Global longitudinal strain: a marker of functional and electrical involvement in myotonic dystrophy type 1?

Abstract

Background: Myotonic dystrophy type 1 (MD1) is the most frequently inherited multisystem neuromuscular disease in adults with major cardiac involvement, including conduction system abnormalities and myocardial dysfunction. Subclinical cardiac involvement has been demonstrated by conventional and tissue echo Doppler parameters and a positive correlation between neuromuscular and cardiac involvement has been reported. There are no data referring to speckle tracking strain analysis in this population. The purpose of this study was to evaluate global longitudinal strain (GLS) in MD1 patients and to assess its relation with the severity of muscle impairment and with electrocardiographic conduction abnormalities. Methods: 25 patients with MD1 and no symptoms or physical signs of heart disease and 13 age and sex matched healthy volunteers were prospectively enrolled. Clinical, electrocardiographic and echocardiographic data were collected. Myocardial deformation evaluation was made through speckle tracking derived strain and strain rate imaging. In patients with MD1, severity of muscle impairment was evaluated through the modified Rankin scale (mRS). Results: Mean age of the study population was 36.7±12.5 years and 50.0% were male. Sinus rhythm was documented in 88.0% of the patients (22) and 16% (4) presented first degree atrioventricular (AV) block. No differences were found between patients and controls regarding atrial and ventricular volumes, left ventricle ejection fraction, right ventricle S' wave velocity or usual diastolic measurements. Patients presented a significantly lower global GLS than controls (-16.6±3.6% vs. -18.7±1.8%, p=0.022). When comparing segmental longitudinal strain, no differences were found between patients and controls. In subjects with MD1, the presence of functional incapacity accessed by the mRS was associated with lower GLS: -15.7±3.3% in patients with some degree of clinical disability (mRS ≥ 1) vs. -18.8±3.1% in those with no muscular symptoms (mRs 0), p=0.046. Furthermore, in sinus rhythm patients, GLS correlated with the duration of PR interval (r=0.52, p=0.017), meaning that patients with absolute lower (worse) GLS presented more delayed atrioventricular conduction. No correlation was found between GLS an QRS duration. Conclusions: Global longitudinal strain is reduced MD1 patients and it seems to correlate with functional disability and electrical involvement. These results might represent a new marker of early and occult cardiac dysfunction in this population.