Aims: Echocardiographic characteristics to distinguish physiological left ventricular (LV) hypertrophy from pathology is warranted in early adolescent athletes. This study aimed to explore the phenotype, progression and potential grey zone of LV hypertrophy during adolescence in athletes and hypertrophic cardiomyopathy (HCM) genotype positive patients.Methods: In this longitudinal observation study, we compared 76 12-year-old athletes to 55 age- and sex-matched HCM genotype positive patients. Echocardiographic parameters were evaluated by paediatric reference values (Z-scores). HCM genotype positive patients were included if they had no or mild LV hypertrophy (maximum wall thickness <13 mm, Z-score <6 for interventricular septum diameter (IVSd) or posterior wall thickness). We collected clinical data, including cardiac events.Results: Mean follow-up-time was 3.2 +/- 0.8 years. At baseline, LV hypertrophy was found in 28% of athletes and 21% of HCM genotype positive patients (p = 0.42). Septum thickness was similar (ZIVSd 1.4 +/- 0.9 vs 1.0 +/- 1.3, p = 0.08), and increased only in HCM genotype positive patients (ZIVSd progression rate -0.17(SE0.05), p = 0.002 vs 0.30(SE0.10), p = 0.001). LV volumes were greater in athletes (ZLVEDV 1.0 +/- 0.6 vs -0.1 +/- 0.8, p < 0.001, ZLVEDV progression rate -0.05(SE0.04), p = 0.21 vs -0.06(SE0.04), p = 0.12). Cardiac arrest occurred in two HCM genotype positive patients (age 13 and 14), with ZIVSd 8.2-11.5.Conclusions: LV hypertrophy was found in a similar proportion in early adolescence, but progressed only in HCM genotype positive patients. A potential grey zone of LV hypertrophy ranged from septum thickness Z-score 2.0-3.3. LV volumes remained larger in athletes. Evaluating progression of wall thickness and volume may help clinicians distinguish physiological LV hypertrophy from early HCM.
