Some hearts beat regularly while some don’t. The normal, healthy heart has its own pacemaker called the sinus node that regulates the rate that the heart beats. It produces impulses that travel through electrical pathways in the heart and cause the heart muscle to contract and pump blood as needed by the body. Sometimes this natural mechanism becomes diseased leading to these electrical impulses getting blocked resulting in heart beats that may be too slow, too weak and sometimes irregular. Bradycardia is the name of the condition in which the heart beats too slowly to support the circulatory needs of the body.
If this happens, the person may feel dizzy, weak, or just very tired and even faint. An artificial pacemaker may then be implanted to stimulate the heart at normal rates, to improve blood circulation and thus restoring normal life and general wellbeing to the patient. When people refer to a pacemaker, they are actually discussing a pacing system, which includes the pacemaker and leads. A pacemaker is a small device that is implanted under the skin, typically just below the collarbone. The device delivers electrical impulses to treat slow heartbeats. Leads are thin, soft, insulated wires about the size of a spaghetti noodle. The leads carry the electrical impulse from the pacemaker to your heart and relay information about the heart’s natural activity back to your pacemaker. It is prescribed for people whose hearts are beating too slowly or irregularly. A pacemaker is primarily used to treat fainting spells (syncope) due to slow heart rate, and a special type to treat a certain type of congestive heart failure.
A pacemaker consists of the following components:
Battery: the pacemaker battery is the power supply. It is a small, sealed, lithium battery that will generally last for many years (the average battery lifetime is eight years). The energy from the battery is delivered as tiny electrical impulses that stimulate the heart.
Circuitry: the circuitry is a kind of miniature computer inside the pacemaker. It controls the timing and intensity of the electrical impulses delivered to the heart.
Case: the battery and circuitry are sealed inside a metal case usually titanium.
Connector block: the plastic (Polyurethane) connector, which lies on top of the pacemaker's metal case, provides the connection between the pacemaker and the lead(s).
The lead: The pacing lead is an insulated wire that carries the electrical impulse to the heart, and carries information about the heart’s natural activity in the form of electrical signals back to the pacemaker. One end of the lead is connected to the connector block. The other end is usually inserted through a vein and placed in the right ventricle (the lower chamber) or the right atrium (the upper chamber). Either one or two leads are used depending on the type of pacemaker. At a heart rate of 70 beats per minute, the lead will bend about 100,000 times a day! Therefore, leads are extremely flexible and strong, so that they can withstand the twisting and bending caused by movement of the body and of the beating heart.
So how does a pacemaker work?
A pacemaker is designed to mimic the heart’s natural pacemaker, the sinus node. The pacemaker has two main purposes – pacing and sensing.
Pacing: A pacemaker will send an electrical impulse to the heart through a pacing lead when the heart’s own rhythm is too slow or interrupted. This electrical impulse starts a heartbeat.
Sensing: A pacemaker will also “sense” (see and monitor) the heart’s own natural beat in the form of electrical activity. When the pacemaker senses a natural heartbeat, it will not deliver a pacing pulse. This sensing enables the pacemaker to send impulses to stimulate only when the heart does not beat on its own when it is expected to.
How are pacemakers implanted?
The procedure to implant a pacemaker does not require open heart surgery, and most people go home within 3 days. Before the surgery, medication may be given to make you sleepy and comfortable. Generally, the procedure is performed under local anesthesia.
The general steps for implanting a pacemaker include:
- A small incision, approximately two to four inches long, will be made in your upper chest area, just below your collarbone
- One or two leads will be guided through a vein into your heart, and the leads will be connected to the pacemaker
- Pacemaker settings will be programmed, and the device will be tested to ensure it is working properly to meet your medical needs
- The pacemaker will be inserted beneath your skin, and the incision in your chest will be closed.
Living with a heart device usually requires some adjustments, such as restricting your arm movements for the first few weeks and visiting your doctor for regular checkups. But pacemakers help millions of people live full and active lives.
