title: Tight mechanism correlation between heart rate turbulence and baroreflex sensitivity: sequential autonomic blockade analysis.
abstract: BACKGROUND
  Heart rate turbulence is a powerful de novo risk predictor for patients surviving acute myocardial infarction. However, little is known about its underlying physiologic mechanism.
  
  
  RESULTS
  Hypothesizing that heart rate turbulence is barorceptor reflex related, we studied heart rate and blood pressure fluctuations at rest and after systematically introduced ventricular premature beats in 16 patients without structural heart disease (10 men and 6 women; mean age 45 +/- 17 years) before and after sequential sympathetic (esmolol 4-mg bolus followed by 120 microg/kg/min intravenously), parasympathetic (atropine 0.04 mg/kg intravenously), and combined autonomic blockade (esmolol plus atropine). Turbulence onset (%) and turbulence slope (msec/beat) were averaged from 10 respective ventricular premature beats. Spontaneous baroreflex sensitivity (msec/mmHg) was calculated from 5 minutes of sinus rhythm recording. The results showed that turbulence slope decreased after atropine (0.71 +/- 0.50 msec/beat vs 5.17 +/- 3.96 msec/beat at baseline; P < 0.01) and combined autonomic blockade (1.23 +/- 1.02 msec/beat; P < 0.01) but was unchanged after esmolol (4.53 +/- 3.30 msec/beat; P > 0.05). Turbulence onset increased after atropine (0.32% +/- 0.35% vs -0.45 +/- 0.94 at baseline; P < 0.05) and combined sympathetic and parasympathetic blockade (0.58% +/- 0.86%; P < 0.05) but was unchanged after esmolol (-0.62% +/- 1.33%; P > 0.05). Turbulence slope was positively correlated with baroreflex sensitivity at baseline (r = 0.78, P < 0.01) and after esmolol (r = 0.8, P < 0.01), but dissociated after atropine (r = 0.16, P > 0.05) and combined autonomic blockade (r = 0.31, P > 0.05). Turbulence onset was negatively correlated with baroreflex sensitivity at baseline (r = -0.61, P < 0.05), after esmolol (r = -0.80, P < 0.01), and after atropine (r = -0.53, P < 0.05).
  
  
  CONCLUSIONS
  Heart rate turbulence of turbulence onset and turbulence slope is critically vagal dependent and highly correlated with spontaneous baroreflex sensitivity, which underscores its clinical importance in cardiovascular risk stratification.
authors.affiliation: Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital, Taipei.
authors.forename: Lian-Yu
authors.initials: LY
authors.lastname: Lin
authors.forename: Ling-Ping
authors.initials: LP
authors.lastname: Lai
authors.forename: Jiunn-Lee
authors.initials: JL
authors.lastname: Lin
authors.forename: Chao-Cheng
authors.initials: CC
authors.lastname: Du
authors.forename: Wen-Yi
authors.initials: WY
authors.lastname: Shau
authors.forename: Hsiao-Lung
authors.initials: HL
authors.lastname: Chan
authors.forename: Yung-Zu
authors.initials: YZ
authors.lastname: Tseng
authors.forename: Shoei K Stephen
authors.initials: SK
authors.lastname: Huang
mesh_terms: D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001341:Autonomic Nervous System / Q000187:drug effects / Q000503:physiopathology*; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology*; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018879:Ventricular Premature Complexes / Q000503:physiopathology*