SYMPOSIUM Cardiac Arrhythmias (Part 3) The Sick Sinus Syndrome

course. All ages are affected and the diagnosis must be considered if there is a modest degree of sinus bradyeardia (SB), even if asymptomatic, as SB is less benign than was heretofore thought. Inappropriate or relatively slow sinus rates (RSSR) under stressful conditions are equally as important as SB. Inadequacy of the sinoatrial node (SAN) may be manifested by one or more of the following: (1) persistent severe and unexpected sinus bradyeardia; (2) cessation of sinus rhythm (sinus arrest) for short intervals during which no other (escape) rhythm arises, or for somewhat longer periods with replacement of sinus rhythm by an atrial or junctional rhythm; (3) long periods of sinus arrest without the appearance of a new pacemaker and resulting in total cardiac arrest (ventricular arrhythmias may then follow); (4) chronic atrial fibrillation because the SAN is permanently silent, or repeated episodes of transitory atrial fibrillation due to total cessation of sinus rhythm at these times. Atrial fibrillation is often, but not always, accompanied by a slow ventricular rate (not produced by digitalis but resulting from an accompanying organic A-V block and the patient has binodal disease); (5) inability of the heart to resume sinus rhythm following cardioversion for atrial fibrillation (most likely if the ventricular rate is slow as mentioned above); and (6) episodes of sinoatrial exit block which are not related to drug therapy. These six items form the indirect evidences for the SSS and represent primary physiologic manifestations. Provocative tests are of value although not wholly satisfactory. Therapy for the chronic form will eventually be a ventricular artificial pacemaker. The natural history of the SSS is imperfectly known but probably covers 5-10 years, at least.