Arrhythmias in DMD
Despite a compelling substrate and abnormal conduction system tissue, arrhythmia burden in DMD is generally attributed to accumulated cardiac injury and systolic dysfunction. The most common finding on ambulatory monitoring of patients with DMD is sinus tachycardia. Often in response to pulmonary pathology or cardiac dysfunction, atrial arrhythmias including flutter and fibrillation may develop7. In a study of 151 patients with dystrophinopathy (Duchenne and Becker’s), arrhythmias were significantly associated with decreased function, as well as independently with increased age20. In the study over 300 Holter monitor studies from Texas Children’s Hospital were evaluated, and burden of supraventricular tachycardia (SVT), ventricular tachycardia (VT), or frequent ventricular premature contractions (VPCs) were noted. Overall, 44% of patients with DMD and 57% of patients with BMD had arrhythmias, with clinically significant arrhythmia, either SVT or VT, occurring in 10% and 25% of those patients respectively20. Though PR interval and QRS disturbances have demonstrated the progressive impact of dystrophin deficiency on cardiac conduction, complete atrioventricular block is rare21,22. There was correlation between atrial arrhythmias and sudden cardiac death in dystrophin-deficient cardiomyopathies controlling for decreased systolic function. In fact atrial arrhythmias were present in 68% of all holter monitors in one study on 235 patients with DMD23. Non-sustained atrial tachycardia, including frequent premature atrial contractions, are more common in patients with decreased systolic function. None of the patients experienced sustained atrial tachycardia and just 5 patients (2%) experienced ventricular tachycardia. Other rare arrhythmias including bundle branch reentry ventricular tachycardia, have been noted7,23. Atrial fibrillation and flutter, certainly common in the adult dilated cardiomyopathy population, is much rarer in children. When these occur, increased cardiac rhythm monitoring and treatment with standard antiarrhythmic therapies is recommended2.