Deformation imaging: a new season for the athlete's heart.

Echocardiography has played a fundamental role in the description of cardiac adaptation to exercise. The ability to quantify ventricular size, wall thickness, systolic function, and ventricular filling properties has servedtocharacterizeremodeling attributedtoathletictraining.While most forms of athletic training result in an increase in left ventricular (LV) mass with preservation of systolic function and enhancement of diastolic filling, endurance training typically results in eccentric hypertrophy whereas resistance training promotes concentric hypertrophy. 1 Though most sporting activities actually consist of a mixture of endurance and resistance exercise, these constructs have been helpful to distinguish physiologic adaptation, the ‘‘athlete’s heart,’’ from pathologic entities such as hypertrophic cardiomyopathy. 2 Deformation imaging has advanced our understanding of myocardial mechanics and consequently the cardiac adaptation to exercise. In the evaluation of the athlete’s heart, the focus has been on structure-chamber size, wall thickness, patterns of hypertrophy, and the exclusion of occult structural abnormalities. Diastolic parameters have been useful to confirm normal filling and differentiate between physiologic and pathologic hypertrophy. The assessment of systolic function has typically been with global measures such as ejection fraction or fractional shortening. Now, the capacity exists to assess myocardial function more directly by measuring longitudinal, circumferential, and radial strain aswell as twist(the basalto apical difference in LV rotation) in both systole and diastole. 3 These indices, while numerous and at times complex, promise to unlock the basic functional changes in the myocardium that occur with training and during exercise. The study by Lee and colleagues in this issue of the Journal 4 adds to our understanding of the cardiac adaptation to endurance training in healthy middle age males. The authors found that endurance training results in the ability to enhance systolic twist during exercise as well as the ability to augment early diastolic filling by maintaining the time to peak untwist velocity. These properties were similar to young, healthy controls but dissimilar to healthy untrained age matched controls. This is the first description of such findings in middle aged endurance athletes and adds to a growing literature describing the effects of athletic training on myocardial mechanics. Enhancement of systolic twist has been demonstrated in athletes at rest, but the findings have not been completely consistent. A study of university rowers following a ninety day period of endurance training demonstrated significant increases in peak LV systolic twist as well as peak early diastolic untwisting rate. 5 A study comparing young cyclists, soccer players, and basketball players to controls demonstrated an increase in apical twist only in the cyclists. 6 LV torsion at rest was compared in soccer players to controls and the soccer players were found to have reduced twist and basal and apical radial strain. 7 In a study of cyclist compared to controls, apical radial strain and LV torsion were lower in the cyclists! 8 In the current study, systolic twist values at rest were not significantly different between the controls and trained middle aged males. The heterogeneity of these findings is difficult to explain. It appears that training can enhance systolic twist, but that when compared with controls in the resting state, systolic twist may not always differentiate the athlete’s heart. The specific athletic endeavor as well as the intensity and duration of training may play an important role in the magnitude of effect on systolic twist at rest. Other systolic indices of deformation have been shown to be accentuated in the athlete’s heart at rest. In an earlier study of university rowers, following a ninety day period of endurance training, an increase in peak systolic tissue velocities, radial strain, and longitudinal strain with a base to apex gradient was noted. Circumferential strain increased in the LV free wall but decreased in the septum. 9 Acomparisonofprofessional soccerplayerstocontrols andpatients withhypertrophic cardiomyopathy demonstrated significantly higher radial and transverse strain, but lower longitudinal strain in the soccer players than controls. Compared to patients with hypertrophic cardiomyopathy, soccer players had higher values for radial, transverse, and circumferential strain. 10 The relationship between the various deformation indices is complex. In disease states, for instance, circumferential strain and twist may compensate for diminished longitudinal strain. 3 Given that a subset of the available deformation indices are evaluated in the studies of athletes, it is difficult to know if certain indices are up or down regulated due to an enhanced or diminished effect of other indexes. The effect of exercise on deformation indices has typically demonstrated an augmented reserve in trained athletes. The current study demonstrates the ability of endurance training to augment systolic twist during sub maximal exercise. Donal and colleagues compared young ( 50 years) male athletes to age matched controls and found that both athletic groups had higher LV mass and LV volumes. Stroke volume and global longitudinal strain during exercise was greater in the athletic groups, with the global strain during exercise being highest in the younger athletes. 11 Unfortunately, the absence of a young, trained group in Lee’s study did not allow comparison of the magnitude of the training effect between young and middle aged subjects, as was possible in Donal’s study. In a study comparing elite soccer players with controls, despite similar strain values at rest, mid-ventricular and apical strain were augmented and significantly higher in athletes following hand grip exercise. 12