Introduction .– Conduction system disease and heart failure have a major impact on the prognosis of patients with myotonic dystrophy type 1 (DM1). An early detection of myocardial involvement could improve patient prognosis.

Objective .– We aimed at determining whether global strain measured by speckle tracking imaging (SPI) could display impaired myocardial contractility in DM1 patients with normal left ventricular ejection fraction (LVEF).

Methods .– Patients with genetically proven DM1, aged 18 to 50 years, with LVEF > 55%, underwent clinical neurological and cardiac workups, ECG, and echocardiography with SPI analysis, including measurements of global longitudinal systolic strain in 4, 3, and 2 chambers apical views (4C, 3C, 2C), and mean radial and circumferential strain in the left parasternal short axis view. DM1 patients were compared to healthy controls matched in a 1:1 ratio on age ± 5 years and sex.

Results .– Among DM1 patients (age = 37.9 ± 9.3 years, female = 20), conduction blocks were identified in 15 patients, a history of supraventricular arrhythmias in 4, and ventricular arrhythmias in 2. Compared to controls, DM1 patients had similar LVEF (63.4 ± 4.1 vs 62.0 ± 4.0%, P = NS), lower 4C longitudinal global strain (−19.2 ± 2.3 vs −17.8 ± 2.5%, P = 0.02), and higher mean circumferential strain (−17.8 ± 2.4 vs −19.5 ± 3.5%, P = 0.01). 2C global strain was lower although not significantly different (−19.9 ± 2.6 vs −18.8 ± 2.9%, respectively, P = 0.07), global 3C longitudinal and mean radial strain were similar in both groups. 4C longitudinal global strain was significantly correlated with the PR interval determined on the ECG ( r = 0.396, P = 0.013).

Conclusions .– 4 C global longitudinal strain measured by SPI displayed subclinical impairment of myocardial contractility in patients with DM1.