a Cardiovascular Rehabilitation Unit, Department of Rehabilitation Sciences, Faculty of Physical Education and Physical Therapy, K.U. Leuven (University of Leuven), Belgium
b Hypertension and Cardiovascular Rehabilitation Unit, Department of Molecular and Cardiovascular Research, Faculty of Medicine, K.U. Leuven, Belgium
c Cardiology Unit, Department of Molecular and Cardiovascular Research, Faculty of Medicine, K.U. Leuven, Belgium
d Faculty Chair Health and Lifestyle, Faculty of Health Care, University of Professional Education, Utrecht, The Netherlands
e Department of Cardiovascular and Respiratory Rehabilitation, Rijnlands Rehabilitation Center, Leiden, The Netherlands
Received October 6, 2003;
accepted April 5, 2004
* Corresponding author. Present address: Cardiovasculaire Revalidatie, U.Z. Leuven, Herestraat 49, B-3000 Lueven, Belgium. Tel.: +32-16-348-707; fax: +32-16-343-766
E-mail address: Luc.Vanhees{at}uz.kuleuven.ac.be
This paper was guest edited by Prof. H. Saner, Inselspital, Bern, Switzerland
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Abstract |
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Methods and results 92 ICD patients were compared with a control group of 473 patients. A maximal cycle-spiroergometric test was performed until exhaustion before and after an ambulatory exercise training programme. Exercise training was offered 3 times a week for 3 months. The cut-off heart rate was set at (ICD detection rate 20 beats/min). At baseline, the ICD patients had a lower peak oxygen uptake (VO2) compared to the control group. Training effects were smaller for peak VO2 (mL/min/kg) and oxygen pulse in the ICD group (18 vs. 27%, and 11 vs. 17%,
, respectively). Several appropriate shocks were delivered during (
), and in between (
), testing or training and one inappropriate shock during training.
Conclusions ICD patients can safely participate in an exercise training programme with favorable results. A randomised control study with evaluation of the physical and the psychosocial effects is warranted.
Key Words: Exercise testing Exercise training Oxygen consumption Arrhythmia
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Introduction |
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The beneficial effects of cardiac rehabilitation in terms of secondary prevention and on physiological and psychosocial functioning of cardiac patients in general are well-established.5 Some recommendations are available for exercise testing and training in cardiac patients with ICD68 or in patients at risk for malignant ventricular arrhythmias.911 Nevertheless, very few studies have reported on the safety and feasibility of exercise training and on the effects of physical training in patients with ICD.1214
Friedman et al.13 described two cases of patients with ICD, who were included in a cardiac rehabilitation programme in 1996. The first clinical study was published in 2001 and compared exercise performance and the effect of physical training in ICD patients () with a matched cardiac control group (
).14 Finally, a very recent paper reported on the effects of a comprehensive cardiac rehabilitation programme in comparison to usual care in 11 patients with ICD.12 The preliminary results from these small studies indicated that exercise testing and training was feasible and safe in patients with ICD and that physical training increased their exercise performance. These studies, however, were performed in a very limited number of patients and it was generally acknowledged that the results needed confirmation from a larger cohort of patients.
The aim of the present study is to test, in a larger sample, the hypothesis that exercise training in ICD patients could lead to similar benefits as in other cardiac patients. Exercise performance and the effect of a 3-month exercise training programme were compared in a large group of patients with and without ICDs.
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Methods |
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Implantable Cardioverter Defibrillators
All ICDs were third or fourth generation tiered therapy devices, capable of delivering shock therapy in a "VF zone" and of anti-tachycardia pacing and shock therapy in 1 or 2 ventricular tachycardia "VT-zones". The ICDs were single-chamber, dual-chamber or three-chamber (bi-ventricular) devices and were capable of storing electrocardiograms during events.
Exercise testing
The maximal exercise tests on the bicycle ergometer (Ergometrics 800S®, Ergometrics, Bitz, Germany) were performed in a laboratory where room temperature was stabilised at 1822 °C. The initial workload of 20 W (Leuven) or 5 W (Leiden) was increased by 20 W every minute until exhaustion or until reaching a heart rate threshold in the ICD group. This threshold was set at the detection rate of the lowest zone in which therapies were programmed minus 20 beats/min.
