Sick sinus syndrome.

Disease in the sinus node may cause bradyarrhythmias or tachyarrhythmias. Bradyarrhythmias occur because of impaired automaticity (with or without sinus arrest) or because of sinus node exit block. Reentrant or automatic rhythms may produce tachyarrhythmias. Symptoms and signs of sick sinus syndrome include lightheadedness, palpitation, syncope and peripheral or cerebral emboli. After diagnosis by Holter monitoring, symptomatic patients usually improve with placement of a permanent cardiac pacemaker.