Definition & Overview
A pacemaker is a small electronic device that is surgically implanted under the skin, just beneath the collarbone, to help manage abnormal or irregular heartbeat or arrhythmias. The device sends electrical pulses to the heart muscle to stimulate the heart to beat at a normal rate. It is composed of a small titanium encased pulse generator powered by a lithium battery, and is attached to the leads or wires that are also attached to the heart. Pacemaker pulse generators and their batteries are typically checked every four months and in general, replaced every five to ten years or when they reach their replacement indicator. Other reasons for their removal are device infection and when the device malfunctions. Meanwhile, the leads of the pacemaker can be left in place although they may have to be replaced eventually.
Trained cardiologists insert and remove pacemaker pulse generator through a simple incision procedure under local anaesthetic. The process usually takes less than an hour.
The pacemaker is implanted into the soft tissues beneath the skin below the clavicle. This type of implantation is called prepectoral implantation because the pacemaker is inserted into the pectoral muscle.
The pacemaker leads or wires are inserted into a major vein called the subclavian vein transvenously. The leads, on the other hand, are inserted intravenously (into the vein). The other end of the lead goes out of the vein and attaches directly to the appropriate heart muscle. The other ends are attached to the pulse generator, which contains the chip and the battery.
Pacemakers store and transmit information using a chip. The data stored in the chip can be downloaded during the patient's follow-up visit with his or her doctor. For new-generation pacemakers, it is now possible to transmit the data from the pacemaker and uploaded to the Internet for the doctor to download.
Who Should Undergo and Expected Results?
The insertion of a pacemaker and its pulse generator is indicated for patients who have been diagnosed with arrhythmias. As mentioned earlier, the pulse generator can be removed and then replaced in case of device infection, malfunction, and when it reaches its replacement indicator.
An arrhythmia is a sign that the flow of electrical impulses around the heart’s chambers is not strong enough or unstable causing the heart to quiver. Tachycardia (too fast) and bradycardia (too slow) are two typical examples of irregular heartbeat conditions that indicate the need for a pacemaker.
There are two kinds of bradycardia: sinus bradycardia and heart block. Sinus bradycardia is a condition where the heart’s natural pacemaker operates slowly making the heart muscle to beat slowly as well. Heart block, on the other hand, is a term used to describe a delay in the conduction system of the heart. Blocks or delays occur along the ventricles and atria due to underlying heart diseases. This block or delay prevents the heart from achieving its heartbeat rhythm, which leads to a reduced total cardiac output. Cardiac output refers to the amount of blood the heart is able to pump in one minute. A lower or higher cardiac output signifies an abnormality.
How is the Procedure Performed?
The insertion or removal of a pacemaker pulse generator is done by a trained cardiac electrophysiologist or cardiologist. It is done in a sterile lab environment due to the sensitivity of the heart tissues to microbial agents such as bacteria or fungi.
The patient is placed under local anaesthesia or conscious sedation to make the entire medical procedure as pain-free as possible. In some cases, general anaesthesia is used when there’s a need to open the chest wall to gain access to the heart.
The insertion and removal of a pacemaker pulse generator are relatively simple procedures. For the insertion, the skin near the collarbone is cut to make way for the pulse generator. Leads or wires are attached to the pulse generator and inserted into the subclavian vein. The leads are guided until they reach the target or appropriate heart muscle where electric signals from the pulse generator are sent.
For removal or replacement procedures, the old incision is reopened and the pulse generator is removed or replaced with a new one. For replacement, if the existing leads are still functioning optimally, they will not be replaced and are connected to the new pulse generator.
There are only a few cases when a new set of threaded leads is replaced and this is usually due to the leads not conducting impulses efficiently. A computer designed to extract information stored in the chip inside the pulse generator detects this almost instantly. Therefore, any mechanical failure can be identified and taken care of immediately.
Leads usually last a lifetime without causing trouble to the surrounding tissues. There are only a few reported cases of error or failure. When the leads break or lose contact with the heart muscle, or fail due to any reason, new leads are put in place but the old ones are left behind.
Normally, when leads are installed, new tissues bind to them and attach them to nearby organs such as the lungs and the heart. This creates scar tissues around the leads that can be challenging to remove. The removal of used leads is only required when the entire pacemaker system has been infected and causes necrosis to nearby tissues.
Possible Risks and Complications
Invasive medical procedures such as the installation or removal of a pacemaker pulse generator come with some complications. One of these is bacterial infection around the area where the leads are. These infections are classified as either pocket infections or deep infections depending on the severity of the contamination.
An infection is considered a pocket infection when it is subcutaneous, meaning it occurs below or near the skin. Meanwhile, any part of the leads that are in the deep section of the veins near the heart could get infected and manifest an abnormal growth called vegetation. This condition can also bring about bacteremia or the presence of bacteria in the blood.
Other risks also include bleeding at the incision or catheter insertion site, which can be addressed using additional sutures. Damage to the blood vessels can also occur.
Brian Olshansky, MD and David L Hayes, MD; “Patient education: Pacemakers Beyond the Basics”; http://www.uptodate.com/contents/pacemakers-beyond-the-basics
John Hopkins Medicine; “Pacemaker Insertion”; http://www.hopkinsmedicine.org/healthlibrary/testprocedures/cardiovascular/pacemakerinsertion_92,p07980/