Systolic and diastolic blood pressure were measured every 3 min (STBP-780®, Colin, Komaki, Japan or Bosotron 2®, Bosch and Sohn, Germany). Heart rate, a 12-lead electrocardiogram (Max Personal Exercise Testing®, Marquette, Wisconsin, USA or Jaeger Stress Test System, Mijnhardt, Bunnik, The Netherlands) and respiratory data (STPD: "standard temperature pressure dry" conditions of the gas) through breath-by-breath analysis (Oxycon Alpha® or Oxycon Pro®, Jaeger, Mijnhardt, Bunnik, The Netherlands) were registered continuously. Pulmonary ventilation was measured by means of a turbine flow meter. The gas analysers and the flow meter were calibrated before each test according to the manufacturer's instructions. Oxygen uptake (VO2) and carbon dioxide output (VCO2) were determined from the continuous measurement of oxygen and carbon dioxide concentration in the inspired and expired air. The respiratory gas exchange ratio (carbon dioxide output/oxygen uptake; RER), ventilatory equivalent for oxygen (pulmonary ventilation/oxygen uptake) and oxygen pulse (oxygen uptake/heart rate) were calculated.
Exercise training
In both locations an ambulatory supervised exercise training programme was offered for a period of 3 months with a recommended frequency of 3 times a week. Each session of 90 min consisted of cycling, running, arm ergometry, rowing, callisthenics, strength training and relaxation. In Leuven, the exercise intensity was individually determined for each patient by calculating an interval for training heart rate, using the formula of Karvonen: resting heart rate+6090%(peak heart rateresting heart rate). In Leiden, exercise intensity was set at 5080% of maximal intensity. When no inappropriate arrhythmias or cardiac events occurred after 6 weeks in Leiden, outdoor activities such as walking and jogging, strength endurance training and recreational sports were added to the training programme. ICD patients were limited by a maximal heart rate during training (ICD detection rate minus 20 beats/min). All patients were offered 45 informative modules in which information was given by the cardiologist, psychologist, social workers, dietician and physiotherapist.
Statistical methods
Data were analysed by using SAS statistical software version 8.0 for windows (Sas Institute Inc, Cary, NC, USA). Data are reported as means±SD or as number of patients and frequency rate for dichotomous variables. Comparisons were made by means of paired and unpaired Student's t tests or by the Wilcoxon signed rank test. Categorical data were tested by or by Fisher's exact test where appropriate. Regression analyses were performed on the study cohort of 1942 patients to determine whether ICD was associated with exercise performance or with its change after training. First, the unadjusted association between ICD and the dependent variables, peak VO2, absolute and relative change in peak VO2 (respectively) after training was determined. Second, multiple regression analyses were performed to adjust the influence of ICD for other determinants of the dependent variables, which had been identified by means of a stepwise selection procedure. The following list of independent variables were included in this procedure: age, body mass index, gender, underlying heart disease and interventions, family history of heart disease, hypertension, previous and current smoking habits, dyspnoea, angina pectoris, systolic and diastolic blood pressure at rest, resting heart rate, peak heart rate, ST depression during exercise testing, arrhythmia, training intensity and frequency and having a cardioverter defibrillator implantation. The significance level was 12.5% for inclusion and 5% for exclusion from the stepwise building procedure. All statistical tests were two-sided at a significance level of 5%.
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Results |
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Absolute training-induced changes are illustrated in Table 3, relative changes in Fig. 1. Both the ICD and control group significantly increased VO2, oxygen pulse and heart rate at peak exercise (). At three months peak VO2 (1684±587 vs. 2113±549 mL/min or 20.5±6.4 vs. 27.8±6.9 mL/min/kg) and peak oxygen pulse (13.3±4.4 vs. 15.4±3.5 mL/beat) remained lower in patients with ICD (
). ICD patients made smaller absolute improvements in aerobic power compared with controls (
). Relative improvements of peak VO2 (mL/min/kg) and oxygen pulse were also smaller in patients with ICD (
and
, respectively). Relative changes in peak VO2 (mL/min) were not significantly different between groups. Body weight in ICD patients was, however, increased over three months by 2.2±3.5 kg (
), in contrast to controls (
) who decreased weight by 0.4±3.3 kg (
). There were no differences between ICD and control group in training-induced changes in systolic blood pressure or in resting and peak heart rate. Heart rate at a submaximal workload (80 W) was decreased more in controls.
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Events
Three ICD patients did not finish the rehabilitation programme after receiving appropriate shocks for ventricular tachycardia during exercise and one patient, did not finish the programme after experiencing multiple shocks some days following exercise training. From the remaining 92 patients, one patient with an ICD developed ventricular tachycardia during exercise testing without defibrillator shock intervention of the device and without adverse clinical manifestations but requiring over-pacing. Another ICD patient experienced asymptomatic ventricular tachycardia at 170 beats/min during training, with intervention of the device. During training one patient received an inappropriate shock requiring no further treatment. Between training sessions, the ICD delivered appropriate therapy shocks after ventricular tachycardia in 6 cases. No inappropriate treatments were delivered outside the training sessions.
