Indications for Cardiac Pacemaker Implantation in Myotonic Dystrophy

, Neurology Service, VA Medical Center, Neurology Department, Georgetown University Medical School, Washington, DC; , Medical Service, VA Medical Center, and the Department of Medicine, Georgetown University Medical School; , Biostatistics, Washington Hospital Center, and George Washington University Medical School, Washington, DC


Medscape General Medicine. 1999;1(2) 

In This Article

Abstract and Introduction


Objectives: To determine risk factors for cardiac complications in patients with myotonic dystrophy, and to determine whether permanent cardiac pacemakers may be beneficial in the treatment of myotonic dystrophy heart disease.
Background: Myotonic dystrophy affects the cardiac conduction system. Cardiac pacemakers are easily implanted and can be life-saving in patients with severe or complete heart block.
Methods: A total of 94 patients with myotonic dystrophy were examined; 46 were followed for a mean of 6.4 (± 3.5 SD) years to determine predictors of the end point events of sudden death, Stokes-Adams attacks, or onset of atrial fibrillation. The end points were chosen to determine when cardiac pacemakers should be implanted (Fig. 1).
Results: Four out of 5 patients (and all 4 patients >60 years of age) with PR intervals longer than 275 msec had sudden death (n=1), Stokes-Adams attacks (n=1), or onset of atrial fibrillation (n=2). Conversely, only 1 of 89 patients with a PR interval shorter than 275 msec had end point events; 1 patient, aged 63 years, developed left bundle branch block and palpitations accompanied by dyspnea, which responded to a pacemaker.
Conclusions: We recommend that patients with myotonic dystrophy and any indication or a family history of myotonic heart disease have at least a yearly electrocardiogram, particularly if they have a prolonged baseline or progressively increasing PR interval, or symptoms suggestive of heart block.

Figure 1. Increase in PR Interval With Age (Myotonic Dystrophy Patients)


Myotonic dystrophy, a slowly progressive, hereditary disease, is the most common form of muscular dystrophy, heart block being the most clinically significant type of cardiac involvement more often than symptomatic cardiac arrhythmias.[1] It appears that prolonged PR and QRS intervals may be the most easily and inexpensively obtained predictors of heart block, and that their changes may be progressive.[2] Sudden death occurs less often than heart block. Although there is a high prevalence of late potentials in patients with myotonic dystrophy, it is not known whether late potentials carry the same predictive value for sudden death as they do in patients with myocardial ischemia.[3,4,5] The prevalence of late potentials is not known in other neuromuscular diseases.

Other investigators have shown that progressive heart block may be the etiology of sudden death in many patients with myotonic dystrophy.[6,7,8,9,10,11] However, ventricular tachycardia also may play a role in the etiology.[12,13,14] The conduction block occurs throughout the cardiac conduction system, though electrophysiologic testing has shown preferential involvement of the His-Purkinje system, resulting in prolongation of the HV interval.[6,15] The block below the His bundle may be responsible for syncope or sudden death.[16]

In order to determine which medical intervention was most appropriate, we followed a number of patients with thorough, noninvasive cardiac evaluation. We then compared them with normal, healthy volunteers and patients with similar weakness due to Charcot-Marie-Tooth disease, which is not known to produce cardiac disease.[15,17] The critical question of the study was, What are the predictors of the need for treatment of heart block in patients with myotonic heart disease?