Exercise also enhances cardiac output at maximal workloads,6 improves mitochondrial size and density,7 increases skeletal muscle oxidative enzymes, reduces endothelial dysfunction,8 and decreases circulating catecholamines.9 Whether these physiologic adaptations will ultimately reduce mortality and morbidity is yet to be determined by a large prospective trial, although there is at least 1 small trial showing reduction in hospitalizations and improved 1-year survival.10 A recent meta-analysis of 801 CHF patients enrolled into randomized parallel group trials of exercise training also demonstrated evidence of mortality reduction with training.11 Although the majority of previous studies of exercise training in CHF have been hospital based,10,12,13 there are a number of studies confirming the effectiveness of home-based programs.9 Small trials have suggested that electrical muscle stimulation (EMS) can produce improvements in muscle strength and metabolic measures of
From the 1University Hospitals Coventry & Warwickshire, Department of Cardiology, Coventry, UK; 2University College Dublin, School of Physiotherapy & Performance Science, Belfield, Dublin, Ireland; 3Biomedical Research Ltd, Galway, Ireland and 4University of Hull, Department of Academic Cardiology, Castle Hill Hospital, Kingston-upon-Hull, UK. Manuscript received March 12, 2008; revised manuscript received October 28, 2008; revised manuscript accepted November 4, 2008. Reprint requests: Prithwish Banerjee, University Hospitals Coventry & Warwickshire, Department of Cardiology, Clifford Bridge Road, Coventry, UK, CV2 2DX. Tel: þ2476 965670; Fax: þ2476 966056. E-mail: [email protected] Dr. Banerjee’s salary was funded by BioMedical Research Ltd., Galway, Ireland. 1071-9164/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.cardfail.2008.11.005
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320 Journal of Cardiac Failure Vol. 15 No. 4 May 2009 exercise capacity in highly selected patients around the time of cardiac transplantation.14,15 One further small, uncontrolled trial in less symptomatic patients also demonstrated the safety of EMS, and suggested improvements in quality of life and exercise capacity.16 We have previously reported that EMS of the thigh muscles is not only effective in evoking cardiovascular responses,17 with minimal gross movement of the limbs or joints, but is reproducible17 and can also produce training benefits in normal volunteers in home-based programs.18 Research Hypothesis Patients with CHF are usually elderly (of incident cases, around 50% are older than age 8019) and comorbidity that affects the capacity of patients to take part in exercise training is present in the majority of patients.20 The aim of the present study was to assess whether a training effect could be achieved with a home-based program of EMS training in patients with CHF. Our hypothesis was that EMS does provide training benefits similar to exercise training in patients with CHF. Methods Subjects Eighteen patients (9 males, 9 females; age 67 6 9) with stable CHF from left ventricular systolic dysfunction with New York Heart Association Class II-III symptoms were recruited from a community-based heart failure outpatient clinic at Castle Hill Hospital, Kingston-upon-Hull, UK. CHF was defined as the presence of symptoms of breathlessness or fatigue on exertion in the presence of a left ventricular ejection fraction on echocardiography of #35% with no other cause of breathlessness. The condition had to be of at least 3 months’ duration with no exacerbation or change in medication in the preceding 3 months. Patients were on otherwise optimal therapy including b-blockers if tolerated. Patients were excluded from the study if they suffered from insulindependant diabetes mellitus, neurologic or psychiatric disorders, or serious cardiac arrhythmias; were pregnant or lactating, were on drugs that interfered with the neuromuscular system, had a permanent pacemaker in situ, had a recent history of leg trauma, or regularly participated in physical exercise or sport. Atrial tachyarrhythmia was not an exclusion criterion. Experimental Design A crossover study design was used and subjects were randomized to study group A or B. Group A completed an 8-week EMS training program followed by a 2-week washout period, and then an 8-week control period during which they maintained their habitual activity level. Subjects allocated to group B underwent the same interventions in a reversed schedule (ie, habitual activity followed by washout period followed by EMS training). A washout period was chosen to completely eliminate the effect of the first 8-week period of intervention and return to the baseline level before embarking on the second 8-week period of intervention. In all cases, measurements of exercise capacity and muscle strength and body mass index (BMI) were taken at baseline, at 8 weeks, and at 18 weeks. Subjects were not required to wear activity
monitoring devices or complete habitual activity questionnaires during the study period. However, they were questioned regarding their activity levels at each measurement session to ensure that they did not change their habitual activity level at any stage of the study other than participating in EMS training. Measurements Exercise capacity was evaluated in 2 ways. First, subjects completed a Bruce treadmill exercise test, modified by the addition of a ‘‘stage 0’’ at onset consisting of 3 minutes of exercise at 1.61 km/hr (1 mile/h) with a 5% gradient, while cardiopulmonary gas exchange was simultaneously assessed. Subjects wore a tightly fitting face mask to which was connected a capnograph and a sample tube enabling online ventilation and metabolic gas exchange measurements (Jaeger Oxycon Delta system, Wu¨rtzburg, Germany). In all cases in this investigation, the reason for terminating the treadmill test was subject fatigue or limiting breathlessness, but subjects were encouraged to achieve a respiratory exchange ratio of 1.0 if possible. Peak VO2 and test duration were used as indicators of test performance. Peak VO2 was calculated from the average VO2 measurement during the last 30 seconds of the treadmill test at each test session. Second, subjects were assessed using the 6MWT.21 A 15-m flat, obstacle-free corridor, with chairs placed at either end was used. Patients were instructed to walk as far as possible, turning 180 every 15m in the allotted time of 6 minutes. Patients walked unaccompanied so as not to influence walking speed. After 6 minutes, patients were instructed to stop and total distance covered was calculated to the nearest meter. Standardized verbal encouragement was given to patients after 2 minutes and 4 minutes. Isometric muscle strength was assessed using a dynamometer (AFTI Torque/Force Indicator). Subjects sat in a custom-made chair with their hips and knees at 90 . Their right shin was strapped into a cuff and they performed 3 maximal isometric contractions against a fixed resistance, and force generated was measured in newtons. The result was taken as an index of maximal isometric quadriceps strength. Body weight was assessed using the BMI. This was calculated from the subjects’ height (measured with SECA height monitor) and body mass (measured using Soehnle S-20 Scales). BMI is expressed in kg/m2. Echocardiography was performed for detailed assessment of cardiac structure as well as for left ventricular systolic and diastolic function. Two dimensional M-mode and Doppler echocardiography were performed on all subjects. Left ventricular ejection fraction (LVEF) was assessed by M-mode and where required, by Simpson’s technique. We regarded LVEF to be the main measure of overall left ventricular systolic function. Diastolic function was assessed using mitral inflow Doppler. Mitral inflow Doppler parameters included E velocity, A velocity, E/A ratio, deceleration time of the E wave, and isovolumetric relaxation time. Stimulation A specially designed hand-held muscle stimulator (BioMedical Research Ltd, Galway, Ireland) powered by a 9V battery was used to produce EMS training in this investigation. The stimulator current waveform was designed to produce rhythmical contractions in the leg muscle groups occurring at a frequency of 4Hz. The maximum peak output pulse current used was 300 mA. Impulses were delivered through 5 silicon rubber electrodes on each leg (area per leg5600cm2) as illustrated in Fig. 1. These were applied to the
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during this session. Metabolic gas exchange (using open circuit spirometry), heart rate, blood pressure, and electrocardiogram were monitored and recorded during this session. This first supervised session was incorporated to instruct the patient in using the equipment properly and to establish the safety of EMS in the heart failure patients. If they tolerated the session well without any untoward changes in symptoms, heart rate, rhythm, or blood pressure, it was felt that it would be safe to allow them to perform EMS unsupervised at home. Data Analysis
Fig. 1. Location of stimulating electrodes.
