Engineering Topic #4: Pacemakers

Definition

A pacemaker is a small, battery-operated device that helps the heart beat regularly and at an appropriate rate.

Information

A pacemaker generally has two parts:

* Generator - contains the battery and the information to control the heartbeat
* Leads - wires used to connect the heart to the generator and send the electrical impulses to the heart to tell it to beat

Today's generators weigh a little less than an ounce (30 grams). The pacemaker's battery can last about 7 to 8 years. It will be regularly checked by your doctor, and replaced when necessary.

Traditional pacemakers help control the right side of the heart to control the heart beat. This is called AV synchronization. A special type of pacemaker, called a biventricular pacemaker, works on both sides of the heart,. It synchronizes the right and left chambers (ventricles) of the heart and keeps them pumping together. This is called cardiac resynchronization therapy. All of today's biventricular pacemakers can also work as an implantable cardio-defibrillator (ICD).

IMPLANT SURGERY

A pacemaker must be implanted under the skin. This procedure usually takes about 1 hour. You will be given a sedative to help you relax, but you will be awake during the procedure. Pain medicine will be given during the procedure.

A small cut is made, usually on the left side of the chest. The health care provider uses x-rays to place the wires (leads) in the heart. After the leads are in place, they are connected to the pacemaker. The pacemaker is placed into the chest area, and the skin around it is closed with stitches. Most patients go home within 1 day of the procedure.

COMPLICATIONS

Complications of pacemaker surgery include bleeding, infection, dropped lung (uncommon), abnormal heart rhythms, and puncture of heart leading to bleeding around the heart (rare).

A pacemaker can usually sense if the heartbeat is above a certain level, at which point it will automatically turn off. Likewise, the pacemaker can sense when the heartbeat slows down too much, and will automatically turn back on in order to start pacing again.

WHY IT IS USED

A pacemaker is often the treatment of choice for people who have a heart condition that causes their heart to beat too slowly (bradycardia).

Less commonly, pacemakers may also be used to stop an abnormally rapid heart rate (tachycardia).

Biventricular pacemakers have been used to treat severe heart failure.

Advancements in pacemaker function

When first invented, pacemakers controlled only the rate at which the heart's two largest chambers, the ventricles, beat.

Many advancements have been made to enhance the control of the pacemaker once implanted. Many of these enhancements have been made possible by the transition to microprocessor controlled pacemakers. Pacemakers that control not only the ventricles but the atria as well have become common. Pacemakers that control both the atria and ventricles are called dual-chamber pacemakers. Although these dual-chamber models are usually more expensive, timing the contractions of the atria to precede that of the ventricles improves the pumping efficiency of the heart and can be useful in congestive heart failure.

Rate responsive pacing allows the device to sense the physical activity of the patient and respond appropriately by increasing or decreasing the base pacing rate via rate response algorithms.

The DAVID trials[20] have shown that unnecessary pacing of the right ventricle can lead to heart failure. The newer bi-ventricular devices can keep the amount of right ventricle pacing to a minimum and thus prevent worsening of the heart disease.

http://en.wikipedia.org/wiki/Artificial_pacemaker
http://healthguide.howstuffworks.com/pacemaker-dictionary.htm
http://www.americanheart.org/presenter.jhtml?identifier=4676