1. Onassis Cardiac Surgery Center, Athens 17674, Greece
2. Department of Cardiology, Aghia Sophia Children's Hospital, Athens 11527, Greece
3. Exercise Physiology and Sports Medicine Clinic, Center for Adolescent Medicine and UNESCO Chair on Adolescent Health Care, First Department of Pediatrics, Medical School, National and Kapodistrian University of Athens, Aghia Sophia Children's Hospital, Athens 11527, Greece
4. Laboratory of Clinical Virology, School of Medicine, University of Crete, Heraklion 71003, Greece