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 manife sts itself chiefly as abnormalities of specialized tissues. Current ec hocardiographic techniques permit assessment of left ventricular diast olic filling properties and might detect subtle myocardial myotonia. T wenty patients (mean age 37 +/- 13 years) with myotonic muscular dystr ophy were studied. Twenty normal subjects (mean age 34 +/- 12 years), served as controls. Each subject had two-dimensional targeted M-mode e chocardiograms of the posterior left ventricular wall to measure the r ate of early diastolic relaxation, which was defined as diastolic endo cardial 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 i sovolumic relaxation (IVR) time. Normal controls had DEVM = 19 +/- 3 c m/sec, IVR = 72 +/- 7 msec, E/A = 1.6 +/- 0.5, and DT = 193 +/- 18 mse c. Two SDs below the mean normal DEVM was 13.3 cm/sec. Two patient gro ups emerged: group A (10 patients) had abnormally slow DEVM (less than or equal to 13.2 cm/sec) and group B (10 patients) had normal DEVM (> 13.2 cm/sec) with DEVM = 11 +/- 2 cm/sec and 20 +/- 4 cm/sec, respecti vely. 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 1 75 +/- 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 me asurements of posterior left ventricular wall early relaxation rates a nd Doppler evaluation of mitral inflow profiles provide evidence of oc cult myocardial myotonia in myotonic dystrophy.