BACKGROUND: The diagnosis of subtle structural heart disease in competitive 
athletes with ventricular arrhythmias (VAs) and an apparently normal heart is 
challenging. Three-dimensional electroanatomic mapping (EAM) has been 
demonstrated to reliably identify low-voltage areas that correspond to different 
cardiomyopathic substrates.
OBJECTIVE: The purpose of this study was to test whether EAM may help in the 
diagnosis of concealed cardiomyopathies in athletes with VAs and an apparently 
normal heart.
METHODS: We studied 13 consecutive competitive athletes (12 males, age 30 ± 13 
years) who had documentation of VAs within the previous 6 months on 12-lead 
electrocardiogram (ECG), 24-hour Holter ECG, or ECG exercise testing and who 
were judged as having a structurally normal heart after a thorough noninvasive 
evaluation, including signal-averaged ECG, transthoracic echocardiogram, and 
cardiac magnetic resonance imaging. Depending on the presumed site of VA origin 
according to 12-lead ECG criteria, patients underwent right or left ventricular 
EAM and EAM-guided endomyocardial biopsy.
RESULTS: Presenting arrhythmias included sustained ventricular tachycardia (n = 
3), multiple episodes of nonsustained ventricular tachycardia (n = 7), and 
frequent ventricular ectopic beats (>1,000 during 24 hours; n = 3). Three 
patients had a history of syncope. Twelve (92%) patients had at least one 
low-voltage region at EAM, which corresponded at EAM-guided endomyocardial 
biopsy to the histological diagnosis of active myocarditis in seven patients and 
of arrhythmogenic right ventricular cardiomyopathy in five. In one patient the 
histological evidence of contraction band necrosis allowed the unmasking of 
caffeine and ephedrine abuse.
CONCLUSIONS: Electroanatomical substrate mapping may help diagnose concealed 
myocardial diseases in competitive athletes presenting with recent-onset VAs and 
an apparently normal heart. Further studies are warranted to assess the 
prognostic implications of such subtle myocardial abnormalities.