Aerobic Exercise Improves Heart Rate Variability After an Implantable Cardioverter Defibrillator (ICD)

Purpose: The purpose of the study was to determine the effect of moderately strenuous aerobic exercise training on heart rate variability (HRV) and heart rate turbulence (HRT) in patients with an implantable cardioverter defibrillator (ICD). Methods: Patients were randomized to a 24-week home-based aerobic exercise (EX) training program (n = 84) or to usual care (UC) (n = 76). All subjects underwent 24-h Holter monitoring at baseline, 8 and 24 weeks. Generalized estimating equations were used to test the effects of exercise on HRV and HRT outcomes. Results: The study group was comprised of n = 160 patients (124 M, 36 F, age 54.9 +/- 12.2 years) with an ICD for primary (43%) or secondary prevention (57%). Compared to UC, EX was associated with a significant improvement in parasympathetic HRV for root mean square of successive differences (rMSSD; p = .05) at 8 weeks and global HRV for standard deviation of all normal (N-N) intervals (SDNN; p = .05) and standard deviation of 5-min averages N-N intervals (SDANN; p = .03) at 24 weeks. When stratified by adherence, those who were >= 80% adherent (minutes/week) had significant improvements in parasympathetic HRV (rMSSD, pNN50) and global HRV (SDNN, SDANN) at 8 weeks, and a further significant improvement in global HRV (SDNN, SDANN, SDNN index) at 24 weeks. Neither HRT nor ventricular ectopy changed with exercise training. Conclusion: Moderately strenuous aerobic exercise improved parasympathetic and global HRV indices following an ICD, with greater adherence associated with greater improvements.Clinical trial registration Clinicaltrials.gov: NCT 00522340.