J Clin Neurol.  2013 Jul;9(3):186-191. 10.3988/jcn.2013.9.3.186.

Prolonged Corrected QT Interval in Patients with Myotonic Dystrophy Type 1

• Park KM
• Shin KJ
• Kim SE
• Park J
• Ha SY
• Kim BJ

• KMID: 2287557
• DOI: http://doi.org/10.3988/jcn.2013.9.3.186

Abstract

BACKGROUND AND PURPOSE
Sudden cardiac death is one of the leading causes of death in patients with myotonic dystrophy type 1 (DM1). It has been proposed that a prolonged QT interval is associated with sudden cardiac death in several neurological diseases, including multiple system atrophy, idiopathic Parkinson's disease, and diabetic autonomic neuropathy. However, analyses of the corrected QT (QTc) interval in DM1 patients are rare in the literature. The purposes of this study were to determine the association between the QT interval and DM1, and the affecting factors.
METHODS
Thirty-nine patients diagnosed with DM1 through genetic testing were enrolled. The QTc interval (calculated using Bazett's formula: QTc=QT/radicalRR) was compared between these patients and 39 normal healthy controls. The clinical and laboratory factors affecting QTc interval in the patient group were investigated.
RESULTS
The QTc interval was significantly longer in the DM1 group (411.2+/-44.7 msec, mean+/-SD) than in the normal control group (355.6+/-20.6 msec). Intragroup analysis revealed that a prolonged QTc interval in DM1 patients was associated with being female and older, having a longer disease duration, and exhibiting abnormal electrocardiography findings.
CONCLUSIONS
The higher incidence of sudden cardiac death in the DM1 population is associated with the observed prolonged QTc interval in those patients.

Keyword

myotonic dystrophy; corrected QT interval; Bazett's formula; sudden cardiac death

MeSH Terms

Cause of Death
Death, Sudden, Cardiac
Diabetic Neuropathies
Electrocardiography
Female
Genetic Testing
Humans
Incidence
Multiple System Atrophy
Myotonic Dystrophy
Parkinson Disease

Figure

• 

  Fig. 1 Corrected QT (QTc) interval in myotonic dystrophy type 1 according to the muscular disability rating scale (MDRS) score. In the box plots, the central line represents the median value (Kruskal-Wallis test, p=0.245), each box spans from the 25th to 75th percentiles, and error bars extend from the 10th to 90th percentiles.

• 

  Fig. 2 QTc interval in DM1 patients according to their age, age at onset, disease duration, and cytosine-thymine-guanine (CTG) repeat number. Univariate regression analysis for age (p<0.01, R2=0.20), age at onset (p=0.25, R2=0.04), disease duration (p<0.01, R2=0.21), and CTG repeat number (p=0.99, R2=0.00). DM1: myotonic dystrophy type 1, QTc interval: corrected QT interval.

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