[Sinus node syndrome].

Recently disorders of sinus node function have found increasing interest in clinical medicine thanks to new diagnostic and therapeutic developments. This paper represents a comprehensive review of these conditions, combined under the name "Sick Sinus Syndrome" (SSS). Besides a detailed analysis of 63 cases seen at our institution, the results of other groups are compared and extensively discussed. The clinical picture of the SSS is characterized by a wide variety of bradycardiac and tachycardic atrial arrhythmias, occurring separately or in combination. These can be classified in three subgroups: Patients with exclusive sinus bradycardia; patients with sinoatrial exit block or transient episodes of sinus arrest with or without AV escape rhythms; and finally patients with the bradycardia/tachycardia-syndrome, which are complicated by additional atrial tachyarrhythmias. The symptomatology of the SSS is multiform and extends from symptomless cases and those with only general signs of reduced cardiac function to patients with recurrent severe syncopal attacks which may lead to cerebral damage and even death. Besides the typical history, the diagnosis of the SSS primarily rests upon the ECG, especially the long term ECG recorded continuously on a 24 hrs. tape (Holter technique). Also the exercise ECG is of some value, characteristically showing an inadequate increase in the sinus rate, sometimes with AV escape systoles and -rhythms. In addition various provocative tests have been devised which are of help to differentiate between a pathologic and a normal sinus node function. Among these the determination of the sinus node recovery time following overdrive atrial pacing has gained wide acceptance. In most cases the exact etiology of the SSS is not known. In addition to coronary and inflammatory heart diseases a primarily degenerative lesion of the sinus node, comparable to cases with "primary heart block" are discussed. There is also a remarkably frequent past history diththeria. Rarer causes of the condition represent cases with cardiomyopathy, thyreotoxic heart disease, collagen and other disorders and also a familial manifestation of the SSS has been described. Therapeutically, pharmacologic treatment with vagolytic, beta-adrenergic or the common antiarrhythmic drugs is often unsuccessful, especially in the treatment of the Brady-Tachy-Syndrome. Digitalis glycosides, however, are frequently of some value, as they represent an effective prophylactic agent against atrial tachyarrhythmias without prolonging the sinus node recovery time or reducing significantly the sinus rate. While a few patients do not require any treatment, an artificial cardiac pacemaker has to be inserted in most cases. Atrial stimulation may be superior to ventricular on-demand pacing in some patients, and also a special system for the treatment of the SSS combined with significant AV block (binodal disease) has been designed, the bifocal sequential pacemaker.