body via a pair of tight fitting shorts, which extended to the knee. This array of electrodes produced simultaneous contractions in the quadriceps, hamstrings, gluteal, and calf muscles with electrical contact provided by a lotion. Study Procedure A training schedule and prescription was given to all subjects during the 8-week EMS training phase of the study. Subjects were requested to complete 5 1-hour training sessions per week at times of their own choosing in their own homes. The first and last 10 minutes of training sessions comprised gradual warm-up and cool-down periods. This was achieved by means of gradually increasing or decreasing the output intensity of the stimulator as appropriate. For the remaining 40-minute period, subjects were requested to set the stimulator to their target training intensity defined as 90% of the heart rate (HR) reserve. HR reserve was defined as the difference between a subject’s resting and maximum predicted heart rates. The subjects were told to attempt to increase their heart rates to the maximum possible by gradually increasing the stimulator output to aim to stop just short of crossing the 90% limit of their HR reserve. Subjects were given an individualized training prescription with their own HR limit for exercise and were required to wear HR monitors during each session. In general, all subjects were encouraged to increase the output intensity of the stimulator to at least 40% of the maximum output because our previous studies had demonstrated good levels of cardiovascular responses at this output. It was advised that the training session should be conducted with the subjects in the supine, standing, or sitting positions, but they were not allowed to walk around. There was no change in the prescription of the training protocol over the 8 weeks. Subjects were asked to complete a training log at the end of each session during their training period. An in-house questionnaire to assess satisfaction with the shorts was also handed out to each subject for completion. During the control phase of the study, subjects were asked not to undertake any physical exercise above and beyond their habitual exercise level. Each subject, whether assigned to Group A or B, completed their first stimulation session under the supervision of the investigator in the exercise physiology laboratory. Subjects were supine
Subjects acted as their own control for the purposes of statistical analysis Differences in the measured variables under each of the 3 conditions, baseline, EMS training response, and control response were first compared using repeated measures analysis of variance. Post-hoc paired t-tests were subsequently used to compare differences between baseline and EMS-EX response. The level of significance was set at P ! .05. The relationships between changes in measured variables after EMS training and baseline values were analyzed by means of calculating the Pearson product moment correlation coefficient (r).
Results Out of the 18 subjects recruited to the study, 8 subjects dropped out during the course of the study. We observed no sex or age bias in the subjects who dropped out of the study. The reasons for dropout included worsening of stable heart failure (3 subjects), too large in size to fit into the largest size of shorts (2 subjects), inability to tolerate EMS (2 subjects), and personal reasons (1 subject). Of the 3 that experienced worsening of heart failure, 2 had completed the control phase but not commenced EMS training. The third subject had completed EMS training in the first part of the study and was almost at the end of the control phase when his heart failure worsened. The 10 subjects that completed the study included 9 males and 1 female with a mean age of 66 6 7 years, and a mean LVEF of 34 6 6%. Nine were in NYHA Class II and 1 in NYHA Class III. The average resting heart rate, blood pressure, and BMI at baseline were 63 6 14 beats/ min, 140 6 29/79 6 15mm Hg and 28 6 3kg/m2, respectively. The underlying etiology of the heart failure was ischemic heart disease in 8 subjects and idiopathic dilated cardiomyopathy in 2 patients. All subjects were on optimal treatment for heart failure. Individual baseline information on the 10 subjects is provided in Table 1. Group mean ( 6 SD) values for each of the measured variables representing baseline values and EMS training and control responses are shown in Table 2. Repeated measures analysis of variance testing demonstrated significant treatment effects within subjects, so we carried out post-hoc comparisons between baseline and EMS training values using 2-sided paired t-tests (Table 2). There were no significant differences between values for baseline and control intervention in treadmill walking time, peak VO2, 6MWT, and quadriceps strength (P O .05). EMS produced a significant increase in treadmill walking time, peak VO2, 6MWT, and quads
322 Journal of Cardiac Failure Vol. 15 No. 4 May 2009 Table 1. Individual Data on All 10 Patients Outlining Baseline Characteristics and Medications Patient (n510) 1 2 3 4 5 6 7 8 9 10 Mean
Age (y) 62 71 64 75 73 57 70 58 64 58 66
Sex M M M M M M F M M M
LVEF (%)
NYHA Class
Underlying Etiology
Baseline VO2 (mL/min)
Baseline 6MWT (M)
29.0 45.0 28.0 31.0 38.0 34.0 26.0 33.0 42.0 30.0 34
II III II II II II II II II II
IHD DCM IHD IHD IHD DCM IHD IHD IHD IHD
17.6 14.4 18.7 19.6 23.8 22.2 16.9 22.4 14.2 23.2 19.3
420.0 375.0 442.5 465.0 405.0 510.0 438.8 382.5 300.0 412.5 415.1
ACE
ARB
b-Blocker
Diuretic
Y Y Y N N Y Y Y Y Y
N N N Y Y N N N N N
Y Y Y Y Y Y Y Y Y Y
Y Y Y Y N N N Y N Y
LVEF, left ventricular ejection fraction; NYHA, New York Heart Association; VO2, oxygen consumption; 6MWT, 6-mile walk test; ACE, angiotensinconverting enzyme; ARB, angiotensin receptor blocker; IHD, ischemic heart disease; DCM, dilated cardiomyopathy.
strength compared with both baseline values and the control response (Fig. 2). The increase in peak VO2 after EMS was approximately 10%. The group mean respiratory exchange ratio for peak VO2 at baseline, after EMS training, and after detraining were 1.0, 1.1, and 1.0, respectively, suggesting that patients had completed maximal exercise. There was a small change in BMI with EMS, but this did not achieve statistical significance in comparison with the control. We analyzed the relationship between baseline values for the measured variables and the percent change in these variables after EMS training (Table 3). The strongest relationship observed was that between baseline and percent change in 6MWT (Fig. 3, r50.56, r250.31). There was no change in ventilatory response to exercise induced by training, nor peak heart rate and blood pressure (data not shown). LVEF and diastolic function also did not change (Table 4). Analysis of the log sheets returned by the patients revealed that the mean of maximum stimulation intensity used by them during their EMS sessions was 46.2% (range 32%e81%) of the maximum generator output, with most of the patients using stimulation levels of between 45% and 50% for the majority of the EMS sessions. The average EMS training heart rate reserve was 57% of heart rate-max. Analysis of the in-house questionnaires related to the experience of using the shorts suggested a good level of satisfaction with the product. The overall level of satisfaction
with the shorts, graded on a scale of 10, with a score of 10 meaning most satisfied, was calculated as a mean score of 7.3 (range, 6 to 10). Discussion Many heart failure patients may be unable to pursue conventional physical exercise because of advanced age, associated frailty, and comorbidity. A huge amount of evidence exists, though, that exercise training benefits patients with CHF. Alternative methods of training need to be explored to extend these training benefits to as large a section of the CHF population as possible. We have previously demonstrated that EMS training in healthy volunteers produces cardiovascular responses17 and training benefits.18 Our aim was to investigate whether EMS training would produce training benefits in heart failure patients. Our finding from this study was that sedentary CHF patients can be trained with electrical muscle stimulation of the legs resulting in significant improvements in exercise capacity and muscle strength. This is in agreement with our research hypothesis and completes a set of studies we have undertaken with EMS to establish that it produces cardiovascular effects that are reproducible as well as has training benefits. We found that the worse the exercise capacity at baseline, the more the gain to the patient as evidenced from the changes to 6MWT and quadriceps strength (Fig. 3a,b).
