Aerobic exercise improves fitness and heart rate variability after an implantable cardioverter defibrillator

Abstract

Purpose: The purpose of this study was to determine the effects of an 8-week aerobic exercise program on (1) cardiopulmonary fitness and activity, (2) heart rate variability (HRV), (3) health outcomes, and (4) high sensitivity C-reactive protein (hsCRP) in survivors of sudden cardiac arrest who have an implantable cardioverter-defibrillator (ICD).

Methods: A single group pre-post exercise program with a 6-month follow-up was used in 10 ICD recipients. The exercise intervention consisted of supervised outpatient aerobic exercise 3 hours per week plus home walking 2 hours per week for 8 weeks. Patients were told to walk for 30 minutes on all or most days of the week for the remaining 4 months. Measures were taken at baseline, 8 weeks, and 24 weeks.

Results: Cardiopulmonary fitness (exercise time, oxygen uptake at anaerobic threshold, metabolic equivalents), HRV (standard deviation of all R-R intervals, root-mean square of successive differences, high-frequency power), health outcomes (Short Form-12 physical and mental health, anxiety, depression), and hsCRP were improved after 8 weeks of exercise. Sustained effects of the exercise program were noted in daily activity (RT3 vector magnitude per minute), HRV (standard deviation 5-minute segments, root-mean square of successive differences, percent R-R change by 50 milliseconds high frequency power), and health outcomes (Short Form-12 physical health).

Conclusion: Sudden cardiac arrest survivors who have an ICD are a group of cardiac patients who can potentially benefit the most from exercise by stabilizing autonomic function and reducing the incidence of arrhythmias. Although causal conclusions cannot be drawn from this study, further testing of aerobic exercise interventions in this population appears warranted.