A pacemaker is an electronic device used to treat patients who have symptoms caused by abnormally slow heartbeats. A pacemaker is capable of keeping track of the patient's heartbeats. If the patient's heart is beating too slowly, the pacemaker will generate electrical signals similar to the heart's natural signals, causing the heart to beat faster. The purpose of the pacemaker is to maintain heartbeats so that adequate oxygen and nutrients are delivered through the blood to the organs of the body.
What is the normal function of the heart ?
The heart is an organ consisting of four chambers that pump blood. The two upper chambers are called the right and left atria, and the two lower chambers are called the right and left ventricles. The right atrium receives venous blood (oxygen-poor blood) from the body and pumps it into the right ventricle. The right ventricle pumps the oxygen-poor blood to the lungs to receive oxygen. The oxygen-rich blood from the lungs then travels to the left atrium and is pumped by the left atrium into the left ventricle.
The left ventricle delivers the oxygen-rich blood to the rest of the body. In addition to oxygen, the blood transports other nutrients (glucose, electrolytes, etc.) to the organs. In order to keep a body healthy, the heart must maintain an adequate heartbeat (heart rate) so that sufficient amount of oxygen and nutrients are delivered by the left ventricle to the body.
The heartbeat (heart rate) is normally governed by the frequency of electrical signals which are generated by the heart's natural pacemaker called the SA node. The SA node is located on the wall of the right atrium.
Electrical signals from the SA node travel along special conduction tissues on the walls of the atria, causing the atria muscles to contract and pump. These same electrical signals then travel to the AV node, a small area in the heart that serves as an electrical relay station between the atria and the ventricles. From the AV node, these electrical signals travel along special conduction tissues to reach the walls of the ventricles, causing the ventricles to pump.
Normally, the heart can vary the amount of blood delivered to the body by varying the frequency of the signals originating from the SA node. When a person is resting and the oxygen consumption of the body is low, the frequency of signal generation by the SA node decreases, thus slowing the heart rate. During exercise or excitement, the frequency of signal generation by the SA node increases and the heart rate accelerates.
What are the causes of slow heart rates ?
Abnormally slow heart rates (bradycardias) can result from diseases affecting the SA node, the conduction tissues, and the AV node. Sick sinus syndrome is a disease wherein the SA node cannot generate signals frequently enough to maintain adequate heart rate. Heart blocks are conditions where diseases (such as heart attacks) or degeneration (due to processes such as aging) of the AV node and/or the conduction tissues impair the transmission of signals from the SA node to the heart muscles.
Some medications can cause bradycardia. Examples of these medications include calcium channel blockers such as verapamil (Calan) and beta-blockers such as propanolol (Inderal) and digoxin (Lanoxin). These medications can also aggravate bradycardias in patients with existing diseases of the SA node, AV node, and other parts of the heart's conduction system.
The most common cause of bradycardia is degeneration of the conduction system that occurs as part of the aging process. Thus, people are more likely to need a pacemaker as they get older, both as part of the aging process and because older patients tend to have more medical problems that can cause slow heartbeats.
What happens when the heart beats too slowly ?
When the heart beats too slowly, an insufficient amount of blood reaches the organs. An insufficient supply of oxygen and nutrients can lead to malfunction and failure of the organs. The organ most affected by the lack of oxygen and glucose is the brain. Symptoms of insufficient blood supply to the brain include lightheadedness, forgetfulness, and loss of consciousness. Symptoms of inadequate blood supply to the muscles include tiredness, malaise, and fatigue. An insufficient blood supply to other organs can lead to heart, kidney, and liver failure. When an abnormally slow heart rate causes symptoms and/or organ failures, treatment for the slow heart rate becomes necessary.
Highly trained athletes with efficient cardiovascular systems can deliver all the oxygen and the nutrients the body needs with very slow heart rates. They typically have abnormally slow heart rates without any adverse symptoms or organ failures. Slow heart rates because of physical fitness do not need treatment.
How can an abnormally slow heart rate be increased ?
There is no medicine available in oral (pill) form that can be taken regularly to increase the heart rate. Currently, the only method to consistently increase the heart rate is the use of a pacemaker to send electrical signals to generate heartbeats.
Temporary pacemakers are usually used first, especially if the abnormally slow heart rate is believed to be transient (lasting only days) and caused by conditions that are reversible or correctable. Temporary pacemakers are easily disconnected if the heart rate returns to normal.
