Editor's note: Commentary based on D'Ascenzi F, Anselmi F, Focardi M, Mondillo S. Atrial enlargement in the athlete's heart: assessment of atrial function may help distinguish adaptive from pathologic remodeling. J Am Soc Echocardiogr. 2018;31:148-57.

The following are ten key points on atrial enlargement in the athlete's heart:

1. The hemodynamic effects of intensive endurance exercise can result in the balanced enlargement of all four chambers of the heart. Left atrial (LA) and right atrial (RA) enlargement are characteristic features of the "athlete's heart."
2. Exercised-induced remodeling of the atria can result in a diagnostic challenge in differentiating an athletic heart from pathologic cardiomyopathies. This review article summarizes the available data describing the exercise-induced morphofunctional changes of the atria and provides parameters that can help to differentiate physiology from pathology.
3. Age, type of sport, level of competition and years and intensity of training all influence the degree of atrial remodeling. The role of gender is less well defined. Appropriate interpretation of echocardiographic data in an athlete requires incorporation of all this information.
4. Multiple studies confirm that the left atrium (LA) is larger in an athletic population compared to non-athletic control groups. A meta-analysis of 54 studies comprising 7,189 elite athletes and 1,375 controls describes a 30% increase in LA volume index in athletes. The upper limit of normal was established at 35.8ml/m² for male athletes compared to <34ml/m² in the general population. The degree of LA enlargement varies greatly between studies and is likely related to the different populations studied. In one study of elite rowers, 43% had some degree of LA enlargement, which was classified as severe in 4.4%.
5. Due to the complex geometry of the right heart, there are less data regarding training induced changes of the right atrium (RA). Available studies confirm comparable findings between exercise-induced adaptations of the RA and LA. A meta-analysis of 46 studies comprising 6,806 athletes established an upper limit of normal of 23cm² for the RA area in athletes, this is compared to 18cm² for the general population.
6. Atrial enlargement appears related to volume overload due to the sustained increase in cardiac output during athletic training. Changes in atrial size can be seen after 3-4 months of intensive training. The adaptation is dynamic and can be reversed after detraining. Therefore, there is a clear causal relationship between intensive exercise and atrial enlargement.
7. Despite changes in LA volume, non-invasive assessment of LV filling pressures (E/e') remain normal indicating that the increases in LA volume in athletes is driven by volume overload and not pressure overload.
8. Assessment of atrial function plays a fundamental role in differentiating athlete's heart from pathology. The atria initially act as a "reservoir" during ventricular systole as the LA fills with blood from the pulmonary veins, then a "conduit" as blood passively flows into the ventricle during early diastole and finally as a "booster" during atrial systole. These functions can be measured on echocardiography by quantifying phasic volumes. The LA responds to exercise induced increases in pre-load by augmenting reservoir and conduit functions, while LA active emptying is lower in athletes.
9. Speckle tracking echocardiography demonstrates a characteristic pattern of deformation of the atria in athletes with a low stiffness index, normal reservoir function and reduced active contribution of the atrium to ventricular filling at rest. Therefore in athletes there is a shift to more rapid passive atrial emptying in early diastole with less contribution from active atrial contraction likely related to increased LV compliance in athletes.
10. A reduction in atrial reservoir function or an unbalanced enlargement of the atria should raise the suspicion of pathology.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Noninvasive Imaging, Sports and Exercise Cardiology, Atrial Fibrillation/Supraventricular Arrhythmias, Echocardiography/Ultrasound, Sports and Exercise and Imaging

Keywords: Sports, Athletes, Atrial Remodeling, Pulmonary Veins, Systole, Atrial Fibrillation, Diastole, Heart Atria, Atrial Function, Echocardiography, Cardiac Output, Hemodynamics, Cardiomyopathies

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