The largest multicenter study, led by Dr. William J. Groh at the Indiana University School of Medicine, has identified risk factors that can lead to sudden death for adult patients with myotonic dystrophy type 1, the most common form of muscular dystrophies seen in adults. Over 10 years, neurologists and cardiologists assessed 406 adult patients, from 23 neuromuscular disease clinics in the United States, with genetically confirmed myotonic dystrophy type 1 using clinical history, genetic assessment and electrocardiograms (ECG) to determine the risk factors that cause arrhythmias and sudden cardiac death. Sudden death is defined as death that occurs in a stable patient within one hour of the onset of symptoms. With this study, the authors have been able to identify the 20% of patients at highest risk of sudden death. Of those, one-third died of sudden death likely attributable to cardiac arrhythmia. In terms of predictors of sudden death, severe ECG abnormality and a clinical diagnosis of atrial tachyarrhythmia were found to be independent risk factors in this population. These risk factors will enable physicians to evaluate patients with myotonic dystrophy to hopefully prevent sudden death through further evaluation including electrophysiological studies (using catheters in the heart) or by surgically implanting a cardioverter-defibrillator. Another important outcome of the study was the discovery that pacemakers, commonly used to treat some forms of arrhythmia, did not help these patients prevent sudden death.

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