Table 2. Group Mean Scores after EMS Training and Rest Period (n510)
Baseline Values Treadmill walking time (min) Peak VO2 (L/min) 6-minute walkingdistance (M) Quadriceps strength (N) BMI (kg/m2)
9 1.7 415 377.9 27.9
6 6 6 6 6
2 0.4 57 110.4 3.1
EMS Training Response 10.68 1.8 455 404.9 27.5
6 6 6 6 6
3.20 0.4 55 108.6 3.2
Control Response 9.38 1.7 394 363.4 27.7
6 6 6 6 6
Within-Subject Effects Level of Significance
3.24 0.4 48 109.5 3.4
BMI, body mass index; EMS, electrical muscle stimulation; VO2, oxygen consumption. All values are group mean 6 SD. Level of significance calculated using repeated measures analysis of variance F-test (sphericity assumed). Post-hoc comparisons carried out using 2-sided paired t-tests. P 5 0.08 for BMI when EMS training response compared to control response.
P P P P P
! ! ! ! !
.001 0.05 .0001 .005 .05
Post hoc Comparison Baseline versus EMS Response P5.001 P50.03 P5.0001 P5.005 P5.007
Electrical Stimulation Induced Cardiovascular Exercise in Heart Failure
Peak VO2 (L/min)
2.7 2.2 1.7 1.2
6-min Walk Distance (m)
0.7
Baseline Measurement
Post 6-weeks of EMS Training
Post 6-weeks of Habitual Activity
Baseline Measurement
Post 6-weeks of EMS Training
Post 6-weeks of Habitual Activity
Baseline Measurement
Post 6-weeks of EMS Training
Post 6-weeks of Habitual Activity
550 500 450 400 350 300 250
Quad Strength (n)
600 550 500 450 400 350 300 250 200
Fig. 2. Subject responses at baseline and following EMS training and control response. Thin lines represent individual responses and the thick line the group mean response. Graphs are for Peak VO2, 6 min walk test distance and quad strength.
However, this study was a hypothesis generating study, unblinded with a small number of patients and therefore definite conclusions cannot be made from the results. There was a 10% increase in peak VO2 and exercise time on the treadmill after EMS training in this study. This is
Banerjee et al
particularly significant because this was achieved on top of maximal medical therapy for CHF that all patients received. A previous study comparing EMS training with conventional bicycle exercise in CHF patients found no increase in peak VO2 after EMS training,22 but other studies have demonstrated increases in peak VO2 of the order of 9.4% to 13.6%,16,23 similar to findings in our study. In our study, there were also increases in 6-minute walking distance (7.5%) and leg muscle strength (25%), both of potential benefit to an elderly heart failure patient. Similar results have been observed in previous studies using EMS training.14e16,22 EMS training appears to be ideally suited for the heart failure patient not able to pursue a more physical form of exercise with appreciable benefits to functional capacity. It would be fair to speculate that patients with more advanced heart failure may be particularly suitable for EMS, too. There was variability in the responses of the 10 patients that participated in the study but apart from 1 patient that had a reduced peak VO2 and another patient that had reduced quadriceps strength, the post-EMS responses were increased compared with baseline. Both these patients achieved relatively low levels of EMS stimulation intensity. We did not observe any significant changes in BMI in our subjects after EMS training. This is not a surprising result because we did not control for other factors that may influence body weight during our study period, such as food intake. It would be useful to examine the effect of this form of exercise on body weight in future studies carried out over longer periods with good control over other influencing factors. Quadriceps strength increased significantly with EMS training. This increase in efficiency of leg muscles could well have contributed to the increase in VO2 and 6MWT. There was no change in LVEF with EMS training. This is consistent with findings of the study by Maillefert et al16 and in line with the fact that EMS does not affect central hemodynamics in a major way. Left ventricular diastolic function was also not affected by EMS training. Our experience with EMS in the heart failure population suggests that it is safe. During supervised sessions, there were no untoward changes in heart rate or blood pressure and none of the patients demonstrated any cardiac rhythm disturbance. There were no reports of any cardiac symptoms during either the supervised session or the training program at home.
Table 3. Analysis of the Relationship between Baseline Status and % Change after EMS (n510)
Treadmill walking time (min) Peak VO2 (L/min) 6-minute walkingDistance (m) Quadriceps strength (N) BMI (kg/m2)
Relationship Between Baseline Level and % Change after EMS
Group Mean (6SD) % Change Between Baseline and EMS Response
R
P
6 6 6 6 6
0.20 0.28 0.56 0.37 0.35
.001 .03 .0001 .005 .007
22.5 9.3 9.9 7.8 1.9
323
15.2 12.2 5.4 6.6 1.7
BMI, body mass index; EMS, electrical muscle stimulation; VO2, oxygen consumption. Correlation analysis based on calculation of Pearson’s product moment correlation coefficient.
324 Journal of Cardiac Failure Vol. 15 No. 4 May 2009
% increase in 6MWT distance
A
30
20
10
R=0.56 P<0.05 0 250
300
350
400
450
500
550
B
20
% change in quad strength
Baseline 6MWT distance (m)
15 10 5 0 200
250
300
350
400
450
500
550
600
-5 -10
Baseline quadriceps strength (N)
Fig. 3. (A) Relationship between baseline 6MWT distance and % change in distance post stimulation. (B) Relationship between baseline quadriceps strength and % change in strength post stimulation.
Although 8 patients dropped out of the study, the reasons were predominantly related to the performance of the EMS shorts. The 2 patients that could not tolerate EMS complained of a painful sensation during stimulation over the left buttock, which later was discovered to be due to a fault in the electrical connections in those shorts. Two other patients were too big for the maximum available size of the shorts. In the 3 that had worsening of heart failure, EMS training did not appear to be the culprit. One other dropout had personal reasons. The EMS stimulation was generally well tolerated by subjects with a good level of compliance. All the 10
patients that completed the study tolerated the stimulation well. Of the 18 that were recruited, only 2 failed to tolerate the stimulation well, but this was due to a fault in the electrical connections in those shorts, as mentioned. Good levels of stimulation intensities were achieved by the heart failure patients confirming compliance with instructions for training and must have been instrumental in obtaining the final beneficial results after EMS training. However, we relied on self-reported compliance to measure adherence to the training program. This may have resulted in an overstating of the actual frequency of training sessions undertaken by subjects. Shankar and coworkers have reported that selfreported adherence and objectively measured evidence of adherence might vary in up to 50% of subjects.24 The majority of subjects selected a stimulation intensity that was sufficient to produce a heart rate reserve in their training zone. The average EMS training heart rate reserve was 57% of HR-max. This is consistent with the lower end of the training intensity zone recommended by the American College of Sports Medicine (55% to 90% of HR-max).25 Previous work in patients with heart failure has suggested that low-intensity exercise can result in a training effect.13,26 EMS training therefore appears to produce an acceptable heart rate response for training effects as well as a significant overall cardiovascular response evidenced by a rise in peak VO2. The advantages of EMS of the lower limb muscles as a method of training in CHF are that it is home-based, requires less motivation to use and less baseline functional capacity to perform, and could be performed by patients unable to undertake conventional training either due to heart failure itself or comorbidities. No voluntary effort is needed for this form of exercisedthe work is created by means of EMSinduced muscle contractions. The equipment used in our study is particularly attractive because it is robust, compact, user-friendly, and produces a high level of performance. Rapidly advancing technology promises even better quality shorts in the near future with lesser degrees of discomfort during stimulation. However, there is a fair way to go before EMS finds a regular place in the treatment of heart failure, if, as we hope, it will. Further larger trials with EMS on a group of CHF patients that has been shown to be intolerant or not suitable for regular exercise are required to follow-up on the
Table 4. Results of EMS Exercise Training on Echocardiographic Variables Echo Variables(n510) LVDD (cm) LVDS cm LVEF (%) E velocity (m/s) A velocity (m/s) E/A IVRT (ms) DT (ms)
Group Mean (6SD) after EMS training 7.1 5.7 35.3 0.7 0.8 0.8 107.1 298
6 6 6 6 6 6 6 6
7 0.4 3.9 0.2 0.2 0.4 21.6 85
Group Mean (6SD) after Rest
P Value
6 6 6 6 6 6 6 6
0.1131 0.0708 0.0911 0.1711 0.3546 0.1915 0.4359 0.1145
6.8 5.6 36.4 0.7 0.7 1 106.2 248.9
4.4 0.4 3.5 0.2 0.2 0.7 24.6 68.1
EMS, electrical muscle stimulation; LVDD, left ventricular end diastolic dimension; LVDS, left ventricular end systolic dimension; LVEF, left ventricular ejection fraction; E/A; IVRT, isovolumetric contraction time; DT, deceleration time of the E wave.
