Study Shows How to Better Predict Pacemaker Needs in Myotonic Dystrophy Patients

A recent study has examined what risk factors exist for patients diagnosed with myotonic dystrophy, the most common of all muscular dystrophies. This is a progressive, hereditary condition.

Regarding cardiac involvement, heart block is the most significant clinical presentation. Unfortunately, it is also the cause of sudden death in some patients. Fortunately, a pacemaker can help.

This study compared myotonic heart disease patients, healthy participants, and those diagnosed with Charcot-Marie-Tooth (CMT) disease to understand what may predict those who need treatment for heart block in patients who have myotonic heart disease and what treatments are most beneficial.

CMT is a condition that can cause similar weakness to myotonic dystrophy but does not cause heart disease.

Researchers suspected that pacemakers may be advantageous for this patient population, especially for those with a complete heart block.

The Study

This study included 94 myotonic dystrophy patients.  54 patients were male and 42 were female, and they had an average age of 39. 46 of these patients were followed for an average of 6.4 years. All patients in the study had a cardiac history.

Researchers aimed to examine predictors of stokes-Adams attacks, atrial fibrillation onset, and sudden death. If they are able to understand what can predict these things, they will be able to better understand when pacemakers should be utilized. Currently, the only treatment we know to be effective for a heart block is a pacemaker.

There were 12 patients with CMT serving as control. These patients were matched to have a similar age of onset of disease as well as a similar degree of muscle weakness. Additionally, there were 13 healthy controls. Both of these control groups were matched for height, age, weight, sex, and body surface area.  

A variety of non-invasive cardiac tests were performed throughout the study such as ECGs, Holter monitors, echocardiography, exercise tolerance tests, and more. Tests were examined by a cardiologist who was blind to the participant they were evaluating.


4/5 patients who had a PR interval (the period from the start of the P wave to the start of the QRS complex in electrocardiography) longer than 275 msec experienced a stokes-Adams attack, atrial fibrillation onset, or sudden death.

However, only one of 89 patients who had a PR interval that was shorter than 275 msec experienced one of those outcomes.

One individual experienced a left bundle branch block as well as palpitations and dyspnea. All of these responded adequately to a pacemaker.

Looking Forward

This study determined that the best predictors for needing a pacemaker (all of which are readily available, practical, cost-effective, and reliable) are a PR interval which is at least 240 msec at baseline and increasing evidence of a heart block.

A pacemaker is therefore recommended when the PR interval is 240 msec, especially as this interval will continue to progressively lengthen.

As a result, the researchers recommend that all patients who have myotonic dystrophy or myotonic heart disease in their family history receive an electrocardiogram every year. This is especially important if their PR interval has been increasing or if there are other symptoms which could suggest a heart block.

Although the researchers explain they need to conduct a larger study, the results from this one are clear. Few myotonic dystrophy patients necessitate a pacemaker, but those who may be must be evaluated and monitored.

You can read more about this study and its findings here.

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