BACKGROUND: Patients with myotonic muscular dystrophy (DM) are at risk for 
atrioventricular block and left ventricular (LV) dysfunction. Noninvasive 
detection of diffuse myocardial fibrosis may improve disease management in this 
population.
OBJECTIVE: To define functional and postcontrast myocardial T1 time cardiac 
magnetic resonance characteristics in patients with DM.
METHODS: Thirty-three patients with DM (24 with type 1 and 9 with type 2) and 13 
healthy volunteers underwent cardiac magnetic resonance for the assessment of LV 
indices and the evaluation of diffuse myocardial fibrosis by T1 mapping. The 
association of myocardial T1 time with electrocardiogram abnormalities and LV 
indices was examined among patients with DM.
RESULTS: Patients with DM had lower end-diastolic volume index (68.9 mL/m(2) vs 
60.3 mL/m(2); P = .045) and cardiac index (2.7 L/min/m(2) vs 2.33 L/min/m(2); P 
= .005) and shorter myocardial T1 time (394.5 ms vs 441.4 ms; P < .0001) than 
did control subjects. Among patients with DM, there was a positive association 
between higher T1 time and LV mass index (2.2 ms longer per g/m(2); P = .006), 
LV end-diastolic volume index (1.3 ms longer per mL/m(2); P = .026), filtered 
QRS duration (1.2 ms longer per unit; P = .005), and low-amplitude (<40 mcV) 
late-potential duration (0.9 ms longer per unit; P = .01). Using multivariate 
random effects regression, each 10-ms increase in myocardial T1 time of patients 
with type 1 DM was independently associated with 1.3-ms increase in longitudinal 
PR and QRS intervals during follow-up.
CONCLUSIONS: DM is associated with structural alterations on cardiac magnetic 
resonance. Postcontrast myocardial T1 time was shorter in patients with DM than 
in controls, likely reflecting the presence of diffuse myocardial fibrosis.