title: Recovery of heart rate variability and ventricular repolarization indices following exercise.
abstract: BACKGROUND
  There is a heightened risk of sudden cardiac death related to exercise and the postexercise recovery period, but the precise mechanism is unknown. We have demonstrated that sympathoexcitation persists for ≥45 minutes after exercise in normals and subjects with coronary artery disease (CAD). The purpose of this study is to determine whether this persistent sympathoexcitation is associated with persistent heart rate variability (HRV) and ventricular repolarization changes in the postexercise recovery period.
  
  
  RESULTS
  Twenty control subjects (age 50.7 ± 1.4 years), 68 subjects (age 58.2 ± 1.5 years) with CAD and preserved left ventricular ejection fraction (LVEF), and 18 subjects (age 57.6 ± 2.4 years) with CAD and depressed LVEF underwent a 16-minute submaximal bicycle exercise protocol with continuous ECG monitoring. QT and RR intervals were measured in recovery to calculate the time dependent corrected QT intervals (QTc), the QT-RR relationship, and HRV. QTc was dependent on the choice of rate correction formula. There were no differences in QT-RR slopes among the three groups in early recovery. HRV recovered quickly in controls, more slowly in those with CAD-preserved LVEF, and to a lesser extent in those with CAD-depressed LVEF.
  
  
  CONCLUSIONS
  Despite persistent sympathoexcitation for the 45-minute recovery period, ventricular repolarization changes do not persist for that long and HRV changes differ by group. Additional understanding of the dynamic changes in cardiac parameters after exercise is needed to explore the mechanism of increased sudden cardiac death risk at this time.
authors.affiliation: Division of Cardiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.
authors.forename: Marc K
authors.initials: MK
authors.lastname: Lahiri
authors.forename: Alexandru
authors.initials: A
authors.lastname: Chicos
authors.forename: Dan
authors.initials: D
authors.lastname: Bergner
authors.forename: Jason
authors.initials: J
authors.lastname: Ng
authors.forename: Smirti
authors.initials: S
authors.lastname: Banthia
authors.forename: Norman C
authors.initials: NC
authors.lastname: Wang
authors.forename: Haris
authors.initials: H
authors.lastname: Subačius
authors.forename: Alan H
authors.initials: AH
authors.lastname: Kadish
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Goldberger
mesh_terms: D017677:Age Distribution; D001145:Arrhythmias, Cardiac / Q000503:physiopathology; D015992:Body Mass Index; D003324:Coronary Artery Disease / Q000503:physiopathology*; D004562:Electrocardiography / Q000379:methods / Q000706:statistics & numerical data*; D015444:Exercise; D005080:Exercise Test / Q000379:methods / Q000706:statistics & numerical data*; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D017678:Sex Distribution; D013318:Stroke Volume