Author + information
- Published online February 20, 2017.
- Rachel Lampert, MD∗ ()
- Department of Internal Medicine (Cardiovascular Medicine), Yale School of Medicine, New Haven, Connecticut
- ↵∗Address for correspondence:
Dr. Rachel Lampert, Yale School of Medicine, 789 Howard Avenue, Dana 319, New Haven, Connecticut, 06520.
- cardiorespiratory fitness
- exercise training
- implantable cardioverter defibrillator
- ventricular fibrillation
- ventricular tachycardia
The ability of implantable cardioverter defibrillators (ICDs) to save lives in populations at risk for sudden cardiac arrest is well-established. For the most part, quality of life (QOL) is preserved for ICD patients (1). However, ICD shocks, described in 1 study as being punched in the chest or kicked by a mule (2), decrease QOL (3) and lead to psychological distress. Thus, preventing ICD shocks is paramount in allowing ICD patients to enjoy a full QOL. Further, after an ICD shock, many patients curtail their activity (4), likely due to fear and avoidance behaviors in response to the noxious stimulus (4,5). Patients decrease activity even after implant, before receiving a shock (6). As exercise improves QOL, this curtailment of already low activity after a shock creates a vicious cycle of inactivity and poor QOL (7,8).
Intuitively, cardiac rehabilitation, or exercise training, should be an appropriate intervention to increase activity and thus improve QOL for ICD patients. The benefits of exercise training for patients with heart failure are well-established (9). However, although exercise training is safe in patients with heart failure, the impact on ventricular arrhythmias, of increased importance for those with known vulnerability to ventricular tachycardia or ventricular fibrillation such as those with ICDs, was harder to predict. The “paradox of exercise” has been well-described—although in the long term exercise decreases mortality, immediately, exercise can trigger arrhythmias (10). This is not really a “paradox,” but rather a reflection of the impact of exercise on the autonomic nervous system and, in turn, the impact of the autonomic nervous system on arrhythmia. Overall, physical fitness increases vagal activity, which decreases vulnerability to ventricular fibrillation. For example, experimental studies show that exercise-trained dogs are less likely to fibrillate during myocardial infarction (11). While actually exercising, however, sympathetic activity surges, potentially triggering arrhythmias. Thus, although the most physically fit are overall less likely to die than the sedentary, even the physically fit are more likely to die during exercise than rest (12).
Based on these theoretical benefits and risks, a number of studies have evaluated whether exercise training is safe for patients with ICDs, and whether it is efficacious in terms of increasing fitness. In this issue of JACC: Clinical Electrophysiology, Pandey et al. (13) report the results of a meta-analysis of 6 studies (5 randomized controlled trials) of exercise-training in patients with ICDs, finding that exercise increases cardiorespiratory fitness (VO2 max) without increasing, and, in fact, decreasing shocks. The findings regarding increased fitness with supervised exercise are not surprising and several of the studies showed this alone.
The question of impact of exercise training on shocks, however, was ripe for meta-analysis, because many of the individual studies in the meta-analysis showed a tantalizing but nonsignificant trend toward improvement in shocks with exercise training. Due to the concerns detailed herein, shocks in these studies were actually a safety outcome rather than the efficacy outcome shown here. This meta-analysis is thus the first and most definitive demonstration that exercise training is beneficial for decreasing arrhythmias leading to ICD shocks.
The authors note a number of important issues in designing an exercise program for ICD patients. As they note, a stress test before embarking on an exercise program, to guide target heart rates as increasing fitness, to ensure that heart rates with exercise are below the ICD’s rate cutoffs for therapy, and to identify patients who may be more prone to exercise-induced arrhythmias, is imperative.
It is an unfortunate aspect of the study that appropriate shocks, inappropriate shocks, and antitachycardia pacing–terminated ventricular tachycardias are rolled into a single endpoint. This is unavoidable due to the heterogeneity of the endpoints of the studies included in the meta-analysis. These events are different, and it would be interesting to understand the impact of each. However, because appropriate shocks, inappropriate shocks (14), and antitachycardia pacing–terminated ventricular arrhythmias (15) all have detrimental effects on mortality, this does not detract from the overall importance of the study.
Several questions remain unanswered. First, what is the best format to deliver exercise training to patients with ICDs? Compliance with center-based programs is known to be suboptimal (16). In one of the studies included in this meta-analysis, Dougherty et al. (17) randomized ICD patients to a home-based program, which included an initial cardiopulmonary exercise test to individualize heart rate targets, followed by 8 weeks of an aerobic training phase and a 16-week maintenance phase. Those in the exercise training group showed improvement in fitness, no adverse events, and a nonsignificant decrease in shocks. Further research into home-based programs is needed. This may be true particularly in the elderly, an increasing percentage of ICD recipients, for whom transportation to a center for cardiac rehabilitation may be even more of an issue.
In summary, these data now demonstrate convincingly that ICD patients benefit from exercise training in reduction of shock. Currently, many insurers do not reimburse exercise training after ICD implantation, or even after ICD shock. These data clearly support the benefits of cardiac rehabilitation in preventing shocks, which improves QOL in those with ICDs. Cardiac rehabilitation programs should be reimbursed after implant to prevent ICD shocks, and after an ICD shock to get patients back on their feet.
↵∗ Editorials published in JACC: Clinical Electrophysiology reflect the views of the authors and do not necessarily represent the views of JACC: Clinical Electrophysiology or the American College of Cardiology.
Dr. Lampert has reported that she has received research grants (>$10,000) and modest consulting fees ($5 to $10,000) from Medtronic.
All authors attest they are in compliance with human studies committees and animal welfare regulations of the authors' institutions and Food and Drug Administration guidelines, including patient consent where appropriate. For more information, visit the JACC: Clinical Electrophysiology author instructions page.
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