Much praise should be given to Ferrer1 who has popularized the sick sinus syndrome. As a result of her endeavors, many lives have been prolonged and numerous patients have been freed from disturbing neurological and/or cardiac symptoms. It is estimated that sinus node disorders currently account for 50% of the pacemakers implanted. Ferrer's contributions also have stimulated fundamental investigations of sinus node anatomy and electrophysiology, as emphasized in Bower's excellent review in this issue (p 133). Despite our better understanding of the sick sinus syndrome through clinical observations and research, there remain many unanswered problems and questions.
The sick sinus syndrome is not a single entity, but is characterized by a spectrum of cardiac rhythm disturbances that include marked sinus bradycardia, sinus arrest, sinus standstill, sinoatrial block, the tachycardiabradycardia syndrome, sinus bradycardia with conducted or nonconducted atrial premature systoles, atrial fibrillation with a slow ventricular response not due to