Pacemakers: normal function.

AV sequential pacemakers are particularly useful in patients who have developed "pacemaker syndrome" with single-chambered ventricular demand units, since the normal atrioventricular relationship is then restored. Fully automatic pacemakers are indicated for patients with AV block, with or without sinus node dysfunction, or with moderate sick sinus syndrome and AV nodal or His-Purkinje disease, with at least some ability to increase atrial rate with exercise.