Letter on “Cardiac Rehabilitation in Patients With Implantable Cardioverter‐Defibrillator”

To the Editor, We read with great interest the recent scoping review by Gómez et al. evaluating the role of cardiac rehabilitation (CR) in patients with implantable cardioverter-defibrillators (ICDs) [1]. The topic is highly relevant, as fear of physical activity and concerns related to device-associated complications remain major barriers to participation in CR programs. While the review provides valuable clinical insights, we believe that several methodological and conceptual issues deserve further consideration. Although the authors conclude that CR is “safe and effective” in ICD patients, this statement appears overly generalized given that only four studies were included. Scoping reviews are descriptive by nature and are not designed to support definitive safety or efficacy claims [2]. Moreover, the most recent included study dates back to 2014. Since that time, substantial advances in ICD technology—including widespread use of cardiac resynchronization therapy with defibrillators (CRT-D), refined antitachycardia pacing algorithms, and improved shock-reduction strategies—have reshaped the contemporary ICD population [3, 4]. Consequently, the external validity of these conclusions for current clinical practice remains limited. A further concern relates to the marked heterogeneity in exercise testing methods and rehabilitation protocols across the included studies. Some investigations relied on cardiopulmonary exercise testing (CPET), others on the 6-minute walk test, while some prescribed exercise intensity solely on the basis of heart rate or perceived exertion [1]. However, heart rate response is often blunted in ICD patients due to beta-blockers and other rate-controlling therapies, limiting its reliability as a physiological marker of exercise intensity [5]. CPET-derived thresholds such as ventilatory threshold represent more reliable tools for individualized exercise prescription in this population [6]. The absence of standardized physiological criteria weakens the precision of the “safe exercise” concept emphasized in the review. Finally, although ICD shock risk is extensively discussed, the role of autonomic regulation—one of the major determinants of both arrhythmic risk and exercise adaptation—is insufficiently addressed. Parameters such as heart rate recovery, heart rate variability, and ventilatory efficiency are well-established markers of autonomic balance and prognosis [7]. Exercise-induced improvements in autonomic function may represent a key mechanism by which CR reduces arrhythmic vulnerability, beyond simple avoidance of shock-triggering heart rates. In conclusion, while Gómez et al. provide an important contribution to the field, the safety and effectiveness of CR in ICD patients should be interpreted cautiously in light of limited sample size, outdated device technology, non-standardized exercise prescription, and insufficient integration of autonomic physiology. Future studies incorporating CPET-based exercise prescription, contemporary ICD/CRT-D systems, and autonomic markers are warranted.