Introduction: Cardiac involvement is frequent in inflammatory myopathies. Electrocardiogram (ECG) may show evidence of this involvement and its changes should be well-known and described. Objectives: Due to the lack of studies in the literature, we conducted an analysis of the ECG findings in patients with dermatomyositis (DM) and polymyositis (PM), comparing them with a control group. Methods: This cross-sectional study compared the ECG of 86 individuals with no rheumatic disorders (controls) with 112 patients (78 DM and 34 PM), during 2010 to 2013. The ECG findings between DM and PM were also compared. Results: Demographic characteristics, comorbidities and ECG abnormalities were similar between controls and patients (p > 0.05), except for a higher frequency of left ventricular hypertrophy (LVH) in patients (10.7% vs. 1.2%, p = 0.008). Demographic characteristics, comorbidities, clinical and laboratory manifestations, were also similar between the groups PM and DM, except for the presence of cutaneous lesions only in DM. One third of the patients had ECG abnormalities, which were more prevalent in PM than DM (50% vs. 24.4%, p = 0.008). LVH, left atrial enlargement, rhythm and conduction abnormalities were more frequent in PM than DM (p < 0.05 for all), especially the left anterior fascicular block. Conclusions: We showed distinct ECG changes between DM and PM and a higher frequency of LVH in patients compared to controls. Investigation of cardiac involvement should be considered even in asymptomatic patients, especially PM. Further studies are necessary in order to determine the correlation of ECG findings with other complementary tests, clinical manifestations, disease activity and progression to other cardiac diseases.
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