Profound cardiac conduction delay predicts mortality in myotonic dystrophy type 1.

BACKGROUND: Myotonic dystrophy type 1 (DM1) is known to affect mainly the musculoskeletal system. Early mortality is related to respiratory disease and possibly additional cardiovascular complications. AIMS: To identify possible cardiovascular disturbances that could predict survival of DM1 patients.
METHODS: We studied 30 DM1 patients (mean age 41 +/- 13.5 years, range 16-71, 15 women) who were cardiovascularly stable and compared them with 29 controls (mean age 55 +/- 7.8 years, range 42-66, 14 women) using electrocardiography (ECG) and conventional transthoracic echocardiography. The subgroup that survived a follow-up period of 17 years was re-examined using the same protocol.
RESULTS: Of the 30 patients, 10 died of a documented respiratory cause and three of acute myocardial incidents. Compared with controls, left ventricular cavity size, corrected to body surface area, was slightly enlarged at end systole (P < 0.05) and hence fractional shortening was reduced (P < 0.01). Nine patients had first-degree heart block and 15 had a QRS duration >90 ms. Of all ECG and echocardiographic measurements, the sum of QRS duration + PR interval was the best predictor of mortality as shown by the area under the receiver operating characteristic curve of 85%, sensitivity of 70% and specificity of 84%.
CONCLUSIONS: These findings suggest that silent cardiac dysfunction in DM1 patients may cause significant disturbances that over time result in serious complications. Regular follow-up of such patients with detailed electrical and mechanical cardiac assessment may suggest a need for early intervention that may avoid early mortality in some.