Abstract 12569: Aerobic Exercise Improves Heart Rate Recovery After an ICD
Background and Purpose: Sudden cardiac arrest is thought to be due to alterations in the autonomic nervous system. Heart rate recovery (HRR) after exercise testing is mediated by parasympathetic reactivation. Low HRR (≤ 12 bpm after 1 minute) is independently associated with all-cause mortality. Aerobic exercise improves parasympathetic cardiovascular functioning by lowering HR and increasing stroke volume. The purpose of this study was to determine if HRR at 1 and 5 minutes could be improved with aerobic exercise in persons with an ICD.
Methods: 160 patients with a prior ICD implant (40% primary prevention and 60% secondary prevention), mean age 55 ±12 years, 77.5% male, 89% Caucasian, and 100% beta-blocked, entered a randomized clinical trial of aerobic exercise after an ICD. Aerobic exercise consisted of home walking 5 hours/week x 8 weeks, followed by walking for 150 minutes/week x 16 weeks at 60-80% of maximum HR achieved at treadmill test. At baseline, 8 weeks, and 24 weeks participants completed a cardiopulmonary exercise test using a modified Balke treadmill protocol. HRR was calculated [peak heart rate (HR)-recovery at 1 and 5 minutes] using 12 lead EKG recordings. Analysis of co-variance was used to determine if a change in HRR from baseline to 8 weeks and 24 weeks was related to exercise training.
Results: In the sample, lower mean baseline HRR (bpm) at 1 and 5 minutes was associated with having an ICD implanted for primary prevention (p≤0.001), BMI>29 (p≤0.001), sedentary life-style (p≤0.001), diabetes (p≤0.001), hypertension (p≤0.001), age >55yrs (p≤0.001), and EF%≤35% (p≤0.001). Mean HRR was significantly improved in exercise vs usual care at 8 weeks [1 minute p≤0.01, (mean+SD: EX 18.8±9.3 UC 16.4±9.6 bpm)] and [5 minutes p≤0.003 (EX 40.5±9.3 UC 37.0±9.6 bpm)], but not at 24 weeks [1 minute p≤0.20, (mean+SD: EX 18.2±9.5 UC 17.2±8.4 bpm)] and [5 minutes p≤0.09 (EX 39.8±16.0 UC 37.5±14.4 bpm)].
Conclusions: HRR can be improved with aerobic exercise training in patients at high risk for cardiac arrest who have an ICD, perhaps through augmenting parasympathetic cardiovascular mechanisms. Low HRR is a surrogate marker for poor health and risk for mortality.
- © 2013 by American Heart Association, Inc.