title: Sympathetic excitation during exercise as a cause of attenuated heart rate recovery in patients with myocardial infarction.
abstract: BACKGROUND
  Heart rate recovery (HRR) after exercise is known as a predictor of cardiac death in patients with heart disease. The mechanism is not fully understood, although a parasympathetic mechanism has been reported. To elucidate the factors that influence HRR, we evaluated the relationship of HRR with exercise performance and plasma norepinephrine (NE), lactic acid and B-type natriuretic peptide (BNP) responses to exercise testing.
  
  
  METHODS
  The study population consisted of 52 male patients (age 58 +/- 9.6 years) who had experienced myocardial infarction without residual ischemia, uncompensated heart failure or atrial fibrillation. All subjects underwent a symptom-limited cardiopulmonary exercise test without a cool-down period and echocardiography. NE, lactic acid and BNP were measured at rest and at peak exercise.
  
  
  RESULTS
  HRR did not correlate with the left ventricular ejection fraction, peak VO(2), lactic acid and BNP. HRR significantly correlated with the increment in heart rate (HR) from rest to peak exercise (DeltaHR) (r=0.30, p<0.05). When we divided DeltaHR into two phases at the anaerobic threshold (AT), HRR significantly correlated with DeltaHR (peak-AT) (r=0.409, p<0.01), but not with DeltaHR (AT-rest). There was a significant negative correlation between HRR and NE both at rest and at peak exercise (r=-0.286, p<0.05, r=-0.310, p<0.05). HRR was also correlated significantly with DeltaHR/logDeltaNE as an index of sensitivity to NE (r=0.421, p<0.01). Based on multiple regression analysis, DeltaHR and logDeltaNE predicted HRR (R(2)=0.467, p=0.0027).
  
  
  CONCLUSIONS
  Present findings suggest that enhanced sympathetic excitation at maximum exercise suppresses parasympathetic reactivation and results in attenuation of HRR.
authors.affiliation: Division of Cardiology, Hepatology, Geriatrics, and Integrated Medicine, Department of Internal Medicine, Graduate School of Medicine, Nippon Medical School, Tokyo, Japan. ushijima@nms.ac.jp
authors.forename: Akiko
authors.initials: A
authors.lastname: Ushijima
authors.forename: Nagaharu
authors.initials: N
authors.lastname: Fukuma
authors.forename: Yuko
authors.initials: Y
authors.lastname: Kato
authors.forename: Noriko
authors.initials: N
authors.lastname: Aisu
authors.forename: Kyoichi
authors.initials: K
authors.lastname: Mizuno
mesh_terms: D000368:Aged; D015536:Down-Regulation / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006339:Heart Rate; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000532:radiotherapy*; D020097:Natriuretic Peptide, Brain / Q000097:blood; D009638:Norepinephrine / Q000097:blood; D010275:Parasympathetic Nervous System / Q000502:physiology / Q000503:physiopathology; D013564:Sympathetic Nervous System / Q000502:physiology*
chemical_list: D020097:Natriuretic Peptide, Brain; D019344:Lactic Acid; D009638:Norepinephrine