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).
Conclusion: 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.