Electrical Stimulation Induced Cardiovascular Exercise in Heart Failure
exciting preliminary results of this study. It is in these patients that EMS training might find a niche. For the moment, the main potential benefit of EMS would seem to be where conventional exercise is not appropriate. 4.
Limitations
This was a small pilot study of a new training technique for patients with CHF. The small sample size limits our ability to explore the relation between baseline characteristics, intensity of EMS training, and the degree of change in measured variables after training. For these reasons, the findings of the trial cannot as yet be applied in general to the whole population of patients with CHF. Neither the investigators nor the patients were blinded in this study. We did not find a relation between physiologic responses during EMS training, such as heart rate, and the degree of training effect. We cannot rule out the possibility that subjects made errors during monitoring or recording their HR during training so these results should be interpreted with caution. In a previous study, we demonstrated a clear doseresponse relation between stimulation intensity and immediate physiological response (measured using VO2, VCO2, VE, HR) with this form of EMS.17 The relationship between training stimulus intensity and outcome needs further study. This form of exercise is not likely to be suitable for all individuals; some individuals find EMS in general difficult to tolerate. Indeed, 2 subjects in the present study were unable to tolerate the sensation of the EMS. However, most subjects tolerated it well. The dimension and structure of the lower limb muscles was not measured in this investigation.
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Conclusion 13.
We have shown that an 8-week training program using EMS results in an increase in peak VO2 of approximately 10%, increase in 6MWT distance of 7.5%, and increase in quadriceps muscle strength of 25% in sedentary patients with mild to moderate chronic stable heart failure. Improvement in these variables was greater in those patients with greater limitation at baseline. It should be emphasized that these findings are preliminary and based on a small number of patients. Larger trials using EMS training are needed to confirm our findings from this study.
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References 18. 1. Pin˜a IL, Apstein CS, Balady GJ, Belardinelli R, Chaitman BR, Duscha BD, et al. Exercise and heart failure: a statement from the American Heart Association Committee on Exercise, Rehabilitation, and Prevention. Circulation 2003;107:1210e25. 2. Working Group on Cardiac Rehabilitation & Exercise Physiology and Working Group on Heart Failure of the European Society of Cardiology. Recommendations for exercise training in chronic heart failure patients. Eur Heart J 2001;22:125e35. 3. Swedberg K, Cleland J, Dargie H, Drexler H, Follath F, Komajda M, et al. Task Force for the Diagnosis and Treatment of Chronic Heart
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Failure of the European Society of Cardiology. Guidelines for the diagnosis and treatment of chronic heart failure: executive summary (update 2005): The Task Force for the Diagnosis and Treatment of Chronic Heart Failure of the European Society of Cardiology. Eur Heart J 2005;26:1115e40. McKelvie RS, Teo KK, Roberts R, McCartney N, Humen D, Montague T, et al. Effects of exercise training in patients with heart failure: the Exercise Rehabilitation Trial (EXERT). Am Heart J 2002;144:23e30. Tyni-Lenne R, Gordon A, Europe E, Jansson E, Sylven C. Exercisebased rehabilitation improves skeletal muscle capacity, exercise tolerance, and quality of life in both women and men with chronic heart failure. J Card Fail 1998;4:9e17. Cheetham C, Green D, Collis J, Dembo L, O’Driscoll G. Effect of aerobic and resistance exercise on central hemodynamic responses in severe chronic heart failure. J Appl Physiol 2002;93: 175e80. Hambrecht R, Fiehn E, Yu J, Niebauer J, Weigl C, Hilbrich L, et al. Effects of endurance training on mitochondrial ultrastructure and fiber type distribution in skeletal muscle of patients with stable chronic heart failure. J Am Coll Cardiol 1997;29:1067e73. Gielen S, Erbs S, Schuler G, Hambrecht R. Exercise training and endothelial dysfunction in coronary artery disease and chronic heart failure: from molecular biology to clinical benefits. Minerva Cardioangiol 2002;50:95e106. Hambrecht R, Gielen S, Linke A, Fiehn E, Yu J, Walther C, et al. Effects of exercise training on left ventricular function and peripheral resistance in patients with chronic heart failure: a randomized trial. JAMA 2000;283:3095e101. Belardinelli R, Georgiou D, Cianci G, Purcaro A. Randomised, controlled trial of long-term moderate exercise training in chronic heart failure. Effects on functional capacity, quality of life, and clinical outcome. Circulation 1999;99:1173e82. Piepoli MF, Davos C, Francis DP, Coats AJ. ExTraMatch collaborative. Exercise training meta-analysis of trials in patients with chronic heart failure (ExTraMatch). Br Med J 2004;328:189. Wielenga RP, Huisveld IA, Bol E, Dunselman PHJM, Erdman RAM, Baselier MRP, et al. Safety and effects of physical training in chronic heart failure. The results of the Chronic Heart failure and graded Exercise study (CHANGE). Eur Heart J 1999;20:872e9. Belardinelli R, Georgiou D, Scocco V, Barstow TJ, Purcaro A. Low intensity exercise training in patients with chronic heart failure. J Am Coll Cardiol 1995;26:975e82. Quittan M, Wiesinger GF, Sturm B, Puig S, Mayr W, Sochar A, et al. Improvement of thigh muscles by neuromuscular electrical stimulation in patients with refractory heart failure: a single-blind, randomized, controlled trial. Am J Phys Med Rehabil 2001;80:206e14. Vaquero AF, Chicharro JL, Gil L, Ruiz MP, Sanchez V, Lucia A, et al. Effects of muscle electrical stimulation on peak VO2 in cardiac transplant patients. Int J Sports Med 1998;19:317e22. Maillefert JF, Eicher JC, Walker P, Dulieu V, Rouhier-Marcer I, Branyl F, et al. Effects of low-frequency electrical stimulation of quadriceps and calf muscles in patients with chronic heart failure. J Cardiopulm Rehabil 1998;18:277e82. Banerjee P, Clark A, Witte K, Crowe L, Caulfield B. Electrical stimulation of unloaded muscles causes cardiovascular exercise by increasing oxygen demand. Eur J Cardiovasc Prev Rehabil 2005;12:503e8. Banerjee P, Caulfield B, Crowe L, Clark A. Prolonged electrical muscle stimulation exercise improves strength and aerobic capacity in healthy sedentary adults. J Appl Physiol 2005;99:2307e11. Senni M, Tribouilloy CM, Rodeheffer RJ, Jacobsen SJ, Evans JM, Bailey KR, et al. Congestive heart failure in the community: a study of all incident cases in Olmsted County, Minnesota, in 1991. Circulation 1998;98:2282e9. Pinsky JL, Jette AM, Branch LG, Kannel WB, Feinleib M. The Framingham Disability Study: relationship of various coronary heart disease manifestations to disability in older persons living in the community. Am J Public Health 1990;80:1363e7.
