Wed, 25 Sep 2002

Pacemaker for the slowly beating heart

A. Fauzi Yahya, Contributor, Jakarta

Worldwide, there are about three million people with pacemakers, a small smart device used to regulate heart rhythm, and every year, 600,000 pacemakers are implanted.

Although most people who receive pacemakers aged 60 years or older, people of any age -- even children -- may need pacemakers.

Most are implanted to prevent the heart from beating too slowly. Some new types of pacemaker may be helpful in certain patients with congestive heart failure. Pacemakers have become a reliable means of helping people live longer and improve their lifestyles despite having a slow heart rhythm.

* Heart's electrical system

The heart, like any mechanical pump, needs an electrical source to drive it. It has its own natural electrical system (cardiac conduction system) which is called the sinoatrial (SA) node or sinus node. It's a small mass of specialized cells in the top of the upper right chamber (right atria). It makes the electrical impulses that cause the heart to beat. A chamber of the heart contracts when an electrical impulse moves across it.

For the heart to beat properly, the signal must travel down a specific path to reach the ventricles -- the heart's lower chambers. It causes the ventricles to contract and squeeze blood out to the body and lungs. At rest, the normal SA node fires at an average rate of 60-80 beats per minute. The SA node can increase the frequency of the signal 2- to 3- fold, such as during stress or exercise, to speed up the heart rate in order to meet the body's increased metabolic demands. Each signal that passes through the conduction system results in one heartbeat.

Why might someone need a pacemaker?

Any interruption in the normal flow of the electrical signal through the cardiac conduction system can cause an abnormality in the heart's rhythm.

The SA node can "slow down" as the result of the normal aging process. This can cause the heart to beat too slowly or fail to accelerate the heart rate with normal activity or exercise. This condition is called sick sinus syndrome which is the most common reason for pacemaker implantation.

The other leading cause for pacemaker implantation is a "block" somewhere in the electrical pathway which does not allow the electrical activity to spread to all of the necessary portions of the heart muscle. The underlying cause of this may be scar tissue, most frequently from previous heart attacks.

The slowly beating heart does not circulate enough blood to meet the metabolic needs of the body and resultantly can cause shortness of breath, fatigue, activity intolerance, a loss of consciousness (syncope), or even death. In other cases, people may have no symptoms but are at high risk for dangerously slow heart rates because of disturbances of the electrical system of the heart. A pacemaker may be recommended for these people before symptoms occur.

* Pulse generator and wires

The artificial pacemaker implanted by physicians corrects both causes of slow heart beating by providing electrical signals to tell the heart to beat at the proper rates and by delivering the signal to the appropriate chambers of the heart.

The pacemaker system includes the pulse generator and wires (leads) that connect the pacemaker to the heart. The generator unit is slightly larger than a man's wristwatch and contains a lithium battery (generally lasting from six to 10 years) and computer circuits (Photo left).

The computer circuits continuously monitor the heart's natural rhythm and delivers an electrical signal to cause the heart to beat at the desired rate. The electrical signal that is sent from the pacemaker is strong enough to stimulate the heart to beat but not strong enough for you to feel.

Many pacemakers implanted today also may have rate responsiveness features that allow temporary pacing of the heart at a faster rate during periods of exercise. Single-chamber pacemakers have only one wire connected to the heart and dual chambers pacemakers have wires to both the top and bottom chambers of the heart. Your cardiologist will recommend which type of pacemaker needed.

So, how is the pacemaker implanted?

The pacemaker is implanted by a minor surgical procedure performed under local anesthesia. A small incision (2-3 inches) is made under the collarbone either on the right or left side of the chest.

The wires are placed through a blood vessel beneath the collar bone and threaded down to the inside of the heart under a special type of x-ray (fluoroscope). The wires are then attached to the inner surface of the heart muscle (Photo right). Once the wires are positioned inside the heart muscle, the physician will create "a small pocket" to fit the pulse generator under the skin of the chest. The wires are then plugged in to the pulse generator and firmly tightened in place. The pulse generator is then placed in to the pocket and the skin is sutured back together.

The procedure usually takes about one or two hours and the risk of procedure complications is about 1 to 2 percent.

Other than restrictions on heavy lifting and extreme motion of the arm on the side of the pacemaker for several weeks, recovery from the procedure is minimal. Most patients return to normal activities within a few days.

It is recommended that patients carry an identification card that provides specific information on the type of leads and pacemaker implanted. Such a card can be shown to healthcare professionals during medical evaluations and to security personnel at airports.

The writer is a cardiovascular fellow at Cardiology Department of Medical School University of Indonesia/National Cardiovascular Center Harapan Kita, West Jakarta.