Review: Gender Affects the Impact of Exercise on the Heart

Exercise-induced cardiac remodeling is a well-documented phenomenon, but the expected range of changes in female athletes has not been well studied. Women now participate in competitive sports in nearly equal numbers as men, from high school through the Olympics, so defining the limits of normal adaptation in female athletes is important.

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In Current Treatment Options in Cardiovascular Medicine, Massachusetts General Hospital researchers Bradley J. Petek, MD, resident physician on the Internal Medicine Associates Team, and Meagan M. Wasfy, MD, sports cardiologist in the Cardiovascular Performance Program, review recent research evaluating the cardiovascular impact of exercise based on gender.

Electrocardiography

Female athletes are less likely than male athletes to have electrocardiograms (ECGs) that are strikingly different from those seen in the general population, the authors say:

• Several normal ECG variants in athletes are less common in females than in males who perform at a similar competitive level. These include elevated QRS voltage consistent with left ventricular hypertrophy, normal early repolarization and incomplete right bundle branch block. The causes of these gender differences are unclear.
  
  
• Anterior precordial T-wave inversions are more common in female athletes than in males. When they are limited to leads V1 to V3, they are not commonly associated with structural cardiac disease. International consensus guidelines for ECG interpretation in athletes suggest that this pattern should not prompt further evaluation unless there are other clinical factors to consider or concern for arrhythmogenic right ventricular cardiomyopathy.
  
  
• Independent of athletic remodeling, females have longer corrected QT (QTc) intervals than males do. In the international consensus guidelines, the only gender-based screening criteria are that male athletes with QTc > 470 ms and females with QTc > 480 ms should be evaluated for long QT syndrome.

Cardiac Structural Remodeling: Left Ventricle

Studies have consistently shown that left ventricle chamber size, wall thickness and mass are smaller in female athletes than in males. However, it is difficult to use these findings to establish cut-offs for normality for two reasons:

1. The most accurate method of normalizing heart size for body habitus is unclear. When left ventricle chamber size is normalized to body surface area, females exhibit slightly larger chambers. Complicating matters further, the difference in size is lessened or even reverses when ventricular dimensions and mass are normalized to body surface area using more sophisticated methods such as lean body mass or allometric scaling.
   
   
2. The degree of exercise-induced cardiac remodeling also varies within genders, depending on factors such as ethnicity and sport type.

For interpreting cardiac imaging in athletes, Drs. Petek and Wasfy advise an individualized approach that integrates gender with other variables that affect exercise-induced cardiac remodeling such as body size, ethnicity and sport type.

Cardiac Structural Remodeling: Right Ventricle

Right ventricle dilation is most commonly found in endurance athletes. Gender differences in right ventricle size parallel those found in the left ventricle: female athletes have smaller dimensions than males do, but this difference reverses when right ventricle chamber size is normalized to body surface area.

The authors emphasize that large right ventricle size alone does not establish a diagnosis of arrhythmogenic right ventricle cardiomyopathy. It must be present along with abnormal morphologic characteristics, as outlined in international consensus guidelines.

Cardiac Structural Remodeling: Atria

In studies of atrial adaptation to exercise, female athletes have shown greater atrial volumes than controls. This is important because atrial remodeling might mediate the two- to tenfold higher risk of atrial fibrillation in long-time endurance athletes. It is unknown whether that risk applies equally to female and male athletes.

Risk of Sudden Cardiac Death

The prevalence of genetic forms of cardiomyopathy, specifically hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy, is slightly lower in females than males. These are among the most common causes of sudden cardiac death in young athletes. Notably, these diseases can overlap structurally with exercise-induced cardiac remodeling.

Even after accounting for the gender difference in the prevalence of cardiomyopathy, the incidence of sudden cardiac death is five- to tenfold lower in female athletes than in male athletes. The reasons for this difference are unclear. It is possible, the reviewers say, that female athletes with cardiac disease may be less likely to suffer sudden cardiac death than male athletes with the same conditions. It is also possible that differences in sport type, intensity, hormonal milieu or other yet to be determined factors between female and male athletes account for this apparent protection.

Drs. Petek and Wasfy look forward to future investigation of the differences between female and male athletes in the relationship between exercise and associated cardiac adaptations. Such research, they note, will have broad applications by improving knowledge of how exercise benefits the heart in healthy individuals and how it interacts with common forms of cardiovascular disease.

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