Permanent pacemakers are necessary when the slow heart rate becomes chronic (lasting more than a few days) or is believed to be irreversible.
What is the design of permanent pacemakers ?
A permanent pacemaker has two parts; the pacemaker chamber and the lead(s). The pacemaker chamber contains a timing device for setting the pacing rate, a circuitry that detects electrical signals from the heart, and a battery.
In some patients who need permanent pacemakers for abnormally slow heart rates, fluctuations of the heart rate can occur. The pacemaker is capable of "listening" to the natural electrical signals from the heart. When the heart is beating normally, the pacemaker does nothing. When the heart stops beating or beats too slowly, the pacemaker takes over generating electrical signals for the heart at a frequency set by the doctor.
While temporary pacemakers are housed in chambers outside of the body and can use external electrical power sources, permanent pacemakers are implanted inside the body and therefore need their own batteries. Most of the modern permanent pacemaker chambers are small, weighing less than 30 grams. These small, lightweight devices are comfortable to wear inside the body and are barely visible. The small batteries inside the pacemaker chambers are also durable. Most implanted pacemakers have batteries that will last 7-10 years before needing to be replaced.
The conducting wire(s) that carry electrical signals between the heart and the pacemaker is usually made of platinum. These wires are insulated with silicone or polyurethane. The insulted wires are called leads. Some pacemakers have only one lead, and are called single-chamber pacemakers. Others have two leads and are called dual- chamber pacemakers.
The pacemaker lead is inserted through a vein in the chest into the heart. The tip of the lead is placed in contact with the inner wall of the right atrium or the right ventricle, while the other end of the lead is connected to the pacemaker chamber. These leads are safe, and generally do not injure or cause infections in the veins or the heart.
How are pacemakers implanted ?
Pacemaker systems are often implanted under local anesthesia in a cardiac catheterization laboratory. Implantation of a pacemaker is considered a minor procedure. Some hospitals with electrophysiology laboratories implant pacemakers there. Hospitals without catheterization labs implant pacemakers in the operating room.
Patients are typically awake or only mildly sedated during the procedure. A local anesthetic is injected under the skin over the area where the pacemaker will be implanted, usually in the right or left upper chest near the collarbone. The numbing injection keeps the patient from feeling pain when a small incision is made over the same area to create a small space. The pacemaker lead is then inserted into a vein located in the upper chest near the collarbone. The lead is placed in the right atrium or the right ventricle with the visual guidance of x-rays. The tip of the lead is then attached to the inner surface of the heart by small tines or with a small screw. If there is more than one lead, the process is repeated. Because there are no nerve endings inside the blood vessels and the heart, the patient usually does not feel the placement of the lead(s).
The other end of the lead(s) is then connected to the pacemaker chamber, which is then placed under the skin. Closing the incision with sutures completes the process. The procedure usually takes about an hour. Patients are discharged the same or the next day if there are no complications. Patients are given antibiotics to prevent possible infection, and sent home with pain medications to alleviate post-surgical pain at the incision site.
Occasionally, leads are placed on the outer surface of the heart, a process called epicardial (outside the heart) implantation. When leads are placed in this manner, the chest wall is opened surgically. The lead or leads are placed onto the heart surface, and the pacemaker chamber is implanted underneath the skin in the upper abdomen. Because epicardial implantation is more difficult and requires more extensive surgery, this procedure is used when leads cannot be placed inside the heart via the blood vessels. These situations occur most frequently in children who are too small to have a lead placed in the blood vessels, or in adult patients with congenital heart disease. Also, as children grow, the distance between the pacemaker and the heart increases. Thus the lead(s) between the heart and the chamber becomes too short.
What are possible complications of pacemaker implantation ?
Pacemaker implantation is a safe procedure in experienced hands. The death rate due to a direct complication from pacemaker implantation is less than one in 10,000 implantations. Complications occur less than 1% of the time and include bleeding, bruising, and infection at the implantation site, introduction of air into the space between the lung and chest wall (necessitating chest tube placement), perforation of the heart (requiring urgent drainage of the blood from the sac surrounding the heart), stroke, heart attack, and damage to blood vessels.
What are the types of pacemakers ?
Pacemakers may contain one or multiple leads. A single-chamber pacemaker has one lead while a dual-chamber has two leads.