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Discussion |
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Exercise performance at baseline was lower in ICD patients, which could possibly be related to the higher incidence of a decreased LVEF in this group. From multiple regression analysis in the total database, ICD implantation was confirmed to be an independent determinant of aerobic power in cardiac patients. The respiratory exchange ratio at peak exercise indicates both groups achieved similar levels of exhaustion. The lower heart rates during exercise in ICD patients in this study are not due to differences in the intake of drugs with negative chronotropic properties.
Psychosocial well-being is an important aspect to consider when working with ICD patients, and could not be assessed in this study. The incidence of anxiety in this patient population is high, with approximately 2487% of the patients experiencing increased symptoms of anxiety. The diagnostic rates for clinically significant anxiety disorders range from 13% to 38%.15 It has been established that in patients with an ICD, fear of exercise is increased because of their concern for ICD discharges, which thus causes them to limit their everyday activities.16 One report introduced the idea of "catastrophic cognitions", meaning that patients with high anxiety scores tend to interpret physical symptoms as signs of danger.17 As physical activity causes a lot of physical sensations, it is possible that activities requiring considerable effort are avoided by these patients. This relative inactivity would result in physical deconditioning which in turn could at least partly explain the lower baseline level in exercise performance in ICD patients. It has been suggested that psychological interventions utilising cognitive behavioural aspects could reduce symptoms of anxiety.16,18 Regarding the patient's well-being and general functioning, this would improve the health-related quality of life and be of benefit for the patient's physical fitness as well.16
Aerobic power significantly improved after 3 months of cardiac rehabilitation in both groups. The 21% improvement in peak VO2 (mL/min) in the ICD group is comparable to the 20% improvement described in a previous study.14 Fitchet et al.,12 also described 11 ICD patients able to increase treadmill exercise duration by 16% after 3 months of comprehensive cardiac rehabilitation, whereas no changes had occurred over a similar period of `usual care' which preceded rehabilitation.
For unclear reasons patients with an ICD increased in body weight with physical training, whereas controls decreased in weight. Part of the increase in peak VO2 (mL/min) in ICD patients was thus probably related to increased body weight. This may explain why peak VO2, adjusted for body weight, more clearly revealed the differences in the trainability of aerobic power between both groups, whereas less progress was made by ICD patients (18% vs. 27%). This larger study does not confirm previous findings in a small study, where relative increases in aerobic power were comparable in patients with () and without (
) ICD.14 The present results thus indicate some limitation to improve exercise performance in ICD patients despite the similar training dosage as other cardiac patients. This difference in trainability of exercise performance in patients with ICD may partially be explained by the greater percentage of patients with lower LVEF in the ICD group.
Myocardial ischaemia during exercise can induce life-threatening arrhythmias in any patient19,20, but patients with a history of arrhythmias or cardiac arrest, such as ICD patients, are at a particularly higher risk during exercise.6,7,11 In this study, ventricular premature beats in couplets, triplets or runs during exercise testing were observed more frequently in patients with ICD than in controls. Furthermore, there were appropriate ICD interventions for ventricular tachycardia during exercise in 5 patients, of whom 3 discontinued the rehabilitation programme and were excluded from the present analysis. One clinical study previously reported appropriate interventions for ventricular tachycardia during exercise in 2 patients.14
Between training sessions appropriate discharges occurred in 7 patients in this study, of which one occurred in a patient who later dropped-out of the rehabilitation programme and was therefore excluded from the study. Another clinical study reported only 2 discharges and one anti-tachycardia pacing in between sessions.12 The present study, however, contained a larger cohort of patients in reference to earlier studies12,14, therefore the incidence of ICD discharges, especially in between training sessions, was somewhat higher.
Finally, inappropriate ICD discharges in the event of supra-ventricular tachyarrhythmias are a well-recognised risk2125, which have been described to induce life-threatening ventricular tachyarrhythmias in some individuals.2628 In the present study, however, only one inappropriate ICD shock without pro-arrhythmic effect was delivered to a patient in sinus tachycardia during exercise training and none in between sessions. No other clinical studies reported inappropriate discharges during or in between exercise.12,14 Although inappropriate therapies during exercise thus seem scarce and did not result in major complications, the possibility should not be ruled out.
One could criticise the present study regarding the patient population, since the ICD group consisted of patients referred to different rehabilitation programmes (Leiden/Leuven). However, the procedures for exercise testing and training were comparable. Both used cycle ergometer testing with similar equipment and protocols. The comprehensive rehabilitation programmes each consisted of similar exercise training components and information sessions.
In conclusion, the results of this study demonstrate that cardiac rehabilitation with exercise training is feasible and produces favourable results in ICD patients. Patients with an ICD can safely participate in an exercise training programme where careful supervision by qualified staff and constant vigilance during exercise activities are strongly recommended. There is evidence that the effect of training is somewhat lower than in control patients. Therefore, a randomised control study with evaluation of the physical as well as the psychosocial effects is warranted.
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Acknowledgments |
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References |
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