Sick sinus syndrome with normal atropine response--a case report.

A 76-year-old woman was admitted due to recurrent syncope. Sinus bradycardia and intermittent sinus pauses (up to 2.24 sec) were documented by 24 hour Holter electrocardiogram. Although intravenous atropine can increase the sinus rate up to 100 bpm, electrophysiologic study showed marked prolongation of sinus node recovery time both at the control state and after autonomic blockades. Sick sinus syndrome was diagnosed, even with a normal atropine test, and a permanent pacemaker resulted in resolution of the syncope.