CARDIAC DISEASE IN MYOTONIC-DYSTROPHY

Cardiac disease is a well-known complication of myotonic dystrophy, un derstanding of which has been increased by recent advances in both mol ecular techniques and cardiological investigations. Conduction disturb ances and tachyarrhythmias occur commonly in myotonic dystrophy. These have been shown to have a broad correlation in severity with both neu romuscular disease and the extent of the molecular defect in some, but not all, studies. Clinical evidence of generalised cardiomyopathy is unusual. The rate of progression differs widely between individuals; s udden death may be caused by ventricular arrhythmias or complete heart block, and this can be at an early stage of disease. A familial tende ncy towards cardiac complications has been shown in some studies. The histopathology is of fibrosis, primarily in the conducting system and sino-atrial node, myocyte hypertrophy and fatty infiltration. Electron microscopy shows prominent I-bands and myofibrillar degeneration. Myo tonin protein kinase, the primary product of the myotonic dystrophy ge ne, may be located at the intercalated discs and have a different isof orm in cardiac tissue. The role of other genes or the normal myotonic dystrophy aIlele in myotonic heart disease has yet to be determined. S uggestions for clinical management include a careful cardiac history a nd a 12-lead ECG at least every year, with a low threshold for use of 24 h Holter monitoring. Extra care should be taken before, during and after general anaesthetics, which carry a high frequency of cardioresp iratory complications. Finally, myotonic dystrophy should be considere d in previously undiagnosed patients presenting to a cardiologist or g eneral physician with suspected arrhythmia or conduction block.