326 Journal of Cardiac Failure Vol. 15 No. 4 May 2009 21. Olsson LG, Swedberg K, Clark AL, Witte KK, Cleland JG. Six minute corridor walk test as an outcome measure for the assessment of treatment in randomized, blinded intervention trials of chronic heart failure: a systematic review. Eur Heart J 2005;26:778e93. 22. Harris S, LeMaitre JP, Mackenzie G, Fox KAA, Denvir MA. A randomised study of home-based electrical stimulation of the legs and conventional bicycle exercise training for patients with chronic heart failure. Eur Heart J 2003;24:871e8. 23. Vaquero AF, Chicharro JL, Gil L, Ruiz MP, Sa´ncnez V, Lucı´a A, et al. Effects of muscle electrical stimulation on peak VO2 in cardiac transplant patients. Int J Sports Med 1998;19:317e22.
24. Shankar K, Mihalko-Ward R, Rodell DE, Bucher A, Maloney FP. Methodologic and compliance issues in postcoronary bypass surgery subjects. Arch Phys Med Rehabil 1990;71:1074e7. 25. Pollock ML, Gaesser GA, Butcher JD, Despres JP, Dishman RK, Franklin BA, et al. The recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness and flexibility in healthy adults. Med Sci Sports Exerc 1998;30:975e91. 26. Demopoulos L, Bijou R, Fergus I, Jones M, Strom J, LeJemtel T. Exercise training in patients with severe congestive heart failure: enhancing peak aerobic capacity whilst minimizing the increase in ventricular wall stress. J Am Coll Cardiol 1997;29:597e603.
Prolonged Electrical Muscle Stimulation Exercise Improves Strength, Peak VO2, and Exercise Capacity in Patients With Stable Chronic Heart Failure PRITHWISH BANERJEE, MD, DIP CARD, MRCP,1 BRIAN CAULFIELD, B.PHYSIO, M.MED.SCI, PhD,2 LOUIS CROWE, MB, BCh, BAO,3 AND ANDREW L. CLARK, MA, MD, MRCP4 Coventry, United Kingdom; Dublin, Ireland; Galway, Ireland; Kingston-upon-Hull, United Kingdom
ABSTRACT Background: Exercise training can help patients with chronic heart failure but may be limited in its applicability due to age and other comorbidities. This investigation evaluated training responses to prolonged electrical muscle stimulation (EMS) in patients with stable chronic heart failure. Methods and Results: In a crossover designed study, 10 patients (age 66 6 6.5 years, 9 male) were randomized to 8 weeks of training or habitual activity before crossing over to the other limb after a washout period of 2 weeks. Training consisted of electrical muscle stimulation of the major leg muscles for a minimum of 1 hour, 5 days a week. Peak oxygen consumption, 6-minute walking distance test, body mass index, and quadriceps muscle strength were the end points. At baseline the mean values for peak oxygen consumption (VO2), 6-minute walking distance, quadriceps strength, and body mass index were 19.5 6 3.5 mL$kg$min, 415.1 6 56.6m, 377.9 6 110.4N, and 27.9 6 3.1kg/m2, respectively. After training, peak VO2 increased to 21.2 6 5.1 mL$kg$min (P ! .05), walking distance increased to 454.9 6 54.5M (P ! .005), quadriceps strength increased to 404.9 6 108.6N (P ! .005), whereas we did not observe a significant effect on body mass index (P O .05). Conclusions: EMS can be used in sedentary adults with stable chronic heart failure to improve physical fitness and functional capacity. It may provide a viable alternative for patients unable to undertake more conventional forms of exercise. (J Cardiac Fail 2009;15:319e326) Key Words: Cardiovascular exercise, physical fitness, muscle stimulation.
The benefits of exercise training in chronic heart failure (CHF) are well established. Recently published guidelines now recommend a regular program of exercise training for many patients with stable chronic heart failure.1e3 In the Exercise Rehabilitation Trial, 3 months of supervised exercise training in addition to usual care in patients with CHF led to significant increases in 6-minute walk distance (6MWT), peak oxygen consumption (VO2), and muscle
strength of the arms and legs as compared with the control group.4 The improvement in peak VO2 was sustained at 1 year.4 In addition to improving exercise capacity, exercise training in CHF patients improves quality of life in both men and women with moderate CHF.5 Exercise also enhances cardiac output at maximal workloads,6 improves mitochondrial size and density,7 increases skeletal muscle oxidative enzymes, reduces endothelial dysfunction,8 and decreases circulating catecholamines.9 Whether these physiologic adaptations will ultimately reduce mortality and morbidity is yet to be determined by a large prospective trial, although there is at least 1 small trial showing reduction in hospitalizations and improved 1-year survival.10 A recent meta-analysis of 801 CHF patients enrolled into randomized parallel group trials of exercise training also demonstrated evidence of mortality reduction with training.11 Although the majority of previous studies of exercise training in CHF have been hospital based,10,12,13 there are a number of studies confirming the effectiveness of home-based programs.9 Small trials have suggested that electrical muscle stimulation (EMS) can produce improvements in muscle strength and metabolic measures of
From the 1University Hospitals Coventry & Warwickshire, Department of Cardiology, Coventry, UK; 2University College Dublin, School of Physiotherapy & Performance Science, Belfield, Dublin, Ireland; 3Biomedical Research Ltd, Galway, Ireland and 4University of Hull, Department of Academic Cardiology, Castle Hill Hospital, Kingston-upon-Hull, UK. Manuscript received March 12, 2008; revised manuscript received October 28, 2008; revised manuscript accepted November 4, 2008. Reprint requests: Prithwish Banerjee, University Hospitals Coventry & Warwickshire, Department of Cardiology, Clifford Bridge Road, Coventry, UK, CV2 2DX. Tel: þ2476 965670; Fax: þ2476 966056. E-mail: [email protected] Dr. Banerjee’s salary was funded by BioMedical Research Ltd., Galway, Ireland. 1071-9164/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.cardfail.2008.11.005
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320 Journal of Cardiac Failure Vol. 15 No. 4 May 2009 exercise capacity in highly selected patients around the time of cardiac transplantation.14,15 One further small, uncontrolled trial in less symptomatic patients also demonstrated the safety of EMS, and suggested improvements in quality of life and exercise capacity.16 We have previously reported that EMS of the thigh muscles is not only effective in evoking cardiovascular responses,17 with minimal gross movement of the limbs or joints, but is reproducible17 and can also produce training benefits in normal volunteers in home-based programs.18 Research Hypothesis Patients with CHF are usually elderly (of incident cases, around 50% are older than age 8019) and comorbidity that affects the capacity of patients to take part in exercise training is present in the majority of patients.20 The aim of the present study was to assess whether a training effect could be achieved with a home-based program of EMS training in patients with CHF. Our hypothesis was that EMS does provide training benefits similar to exercise training in patients with CHF. Methods Subjects Eighteen patients (9 males, 9 females; age 67 6 9) with stable CHF from left ventricular systolic dysfunction with New York Heart Association Class II-III symptoms were recruited from a community-based heart failure outpatient clinic at Castle Hill Hospital, Kingston-upon-Hull, UK. CHF was defined as the presence of symptoms of breathlessness or fatigue on exertion in the presence of a left ventricular ejection fraction on echocardiography of #35% with no other cause of breathlessness. The condition had to be of at least 3 months’ duration with no exacerbation or change in medication in the preceding 3 months. Patients were on otherwise optimal therapy including b-blockers if tolerated. Patients were excluded from the study if they suffered from insulindependant diabetes mellitus, neurologic or psychiatric disorders, or serious cardiac arrhythmias; were pregnant or lactating, were on drugs that interfered with the neuromuscular system, had a permanent pacemaker in situ, had a recent history of leg trauma, or regularly participated in physical exercise or sport. Atrial tachyarrhythmia was not an exclusion criterion. Experimental Design A crossover study design was used and subjects were randomized to study group A or B. Group A completed an 8-week EMS training program followed by a 2-week washout period, and then an 8-week control period during which they maintained their habitual activity level. Subjects allocated to group B underwent the same interventions in a reversed schedule (ie, habitual activity followed by washout period followed by EMS training). A washout period was chosen to completely eliminate the effect of the first 8-week period of intervention and return to the baseline level before embarking on the second 8-week period of intervention. In all cases, measurements of exercise capacity and muscle strength and body mass index (BMI) were taken at baseline, at 8 weeks, and at 18 weeks. Subjects were not required to wear activity
