DEAR DR. DONOHUE: I decided to write because you can help me. In February 2007, the doctor put a defibrillator in my chest. I don’t know a thing about it. Why does this thing shock? Some people tell me I have a pacemaker. Does a pacemaker shock? When mine shocks, it hurts. – K.M.

A pacemaker and a defibrillator are not the same thing. Pacemakers provide a small and all-but-imperceptible electrical jump-start to the heart when the heart slows down. A defibrillator gives a much bigger shock to a heart that has stopped pumping because of lethal, fast heartbeats that lead to cardiac arrest – a shutdown of heart activity and pumping. It delivers a much greater electric jolt, one that can be felt and is a bit unpleasant. Cardiac arrest leads to more than 450,000 deaths a year in the United States. It can follow on the heels of a heart attack.

Most of today’s defibrillators also can act as pacemakers.

Sometimes the defibrillator shocks when it shouldn’t. If you’re having frequent shocks, a doctor needs to check the device to see if it needs to be reset. Or if you are developing frequent, abnormally fast and inefficient heart rhythms, the doctor can prescribe medicines to suppress those rhythms. A third possible treatment is to find the site where the abnormal rhythms are generated and to eradicate that tissue using a catheter fitted with equipment that emits radio waves.

Defibrillators are about the size of a small bar of soap. They’re placed under the skin of the upper chest below the collar bone. Wires connect them to the heart.

DEAR DR. DONOHUE: During the night and mostly early in the morning hours, my heart speeds up to 200 beats a minute. There is no pain, but it wakes me up and seems to happen if I am lying facedown. I sit up and take my pulse, which is about 70 to 72. I feel my heart slowly return to normal in two to three minutes. I have worn a Holter monitor for 24 hours.

My doctor says not to worry about it. Do you think I have anything to worry about? – S.

For readers: A Holter monitor is a device worn externally that records all heartbeats in a given time period. They can be worn for three or more days. The doctor sees on the recording what kind of abnormal heartbeats occurred.

I have to clear something up with you, S. Is your pulse 72 beats a minute when you feel your heart beating fast? The heartbeat and the pulse are one and the same. How are you counting your heartbeat?

If the episodes occurred while you were being monitored and did not last long, then the doctor can dismiss it as not being worrisome. He should name the rhythm; ask what it is. If the fast heartbeats occurred at times you weren’t wearing the monitor, you need to wear it longer so that the rhythm can be identified for what it is. The booklet on heartbeat irregularities describes the more common kinds of these beats and how they are treated.

Readers can order a copy by writing: Dr. Donohue – No. 107, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.75 U.S./$6 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from

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