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Common questions about pacemakers.

Pacemakers are indicated in patients with certain symptomatic bradyarrhythmias caused by sinus node dysfunction, and in those with frequent, prolonged sinus pauses. Patients with third-degree or complete atrioventricular (AV) block benefit from pacemaker placement, as do those with type II second-degree AV block because of the risk of progression to complete AV block. The use of pacemakers in patients with type I second-degree AV block is controversial. Patients with first-degree AV block generally should not receive a pacemaker except when the PR interval is significantly prolonged and the patient is symptomatic. Although some guidelines recommend pacemaker implantation for patients with hypersensitive carotid sinus syndrome, recent evidence has not shown benefit. Some older patients with severe neurocardiogenic syncope may benefit from pacemakers, but most patients with this disorder do not. Cardiac resynchronization therapy improves mortality rates and some other disease-specific measures in patients who have a QRS duration of 150 milliseconds or greater and New York Heart Association class III or IV heart failure. Patients with class II heart failure and a QRS of 150 milliseconds or greater also appear to benefit, but there is insufficient evidence to support the use of cardiac resynchronization therapy in patients with class I heart failure. Cardiac resynchronization therapy in patients with a QRS of 120 to 150 milliseconds does not reduce rates of hospitalization or death.