Sudden cardiac death due to cardiovascular disease is a significant public health concern worldwide. In recent years, there has been an improvement in the mortality rates of patients who have received an implantable cardioverter defibrillator (ICD), as either a primary or secondary prevention strategy for sudden cardiac death (Nielsen et al, 2019). The mechanisms by which ICD prevents sudden death is anti-tachycardia pacing, high-voltage shock therapy or both (Nielsen et al, 2019).
It is well known that patients with heart conditions (such as post-myocardial infarction and heart failure) have improved outcomes when they receive formal cardiac rehabilitation. However, there is limited evidence and guidance to support cardiac rehabilitation in patients with an ICD (Nielsen et al, 2019).
Objective/s
The purpose of Nielsen et al's review (2019) was to evaluate the benefits and harms of exercise-based cardiac rehabilitation programmes, delivered alone or in combination with psychoeducation components in adults (18 years or older) with an ICD for the prevention of sudden cardiac death (regardless of whether the ICD was for primary or secondary prevention).
Implantable cardioverter defibrillators are battery-powered devices placed in the chest to monitor heart rhythm and detect irregular heartbeats
Intervention/methods
Exercise-based rehabilitation that involved any form of exercise training was compared to treatment as usual, which was no intervention or any other type of cardiac rehabilitation that did not include a component of physical exercise. Exercise-based rehabilitation could be delivered as a supervised or unsupervised activity and conducted in any setting (inpatient, outpatient, community or home), with no restriction placed on the length, intensity, or content of the rehabilitation programme.
The methods used in this review were consistent with those outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins and Green, 2011). A systematic search for randomised controlled trials (RCTs) was conducted across a range of relevant databases with no limitations on date or language. All studies were independently screened by two reviewers, and those meeting the inclusion criteria were extracted independently. Risk of bias was assessed for each study, and, in addition to this criterion and in consistency with other cardiac rehabilitation reviews, three other sources of bias were assessed: performance bias (relating to co-interventions), intention-to-treat analysis and groups balanced at baseline.
Results
A total of eight trials (16 publications) were included in the review, with a total of 1730 participants. Most participants were men with heart failure (the mean age of participants ranged from 54 to 65 years). Only two trials included psychoeducation in addition to the physical exercise training. The delivery of the intervention varied across studies from two to seven sessions per week, with the duration of each session varying from 10 to 60 minutes, and the duration of the programme varying from 8 to 26 weeks. Follow-up of participants varied from the end of the intervention to up to 45 months (median follow-up of 18 months).
In relation to the primary outcomes of interest, there was no evidence of a difference between the exercise-based rehabilitation group and control groups for all-cause mortality (based on one trial of low-quality evidence at the end of the intervention and three trials of very low-quality evidence at the longest available follow-up) and serious adverse events (based on two trials of low-quality evidence at the end of the intervention and three trials of very low-quality evidence at the longest available follow-up). Five trials reported on the health-related quality of life at the end of the intervention; however, due to variation in reporting, meta-analysis was not possible. The findings of the studies indicated little or no evidence of a difference between the intervention and control groups.
The reported secondary outcomes of interest included exercise capacity at the end of the intervention, ICD anti-tachycardia pacing, ICD shock, non-serious adverse events, employment and cost-effectiveness. The findings reported no difference between groups except for exercise capacity at the end of the intervention, where the evidence reported an increase in exercise capacity favouring the intervention; however, the authors recommended interpreting this finding with caution, as exercise capacity is a surrogate outcome with questionable clinical significance.
Conclusions
In patients with an ICD for the prevention of sudden cardiac death, there was no evidence demonstrating a benefit in exercise-based cardiac rehabilitation programmes compared with no exercise in terms of all-cause mortality, serious adverse events, health-related quality of life, ICD anti-tachycardia pacing, ICD shock, non-serious adverse events and employment. The findings of Nielsen et al's review (2019) provide very low-quality evidence that patients following exercise-based cardiac rehabilitation experience a higher exercise capacity compared with the no exercise control. The high risk of bias and low level of certainty of the evidence limits the generalisability of these findings.
Implications for practice
The benefits of exercise-based cardiac rehabilitation programmes for adults with an ICD for the prevention of sudden cardiac death remains unclear. There is no demonstrated benefit for these programmes on any of the measured outcomes except, for a potentially positive effect on exercise capacity at the end of the intervention. The quality of the evidence supporting these findings makes it difficult to transfer recommendations to clinical practice. What is known is that cardiac rehabilitation programmes are a complex and often multifaceted intervention (addressing physical, mental and social aspects) (Anderson et al, 2016). The studies in Nielsen et al's review (2019) primarily (with the exemption of two studies) examined physical exercise as a single-component rehabilitation programme. The findings of the review highlight that exercise-based cardiac rehabilitation appears safe with regard to ICD shocks, with no ICD shocks reported during exercise; however, further research from well-designed, adequately powered studies is required to provide evidence of higher certainty on the impact of exercise in patients with an ICD.