|
|
|
Clin. Cardiol. 23, 615–620 (2000)
Yosef Pardo, M.D., C. Noel Bairey Merz, M.D., Ivan Velasquez, M.D., Maura Paul-Labrador, M.P.H., Aalok Agarwala, C. Thomas Peter, M.D.
Division of Cardiology, Department of Medicine, Cedars-Sinai Research Institute, Cedars-Sinai Medical Center, and the Department of Medicine, University of California at Los Angeles School of Medicine, Los Angeles, California, USA
Summary
Background: A protective effect of exercise in preventing sudden cardiac death is supported by studies in healthy populations as well as in patients with cardiac disease. The mechanisms involved in this protective effect are unknown.
Hypothesis: We hypothesized that exercise conditioning would beneficially alter autonomic nervous system tone, measured by heart rate variability.
Methods: We prospectively studied 20 cardiac patients enrolled in a Phase 2 12-week cardiac rehabilitation program following a recent cardiac event. The patients underwent 24 h Holter monitoring at program entry and 12 weeks later. Heart rate variability analysis was assessed for both time domain and spectral analysis.
Results: The group demonstrated a modest mean conditioning effect, indicated by an average reduction in resting heart rate from 81 ± 16 to 75 ± 12 beats/min (p = 0.03), and an increase in training METS from 2.1 ± 0.4 to 3.3 ± 1.1 (p<0.0001). Overall, 15 of 20 (75%) patients demonstrated increased total and high-frequency power, and mean high-frequency power was significantly increased (3.9 ± 1.4 vs. 4.4 ± 1.0 ln, p = 0.05). When stratified according to the magnitude of exercise conditioning, patients achieving an increase of >1.5 training METS demonstrated significant increases in SDNN, SDANN index, SDNN index, pNN50, total power, and high-frequency power (all p<0.05) (see text for explanation of abbreviations).
Conclusions: Exercise conditioning improves heart rate variability in cardiac patients, particularly in patients who achieve a threshold of >1.5 training METS increase over a 12-week period. These study results are supportive of the concept that exercise training lowers the risk of sudden cardiac death via increased vagal tone, which likely beneficially alters ventricular fibrillatory and ischemic thresholds.
Key words: exercise, heart rate variability
This work was supported in part by grants from the Division of Cardiology, Department of Medicine, Cedars-Sinai Medical Center, and Marquette Electronics, Inc. Dr. Pardo was supported, in part, by the Save A Heart Foundation and the Kurian Family Foundation Fellowship, Los Angeles, California.
Address for reprints:
C. Noel Bairey Merz, M.D.
Preventive and Rehabilitative Cardiac Center
Division of Cardiology
Cedars-Sinai Medical Center
444 S. San Vicente Boulevard, Suite 901
Los Angeles, CA 90048, USA
Received: March 22, 1999
Accepted with revision: October 1, 1999