A pacemaker is an artificial device to electrically assist in pacing the heart so that the heart may pump blood more effectively.
The heart's natural pacemaker is an electrical timing device that controls the rate of the heart's muscular contractions, enabling the heart to pump blood under the wide range of demands encountered in daily life.
Everyone's heart speeds up or slows down under different conditions and may on occasion appear to flutter or miss a beat. These palpitations are usually minor and transitory.
However, sometimes the heart's electrical system malfunctions and serious rhythm disorders result. These cardiac arrhythmias can be debilitating and even life-threatening, but the recent availability of artificial pacemakers and the recent advent of implantable defibrillators have revolutionized treatment. Today, physicians can help patients by using electronic devices that directly counter these serious rhythm disturbances.
Implantable electronic devices have been developed to treat both abnormally slow heart rates (bradycardias) and excessively rapid heart rates (tachycardias). Such rhythm disorders arise because of disruptions to the normal production or transmission of electrical impulses within the heart.
The heart's natural pacemaker is the sinus node (SN), located in the upper right atrium near the point where blood returning from the head and limbs reenters the heart. Specialized cells in this node emit electrical impulses at the rate of about 70 per minute. These impulses spread throughout the atria and travel to the ventricles via the atrioventricular node (AV node).
The electrical system ensures that impulses reach the right part of the heart at the right time and at the right pace, coordinating the contraction of the heart muscle so that it can pump effectively.
When the sinus node fails to generate impulses or transmission is blocked in some part of the electrical system, an abnormally slow heart rate can result. Assuming that this bradycardia is not the side effect of a medication or produced by some other reversible condition, the most likely cause is disease in the sinus node, the AV node, or some other part of the conduction pathway.
If the patient is experiencing symptoms and the heart beat is extremely slow (below 45 or 50), the condition may be markedly improved by an artificial pacemaker. There are, however, many people who function normally with slow heart rates of 40-50 and evidence of some degree of heart block. Pacemakers are generally reserved for those with symptoms and advanced degrees of block.
Function Of Pacemakers
Since their introduction in the 1960s, pacemakers have steadily shrunk in size and grown in sophistication, yet their basic function remains the same. The job of the pacemaker is to maintain a safe heart rate by delivering to the pumping chambers appropriately timed electrical impulses that replace the heart's normal rhythmic pulses.
The device designed to perform this life-sustaining role consists of a power source the size of a silver dollar (containing the battery), and control circuits, wires or "leads" that connect the power source to the chambers of the heart. The leads are placed in contact with the right atrium or the right ventricle, or both. They allow the pacemaker to sense and stimulate in various combinations, depending on where the pacing is required.
Types Of Pacemakers
A physician will prescribe a pacemaker with a pacing mode and rate that is best suited to the patient's needs, taking into account the patient's age and activity level, as well as the nature and degree of heart malfunction.
Ventricular demand pacemaker helps a patient who has slow ventricular rate caused by blockage of the electrical impulses to the ventricles, employing the most basic pacing mode - a pacemaker with a single lead to the right ventricle. "Demand" signifies that the device will provide impulses only when needed. The pacemaker is individually programmed to maintain the patient's natural, intrinsic ventricular rate which usually falls between 50 and 70 beats per minute.
Dual-chamber pacemakers have been developed for patients whose heart disease or lifestyle requires a more adaptable device. These respond with different heart rates to the varying demands of the heart. They stimulate the ventricles at the rate sensed in the atria and can enable even a patient with complete heart block-that is, a condition in which no impulses are getting through from the upper to the lower heart chamber-to enjoy exercising again.
It is important that you know and keep a record of the type of pacemaker you have. In the event of an illness in the future, another physician will need that information in order to better care for you.
Once in a while, pacemakers can cause the complications they are meant to prevent. About 7 percent of people with single-chamber devices develop low blood pressure, dizziness, and fainting which are symptoms of pacemaker syndrome.
This occurs when the lower chambers of the heart contract before, instead of after, the upper chambers pushing blood back into the veins that normally bring it to the heart. Pacemaker syndrome is treated by trading the single-chamber device for a dual-chamber one.
Some people whose pacemakers limit their maximum heart rate worry that they will not benefit from exercise because they cannot raise this rate as much as they would like. This is generally not true because there is nothing particularly beneficial about an increased heart rate per se, although it is often used by exercisers as evidence of a certain level of stress. Exercise tones the muscles, limbers the joints, and offers psychological advantages that cannot be measured by something as simple as heart rate.
Generally, people with pacemakers do not have to stay away from electrical appliances. Microwave ovens, cellular phones, hair dryers, and airport metal detectors will not deprogram the device. To be sure, ask your physician.
Having CT (computed tomography) scans is safe for people with pacemakers, but they should not be exposed to magnetic resonance imaging (MRI).