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Exercise-induced cardiac remodeling during adolescence

Exercise-induced cardiac remodeling (EICR) and corollary attributes of the ‘‘athlete’s heart’’ have been thoroughly documented among adults. Comparatively less is known about the impact of exercise on cardiac morphology among children and adolescents. Several prior cross-sectional studies document cardiac differences between pediatric athletes and non-athletes but do not establish a causal relationship between exercise exposure and cardiac adaptation, and longitudinal pediatric exercise training studies in the published literature are very limited and have not focused on left ventricular (LV) adaptation in male adolescents. We therefore conducted a prospective, longitudinal repeated-measures pilot study of endurance exercise-naive adolescent boys participating in a 10-week introductory competitive rowing program. Echocardiography was performed before and after rowing training (Vivid-Q/ EchoPAC v112, GE Healthcare, Milwaukee, Wisconsin, USA). Echocardiographic parameters were measured in triplicate and averaged over three cardiac cycles. Age, sex, and body-surface-area adjusted Z-scores were computed using established nomograms. Cardiac parameters were additionally compared against reference values and Z-scores specific for populations of adolescent male athletes. Normality of distributions was assessed with Shapiro–Wilk test, and preand post-training measures of LV structure were compared using two-tailed t-tests. Adolescent males without known cardiovascular disease (n1⁄4 13, median age 15.0 years (interquartile range 14.6–15.1), height 183 cm (173–183), weight 68 kg (58–71)) performed 8–10 supervised hours of rowing training weekly; approximately 40% of training was interval or high-intensity-based. Fitness, assessed preand post-training by a standardized stair-climbing running test (37 stadium sections totaling 1347 stairs), improved in all subjects (median 34:32min vs. 28:19min). At baseline, each participant had normal LV structure and function, and none had significant valvular pathology. As compared with reference values for adolescent male athletes of similar ages, all baseline findings were within normal ranges (within two standard deviations of population mean). LV adaptations with the training intervention, best characterized as eccentric hypertrophy, included increases in average wall thickness (8.0 0.7 vs. 9.2 0.5mm, p< 0.001), end-diastolic volume (114 20 vs. 127 23mL, p1⁄4 0.001), and mass (122 21 vs. 140 22g, p< 0.001) (Figure 1). There was a trend towards an increase in mitral annular early tissue Doppler velocity (13.9 1.5 to 14.6 0.8 cm/s, p1⁄4 0.08) while LV ejection fraction, global longitudinal strain, and right ventricular size were unchanged. Trainingrelated changes extended beyond ageand size-adjusted normal values in only one subject (post-training general population Z-scores for posterior wall thickness and LV mass 2.6 and 2.3, respectively; Figure 1). However, 11/13 (85%) had increases in at least one of three calculated Z-scores exceeding 1, and 5/13 (38%) demonstrated Z-score increases in excess of two units, representing an increase of two standard deviations on the population nomogram. Comparison against Z-scores specific to athletic populations yielded a similar overall picture, with 9/13 demonstrating an increase of at least one unit (one standard deviation), although no subjects had a Z-score increase in excess of two units and none demonstrated remodeling change exceeding norms for the athletic population (maximum individual post-training Z-score was 1.8). Data from this longitudinal study are among the first documentation of a causal effect of exercise training on ventricular remodeling among healthy adolescent boys and thereby present several notable insights. First, they confirm that significant EICR can occur over a relatively short time period in adolescent boys and provide an important causal framework for the LV hypertrophy