monitoring devices or complete habitual activity questionnaires during the study period. However, they were questioned regarding their activity levels at each measurement session to ensure that they did not change their habitual activity level at any stage of the study other than participating in EMS training. Measurements Exercise capacity was evaluated in 2 ways. First, subjects completed a Bruce treadmill exercise test, modified by the addition of a ‘‘stage 0’’ at onset consisting of 3 minutes of exercise at 1.61 km/hr (1 mile/h) with a 5% gradient, while cardiopulmonary gas exchange was simultaneously assessed. Subjects wore a tightly fitting face mask to which was connected a capnograph and a sample tube enabling online ventilation and metabolic gas exchange measurements (Jaeger Oxycon Delta system, Wu¨rtzburg, Germany). In all cases in this investigation, the reason for terminating the treadmill test was subject fatigue or limiting breathlessness, but subjects were encouraged to achieve a respiratory exchange ratio of 1.0 if possible. Peak VO2 and test duration were used as indicators of test performance. Peak VO2 was calculated from the average VO2 measurement during the last 30 seconds of the treadmill test at each test session. Second, subjects were assessed using the 6MWT.21 A 15-m flat, obstacle-free corridor, with chairs placed at either end was used. Patients were instructed to walk as far as possible, turning 180 every 15m in the allotted time of 6 minutes. Patients walked unaccompanied so as not to influence walking speed. After 6 minutes, patients were instructed to stop and total distance covered was calculated to the nearest meter. Standardized verbal encouragement was given to patients after 2 minutes and 4 minutes. Isometric muscle strength was assessed using a dynamometer (AFTI Torque/Force Indicator). Subjects sat in a custom-made chair with their hips and knees at 90 . Their right shin was strapped into a cuff and they performed 3 maximal isometric contractions against a fixed resistance, and force generated was measured in newtons. The result was taken as an index of maximal isometric quadriceps strength. Body weight was assessed using the BMI. This was calculated from the subjects’ height (measured with SECA height monitor) and body mass (measured using Soehnle S-20 Scales). BMI is expressed in kg/m2. Echocardiography was performed for detailed assessment of cardiac structure as well as for left ventricular systolic and diastolic function. Two dimensional M-mode and Doppler echocardiography were performed on all subjects. Left ventricular ejection fraction (LVEF) was assessed by M-mode and where required, by Simpson’s technique. We regarded LVEF to be the main measure of overall left ventricular systolic function. Diastolic function was assessed using mitral inflow Doppler. Mitral inflow Doppler parameters included E velocity, A velocity, E/A ratio, deceleration time of the E wave, and isovolumetric relaxation time. Stimulation A specially designed hand-held muscle stimulator (BioMedical Research Ltd, Galway, Ireland) powered by a 9V battery was used to produce EMS training in this investigation. The stimulator current waveform was designed to produce rhythmical contractions in the leg muscle groups occurring at a frequency of 4Hz. The maximum peak output pulse current used was 300 mA. Impulses were delivered through 5 silicon rubber electrodes on each leg (area per leg5600cm2) as illustrated in Fig. 1. These were applied to the
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during this session. Metabolic gas exchange (using open circuit spirometry), heart rate, blood pressure, and electrocardiogram were monitored and recorded during this session. This first supervised session was incorporated to instruct the patient in using the equipment properly and to establish the safety of EMS in the heart failure patients. If they tolerated the session well without any untoward changes in symptoms, heart rate, rhythm, or blood pressure, it was felt that it would be safe to allow them to perform EMS unsupervised at home. Data Analysis
Fig. 1. Location of stimulating electrodes.
body via a pair of tight fitting shorts, which extended to the knee. This array of electrodes produced simultaneous contractions in the quadriceps, hamstrings, gluteal, and calf muscles with electrical contact provided by a lotion. Study Procedure A training schedule and prescription was given to all subjects during the 8-week EMS training phase of the study. Subjects were requested to complete 5 1-hour training sessions per week at times of their own choosing in their own homes. The first and last 10 minutes of training sessions comprised gradual warm-up and cool-down periods. This was achieved by means of gradually increasing or decreasing the output intensity of the stimulator as appropriate. For the remaining 40-minute period, subjects were requested to set the stimulator to their target training intensity defined as 90% of the heart rate (HR) reserve. HR reserve was defined as the difference between a subject’s resting and maximum predicted heart rates. The subjects were told to attempt to increase their heart rates to the maximum possible by gradually increasing the stimulator output to aim to stop just short of crossing the 90% limit of their HR reserve. Subjects were given an individualized training prescription with their own HR limit for exercise and were required to wear HR monitors during each session. In general, all subjects were encouraged to increase the output intensity of the stimulator to at least 40% of the maximum output because our previous studies had demonstrated good levels of cardiovascular responses at this output. It was advised that the training session should be conducted with the subjects in the supine, standing, or sitting positions, but they were not allowed to walk around. There was no change in the prescription of the training protocol over the 8 weeks. Subjects were asked to complete a training log at the end of each session during their training period. An in-house questionnaire to assess satisfaction with the shorts was also handed out to each subject for completion. During the control phase of the study, subjects were asked not to undertake any physical exercise above and beyond their habitual exercise level. Each subject, whether assigned to Group A or B, completed their first stimulation session under the supervision of the investigator in the exercise physiology laboratory. Subjects were supine
Subjects acted as their own control for the purposes of statistical analysis Differences in the measured variables under each of the 3 conditions, baseline, EMS training response, and control response were first compared using repeated measures analysis of variance. Post-hoc paired t-tests were subsequently used to compare differences between baseline and EMS-EX response. The level of significance was set at P ! .05. The relationships between changes in measured variables after EMS training and baseline values were analyzed by means of calculating the Pearson product moment correlation coefficient (r).
