Physical conditioning induces numerous cardiovascular adaptations, including vagotonia and increased cardiac volume and mass. These adaptations characterise the 'athletic heart' and account for most of the normal variants in the athlete's electrocardiogram. Common alterations associated with vagotonia include sinus bradycardia, sinus arrhythmia, junctional escape beats, first degree atrioventricular block and second degree (Mobitz type I) atrioventricular block. Common electrocardiographic variants associated with increased cardiac mass and volume include increased voltage, prominent U waves, intraventricular conduction delays, early repolarisation and increased QT intervals. It is sometimes difficult to differentiate the healthy athlete with an athletic heart from the athletic patient with a diseased heart. Thus, further evaluation may be warranted, especially when the athlete also presents with hypertension and/or abnormalities of the cardiovascular physical examination.
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