Pacemakers are most commonly advised in patients whose heartbeat slows to an unhealthy low rate.
ICDs are advised in specific patients who are at risk for potentially fatal ventricular arrhythmias (an abnormal rhythm from the lower heart chambers, which can cause the heart to pump less effectively). There may be other reasons why doctors advise placement of a pacemaker or ICD.
When the heart’s natural pacemaker or electrical circuit malfunctions, the signals sent out may become erratic: either too slow, too fast, or too irregular to stimulate adequate contractions of the heart chambers. When the heartbeat becomes erratic, it is referred to as an arrhythmia.
Arrhythmias can cause problems with contractions of the heart chambers by:
The heart is, in the simplest terms, a pump made up of muscle tissue. The heart’s pumping action is regulated by an electrical conduction system that coordinates the contraction of the various chambers of the heart.
An electrical stimulus is generated by the sinus node (also called the sinoatrial node, or SA node), which is a small mass of specialized tissue located in the right atrium (right upper chamber of the heart). In an adult, the sinus node generates an electrical stimulus regularly (for adults, 60 to 100 times per minute under normal conditions). This electrical stimulus travels down through the conduction pathways (similar to the way electricity flows through power lines from the power plant to your house) and causes the heart’s lower chambers to contract and pump out blood. The right and left atria (the two upper chambers of the heart) are stimulated first and contract a short period of time before the right and left ventricles (the two lower chambers of the heart).
The electrical impulse travels from the sinus node through the atria to the atrioventricular node (also called AV node), where impulses are slowed down for a very short period, then continue down the conduction pathway via the bundle of His into the ventricles. The bundle of His divides into right and left pathways to provide electrical stimulation to the right and left ventricles.
Normally at rest, as the electrical impulse moves through the heart, the heart contracts about 60 to 100 times a minute, depending on a person’s age (infants normally have very high heart rates). Each contraction of the ventricles represents one heartbeat. The atria contract a fraction of a second before the ventricles so their blood empties into the ventricles before the ventricles contract.
Under some abnormal conditions, certain heart tissue is capable of starting a heartbeat, or becoming the pacemaker. An arrhythmia (abnormal heartbeat) occurs when:
In any of these situations, the body may not receive enough blood because the heart cannot pump out an adequate amount with each beat as a result of the arrhythmia’s effects on the heart rate. The effects on the body are often the same, however, whether the heartbeat is too fast, too slow, or too irregular. Some symptoms of arrhythmias include, but are not limited to:
A permanent pacemaker is a small device that is implanted under the skin (most often in the shoulder area just under the collarbone). It sends electrical signals to start or regulate a slow heartbeat. A permanent pacemaker may be used to make the heart beat if the heart’s natural pacemaker (the SA node) is not functioning properly and has developed an abnormally slow heart rate or rhythm, or if the electrical pathways are blocked.
A newer type of pacemaker, called a biventricular pacemaker, is currently used in the treatment of ventricular dyssynchrony (irregular conduction pattern in the lower heart chambers) or heart failure. Sometimes in heart failure, the two ventricles do not pump together in a normal manner. 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.
An implantable cardioverter defibrillator (ICD) looks very similar to a pacemaker, except that it is slightly larger. It has a generator, one or more leads, and an electrode for each lead. These components work very much like a pacemaker. However, the ICD is designed to deliver two levels of electrical energy: a low energy shock that can convert a beating heart that is in an abnormal rhythm back to a normal heartbeat, and a high energy shock that is delivered only if the arrhythmia is so severe that the heart is only quivering instead of beating.
An ICD senses when the heart is beating too fast and delivers an electrical shock to convert the fast rhythm to a normal rhythm. Many devices combine a pacemaker and ICD in one unit for people who need both functions. After the shock is delivered, a “back-up” pacing mode is available if needed for a short while.
The ICD has another type of treatment for certain fast rhythms called anti-tachycardia pacing, a fast-pacing impulse sent to correct the rhythm.
A permanent pacemaker or ICD has three main components:
Pacemakers can “sense” when the heart’s natural rate falls below the rate that has been programmed into the pacemaker’s circuitry.