Results Out of the 18 subjects recruited to the study, 8 subjects dropped out during the course of the study. We observed no sex or age bias in the subjects who dropped out of the study. The reasons for dropout included worsening of stable heart failure (3 subjects), too large in size to fit into the largest size of shorts (2 subjects), inability to tolerate EMS (2 subjects), and personal reasons (1 subject). Of the 3 that experienced worsening of heart failure, 2 had completed the control phase but not commenced EMS training. The third subject had completed EMS training in the first part of the study and was almost at the end of the control phase when his heart failure worsened. The 10 subjects that completed the study included 9 males and 1 female with a mean age of 66 6 7 years, and a mean LVEF of 34 6 6%. Nine were in NYHA Class II and 1 in NYHA Class III. The average resting heart rate, blood pressure, and BMI at baseline were 63 6 14 beats/ min, 140 6 29/79 6 15mm Hg and 28 6 3kg/m2, respectively. The underlying etiology of the heart failure was ischemic heart disease in 8 subjects and idiopathic dilated cardiomyopathy in 2 patients. All subjects were on optimal treatment for heart failure. Individual baseline information on the 10 subjects is provided in Table 1. Group mean ( 6 SD) values for each of the measured variables representing baseline values and EMS training and control responses are shown in Table 2. Repeated measures analysis of variance testing demonstrated significant treatment effects within subjects, so we carried out post-hoc comparisons between baseline and EMS training values using 2-sided paired t-tests (Table 2). There were no significant differences between values for baseline and control intervention in treadmill walking time, peak VO2, 6MWT, and quadriceps strength (P O .05). EMS produced a significant increase in treadmill walking time, peak VO2, 6MWT, and quads
322 Journal of Cardiac Failure Vol. 15 No. 4 May 2009 Table 1. Individual Data on All 10 Patients Outlining Baseline Characteristics and Medications Patient (n510) 1 2 3 4 5 6 7 8 9 10 Mean
Age (y) 62 71 64 75 73 57 70 58 64 58 66
Sex M M M M M M F M M M
LVEF (%)
NYHA Class
Underlying Etiology
Baseline VO2 (mL/min)
Baseline 6MWT (M)
29.0 45.0 28.0 31.0 38.0 34.0 26.0 33.0 42.0 30.0 34
II III II II II II II II II II
IHD DCM IHD IHD IHD DCM IHD IHD IHD IHD
17.6 14.4 18.7 19.6 23.8 22.2 16.9 22.4 14.2 23.2 19.3
420.0 375.0 442.5 465.0 405.0 510.0 438.8 382.5 300.0 412.5 415.1
ACE
ARB
b-Blocker
Diuretic
Y Y Y N N Y Y Y Y Y
N N N Y Y N N N N N
Y Y Y Y Y Y Y Y Y Y
Y Y Y Y N N N Y N Y
LVEF, left ventricular ejection fraction; NYHA, New York Heart Association; VO2, oxygen consumption; 6MWT, 6-mile walk test; ACE, angiotensinconverting enzyme; ARB, angiotensin receptor blocker; IHD, ischemic heart disease; DCM, dilated cardiomyopathy.
strength compared with both baseline values and the control response (Fig. 2). The increase in peak VO2 after EMS was approximately 10%. The group mean respiratory exchange ratio for peak VO2 at baseline, after EMS training, and after detraining were 1.0, 1.1, and 1.0, respectively, suggesting that patients had completed maximal exercise. There was a small change in BMI with EMS, but this did not achieve statistical significance in comparison with the control. We analyzed the relationship between baseline values for the measured variables and the percent change in these variables after EMS training (Table 3). The strongest relationship observed was that between baseline and percent change in 6MWT (Fig. 3, r50.56, r250.31). There was no change in ventilatory response to exercise induced by training, nor peak heart rate and blood pressure (data not shown). LVEF and diastolic function also did not change (Table 4). Analysis of the log sheets returned by the patients revealed that the mean of maximum stimulation intensity used by them during their EMS sessions was 46.2% (range 32%e81%) of the maximum generator output, with most of the patients using stimulation levels of between 45% and 50% for the majority of the EMS sessions. The average EMS training heart rate reserve was 57% of heart rate-max. Analysis of the in-house questionnaires related to the experience of using the shorts suggested a good level of satisfaction with the product. The overall level of satisfaction
with the shorts, graded on a scale of 10, with a score of 10 meaning most satisfied, was calculated as a mean score of 7.3 (range, 6 to 10). Discussion Many heart failure patients may be unable to pursue conventional physical exercise because of advanced age, associated frailty, and comorbidity. A huge amount of evidence exists, though, that exercise training benefits patients with CHF. Alternative methods of training need to be explored to extend these training benefits to as large a section of the CHF population as possible. We have previously demonstrated that EMS training in healthy volunteers produces cardiovascular responses17 and training benefits.18 Our aim was to investigate whether EMS training would produce training benefits in heart failure patients. Our finding from this study was that sedentary CHF patients can be trained with electrical muscle stimulation of the legs resulting in significant improvements in exercise capacity and muscle strength. This is in agreement with our research hypothesis and completes a set of studies we have undertaken with EMS to establish that it produces cardiovascular effects that are reproducible as well as has training benefits. We found that the worse the exercise capacity at baseline, the more the gain to the patient as evidenced from the changes to 6MWT and quadriceps strength (Fig. 3a,b).
Table 2. Group Mean Scores after EMS Training and Rest Period (n510)
Baseline Values Treadmill walking time (min) Peak VO2 (L/min) 6-minute walkingdistance (M) Quadriceps strength (N) BMI (kg/m2)
9 1.7 415 377.9 27.9
6 6 6 6 6
2 0.4 57 110.4 3.1
EMS Training Response 10.68 1.8 455 404.9 27.5
6 6 6 6 6
3.20 0.4 55 108.6 3.2
Control Response 9.38 1.7 394 363.4 27.7
6 6 6 6 6
Within-Subject Effects Level of Significance
3.24 0.4 48 109.5 3.4
BMI, body mass index; EMS, electrical muscle stimulation; VO2, oxygen consumption. All values are group mean 6 SD. Level of significance calculated using repeated measures analysis of variance F-test (sphericity assumed). Post-hoc comparisons carried out using 2-sided paired t-tests. P 5 0.08 for BMI when EMS training response compared to control response.
P P P P P
! ! ! ! !
.001 0.05 .0001 .005 .05
Post hoc Comparison Baseline versus EMS Response P5.001 P50.03 P5.0001 P5.005 P5.007
Electrical Stimulation Induced Cardiovascular Exercise in Heart Failure
Peak VO2 (L/min)
2.7 2.2 1.7 1.2
6-min Walk Distance (m)
0.7
Baseline Measurement
Post 6-weeks of EMS Training
Post 6-weeks of Habitual Activity
Baseline Measurement
Post 6-weeks of EMS Training
Post 6-weeks of Habitual Activity
Baseline Measurement
Post 6-weeks of EMS Training
Post 6-weeks of Habitual Activity
550 500 450 400 350 300 250
Quad Strength (n)
600 550 500 450 400 350 300 250 200
Fig. 2. Subject responses at baseline and following EMS training and control response. Thin lines represent individual responses and the thick line the group mean response. Graphs are for Peak VO2, 6 min walk test distance and quad strength.
