Profound cardiac conduction delay predicts mortality in myotonic dystrophy type 1

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.

To identify possible cardiovascular disturbances that could predict survival of DM1 patients.

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.

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%.

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.