(In the last column, we discussed pacemakers. In this one, we'll continue on the general topic of heart regulation with information about implantable cardioverter-defibrillators.)

An implantable cardioverter-defibrillator is like a pacemaker. Both a pacemaker and an ICD are battery-powered devices installed in the chest to deliver electrical impulses to the heart. In general, a pacemaker is used when the heart beats too slowly; an ICD is used when the heart beats too quickly.Pacemakers jog the heart with mild reminders that patients usually can't feel. Pacemakers are small; some are only as big as a quarter.The electrical impulses from an ICD can feel like being whacked in the chest. These devices are about the size of a stack of three silver dollars.However, ICD devices today function as both an ICD and a pacemaker.ICDs monitor for abnormal rhythms and try to correct them. An ICD can reduce your risk of dying of cardiac arrest by stopping these arrhythmias. ICDs have become standard treatment for anyone who has survived cardiac arrest.An ICD is considered effective in fighting cardiac arrest more than 9 times out of 10. Only 20 years ago, few survived this condition.Cardiac arrest, or sudden cardiac death, is not a heart attack. However, if you had a heart attack, you can be at risk for sudden cardiac death.A heart attack happens where there's a blocked vessel carrying blood to the heart. This condition leads to the damage of heart muscle. The damage may lead to abnormal electrical signals that sometimes cause deadly heart rhythms. An ICD cannot prevent a heart attack.If you've ever watched shows like "Grey's Anatomy" or "ER," you've probably seen a cliché scene in which a doctor demands electrified paddles to shock a troubled heart. An ICD works inside the chest like these paddles.ICDs are installed under the skin either under your collarbone or in your abdomen. They are about the size of a pocket watch. One or two flexible, insulated wires (leads) run from the ICD through your veins to your heart.The surgery to implant an ICD can be performed with local anesthesia and a sedative. Then you stay in the hospital for a day or two.Modern ICD devices have an electronic memory that records the electrical patterns of the heart whenever an abnormal heart beat or arrhythmia occurs. With this information, the electrophysiologist, a specialist in arrhythmias, can study the heart's activity and ask about other symptoms that may have occurred.This record is available for review during regular checkups by the physician, who can monitor the frequency and severity of problems in the heart's electrical conduction system that may lead to cardiac arrest or other serious heart disorders.Like pacemakers, ICDs aren't affected by normal household appliances, but, if you have one, you should avoid strong magnetic fields. For example, stay away from magnetic resonance imaging machines. Power machines are dangerous. Don't go near arc-welding equipment, high-voltage transformers and motor-generator systems.The Times News Inc. and affiliates (Times News) do not endorse or recommend any medical products, processes, or services or provide medical advice. The views of the author do not necessarily state or reflect those of the Times News. The article content is not intended as a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of your physician, or other qualified health provider with any questions you may have regarding a medical condition.