The results of a prospective, randomised trial, published in Circulation, demonstrate that moderately strenuous aerobic exercise, performed at home, for a select group of implantable cardioverter defibrillator (ICD) recipients was highly beneficial at improving cardiovascular performance. Importantly, the exercise did not compromise safety.
Cynthia M Dougherty, Biobehavioral Nursing and Health Systems, University of Washington School of Nursing, Seattle, USA, and others reported that despite its salutary effects on health, aerobic exercise is often avoided after receipt of an ICD because of uncertainties as to whether exercise may provoke acute arrhythmias and ICD shocks.
There are no clinical guidelines that standardise the approach to exercise testing and prescription for ICD recipients. There is also a dearth of data on whether the amount of exercise required to improve aerobic fitness and quality of life outcomes is safely achievable in the home environment, without an attendant increase in ICD shocks, the authors note.
“We prospectively evaluated the effects of a home aerobic exercise training and maintenance programme on aerobic performance, ICD shocks and hospitalisations exclusively in ICD recipients,” Dougherty and colleagues write.
Individuals with single or dual chamber ICDs were eligible for inclusion in the study. They had to have had an ICD implanted for either primary or secondary prevention of sudden cardiac arrest; the ability to communicate in English well and provide informed consent; be taking beta blockers; and willing to go through with the entire exercise programme and all follow-ups.
The investigators randomised 160 ICD recipients (124 men, median age: 55±12 years) to either undergo prescribed exercise or undergo usual care. Of these patients, 43% received an ICD for primary, and 57% for secondary, sudden cardiac death prevention.
The exercise intervention included two phases: an eight-week aerobic training component (home walking for one hour/day, five days/week at 60-80% of heart rate reserve) followed by a 16-week aerobic maintenance component (home walking for 150 minutes/week). Exercise sessions began with five minutes of lower extremity stretching, followed by walking at a pace until the target heart rate was reached and maintained for one hour. A five minute cool-down consisting of lower extremity stretching and slower paced walking concluded each session. Dougherty and colleagues determined adherence to exercise from exercise logs, ambulatory heart rate recordings and weekly telephone contacts.
Those randomised to receive usual care received no exercise directives and were monitored by monthly telephone contact. They were requested not to begin a new exercise programme or change their existing exercise patterns for the duration of the study.
The primary outcome of the study was peak oxygen consumption (peak VO2), measured with cardiopulmonary exercise testing at baseline, eight and 24 weeks. The researchers gleaned information on adverse events by ICD interrogations, patient reports and medical records. Any ICD therapy occurring during or within one hour of completing exercise was defined as being related to the exercise. The data safety and monitoring board judged whether the cause of ICD shocks was related or not related to the exercise.
The results from the study showed that the exercise group significantly increased peak V02ml/kg/min (p=0.002) at eight weeks, which persisted during maintenance exercise at 24 weeks (p<0.001). ICD shocks were infrequent, with four in the exercise group vs. eight in the usual care group. There were no differences in hospitalisations or deaths between groups. Dougherty and colleagues further found that there were no deaths and no sudden cardiac arrests associated with aerobic training or maintenance exercise.
These results led them to conclude that prescribed home exercise is safe and significantly improves cardiovascular performance in ICD recipients without causing shocks or hospitalisations.
“These observations should help dispel concerns by providers and patients alike about the benefits and safety of moderately strenuous exercise after an ICD. Having an ICD should not relegate persons to lifelong sedentary activity because of fear of recurrent arrhythmias or ICD shocks,” the authors write.
Dougherty et al point out that the limitations of this study include the restricted enrollment criteria that excluded individuals with cardiac resynchronisation therapy devices, those not in sinus rhythm, and those with pacemaker dependence. “The results apply to those with an ICD who have similar characteristics to those who enrolled,” they clarify.