What is a pacemaker?
A pacemaker is composed of three parts: a pulse generator, one or more leads, and an electrode on each lead. A pacemaker signals the heart to beat when the heartbeat is too slow or irregular.
A pulse generator is a small metal case that contains electronic circuitry with a small computer and a battery that regulate the impulses sent to the heart.
The lead (or leads) is an insulated wire that is connected to the pulse generator on one end, with the other end placed inside one of the heart’s chambers. The lead is almost always placed so that it runs through a large vein in the chest leading directly to the heart. The electrode on the end of a lead touches the heart wall. The lead delivers the electrical impulses to the heart. It also senses the heart’s electrical activity and relays this information back to the pulse generator. Pacemaker leads may be positioned in the atrium (upper chamber) or ventricle (lower chamber) or both, depending on the medical condition.
If the heart’s rate is slower than the programmed limit, an electrical impulse is sent through the lead to the electrode and causes the heart to beat at a faster rate.
When the heart beats at a rate faster than the programmed limit, the pacemaker generally monitors the heart rate and will not pace. Modern pacemakers are programmed to work on demand only, so they do not compete with natural heartbeats. Generally, no electrical impulses will be sent to the heart unless the heart’s natural rate falls below the pacemaker’s lower limit.
A newer type of pacemaker, called a biventricular pacemaker, is currently used in the treatment of specific types of heart failure. Sometimes in heart failure, the two ventricles do not pump in a normal manner. Ventricular dyssynchrony is a common term used to describe this abnormal pumping pattern. When this happens, less blood is pumped by the heart. A biventricular pacemaker paces both ventricles at the same time, increasing the amount of blood pumped by the heart. This type of treatment is called cardiac resynchronization therapy or CRT.
After a pacemaker insertion, regularly scheduled appointments will be made to ensure the pacemaker is functioning properly. The doctor uses a special computer, called a programmer, to review the pacemaker’s activity and adjust the settings when needed.
Other related procedures that may be used to assess the heart include resting and exercise electrocardiogram (ECG), Holter monitor, signal-averaged ECG, cardiac catheterization, chest X-ray, computed tomography (CT scan) of the chest, echocardiography, electrophysiology studies, magnetic resonance imaging (MRI) of the heart, myocardial perfusion scans, radionuclide angiography, and cardiac CT scan. Please see these procedures for additional information. Note that although an MRI is a very safe procedure, a person with a pacemaker generally should not undergo MRI, as the magnetic fields used by the MRI scanner may interfere with the pacemaker’s function. Any patient with a pacemaker should always speak with his or her cardiologist before undergoing an MRI.
Reasons for the procedure
A pacemaker may be inserted in order to stimulate a faster heart rate when the heart is beating too slowly, and causing problems that cannot otherwise be corrected.
Problems with the heart rhythm may cause difficulties because the heart is unable to pump an adequate amount of blood to the body. If the heart rate is too slow, the blood is pumped too slowly. If the heart rate is too fast or too irregular, the heart chambers are unable to fill up with enough blood to pump out with each beat. When the body does not receive enough blood, symptoms such as fatigue, dizziness, fainting, and/or chest pain may occur.
Some examples of heart rate and rhythm problems for which a pacemaker might be inserted include:
Bradycardia. This occurs when the sinus node causes the heart to beat too slowly.
Tachy-brady syndrome. This is characterized by alternating fast and slow heartbeats.
Heart block. This occurs when the electrical signal is delayed or blocked after leaving the SA node; there are several types of heart blocks.
There may be other reasons for your doctor to recommend a pacemaker insertion.