QT INTERVAL DISPERSION
IN MYOTONIC MUSCULAR DYSTROPHY:
ANALYSIS THROUGH THE BODY SURFACE POTENTIAL MAPPING

Pastore C.A., Samesima N., Tobias N., Kaiser E., Nishioka S., Pedrosa A.,
Martinelli F° M., Ascêncio S., Ramires J.F.
Heart Institute (InCor) of the University of São Paulo Medical School
Av. Dr. Enéas de Carvalho Aguiar, 44 – 05403-000 São Paulo, SP – Brazil

Abstract: 22 patients with Myotonic Muscular Dystrophy (MMD) underwent Body Surface Potential Mapping examination (87 leads, 59 on the chest and 28 on the back), to assess the corrected QT interval (QTc) and QT interval dispersion (QTd) in the various ECG and VCG patterns of MMD, divided into 4 groups: I, patients with no alterations (n=7); II, patients with alterations indicative of MI, fascicular blocks and alterations of the ventricular repolarization (n=9); III, previous patients of group II plus patients with evidence of either left or right bundle branch block (BBB) (n=15); IV, only patients with left (n=4) or right (n=2) BBB.  QTc and QTd mean values in Groups III and IV were statistically greater than in Group I (p<0.05), and Group IV had mean QTc significantly higher than Group II (p<0.05).  In conclusion, increased QTc and QTd values accompanied the ECG/VCG alterations in patients with MMD.

BACKGROUND

The Myotonic Muscular Dystrophy (MMD), also known as the Steinert’s Disease, can cause impairment of the heart, especially the myocardium and the endocardium, leading to some important alterations in the conduction system and modifying the heart’s geometry.

OBJECTIVE

To analyze the corrected QT interval (QTc) and the QT interval dispersion (QTd) in the various electro- and vectorcardiographic (ECG/VCG) patterns presented in the MMD, using the Body Surface Potential Mapping.

METHODS

22 patients suffering from MMD were divided into:  Group I, patients with no ECG/VCG alterations (7 patients);  Group II, patients with ECG/VCG alterations indicative of myocardial infarction, fascicular blocks and alterations of the ventricular repolarization (9 patients); Group III, which comprised the patients enrolled in group II and patients with evidence of either left or right bundle branch block (15 patients); Group IV, consisting only of patients with either left (n = 4) or right (n = 2) bundle branch block (6 patients).  Measurements were taken using a Fukuda-Denshi 7000 Body Surface Potential Mapping equipment (Fukuda-Denshi, Tokyo, Japan), with 87 leads placed on the chest (59 leads) and on the back (28 leads).  Statistical analysis was made using the ANOVA/Tukey and the Kruskal-Wallis tests, taking  p to be significant if < 0.05.

RESULTS

Table I below shows that Groups III and IV presented with QTc and QTd values statistically greater than those of Group I, and that Group IV showed a significantly higher QTc than Group II.

Table 1

	Group I	Group II	Group III	Group IV	p
QTc (ms)	413.6 + 11.8	440.9 + 29.8	468.7 + 46.7	510.3 + 34.8	0.0009
QTd (ms)	54.3 + 9.8	71.1 + 15.2	77.0 + 19.7	85.8 + 23.8	0.0187

CONCLUSION

In patients suffering from Myotonic Muscular Dystrophy, increased QTc and QTd values accompanied the appearance of electro- and vectorcardiographic alterations.