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doi: 10.1097/01.NT.0000335573.41374.e6
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Investigators reported that severely abnormal ECG findings correlated with sudden death in one-third of the patients with myotonic dystrophy in a large clinical trial.

A large percentage of sudden deaths among patients with myotonic dystrophy type 1 seem to result from heart arrhythmias, easily diagnosed defects in cardiac conduction and rhythms, according to the largest study to date in patients with the most common form of the disease.

Researchers studied 406 adults with genetically confirmed myotonic dystrophy type 1 for whom they were able to obtain clinical histories, a genetic assessment of DM1 (for dystrophia myotonica), and electrocardiograms (ECG). Over a mean 5.7-year follow-up period — the entire study lasted 10 years — 20 percent of the patients died. Severely abnormal ECG findings correlated with sudden death in one-third of these deaths, according to the study, reported in the June 19 New England Journal of Medicine.

Led by a team at Indiana University School of Medicine and the Krannert Institute of Cardiology, 23 neuromuscular disease clinics affiliated with the Muscular Dystrophy Association contributed to the study.



Over the ten-year follow-up period, 81 patients died, with the median age at death 54 years, including 27 sudden deaths — 32 from progressive neuromuscular respiratory failure, five non-sudden deaths from cardiac causes, and 17 deaths from other causes. Among these 17 patients, in whom post-collapse cardiac rhythm was determined, a ventricular tachyarrhythmia was observed in nine individuals.

According to lead author William J. Groh, MD, associate professor of medicine at the Indiana University School of Medicine and the Krannert Institute of Cardiology, the study should alert neurologists with these patients to be more aware of the risk of cardiac abnormalities and the need for ECGs where indicated.



“There have not been any previous studies that I'm aware of with good data on incidence of sudden death in myotonic dystrophy type 1 patients,” Dr. Groh told Neurology Today in a telephone interview. “Our goal is to get this information to neurologists and neuromuscular specialists, to make them aware of the risk and encourage them to refer patients to a cardiologist if they have these specific abnormalities.”

Abnormalities included at least one of the following features: rhythm other than sinus, PR interval of 240 msec or more, QRS duration of 120 msec or more, or second-degree or third-degree atrioventricular block, according to the study.

In the study, sudden death was defined as a death in a stable patient within one hour of the onset of symptoms.

A ventricular tachyarrhythmia was diagnosed if the patient had a history of sustained ventricular tachycardia or fibrillation. Cardiac imaging studies assessing left ventricular function were reviewed, and a patient was considered to have systolic dysfunction if it was reported in the study results or if the ejection fraction was less than 50 percent.

In atrial tachyarrhythmia, electrical signals start in the upper heart chambers (atria) and cause the heart to beat too quickly. Atrial flutter and atrial fibrillation are both atrial tachyarrhythmias.

“Patients who had significant abnormalities on their ECG were at a 3.5-times higher risk of sudden death,” said Dr. Groh. “Those with atrial (upper) chamber arrhthymias had a five-times higher risk.”

Patients with severe abnormalities tended to be older, had more severe skeletal-muscle impairment, and were more likely to have heart failure, left ventricular systolic dysfunction, or atrial tachyarrhythmia. They were also more likely to have received a pacemaker or an implantable cardioverter-defibrillator during the follow-up period; however, pacemakers did not appear to have any influence on sudden deaths.

“This is one of the largest follow-up cohorts ever conducted and published,” noted Benedikt G.H. Schoser, MD, a neurologist at the Friedrich Baur Institute of the Ludwig Maximilians University in Munich, Germany.

“For me the most important aspect is that in the group of 41 patients with pacemakers, and 14 with cardioverter-defibrillators, the devices were not capable of preventing sudden cardiac death,” said Dr. Schoser in an e-mail to Neurology Today.

“Unfortunately, the authors did not give any further data or comment on the relationship between repeat episodes of atrial fibrillation and sudden death, ultrasound findings, or evidence of cardiomyopathy,” he noted.

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Dr. Groh said that the findings are especially important for neurologists and neuromuscular specialists because they would identify risk in these patients, many of whom have no symptoms.

Neurologists should ask patients about signs of potential heart problems, such as shortness of breath and erratic heartbeats, and order an ECG if indicated, he advised.

“I recommend an ECG once per year or referral to a cardiologist if neurologists are not comfortable with reading ECG results.”

He also noted that both severe conduction abnormalities and a clinical history of atrial fibrillation were independent risk factors for sudden death in the patients.

“What this data can do is provide neurologists with a good method for evaluating patients in order to make a decision to refer them for further evaluation.”

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Based on the study, it did not appear that pacemakers were predictive of better survival, he noted. “Forty patients had pacemakers and they clearly were not protective, but most of these patients, who were examined at the time of death, had ventricular arrhythmias of the lower [heart] chamber(s), so [a pacemaker] would not have helped. Implantable cardioverter defibrillators (ICD) treat slow and fast heartbeats, so they may offer more protection but we did not have sufficient numbers of patients to study, so we can't say.”

The team is in the early stages of designing a follow-up study that will examine sudden death in myotonic dystrophy patients with ICDs, Dr. Groh told Neurology Today.

At the Olive View-University of California-Los Angeles Medical Center in Sylmar, CA, researchers launched such a pilot study last April. Lead researcher Mark McDonnell, MD, told Neurology Today in a telephone interview that they are documenting ECG abnormalities in 25 myotonic dystrophy patients who have met established criteria for ICDs, and will follow them after the procedures to see if the devices have any effect on sudden cardiac death.

“This is a pilot study to see if it makes a difference in when to place them in myotonic dystrophy patients.”

Although the study by Dr. Groh's team provides worthwhile data that should raise concerns, he said larger studies are needed to better evaluate risks and causes of sudden death. “I think they need a bigger study to get a better picture of these events in myotonic dystrophy,” Dr. McDonnell said. “Most of these patients are pretty disabled and do not exert themselves very much, so you don't see congestive heart failure like you do in other patients with cardiac problems. We have a muscular dystrophy clinic here at UCLA and monitor for arrhythmias. Hopefully these findings will eventually result in some type of clinical guidelines.”

Both Drs. McDonnell and Groh admitted that part of the problem is that most neurologists and cardiologists are not in the habit of working closely together.

“Unfortunately, there's a bit of a disconnect on both sides between neurologists and cardiologists. We're hoping this study can be a bridge,” Dr. Groh told Neurology Today.

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• Groh W, Groh M, Saha C, et al. Electrocardiographic abnormalities and sudden death in myotonic dystrophy type 1. N Engl J Med 2008;358:2688–2697.
    ©2008 American Academy of Neurology