Myotonic dystrophy type 1 (DM1) is a multisystem neuromuscular disease with autosomal dominant transmission that affects smooth and skeletal muscle.1 About 30% of mortality in adults with DM1 is due to cardiac involvement.2 Arrhythmias, conduction system disturbances and myocardial fibrosis are the most frequent changes.3 Detection of early markers may facilitate the identification of patients at risk of developing cardiac complications.

Left atrial (LA) function is a complex process that includes receiving pulmonary venous return during left ventricular (LV) systole, transfer of blood passively into the left ventricle in early diastole, and active contraction in late diastole.4,5

In a comparison of volumetric real-time three-dimensional (3D) echocardiography and 3D speckle tracking echocardiography (3D-STE), the two methods were found to provide comparable and reproducible measurements, and to be interchangeable for quantification of LA dimensions and functional properties.6

Echocardiographic myocardial tracking systems using 3D-STE have provided new insights into ventricular function and atrial mechanics, with many potential clinical applications.7,8 3D formats more closely represent reality than two-dimensional (2D) formats, not only in the assessment of LV function but also in the diagnosis of valvular or myocardial disease. Determination of LV strain by 2D speckle tracking echocardiography (2D-STE) enables identification of changes in LV systolic function in patients with DM1.9,10 However, the applicability of 3D-STE in these patients is not fully established and the available data are scarce.

The aim of this study was to identify early changes in LA mechanics and LV systolic function in patients with DM1 using 3D-STE.

The assessment of myocardial deformation has been proposed as an early marker of subclinical dysfunction in DM1 patients.2 The present study is, to our knowledge, the first to identify changes in both LA and LV strain measured by 3D-STE in these patients.

LA mechanics is considered an important clinical variable and its importance has been demonstrated in a number of conditions.13–19 LA strain curves display the physiology of atrial function. The left atrium has four basic functions: phase 1, reservoir function (collection of pulmonary venous flow during LV systole); phase 2, conduit function (passage of blood to the left ventricle during early diastole); phase 3, active contractile pump function; and phase 4, suction force.20 During the reservoir phase, the left atrium is stretched, and consequently longitudinal atrial strain increases, reaching a positive peak at the end of atrial filling. After the atrium empties, LA strain decreases to a plateau, corresponding to LA diastasis, and then continues to decrease during the LA contraction phase (Figure 1).

In our study, a significant negative correlation was observed between age and LA LS in patients with DM1, which did not occur with the controls, suggesting a faster decrease in LA LS in these patients.

In DM1 patients, 2D-STE is able to identify changes in LS of the right atrium, which correlate with low-voltage areas on electrophysiological study.21 However, LA mechanics has been little studied and validated in these patients, so it is difficult to draw definite conclusions about these findings. We expect that with future larger studies, these changes may prove to be important for early diagnosis and therapeutic decision-making.

Studies with 2D echocardiography are consistent in demonstrating decreased LV GLS in these patients,9,22 as well as changes in GCS.9 In our study, we found significant differences only in GLS, which may mean that these fibers are affected early in the progression of the disease, subsequently being replaced by fibrosis, as demonstrated in previous studies23 and other cardiomyopathies, such as hypertrophic cardiomyopathy.24 The presence of myocardial fibrosis in these patients has been documented by a cardiovascular magnetic resonance study,23 in which myocardial fibrosis was found in 40% of patients and was not related to changes on electrocardiogram, Holter or echocardiogram. This suggests that assessment of myocardial fibrosis by cardiac magnetic resonance may be a useful tool in the assessment of these patients, since myocardial fibrosis may be the substrate for ventricular arrhythmias. Also, high levels of transforming growth factor beta 1, a sensitive marker of fibrosis, have been reported in patients with DM1, indicating a higher risk of arrhythmic events and sudden death.25

Previous studies have shown the usefulness of subclinical detection of cardiac involvement in DM1. In one study of 36 DM1 patients, serial Holter monitoring resulted in pacemaker implantation in 11 patients,26 and implantable loop recorders have been used in small studies of asymptomatic patients, leading to the detection of ventricular arrhythmias and device implantation in four out of seven patients.27,28 A recently published study demonstrated the prognostic value of LV GLS in patients with asymptomatic DM1, concluding that GLS constitutes a strong predictor of cardiovascular events.29

3D wall motion tracking uses a box template to detect speckle motion in 3D. The structures are captured in a full volume and do not move out of plane like in 2D. 3D-STE has also been shown to provide a faster and more complete assessment than 2D-STE, overcoming some of the shortcomings of previous techniques by reducing the intraobserver and interobserver variability inherent in 2D measures and avoiding the angle dependence of strain and strain-rate measures obtained on Doppler tissue imaging.7 Nesser et al.30 assessed the accuracy of measuring LV volumes by means of 3D-STE side by side with 2D-STE using cardiac magnetic resonance as a reference. They observed that measurements by 3D-STE showed higher correlation with cardiac magnetic resonance, smaller biases and narrower limits of agreement. 3D-STE is emerging as a useful tool for a more comprehensive assessment of ventricular function and atrial mechanics and may be valuable in a general and systematic approach to these patients, bearing in mind its possible prognostic impact.

This study has some limitations. One is the small number of patients (total 25), which is in line with the rarity of the disease (estimated prevalence of about 1/10000) and previous studies performed in patients with this condition. It also has the inherent limitations of an observational study and, as pointed out above, the clinical impact of LA deformation changes are still not well understood. Regarding image acquisition, a major limitation for current 3D-STE systems is their relatively low temporal resolution, with typical frame rates of 20-25 volumes/s, and sequential volume acquisition, which is vulnerable to motion artifacts if the patient is unable to cooperate. The software used continues to improve but is not fully validated for the study of the left atrium.

LA LS and LV GLS are significantly decreased in patients with DM1. These results may reflect a subclinical and early marker of myocardial dysfunction in these patients. Studies with 3D-STE can detect changes in myocardial function that may contribute to the assessment and follow-up of these patients. Future prospective studies may open new perspectives on the clinical relevance of these markers.

The authors have no conflicts of interest to declare.