The etiology and natural history of sinus node disorders.

Two aspects of sinus node disorders currently seem to need emphasis--the etiology, which is still a difficult area, and the detailed structuring of the natural history of the sick sinus syndrome (SSS). The latter is becoming much clearer. The multifaceted influences of normal S-A nodal functions are reviewed. Degenerative fibrosis is the commonest abnormality, and coronary artery disease is not a major cause of the syndrome. The framework of the progressive natural history of the SSS in its usual sequential phases can now be constructed. Of course, not every feature of this progression is perceived in each patient. Gradually developing stages are reviewed, new data concerning behavior of rescue rhythms in S-A node disorders are presented, and a brief comment concerning the needs for and complications of pacing is included.