Short and long term effects of exercise training on the tonic autonomic modulation of heart rate variability after myocardial infarction

Abstract

We studied the effects of cardiac rehabilitation on the sympathovagal control of heart rate variability in 30 patients after a first, uncomplicated myocardial infarction. Twenty-two patients completed 8 weeks of endurance training (trained), while eight decided not to engage in the rehabilitation programme for logistical reasons, and were taken as untrained controls. Age, site of infarction, ejection fraction, ventricular diameter and stress test duration were similar in the two groups at baseline. Heart rate variability was evaluated 4 weeks after infarction before starting rehabilitation, and repeated 8 weeks and one year later in both trained and untrained patients. Measures of heart rate variability, obtained from both time- and frequency-domain analysis of a 15 min ECG recording in resting conditions, were as follows: mean RR interval and its standard deviation (RRSD), the mean square successive differences (MSSD), the percent of RR intervals differing > 50 ms from the preceding RR (pNN50), the low and high frequency components of the autoregressive power spectrum of the RR intervals and their ratio (LF/HF). At baseline, heart rate variability was similar in trained and untrained patients. In the short term (8 weeks after infarction), training increased RRSD by 25% (P < 0.01), MSSD by 69% (P < 0.01), pNN50 by 120% (P < 0.01), and reduced LF/HF ratio by 30% (P < 0.01). The effects persisted after one year in trained patients. In untrained patients, the autonomic control of heart rate variability did not change 8 weeks after myocardial infarction and was only slightly modified by time. Thus, exercise training, performed for 8 weeks after a myocardial infarction, modifies the sympathovagal control of heart rate variability toward a persistent increase in parasympathetic tone, known to be associated with a better prognosis. This may partly account for the favourable outcome of patients who undergo rehabilitation.

Effect of exercise on cardiac autonomic function in females with rheumatoid arthritis

“…Our results are confirmed by that of Jurca et al in 2004 who, after 8 weeks of moderate exercise training in females, showed improved vagal modulation of heart rate on 10-min resting ECGs [36]. Many previous studies done on diseased populations to evaluate the effect of short-term exercise intervention on short-term HRV modification assessed only supine variables [37][38][39][40][41][42][43]. Sandercock et al in 2007 observed significant increases in the supine RR interval, SDRR, LF(ln) and HF In the present study, only the RR interval increased significantly in the supine position, while the other variables did not show significant changes in favour of the exercise group.…”

“…Similar studies, e.g. on diabetic [43,45] and cardiac patients [38,40,41], had equal or even less participants. Heart rate variability was the only tool used to assess the function of the autonomic nervous system.…”

Improvements in heart rate variability with exercise therapy

“…(57) found that following an eight-week cardiac rehabilitation program, 21 male and 17 female participants had significant increases in HRV parameters compared with those not participating in the training program. In another study (58), researchers reported a 25% increase in SDNN, a 69% increase in the square root of the mean of the sum of squares of successive N-N interval differences, a 120% increase in the number of successive N-N intervals differing by more than 50 ms divided by the total number of successive N-N intervals and a 30% reduction in LF/HF ratio after 22 MI patients completed an eight-week endurance rehabilitation program. These improvements continued to be observed at one year following participation in the eight-week training program.…”

Reduced susceptibility to ventricular tachyarrhythmias in rats selectively bred for high aerobic capacity

“…Specifically, the incidence of sudden cardiac death is inversely related to the level of regular physical activity (3). Regular physical activity also reduces the incidence of cardiac arrhythmias in individuals with cardiac disorders (7,38,49,55,70,71,79). For example, regular physical activity improved cardiac function and reduced the arrhythmia frequency in individuals with congestive heart failure (27,40).…”