[New aspects in the pathogenesis of the prolonged QT-interval syndrome with syncopal attacks. Intracardiac ECG recordings during atrial stimulation in 4 patients (author's transl)].

Three families with the syndrome of hereditary prolonged QT interval affecting 12 members in two or three generations are described. Four patients with sinus bradycardia and frequent syncopal attacks were investigated by Holter-monitoring, His-bundle electrograms and exercise testing. Corrected QT intervals (QTc) were prolonged from 0.43 to 0.54 seconds at rest. In His-bundle electrograms, during atrial pacing at increasing rates the function of the entire conduction system seemed to be affected. Three patients were treated with pindolol and one patient with a permanent demand pacemaker and pindolol. During progressive exercise testing performed after drug therapy or pacemaker treatment, heart rate increased unsatisfactorily and QTc-intervals lengthened whereas atrial stimulation QTc-intervals remained unchanged. In the patient with a permanent demand pacemaker, electrocardiographic monitoring revealed a period of 25 seconds of ventricular tachycardia occurring at rest and ceasing spontaneously. In the past 1.2 years to 2.5 years (mean 2.1 years) of outpatient follow-up, the patients had normal exercise tolerance and syncopal attacks did not occur on pindolol 30 mg/day. Our findings suggest rather a hypersensitivity of the affected conclusion system in the presence of a normal activity of cardiac sympathetic nerves.