Cardiac magnetic resonance imaging (CMR) in hypertrophic cardiomyopathy (HCM) 
often shows delayed contrast enhancement (DE) representing regions of focal 
myocardial fibrosis. Atrial fibrillation (AF) is a commonly reported 
complication of HCM. We determined the relationship between the presence of left 
ventricular myocardial fibrosis (LVMF) detected by DE-CMR and the occurrence AF 
in a series of patients with HCM. 67 patients with HCM (47 males; mean age 
50.1+/-18.5 years) were studied by CMR measuring mass of LVMF, left ventricular 
mass, volume and function, and left atrial (LA) area. AF was present in 17 (25%) 
patients. LVMF was observed in 57% of patients. AF was significantly more 
frequent in patients who also showed LVMF, compared with the group without LVMF 
(42.1% vs. 3.4%, respectively; p<0.0001). LA size was larger in patients showing 
DE (LA area: 37.4+/-11.1 vs. 25.9+/-6.8 cm(2); respectively, p=0.0001). AF in 
HCM is related with myocardial fibrosis detected by DE-CMR and dilatation of the 
LA. This fact adds to the proven adverse prognostic value of myocardial fibrosis 
in HCM, thus, reinforcing the usefulness of this technique in the assessment of 
these patients.