title: Cardiac fatigue in long-distance runners is associated with ventricular repolarization abnormalities.
abstract: BACKGROUND
  Prolonged exercise can induce cardiac fatigue, which is characterized by biomarker release and impaired myocardial function. The impact on ventricular electrophysiology is largely unknown.
  
  
  OBJECTIVE
  The objective of this study was to examine changes in ventricular repolarization after a 30-km cross-country race in runners aged >or=55 years.
  
  
  METHODS
  Fifteen healthy participants (62 +/- 5 years) were assessed using biomarkers (N-terminal pro-brain natriuretic peptide [NT-proBNP], troponin T [TnT]), tissue Doppler echocardiography, and vectorcardiography at baseline, within 1 hour postrace and on days 1 and 6 postrace.
  
  
  RESULTS
  During the race, NT-proBNP increased from 42 ng/L (interquartile range 25-117) to 187 ng/L (113-464), and TnT increased from undetectable levels to 0.03 microg/L (0.015-0.05). Global strain (19.1% +/- 2.2%) decreased on day 1 (17.2% +/- 1.8%) and day 6 (17.9% +/- 1.5%; P <.01). QT(c) increased from 431 +/- 15 ms prerace to 445 +/- 22 ms postrace and 445 +/- 15 ms on day 1 (P <.05), mainly because of an increased T(peak-end) interval (prerace 108 +/- 13 ms, postrace 127 +/- 43 ms, day 1 127 +/- 43 ms; P <.05). Postrace, T(area) (baseline 75 +/- 26 microVs) peaked on day 1 (105 +/- 42 microVs) and remained high on day 6 (89 +/- 37 microVs; P <.05). Runners with higher baseline NT-proBNP developed greater impairment of myocardial velocities (rho = -0.68 to -0.54; P <.05) and a larger increase in T(area) (rho = 0.73; P <.01).
  
  
  CONCLUSIONS
  Cardiac fatigue induced by prolonged exertion is associated with sustained abnormalities in ventricular repolarization. Runners with higher baseline NT-proBNP are especially liable to such alterations of cardiac function.
authors.affiliation: Department of Cardiology, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Sahlén
authors.forename: Aigars
authors.initials: A
authors.lastname: Rubulis
authors.forename: Reidar
authors.initials: R
authors.lastname: Winter
authors.forename: Per-Herman
authors.initials: PH
authors.lastname: Jacobsen
authors.forename: Marcus
authors.initials: M
authors.lastname: Ståhlberg
authors.forename: Per
authors.initials: P
authors.lastname: Tornvall
authors.forename: Lennart
authors.initials: L
authors.lastname: Bergfeldt
authors.forename: Frieder
authors.initials: F
authors.lastname: Braunschweig