However, this study was a hypothesis generating study, unblinded with a small number of patients and therefore definite conclusions cannot be made from the results. There was a 10% increase in peak VO2 and exercise time on the treadmill after EMS training in this study. This is
Banerjee et al
particularly significant because this was achieved on top of maximal medical therapy for CHF that all patients received. A previous study comparing EMS training with conventional bicycle exercise in CHF patients found no increase in peak VO2 after EMS training,22 but other studies have demonstrated increases in peak VO2 of the order of 9.4% to 13.6%,16,23 similar to findings in our study. In our study, there were also increases in 6-minute walking distance (7.5%) and leg muscle strength (25%), both of potential benefit to an elderly heart failure patient. Similar results have been observed in previous studies using EMS training.14e16,22 EMS training appears to be ideally suited for the heart failure patient not able to pursue a more physical form of exercise with appreciable benefits to functional capacity. It would be fair to speculate that patients with more advanced heart failure may be particularly suitable for EMS, too. There was variability in the responses of the 10 patients that participated in the study but apart from 1 patient that had a reduced peak VO2 and another patient that had reduced quadriceps strength, the post-EMS responses were increased compared with baseline. Both these patients achieved relatively low levels of EMS stimulation intensity. We did not observe any significant changes in BMI in our subjects after EMS training. This is not a surprising result because we did not control for other factors that may influence body weight during our study period, such as food intake. It would be useful to examine the effect of this form of exercise on body weight in future studies carried out over longer periods with good control over other influencing factors. Quadriceps strength increased significantly with EMS training. This increase in efficiency of leg muscles could well have contributed to the increase in VO2 and 6MWT. There was no change in LVEF with EMS training. This is consistent with findings of the study by Maillefert et al16 and in line with the fact that EMS does not affect central hemodynamics in a major way. Left ventricular diastolic function was also not affected by EMS training. Our experience with EMS in the heart failure population suggests that it is safe. During supervised sessions, there were no untoward changes in heart rate or blood pressure and none of the patients demonstrated any cardiac rhythm disturbance. There were no reports of any cardiac symptoms during either the supervised session or the training program at home.
Table 3. Analysis of the Relationship between Baseline Status and % Change after EMS (n510)
Treadmill walking time (min) Peak VO2 (L/min) 6-minute walkingDistance (m) Quadriceps strength (N) BMI (kg/m2)
Relationship Between Baseline Level and % Change after EMS
Group Mean (6SD) % Change Between Baseline and EMS Response
R
P
6 6 6 6 6
0.20 0.28 0.56 0.37 0.35
.001 .03 .0001 .005 .007
22.5 9.3 9.9 7.8 1.9
323
15.2 12.2 5.4 6.6 1.7
BMI, body mass index; EMS, electrical muscle stimulation; VO2, oxygen consumption. Correlation analysis based on calculation of Pearson’s product moment correlation coefficient.
324 Journal of Cardiac Failure Vol. 15 No. 4 May 2009
% increase in 6MWT distance
A
30
20
10
R=0.56 P<0.05 0 250
300
350
400
450
500
550
B
20
% change in quad strength
Baseline 6MWT distance (m)
15 10 5 0 200
250
300
350
400
450
500
550
600
-5 -10
Baseline quadriceps strength (N)
Fig. 3. (A) Relationship between baseline 6MWT distance and % change in distance post stimulation. (B) Relationship between baseline quadriceps strength and % change in strength post stimulation.
Although 8 patients dropped out of the study, the reasons were predominantly related to the performance of the EMS shorts. The 2 patients that could not tolerate EMS complained of a painful sensation during stimulation over the left buttock, which later was discovered to be due to a fault in the electrical connections in those shorts. Two other patients were too big for the maximum available size of the shorts. In the 3 that had worsening of heart failure, EMS training did not appear to be the culprit. One other dropout had personal reasons. The EMS stimulation was generally well tolerated by subjects with a good level of compliance. All the 10
patients that completed the study tolerated the stimulation well. Of the 18 that were recruited, only 2 failed to tolerate the stimulation well, but this was due to a fault in the electrical connections in those shorts, as mentioned. Good levels of stimulation intensities were achieved by the heart failure patients confirming compliance with instructions for training and must have been instrumental in obtaining the final beneficial results after EMS training. However, we relied on self-reported compliance to measure adherence to the training program. This may have resulted in an overstating of the actual frequency of training sessions undertaken by subjects. Shankar and coworkers have reported that selfreported adherence and objectively measured evidence of adherence might vary in up to 50% of subjects.24 The majority of subjects selected a stimulation intensity that was sufficient to produce a heart rate reserve in their training zone. The average EMS training heart rate reserve was 57% of HR-max. This is consistent with the lower end of the training intensity zone recommended by the American College of Sports Medicine (55% to 90% of HR-max).25 Previous work in patients with heart failure has suggested that low-intensity exercise can result in a training effect.13,26 EMS training therefore appears to produce an acceptable heart rate response for training effects as well as a significant overall cardiovascular response evidenced by a rise in peak VO2. The advantages of EMS of the lower limb muscles as a method of training in CHF are that it is home-based, requires less motivation to use and less baseline functional capacity to perform, and could be performed by patients unable to undertake conventional training either due to heart failure itself or comorbidities. No voluntary effort is needed for this form of exercisedthe work is created by means of EMSinduced muscle contractions. The equipment used in our study is particularly attractive because it is robust, compact, user-friendly, and produces a high level of performance. Rapidly advancing technology promises even better quality shorts in the near future with lesser degrees of discomfort during stimulation. However, there is a fair way to go before EMS finds a regular place in the treatment of heart failure, if, as we hope, it will. Further larger trials with EMS on a group of CHF patients that has been shown to be intolerant or not suitable for regular exercise are required to follow-up on the
Table 4. Results of EMS Exercise Training on Echocardiographic Variables Echo Variables(n510) LVDD (cm) LVDS cm LVEF (%) E velocity (m/s) A velocity (m/s) E/A IVRT (ms) DT (ms)
Group Mean (6SD) after EMS training 7.1 5.7 35.3 0.7 0.8 0.8 107.1 298
6 6 6 6 6 6 6 6
7 0.4 3.9 0.2 0.2 0.4 21.6 85
Group Mean (6SD) after Rest
P Value
6 6 6 6 6 6 6 6
0.1131 0.0708 0.0911 0.1711 0.3546 0.1915 0.4359 0.1145
6.8 5.6 36.4 0.7 0.7 1 106.2 248.9
4.4 0.4 3.5 0.2 0.2 0.7 24.6 68.1
EMS, electrical muscle stimulation; LVDD, left ventricular end diastolic dimension; LVDS, left ventricular end systolic dimension; LVEF, left ventricular ejection fraction; E/A; IVRT, isovolumetric contraction time; DT, deceleration time of the E wave.
Electrical Stimulation Induced Cardiovascular Exercise in Heart Failure
exciting preliminary results of this study. It is in these patients that EMS training might find a niche. For the moment, the main potential benefit of EMS would seem to be where conventional exercise is not appropriate. 4.
Limitations
This was a small pilot study of a new training technique for patients with CHF. The small sample size limits our ability to explore the relation between baseline characteristics, intensity of EMS training, and the degree of change in measured variables after training. For these reasons, the findings of the trial cannot as yet be applied in general to the whole population of patients with CHF. Neither the investigators nor the patients were blinded in this study. We did not find a relation between physiologic responses during EMS training, such as heart rate, and the degree of training effect. We cannot rule out the possibility that subjects made errors during monitoring or recording their HR during training so these results should be interpreted with caution. In a previous study, we demonstrated a clear doseresponse relation between stimulation intensity and immediate physiological response (measured using VO2, VCO2, VE, HR) with this form of EMS.17 The relationship between training stimulus intensity and outcome needs further study. This form of exercise is not likely to be suitable for all individuals; some individuals find EMS in general difficult to tolerate. Indeed, 2 subjects in the present study were unable to tolerate the sensation of the EMS. However, most subjects tolerated it well. The dimension and structure of the lower limb muscles was not measured in this investigation.
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Conclusion 13.
We have shown that an 8-week training program using EMS results in an increase in peak VO2 of approximately 10%, increase in 6MWT distance of 7.5%, and increase in quadriceps muscle strength of 25% in sedentary patients with mild to moderate chronic stable heart failure. Improvement in these variables was greater in those patients with greater limitation at baseline. It should be emphasized that these findings are preliminary and based on a small number of patients. Larger trials using EMS training are needed to confirm our findings from this study.
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