[Family with predominance of cardiac involvement in Steinert's disease]. / Família com predominância do comprometimento cardíaco na doença de Steinert.

We report an affected family (mother and two children) with prominent cardiac form as reflected by the mother, 49, with neuromuscular signs (muscular atrophy os face, neck and distally in the extremities) who received an implantable pacemaker after 2 consecutive episodes of syncope and baseline EKG with P-R of 250 ms, QRS of 130 ms (LBBB) and conduction system intervals displaying overt widening (AH of 140 ms with a ERP of junction tissue of 590 ms, and Wenckebach point of 115 bpm; and HV of 80 ms before and 95 ms after pharmacological stress with procainamide). As long as its mode of inheritance is autosomal dominant, the cardiovascular examination of her two affected siblings (F1 and F2) revealed: F1 (male, 31), with P-R of 180 ms and QRS of 100 ms; F2 (female, 27), with P-R of 200 ms and QRS of 100 ms, both with left axis deviation. Echocardiographic studies were normal in both, but Holter studies showed remarkable bradycardia in both and intermittent rate-related (phase 3) LBBB in F2. Also for F1 and F2 conduction system intervals, except for AH (normal in both), displayed severe widening (HV of 70 ms in F1 and of 80 ms in F2, but only in this later with a procainamide stress extra widening to 130 ms). All three patients showed normal NS function, as usual for the disease. F2 is kept under close surveillance for the appearance of any symptom. In conclusion, although rarely symptomatic, the intensity of IV conduction system damage should not be disregarded in this condition.