The sick sinus syndrome.

Clinical and electrophysiological characteristics have been investigated in a group of 30 patients with a sick sinus syndrome. No predictable response to exercise or drugs was observed, although a poor response of the sinus rate to atropine was present. Distal conduction abnormalities were found in seven of 14 patients, in whom detailed electrophysiological measurements were made, and sinus node recovery time was abnormal in all except one. Treatment with permanent pacing not only relieved syncope and dizziness, but made drug treatment of associated tachyarrhythmias feasible. The elusive and intermittent nature of the syndrome is stressed. The pathological findings in one case are described at length.