When the lead from a single-chamber pacemaker is placed in the ventricle, the pacemaker is able to receive signals from and pace only the ventricle. If the lead is placed in the atrium, the pacemaker will be able to receive signals from and pace only the atrium. Depending on the cause and the nature of the bradycardia, the doctor decides where to place the single lead.
Dual chamber pacemakers have two leads: one in the atrium and one in the ventricle. Dual-chamber pacemakers are more complex and sophisticated than single-chamber pacemakers. A dual chamber pacemaker can receive signal from and pace both the ventricle and the atrium. It can also coordinate the signals and contractions of the atria and the ventricles to help the heart beat more efficiently.
In a normal contraction cycle in a normal heart, the atria contract first to deliver blood into the ventricles. The ventricles then contract after a short time interval. Dual-chamber pacemakers can coordinate the electrical signals to the atrium and the ventricle so that this natural sequence of contractions is followed. Following the natural sequence of contractions improves the pumping efficiency of the heart.
Dual-chamber pacemakers are more susceptible to problems because of their greater degree of sophistication. These pacemakers can cause the heart to race inappropriately if confused by the heart's own electrical activity. Also, additional leads mean that more equipment can potentially fail. Thus, not all patients are good candidates for dual-chamber pacemakers. Some patients are better served with a single-chamber pacemaker. A qualified cardiologist or electrophysiologist is ideal to decide which pacemaker is most appropriate.
Can some pacemakers automatically adjust the heart rate ?
Pacemakers can be equipped with a rate of activity response feature. This feature allows the pacemaker to pace faster during periods of physical exertion or stress. The body's metabolic activity increases with exercise and stress. Heightened metabolic activity in turn increases the need for more blood supply to muscles and other organs. Newer pacemakers with rate of activity response features can measure the body's metabolic activity (with sensors) and increase heartbeats by accelerating the pacing rate during exercise and stress. After exercise or stress, the pacing rate returns to the previously programmed setting.
Different rate of activity response pacemakers use various sensors to measure metabolic activity. One type of pacemaker contains a sensor that detects vibration related to activity. The pacing rate accelerates when the pacemaker senses increased vibration. Another type of pacemaker has a sensor that detects the rate of breathing. The pacing rate increases when a person breathes faster. Other types of pacemakers contain sensors that measure changes in body acidity, pressures inside the heart chambers, and body temperature, etc. Each of these sensors has its strengths and weaknesses. Because no one sensor method is perfect, some pacemakers now incorporate multiple sensors to more accurately gauge the body's metabolic activity.
Living with a pacemaker
Most patients can eventually return to normal activities after receiving a pacemaker. In fact, patients with a pacemaker usually feel better and may be able to do more than before.
It is normal to have some pain in the area around the implanted pacemaker for a week or so after the procedure. Patients are given pain medications to alleviate this post-surgical pain. It is also normal to feel some numbness and heaviness around the pacemaker for some months.
Patients can return to most of their normal daily activities a few days after the procedure. During the first weeks after the procedure, the patient is asked not to lift the arm on the side of the pacemaker implantation over the head. This precaution is to avoid dislodging the lead(s) and to allow the lead(s) to become firmly secured inside the heart. The patient is also asked to avoid heavy lifting, contact sports, and other vigorous exercises for a few weeks.
The sutures at the incision site are removed between one to two weeks after the procedure, usually in the doctor's office or in a pacemaker clinic. This is also the time to discuss with the doctor issues regarding activity levels, exercises, symptoms, when and how frequently to check the function and the battery levels of the pacemakers, signs of pacemaker malfunction, and precautions regarding interference from electrical appliances and devices.
Most doctors allow their patients to return to work in one to two weeks, even though the incision may take several weeks to heal completely. Some doctors recommend that their patients subscribe to telephone monitoring services. The pacemaker signals which are transmitted to the doctor' office or the pacemaker clinic by telephone can be analyzed to make sure the pacemaker is functioning properly.
Every patient is given a pacemaker ID card to carry. The ID card contains information regarding the pacemaker. The should be shown to other doctors and dentists. Occasionally, security officers at the airport will request seeing the card.
When to report problems to the doctor
During the first one to two weeks after implantation, fever along with excessive pain, redness, swelling, heat at the pacemaker site, and fluid drainage from the pacemaker site can represent infection. Report these symptoms to the doctor promptly.
