Problems with any part of the heart's electrical system can cause irregular heartbeats called arrhythmias. Most arrhythmias are harmless, but some can be serious. Serious arrhythmias can cause sudden cardiac arrest (SCA), a condition in which the heart suddenly stops beating. If the heart stops beating, blood stops flowing to the brain and other vital organs. SCA usually causes death if it's not treated within minutes.
Several types of cardiac devices are used to treat arrhythmias by detecting the irregular heart beat and immediately generating an electric shock to the heart called defibrillation.
An implantable cardioverter defibrillator (ICD) is a small device placed in the chest or abdomen that has wires with electrodes on the ends that connect to the heart chambers. If the device detects an irregular rhythm, it will use low-energy electrical pulses to restore a normal rhythm. If the low-energy pulses don't restore a normal heart rhythm, the ICD will switch to high-energy pulses for defibrillation. The device also will switch to high-energy pulses if the ventricles start to quiver rather than contract strongly. The high-energy pulses last only a fraction of a second, but they can be painful.
Doctors may also treat arrhythmias with a pacemaker. Pacemakers give off only low-energy electrical pulses. They're often used to treat less dangerous heart rhythms, such as those that occur in the upper chambers of the heart.
People with heart failure may need a special device called a cardiac resynchronization therapy (CRT) device. The CRT device is able to pace both ventricles at the same time. This allows them to work together and do a better job pumping blood out of the heart. CRT devices that have a defibrillator are called CRT-D.
Although rare, some risks related to surgery used to place cardiac devices include unnecessary electrical shocks; swelling, bruising, bleeding or infection in the area where the device was placed; blood vessel, heart or nerve damage; collapsed lung; or heart failure. The longer a device is used, the more likely that some of the related risks will occur.
[1] NIH, National Heart, Lung, and Blood Institute (Nov. 9, 2011).