A pacemaker is a small, battery-powered medical device designed to electrically stimulate the heart muscle in an effort to restore the heart rhythm toward normal.

A pacemaker system consists of two main parts: the pulse generator and pacing leads. The pulse generator houses the battery and electronic circuits (like a small computer). These circuits contain timers that regulate how often the pacemaker must send impulses to stimulate the heart.

The pulse generator is small, measuring approximately 2" x 2" x 1/4" (45mm x 45mm x 6mm) and weighing less than 2 ounces (20-30g).

The pacing leads are flexible, insulated wires that connect to the pulse generator and carry the electronic impulse to the heart. In addition, the leads also carry signals back from the heart to the pulse generator allowing the pulse generator to sense the heart's natural electrical activity.

By sensing the patient's natural rhythm, the pacemaker will only pace the heart when necessary.

Types of Pacemakers

Pacemakers may be single or dual chamber.

Single chamber pacemakers use a single lead attached to either the heart's upper chamber (atrium) or lower chamber (ventricle).

Dual chamber pacemakers use two leads, one attached to the top portion of the heart (atrium), the other to the bottom portion of the heart (ventricle). Leads can be attached either to the inside surface (endocardium) or outside surface (epicardium) of the heart.

Leads attached to the endocardium (inside surface) can be surgically placed through a vein that connects to the heart. The leads are positioned and attached with the help of a type of X-ray called fluoroscopy.

Leads attached to the epicardium (outside surface) require a surgical procedure that includes an incision through the chest wall. The pulse generator is positioned under the skin (and sometimes also under the muscle) in the upper chest near the collar bone or in the abdominal area depending on the age and size of the patient.

The cardiologist, cardiac surgeon, and/or nurse can program the pulse generator as needed with a special pacemaker programmer that communicates with the device once placed in the body.

Reasons for a Pacemaker

The normal heartbeat originates in the heart's natural pacemaker called the "sinus node." The sinus node is usually located in the right atrium, though this location can be different in the setting of some congenital heart defects.

When the sinus node fires, a wave of electricity sweeps across the upper chambers of the heart (the atria) causing the upper chambers to squeeze or contract.

The electrical impulse then travels from the atria to the lower chambers of the heart (the ventricles) by way of the "AV node," located in the center of the heart, resulting in ventricular contraction.

Contraction of the atria followed by the ventricles allows for blood to be pumped to the body. Circulating blood supplies the body with oxygen and nutrients. In addition, circulating blood helps to eliminate the waste products of the body's metabolism.

When the sinus and/or AV nodes do not function normally, an artificial pacemaker may be needed. Some people are born with sinus and/or AV node dysfunction (heart block), especially in the setting of some congenital heart defects.

Sinus and/or AV node dysfunction can also be the consequence of certain surgical procedures.

Many other patients may benefit from pacemaker implantation including patients with abnormally fast heart rates, patients who pass out, patients on medications that slow the natural heart rate, patients with heart valves that leak (regurgitation), patients with an abnormally thick heart (hypertrophic cardiomyopathy), and patients with poor heart function.

Artificial pacing helps to restore the heart rhythm towards normal improving the heart's ability to circulate blood through the body.

Comfort with a Pacemaker

Pacemaker implantation is performed under general anesthesia. After recovering from general anesthesia, the patient will likely experience some soreness in the region of the surgical incision.

Pain after surgery can easily be treated with pain medications taken by mouth or given intravenously. By the second day after surgery, pain is usually easily controlled with over-the-counter pain medications alone like acetaminophen and ibuprofen.

Most often, pain medications are not needed by the third to fourth day following surgery. You cannot feel the pacemaker working as it stimulates your heart to beat.

The generator of the pacemaker system can usually be felt under the skin, but after the incisions are healed it is not uncomfortable.

Risks and Complications with Pacemakers

The most common complications of the implantation procedure are infection and lead dislodgement when leads are attached to the inside surface (endocardium) of the heart. The chance of these complications occurring is very low.

A single dose of antibiotics is given during the operation to prevent infection. Antibiotics may also be given after the operation in selected cases.

If blood loss is excessive, and if the patient is unstable because of the excessive blood loss, a blood transfusion may be necessary. This is very uncommon when pacemaker implantation is the only surgical procedure being performed.

In the unlikely event that a lead moves from its proper position (dislodges), a second surgical procedure may be needed to reposition the displaced lead.

Special Instructions with Pacemakers

Patients are asked not to eat or drink after midnight on the day of the scheduled procedure.

Patients taking blood thinners such as aspirin or Coumadin may be asked to stop the medication several days prior to the procedure. Speak with your physician prior to stopping or changing any medications.

• Other patients taking aspirin or Coumadin may require hospitalization prior to the procedure on order to be switched to a different type of blood thinner.
• All other medications will generally be continued according to their usual schedule.

Restrictions After Getting a Pacemaker

Following the procedure, certain activities will be restricted for days to weeks. All patients with new pacemakers are asked not to participate in contact sports for about six weeks.

In addition, patients will be asked to avoid interaction with certain electronic devices that may interfere with the pacemaker's proper function.

Replacement of the Pacemaker

The most common reason for a repeat operation is the need to replace the pulse generator because the battery is running low. How long the pacemaker's batteries last varies and depends on the pacemaker's settings, as well as how frequently the pacemaker is used.

Generally, pulse generator replacement is required every nine to 12 years. The patient's cardiologist can determine when the pulse generator needs to be replaced well in advance of the batteries running out so that pulse generator replacement can be conveniently scheduled on a non-emergent basis.

Replacement of the pulse generator entails making an incision over the old pulse generator, disconnecting it from the existing pacing leads, and replacing it with a new pulse generator.

In children, this procedure is performed under general anesthesia and the patient is usually discharged from the hospital the following day.

A more urgent need for reoperation may develop if a lead stops working because of dislodgment or fracture. The risk of these complications occurring are rare.

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