Recurrence of weakness, dizziness, or any symptoms that a patient experienced before implantation may represent pacemaker malfunction. Other symptoms possibly related to malfunction include muscle twitches, fast and pounding heartbeats, and shortness of breath. These symptoms should be reported to the doctor.
What outside electrical sources are safe ?
Modern pacemakers are well protected from most household electrical appliances in good condition such as radios, televisions, stereos, microwave ovens, electrical blankets, computers, vacuum cleaners, etc.
What outside electrical sources can interfere with the pacemaker ?
Magnetic resonance imaging (MRI scan) is a diagnostic test for studying the brain, the joints, the spine, the liver, and other organs. The strong magnetic field from the MRI scan can interfere with pacemakers. Patients with pacemakers should not undergo MRI scanning.
Digital cellular phones can interfere with pacemakers. Therefore, the cellular phone should be held on the ear opposite from the side of the pacemaker. Do not carry the phone in the pocket near the chest.
Theft detector gates in certain stores can generate signals that interfere with the pacemaker. While it is safe for patients with pacemakers to quickly walk through these gates, they should not stand at the gates or near them.
Similarly, the metal detector gates at airports can also interfere with the pacemaker. This problem can be avoided by presenting the pacemaker ID card to the security officers and walking around the gates. Hand held security wands (such as those used by security officers) have magnetic fields that can interfere with the device. Scanning by these wands should be avoided.
Heavy-duty electrical powered equipment such as arc welders, a running car engine, and certain electrically powered surgical tools can also cause disturbances with pacemakers. Patients should obtain permission from their doctors prior to driving a car or operating equipment which may fall into the above category. Although a running car should not interfere with a pacemaker during driving, a patient should not lean over a running engine. Any other concerns and precautions should be discussed with your doctor.
When should the battery be replaced ?
Pacemaker leads and batteries are becoming more efficient so that the battery life of the pacemaker continues to increase even as the size of pacemakers decreases.
A modern pacemaker battery can usually last 7-10 years. When the battery is running low, the pacemaker will send a signal that can be detected by the doctor during a routine office or pacemaker clinic visit. A low battery still has time to be replaced electively. The patient should not have to worry that the battery will die unexpectedly.
Since the battery is sealed inside the pacemaker chamber, replacing the battery means replacing the entire chamber.
What newer features can pacemakers have ?
Exciting advances in pacemaker technology will add newer features to help heart patients including : -
The ability of pacemakers to record the natural electrical rhythm of the heart. Some patients experience intermittent symptoms even after implantation of a permanent pacemaker. These symptoms may be due to episodes of irregular fast heart rhythms (such as atrial fibrillation). The heart rhythm recording can help the doctor determine whether abnormal heart rhythms (such as atrial fibrillation) are responsible for the reported symptoms.
Pacemakers will also be used to prevent recurrent episodes of abnormal rapid rhythms such as occur with atrial fibrillation. These pacemakers will be equipped with multiple leads implanted in the atrium. These leads control the electrical activity of the atrium and prevent atrial fibrillation.
Pacemakers may also be used in the future in patients with congestive heart failure. In congestive heart failure, the damaged heart muscles of the ventricles do not pump efficiently. Different diseases such as heart attacks, virus infections, and chronic high blood pressure can damage these muscles. Current treatment of congestive heart failure is with medications such as diuretics, digoxin, and ace-inhibitors. Some studies suggest that permanently pacing the ventricle muscles using one or multiple leads can improve overall heart pumping efficiency in patients with congestive heart failure.
Pacemakers are also now used with increasing frequency in patients with severe symptoms from atrial arrhythmias after treatment by AV node destruction (ablation). Please read the Atrial Fibrillation article for more information.
Pacemakers are being incorporated in implantable defibrillator devices. These combined devices are now capable of treating both fast and slow rhythms in the same patient.
Pacemakers At A Glance
A pacemaker is a battery-operated device.
A pacemaker maintains normal heart rhythm when the heart is not beating properly.
Pacemakers can be temporary or permanent.
A permanent pacemaker is a small case that can be implanted safely under the skin near the shoulders.
A permanent pacemaker corrects the symptoms caused by abnormally slow heart rates, and allows the patient to enjoy normal living.
Permanent pacemakers should be checked for proper functioning and battery levels periodically.
Modern pacemakers are well protected from most electrical appliances.
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