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CLINICAL STUDY: ELECTROPHYSIOLOGY

Intrinsic sinus and atrioventricular node electrophysiologic adaptations in endurance athletes

^* Cardiology Division, Hospital de Clínicas de Porto Alegre, and Department of Medicine, Faculty of Medicine, Federal University of Rio Grande do Sul, Porto Alegre, Brazil

Manuscript received June 19, 2001; revised manuscript received December 7, 2001, accepted December 21, 2001.

^* Reprint requests and correspondence: Dr. Jorge P. Ribeiro, Cardiology Division, Hospital de Clínicas de Porto Alegre, Rua Ramiro Barcelos 2350, 90035-007, Porto Alegre, RS, Brazil.
jpribeiro{at}cpovo.net

OBJECTIVES: In the present study, we evaluated sinus and atrioventricular (AV) node electrophysiology of endurance athletes and untrained individuals before and after autonomic pharmacologic blockade.

BACKGROUND: Endurance athletes present a higher prevalence of sinus bradycardia and AV conduction abnormalities, as compared with untrained individuals. Previous data from our laboratory suggest that nonautonomic factors may be responsible for the longer AV node refractory period found in well-trained athletes.

METHODS: Six aerobically trained male athletes and six healthy male individuals with similar ages and normal rest electrocardiograms were studied. Maximal oxygen uptake (O₂max) was measured by cardiopulmonary testing. The sinus cycle length (SCL), AV conduction intervals, sinus node recovery time (SNRT), Wenckebach cycle (WC) and anterograde effective refractory period (ERP) of the AV node were evaluated by invasive electrophysiologic studies at baseline, after intravenous atropine (0.04 mg/kg) and after addition of intravenous propranolol (0.2 mg/kg).

RESULTS: Athletes had a significantly higher O₂max as compared with untrained individuals. The SCL was longer in athletes at baseline, after atropine and after the addition of propranolol for double-autonomic blockade. The mean maximal SNRT/SCL was longer in athletes after atropine and after propranolol. The WC and anterograde ERP of the AV node were longer in athletes at baseline, after atropine and after propranolol.

CONCLUSIONS: Under double-pharmacologic blockade, we demonstrated that sinus automaticity and AV node conduction changes of endurance athletes are related to intrinsic physiology and not to autonomic influences.

Abbreviations and Acronyms   ANOVA   ANOVA   analysis of variance   AV   atrioventricular   ECG   electrocardiogram   ERP   effective refractory period   SCL   sinus cycle length   SNRT   sinus node recovery time   O2max   maximal oxygen uptake   WC   Wenckebach cycle

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