Without Missing a Beat: A Primer on Cardiac Rhythm Management Devices

When people think about heart disease, they generally think about what cardiologists commonly call “plumbing problems.” These are conditions in which the arteries that bring blood to the heart develop blockages and deprive the heart of the vital oxygen and nutrients it needs to survive. This deprivation can often result in a heart attack or heart failure.

But the heart also has an electrical system. The synchronized transmission of electricity through the heart causes the heart to beat in a coordinated manner, and a breakdown of this electrical system leads to serious, often life-threatening heart rhythms known as arrhythmias. (To learn more, see Background: Cardiac Function and Dysfunction below. ) Electrophysiology is the field of cardiology devoted to the study of arrhythmias, and an electrocardiogram (ECG) measures the electrical activity of the heart in order to identify and characterize these arrhythmias.

In the last 15 years, advances in implanted cardiac rhythm management (CRM) devices have allowed the successful treatment of an expanded range of cardiac conditions stemming from electrical system problems. Implanted CRM devices include one or more of the following three functions (which are described in more detail below): pacemakers, implantable cardioverter-defibrillators, and cardiac resynchronization therapy devices.

CRM devices consist of a hermetically sealed generator device and conductive electrode leads that connect to the generator in an area called the header. Implantable CRM devices usually have three components: a pulse generator, leads, and a programmer.

The pulse generator contains the circuitry that monitors the electrical activity of the patient’s heart and uses algorithms to determine when to deliver an electrical impulse through the leads to pace or shock the heart muscle. It also...