Each individual heartbeat is actually a collection of several muscle movements spurred into action by electrical impulses.
The first electrical signal comes from the heart's own natural pacemaker, the sinoatrial node, comprised of electrically active cells and located in the upper right heart chamber. This node sends a steady stream of electrical signals along a pathway through the heart's upper chambers.
The signals then travel to the electrical bridge - the atrioventricular node - between the upper and lower chambers and, finally, move to the lower chambers. A problem at any point in the electrical pathway can wreak havoc with the regular beating of a heart. Luckily, an artificial pacemaker - a small, battery -operated device - can take over the role of the heart's own electrical system, if necessary.
What is a pacemaker ?
Although it weighs just about an ounce, a pacemaker contains a powerful battery, electronic circuits and computer memory that together generate electronic signals. The signals, or pacing pulses, are carried along thin, insulated wires, or leads, to the heart muscle. The signals cause the heart muscle to begin the contractions that cause a heartbeat.
A pacemaker is implanted just below the collarbone in a procedure that takes about two hours. It is programmed to stimulate the heart at a pre-determined rate, and settings can be adjusted at any time. Routine evaluation, sometimes even via telephone, ensures the pacemaker is working properly and monitors battery life, which generally runs from five to ten years.
When is a pacemaker needed ?
The most common reason for a pacemaker is a heartbeat that slows to an unhealthy rate, or bradycardia. A pacemaker resets the heart rate to an appropriate pace, ensuring adequate blood and oxygen are delivered to the brain and other parts of the body.
Types of pacemakers
Three basic types exist to serve different purposes : -
Single-Chamber Pacemakers : - In a single-chamber pacemaker, only one wire (pacing lead) is placed into a chamber of the heart. Sometimes it is the upper chamber, or atrium. Other times it is the lower chamber, or ventricle.
Dual-Chamber Pacemakers : - In dual chamber pacemakers, wires are placed in two chambers of the heart. One lead paces the atrium and one paces the ventricle. This approach more closely matches the natural pacing of the heart. This type of pacemaker can coordinate function between the atria and ventricles.
Rate-Responsive Pacemakers : - These have sensors that automatically adjust to changes in a person's physical activity.
Other devices : - Some devices, such as implantable cardioverter defibrillators (ICDs), designed primarily for other purposes, can function as pacemakers in certain situations.
When are pacemakers used ?
Pacemakers may be prescribed for a number of conditions, including : -
Bradycardia : - a condition in which the heart beats too slowly, causing symptoms such as fatigue, dizziness or fainting spells. Bradycardia may be caused by the wear and tear of age or by conditions such as sick sinus syndrome (SSS) or heart block.
Atrial fibrillation : - a common heart rhythm disorder in which the upper chambers of the heart beat rapidly and chaotically. Sometimes people with atrial fibrillation can also have slow rhythms. Medicines used to control atrial fibrillation may result in slow rhythms which are treated by pacemakers.
Heart failure : - a condition in which the heartbeat is not sufficient to supply a normal volume of blood and oxygen to the brain and other parts of the body. A special pacemaker can be carefully programmed to increase the force of muscle contractions in the heart. This is called "biventricular pacing" or "resynchronization" therapy.
Syncope : - a condition best known as the common faint, is usually not serious. Some patients faint when their heart rhythm becomes very slow. For a small percentage of people who experience severe and frequent fainting spells, a pacemaker may prevent the heart rate from slowing to the point of fainting.
Dual-Chamber Pacemakers Better for Heart Patients
MONDAY, Jan. 3 (HealthDayNews) -- Dual-chamber pacemakers may be more expensive than single-chamber models, but they're worth it because they reduce the risk of hospitalization and disability, a new study finds.
"Most people in the United States [who need an artificial pacemaker] receive dual-chamber pacemakers," said study co-author Dr. David J. Cohen, an associate professor of medicine at Harvard Medical School. But, he added, "The cost effectiveness of dual-chamber pacemakers had not been studied."
The findings appear in the Jan. 4 online issue of Circulation. For the study, Cohen and his colleagues used four years of data from 2,010 patients enrolled in a clinical trial who needed a pacemaker because of a condition called sick sinus syndrome, in which the sinus node -- the heart's "natural" pacemaker -- becomes defective. Then they projected the trial findings over a patient's lifetime.
People with sick sinus syndrome have very slow heartbeats and are prone to chest pain, dizziness, fainting and fatigue.
An artificial pacemaker is a small, battery-operated device that helps the heart beat in a more regular rhythm.
Cohen's team found the dual-chamber pacemakers reduced the risk of hospitalization and disability, and the added cost was very favorable over a patient's lifetime.
"The dual-chamber pacemaker stimulates both the upper and lower chambers of the heart and more closely approximates the normal heartbeat," Cohen said. Single-chamber models stimulate a single chamber, "which is sufficient to keep blood pumping and keep the person from passing out but in some patients is not tolerated."
Cohen said 1,014 patients had a dual-chamber pacemaker and the other 996 had single-chamber devices. The median age was 74, and 48 percent of the people were women.
Dual-chamber pacemakers cost about $3,000 more than single-chamber devices during the first four years of the study. Over a lifetime, the dual-chamber models had a cost of $59,104; the single-chamber models, $58,160, Cohen said.
Patients with dual-chamber devices were less likely to be hospitalized with heart failure than those who got the single-chamber models. And those with the dual-chamber models had a slightly lower risk of death or stroke, along with much better results on several measures of health-related quality of life.
"Dual-chamber pacemakers, at their current cost, looked like a reasonable value when we looked at it over the lifetime," Cohen said, adding the benefits increased over time after the initial four-year data. "Over the first four years, it looked like a borderline investment," he said.
Cohen and his colleagues found that during the first four years, the dual-chamber pacemakers increased "quality adjusted life expectancy" by 0.013 years per patient at an incremental "cost-effectiveness ratio" of $53,000 per quality adjusted year of life gained.
"In the U.S., treatments that have cost-effectiveness ratios of less than $50,000 are generally considered favorable," he said.
But the dual-chambers' cost effectiveness improved when the researchers projected the results over a lifetime. They estimated the dual-chamber models would increase quality adjusted life expectancy by 0.14 years with an incremental cost-effectiveness ratio of about $6,800 per quality adjusted year of life gained. "That would be a very favorable ratio," Cohen said. It would be comparable, he added, to results from treating severe high blood pressure, or giving statin drugs to lower cholesterol.
Dr. William Weintraub, a professor of medicine at Emory University School of Medicine, called the new research "a very good study and a difficult study to do."
The take-home message for consumers? If you need a pacemaker, get a dual-chamber model. "It is going to make you feel better," Weintraub said.
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The first electrical signal comes from the heart's own natural pacemaker, the sinoatrial node, comprised of electrically active cells and located in the upper right heart chamber. This node sends a steady stream of electrical signals along a pathway through the heart's upper chambers.
