What is a pacemaker insertion?
A pacemaker insertion is the implantation of a small electronic device in the chest (just below the collarbone) to help regulate electrical problems with the heart. When a problem develops, such as a slow heart rate, a pacemaker may be recommended to ensure that the heartbeat does not slow to a dangerously low rate.
The heart's electrical conduction system
The heart is basically a pump made up of muscle tissue that is stimulated by electrical currents, which normally follow a specific circuit within the heart.
This normal electrical circuit begins in the sinus or sinoatrial (SA) node, which is a small mass of specialized tissue located in the right atrium (upper chamber) of the heart. The SA node generates an electrical stimulus at 60 to 100 times per minute (for adults) under normal conditions; this electrical impulse from the SA node starts the heartbeat.
The electrical impulse travels from the SA node to the atrioventricular (AV) node in the bottom of the right atrium. From there the impulse continues down an electrical conduction pathway called the Bundle of His and then on through the "His-Purkinje" system into the ventricles (lower chambers) of the heart. When the electrical stimulus occurs it causes the muscle to contract and pump blood to the rest of the body. This process of electrical stimulation followed by muscle contraction is what makes the heart beat.
A pacemaker may be needed when problems occur with the electrical conduction system of the heart. When the timing of the electrical stimulation of the heart to the heart muscle and the subsequent response of the heart's pumping chambers is altered, a pacemaker may help.
What is a pacemaker?
A pacemaker is a life-saving medical device 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 dyschrony 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.