A pacemaker is a small electronic device implanted under the skin, usually below the collarbone, that monitors the heart’s electrical activity and delivers electrical impulses to maintain a safe heart rate when the heart beats too slowly (bradycardia) or pauses. The device consists of a pulse generator (the device body, containing the battery and electronics) and one or more leads (thin wires) that pass through a vein into the heart. If the heart rate falls below a programmed threshold, the pacemaker delivers a small electrical impulse through the lead to stimulate a heartbeat.
Pacemakers are classified by the number and position of their leads. A single-chamber pacemaker has one lead placed in either the right ventricle or the right atrium. A dual-chamber pacemaker has leads in both the right atrium and right ventricle, allowing coordinated pacing that more closely mimics the natural heartbeat and preserves the atrial contribution to cardiac output. A biventricular pacemaker (used in cardiac resynchronisation therapy) has three leads coordinating both ventricles and the atrium, used in heart failure with electrical dyssynchrony. Leadless pacemakers are a newer development: miniaturised devices implanted directly inside the right ventricle without a traditional lead system.
Pacemakers do not treat ventricular fibrillation or ventricular tachycardia: they address only bradycardia (slow heart rate). Cardiac arrest survivors who also require pacing for bradycardia typically receive a combined device: an implantable cardioverter defibrillator (ICD) with integrated pacing capability. Patients who have a pacemaker alone, without an ICD, are generally those whose cardiac arrest risk is low but whose bradycardia requires pacing support.
Living with a pacemaker involves regular device clinic follow-up, remote device monitoring via home transmitter, and awareness of potential device interactions with certain medical equipment such as MRI scanners (many modern pacemakers are MRI-conditional) and strong magnetic fields. Pacemakers are compatible with most airport security equipment, though carrying a device identification card is recommended.