Types of pacemakersA patient’s medical condition determines the type of pacemaker one may receive. Pacing therapy is diverse because the underlying heart electrical conduction disorders that result in rhythm disturbances are different. If your medical condition or pacing requirements change, your doctor may make some adjustments in certain functions of your pacemaker from outside. Following are brief descriptions of the types of pacemakers available today:
A single chamber pacemaker uses one lead, placed either in the right atrium or the right ventricle, to sense and pace in that chamber.
Dual-chamber pacemakers typically use two pacing leads, one placed in the right atrium and the second placed in the right ventricle; the electrical pulses delivered to the heart are timed so that the atria and ventricles are beating “in sync” with each other.
Trends in pacemakersPacemakers have become smaller in size and improved in functionality since the early days. This, in turn, has led to better patient outcomes, lesser side effects and hospitalizations with longer and better quality of life. Technology has also helped in lowering the cost of managing the disease.
Some of the latest trends in pacemakers which is gaining widespread acceptance is listed below:
3-Chamber Pacemaker: Today, pacemakers are not limited to single chamber. Pacemakers have evolved from stimulating a single chamber of the heart to dual chamber pacing and even three chambers.
A three chamber; or bi-ventricular pacemaker will provide synchronized stimulation of both the right and left lower chambers (ventricles) along with the upper chamber (atrium). This type of cardiac resynchronization therapy (CRT) pacemaker is implanted for a certain group of heart failure patients. This has immensely contributed to these heart failure patient’s quality of life and life expectancy.
MRI compatible pacemakers: Currently patients with pacemakers are not allowed to undergo MRI scans that may be necessary and valuable for evaluating some other medical conditions like stroke.
This is because MRI machines use powerful magnetic and radio frequency energy that could change the settings, temporarily affect the normal operation of, or potentially damage the pacemaker. Medtronic has a pacemaker system which is FDA approved for use in the MRI environment. This pacemaker system has a unique design, developed so that under specific conditions, patients may safely undergo MRI scans. MRI conditional pacemaker has truly emerged as a technological boon for patients who suffer from bradycardia (slow heart beats) who may require an MRI scan in future.
Rate Responsive Pacemakers: In a normal heart the beating rate varies depending on the energy requirement of the body during various daily activities. A rate responsive pacemaker uses a special sensor that detects changes in your body movements during activities.
The pacemaker's circuitry interprets these changes and increases or decreases the pacing rate to meet your body's needs. If you are engaged in physical activity such as walking, exercising, or gardening, the pacemaker automatically adjusts your pacing rate to match your energy requirements for the level of activity. When you slow down, rest, or sleep, the rate decreases accordingly. You do not need to engage in very strenuous activity to benefit from a rate responsive pacemaker. The simple act of walking may require a rate of around 100 beats per minute in many normal individuals. The rate responsive pacemaker understands when it needs to make the heart beat faster or slower and deliver impulses at that rate.
Another interesting trend observed globally, and particularly in the US is monitoring via internet. Home based remote patient monitoring via telephone and internet is already happening in the US. Patients need not visit the hospital for routine check ups. It has also started in India and the number of patients opting for this convenient facility is gradually increasing. This is expected to become standard way of monitoring in future.
Living with your pacemakerYou may be surprised at how fast you recover from pacemaker surgery. There may be some minor discomfort at first, near the incision site. However, usually after a short time, your awareness of the pacemaker will diminish, and you may not even feel its presence. Upon the advice of your doctor and as you begin to feel better; you should gradually be able to return to your normal activities.
Some people with pacemakers have been known to return to such activities as racquetball and tennis. However, it is important that you follow your doctor's advice. Returning to your daily activities should make you feel better, not worse. This is what you and every patient should expect in today's pacing systems: assurance for the future.
The author is interventional cardiologist, Bombay Hospital