How do pacemakers and defibrillators work?

Electrocardiograms, or ECGs, record the electrical activity of your heart. Randy Faris/The Image Bank via Getty Images& A cardiologist explains how they interact with the electrical system of the heart by Virginia Singla, University of Pittsburgh Your heart’s job is to keep your pulse steady to pump blood throughout your body. Sometimes your heart rate is slower when you’re relaxing, and sometimes it’s faster when you’re exercising or stressed. If your heart’s ability to keep the beat starts to go awry, cardiac electrophysiologists like me look for outside help from an implantable device. There are two common implantable devices for the heart: artificial pacemakers and defibrillators. Artificial pacemakers keep blood and oxygen flowing during times of stress. Defibrillators are devices that detect dangerously fast heart rates and deliver shocks like those used during cardiopulmonary resuscitation, also known as CPR, to restart the heart. Understanding how these devices work requires appreciating how the heart’s electrical system works and the weak links that cause malfunctions. The heart’s natural pacemaker system Abnormally slow heart rates result from breakdowns in two principal areas of the heart. First, the sinoatrial, or SA, node sets your “resting” heart rate, usually somewhere between 60 and 100 beats...