What Is a Pacemaker and Who Needs One?

A pacemaker is a small implantable electronic device that monitors the heart's electrical activity and delivers electrical impulses to prompt the heart to beat when it detects that the heart is beating too slowly or has paused. Pacemakers have transformed the treatment of bradyarrhythmias (abnormally slow heart rhythms) — conditions that once caused fainting, disability, and death. Today, more than one million pacemakers are implanted worldwide each year, and modern devices are sophisticated, reliable, and minimally invasive to implant.

HOW THE HEART'S ELECTRICAL SYSTEM WORKS

The heart beats in response to electrical impulses — not mechanical squeezing. Normally, each heartbeat originates in the sinoatrial (SA) node — the heart's natural pacemaker — a cluster of specialized cells in the right atrium that spontaneously depolarizes approximately 60–100 times per minute at rest.

The electrical impulse from the SA node spreads across both atria, causing them to contract. It then reaches the atrioventricular (AV) node — a relay station between the atria and ventricles — which introduces a brief delay (allowing the atria to finish contracting and the ventricles to fill) before transmitting the impulse to the ventricles through the His-Purkinje conduction system, causing the ventricles to contract.