Myocardial myotonia in myotonic muscular dystrophy

We sought to determine whether and to what degree myocardial myotonia might occur in myotonic muscular dystrophy. Cardiac involvement manifests itself chiefly as abnormalities of specialized tissues. Current echocardiographic techniques permit assessment of left ventricular diastolic filling properties and might detect subtle myocardial myotonia. Twenty patients (mean age 37 ± 13 years) with myotonic muscular dystrophy were studied. Twenty normal subjects (mean age 34 ± 12 years), served as controls. Each subject had two-dimensional targeted M-mode echocardiograms of the posterior left ventricular wall to measure the rate of early diastolic relaxation, which was defined as diastolic endocardial velocity maximum (DEVM). Global left ventricular function was quantified. Doppler recordings of mitral inflow measured peak E and A velocities, ratio of E to A (E/A), mitral deceleration time (DT) and isovolumic relaxation (IVR) time. Normal controls had DEVM = 19 ± 3 cm/sec, IVR 72 ± 7 msec, E/A = 1.6 ± 0.5, and DT = 193 ± 18 msec. Two SDs below the mean normal DEVM was 13.3 cm/sec. Two patient groups emerged: group A (10 patients) had abnormally slow DEVM (13.2 cmlsec) with DEVM = 11 ± 2 cm/sec and 20 ± 4 cm/sec, respectively. Mitral inflow parameters showed a longer DT and IVR, with lower E A ratios for group A versus group B, with DT = 203 ± 48 msec and 175 ± 21 msec, IVR = 87 ± 15 msec and 74 ± 7 msec, E A = 1.7 ± 0.7 and 2.3 ± 0.9, respectively. This is the first study in which measurements of posterior left ventricular wall early relaxation rates and Doppler evaluation of mitral inflow profiles provide evidence of occult myocardial myotonia in myotonic dystrophy.