Pacemaker leads may be positioned in the right atrium, right ventricle, or positioned to pace both ventricles, depending on the condition requiring the pacemaker to be inserted. An atrial arrhythmia (an arrhythmia caused by a dysfunction of the sinus node or the development of another atrial pacemaker within the heart tissue that takes over the function of the sinus node) may be treated with an atrial permanent pacemaker whose lead wire is located in the atrium.
When the ventricles are not stimulated normally by the sinus node or another natural atrial pacemaker site, a ventricular pacemaker whose lead wire is located in the ventricle is placed / used. It is possible to have both atrial and ventricular arrhythmias, and there are pacemakers which have lead wires positioned in both the atrium and the ventricle.
An ICD has a lead wire that is positioned in the ventricle, as it is used for treating fast ventricular arrhythmias. Commonly, ICDs will have an atrial lead and ventricular lead.
Pacemakers that pace either the right atrium or the right ventricle are called “single-chamber” pacemakers. Pacemakers that pace both the right atrium and right ventricle of the heart and require two pacing leads are called “dual-chamber” pacemakers. Pacemakers that pace the right atrium and right and left ventricles are called “biventricular” pacemakers.
Pacemaker/ICD insertion is done in the cardiac catheterization laboratory, or the electrophysiology laboratory (EP Lab). The patient is awake during the procedure, although local anaesthesia is given over the incision site, and generally sedation is given to help the patient relax during the procedure. A night or two of hospitalization may be recommended so that the functioning of the implanted device may be observed.
A small incision is made just under the collarbone. The pacemaker/ICD lead(s) is inserted into the heart through a blood vessel which runs under the collarbone. Once the lead is in place, it is tested to make sure it is in the right place and is functional. The lead is then attached to the generator, which is placed just under the skin through the incision made earlier. Once the procedure has been completed, the patient goes through a recovery period of several hours.
Once the device has been implanted, people with pacemakers or ICDs should be able to do the same activities everyone else in their age group is doing. Patients with pacemaker or ICD may still be able do the following:
When involved in a physical, recreational, or sporting activity, a person with a pacemaker or ICD should avoid receiving a blow to the area over the device. A blow to the chest near the pacemaker or ICD can affect its functioning. If a patient does receive a blow to that area, the doctor should be consulted immediately.
Patients should always consult the doctor if they feel ill after an activity, or when they have questions about beginning a new activity.
Although the device is built to last at least five years, it should always be checked regularly to ensure that it is working properly. Different doctors may have different schedules for checking devices, and most are checked in the home using a telephone and special equipment provided by the device manufacturer. Doctors will recommend in-person device checks at specific intervals as well. Any device setting changes must be made in person, by a trained medical professional, using a device programmer.
The doctor may ask the patient to check pulse rate periodically. Any unusual symptoms or symptoms similar to those prior to the device insertion should be reported to the doctor immediately.
Cell phones (less than 3 watts) generally do not appear to interfere with or damage pacemakers. However, it’s best to avoid keeping cell phones in the breast pocket on the side of the device. It’s probably better to use the phone on the opposite ear, as well.
Some devices may need to be adjusted if a person’s medical condition or lifestyle changes. Most adjustments are done noninvasively using a device called a programmer. This is a specialized computer that communicates with the pacemaker or ICD using magnetic signals via a “wand” or loop placed over the device. Doctors will instruct the patient about the schedule of follow-up visits based on your condition and type of device.
If the original leads are working properly, in most cases, they will be left in place and reattached to the new device.
Most devices will last at least 5 to 7 years, depending on use, after which the battery or pulse generator will need to be replaced. Replacing a pacemaker generator may be done on an outpatient basis or may include an overnight stay in the hospital.
Yes, patients can travel by air with the device and drive a car if cleared by the doctor. Airport security detectors are generally safe, but airport security staff should know about the presence of the pacemaker/ICD so that appropriate screening procedure can be followed. If selected to be screened by handheld wand, the patient should politely remind the screener that these wands should not be held over the device area for more than a few seconds.
Patients may be able to enjoy exercise with pacemaker or ICD, but should check with the doctor first.
At first, patients may feel the weight of the device in the chest. However, over time, most people become accustomed to the way it feels. The device generator is very small, about the size of two small coins stacked on top of each other, and weighs very little, depending on the make and model of the device. ICDs are typically slightly larger in size compared to a pacemaker. If the ICD sends a shock to the heart or “fires,” the person will feel this as a jolt or kick in the chest.
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