Why is this review important?
Cardiovascular disease is a leading cause of global mortality, accounting for approximately 17.3 million deaths each year. Sudden cardiac death remains a significant public health issue, even though its rates are declining. 
Implantable cardioverter defibrillators represent an effective way of preventing sudden cardiac death. These devices can perform arrhythmia monitoring, diagnosis, and pacing therapy for tachy (fast) or brady (slow) cardiac rhythm, both of which are potentially life-threatening. They are very similar to a conventional pacemaker, with one right ventricle lead positioned under the skin on the anterior chest wall near the clavicle.
Indications for implantable cardioverter defibrillators are primary prevention in people at risk of tachycardia, fibrillation, or cardiac arrest and/or secondary prevention in those who had a prior sudden cardiac arrest or sustained ventricular tachycardia. 
 
What this review talks about?
The review describes cardiac rehabilitation as a comprehensive, complex intervention including exercise training, education, psychosocial management, behaviour-modification interventions for physical-emotional conditions, nutritional counselling, and risk-factor management of lipids, blood pressure, weight, diabetes mellitus, smoking, etc. 
Reviewers also described adverse effects of implantable cardioverter defibrillators like implant-related complications, inappropriate defibrillator shocks and patients’ experience of psychological difficulties, anxiety, depression, and distress. These psychological problems may negatively impact their health and quality of life and lead to increased hospitalisations and healthcare needs, loss of productivity and employment earnings, and increased morbidity or mortality.
The review assessed the outcomes of cardiac rehabilitation at two time points: the end of the intervention and the longest available follow-up.

Who would be interested in this review?
Patients with implantable cardioverter defibrillators, their loved ones and caregivers, and all the health professionals dealing with these patients.

What is the review Objective?
To assess the benefits and harms of exercise-based cardiac rehabilitation programmes, alone or in combination with a psychoeducational program.

Which studies were included in the review?
Eight studies were selected that compared exercise-based cardiac rehabilitation with no intervention after an implantable cardioverter defibrillator. These studies were published from 2004 to 2017 and included 1730 adult participants treated with exercise-based cardiac rehabilitation for a mean of 12 weeks.

Authors’ conclusions
Considering the very low to moderate quality of evidence for all outcomes, recommendations on exercise-based cardiac rehabilitation for patients with implantable cardioverter defibrillators vary widely. Current evidence shows that it probably makes no difference to anti-tachycardia pacing and inappropriate shock; it may make no difference to all-cause mortality, serious adverse events, and appropriate shock; and it is uncertain whether it improves exercise capacity and health-related quality of life at the end of intervention and at the longest available follow-up.

What next?
Further well-designed, adequately powered randomised trials are needed to assess the impact of exercise-based cardiac rehabilitation in adults with an implantable cardioverter defibrillator. They should report on adverse effects, such as number of hospitalization events.

Comment by Sunita Gudwani