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Association of myotonic dystrophy and sick sinus syndrome, with special reference to electrophysiological and histological examinations.

Sick sinus syndrome is a rare but potentially important cardiac disorder in patients with myotonic dystrophy. We evaluated 3 patients with myotonic dystrophy complicated with sick sinus syndrome using intracardiac electrocardiography and endomyocardial biopsy. Electrocardiography identified sinus arrest, atrial flutter and right bundle-branch block in 2 cases and marked sinus bradycardia and first-degree atrioventricular block in 1 case. Their sinus node recovery times were significantly prolonged as demonstrated by the overdrive suppression test. Two patients had Adams-Stokes syndrome and one had tachycardia with severe palpitations. Therefore permanent pacemaker implantation was indicated in all 3 cases. Light microscopic analysis of right ventricular endomyocardial biopsies showed vacuolar degeneration and nuclear deformity of cardiomyocytes in all cases and endocardial and interstitial fibrosis in 1 case. These findings indicate that pathological changes may occur in any part of the myocardium in patients with myotonic dystrophy.