Grasping a few basic concepts of cardiac physiology will help explain the changes in cardiac dimensions that occur in specific
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11 12 13 Wall thickness (mm) Figure 4-1 Left ventricular dimensions in the athletic heart.
groups of athletes. It is important to remember that the heart maintains its ability to function adequately as a pump by altering heart rate and contractility when a sudden demand is placed on it. However, when chronic demand is imposed on the heart, pump function is maintained by means of dilation and hypertrophy. Therefore, we would expect that athletes who participate primarily in activities that place chronic volume demands on the heart (e.g., runners, swimmers) would increase end-dia-stolic diameter with resultant increases in wall thickness to normalize wall tension. On the other hand, athletes who participate in sports that place chronic pressure demands on the heart (e.g., weight lifters) would be expected to increase wall thickness without corresponding changes in end-diastolic diameter.
These expected changes have been confirmed by numerous authors using noninvasive imaging. Perhaps the earliest work in this regard was that of Morganroth et al,7 who used echocardiography to assess left ventricular (LV) dimensions in 56 athletes. They found LV end-diastolic volume and mass increased in isotonic athletes (those who place volume demands on the heart) compared to controls. On the other hand, isometric athletes (those who place pressure demands on the heart) had increased LV mass but normal end-diastolic volume. Wall thickness was greater in the isometric athletes. These changes can be quite impressive as demonstrated by the work of Pelliccia et al.8 If we consider that 10 mm is usually considered the upper limit of normal for the thickness of the LV free wall and 11 to 13 mm is considered the "gray zone" into which many athletes' LV dimensions may fall, they found 16 of 947 elite athletes studied with echocardiography to have measurements greater than 13 mm. Fifteen of the athletes with the greatest wall thicknesses were rowers or canoeists, and the highest measured LV free wall was 16 mm (Fig. 4-1). It will be important to keep these findings in mind as we discuss some of the pathologic conditions that can cause SCD in athletes, particularly hypertrophic cardiomyopathy.
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