Cardiomyopathy and ventricular dysfunction in a national cohort of patients with myotonic dystrophy type 1

Background Myotonic dystrophy type 1 (DM1) is the most common muscular dystrophy in adults and a major cause of cardiac morbidity and mortality. While conduction disturbances and arrhythmias are well described, data on myocardial involvement, ventricular dysfunction, and functional status in large DM1 cohorts are limited. Purpose We aimed to evaluate the prevalence and characteristics of cardiomyopathy, left ventricular dysfunction, cardiac magnetic resonance (CMR) findings, and functional class in a national cohort of patients with DM1. Methods This was a retrospective multicentre study including patients from 16 Spanish hospitals. The primary objective was to assess the presence of cardiomyopathy, left ventricular systolic dysfunction by echocardiography, CMR data (ventricular function and late gadolinium enhancement [LGE] when available), and New York Heart Association (NYHA) functional class at baseline and during follow-up. Results A total of 549 patients with DM1 were included. Cardiomyopathy phenotypes, ventricular function and NYHA class are summarised in Table 1. Cardiomyopathy was diagnosed in 63 patients (11.5%) at a mean age of 49.7 ± 13.6 years. Dilated cardiomyopathy was the most frequent phenotype (n=43), followed by hypertrophic cardiomyopathy (n=6), while other cardiomyopathies were less common (Table). Left ventricular ejection fraction (LVEF) <40% was observed in 32 patients (5.8%) during follow-up. Most patients were in NYHA class I both at baseline and at the end of follow-up (88% and 74%, respectively), although approximately 14% experienced functional class deterioration over time. CMR data were available in only 9% of patients. Conclusions In this large national DM1 cohort, cardiomyopathy was present in 11.5% of patients, with dilated cardiomyopathy being the predominant phenotype. Left ventricular systolic dysfunction was relatively uncommon but not negligible, and a proportion of patients experienced functional decline. CMR was markedly underused, highlighting the need for systematic myocardial assessment in this population.