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ICD: For Harmonizing an Accelerated Cardiac Rhythm

An implantable cardioverter-defibrillator (ICD) is made of a microcomputer and a long-lasting battery that are encapsulated in a titanium housing. ICDs are typically implanted in the chest area. The implant can detect life-threatening heart rates (racing heartbeat), and react by delivering electrical signals. With a strong, shock-like signal, the ICD terminates ventricular flutter or fibrillation, and protects you from sudden cardiac death. The device does not use such an electroshock to react to every deviation from the natural heart rhythm. More often, the ICD emits weak, painless signals or just regularly paces the heart, preventing it from fibrillating.




Who Receives an ICD?

Your attending physician will recommend implanting a defibrillator if you have already experienced an episode of ventricular fibrillation, or if your accelerated heart rate (tachyarrhythmia) cannot be treated with medication.

What’s the ICD Made Of?

Modern ICDs weigh less than 2.6 oz (275 grams) and are only 0.4" (one centimeter) thick. The housing is made of titanium. At the top of the device are connections for the leads that are fed through a vein and into the right side of the heart. The leads are made of silver, platinum or iridium, and insulated with biocompatible silicone. Sensors at the ends of the leads continually transmit the cardiac signals to the ICD microcomputer. If necessary, the ICD transmits electrical signals through the leads and to the heart. A defibrillation electrode transfers an electroshock to the ventricle in case of an emergency.

The physician uses a programming device to set the ICD parameters in order to meet your personal requirements. The programming device is composed of a programming unit and a data transfer unit that the physician places on your skin, on top of the implant.

Different Therapy Levels

1. Antitachycardia and antibradycardia stimulation

The heart often races just before fluttering or fibrillating. In this case, the ICD delivers weak electrical signals in quick succession. In 60 to 80 percent of all cases, this causes the heart to stop racing before ventricular flutter or fibrillation begins. The ICD also stimulates the heart when it beats too slowly (bradycardia). This is the same kind of stimulation that occurs with a pacemaker.

2. Cardioversion

Another therapy level is possible if the heart does not stop racing in spite of the stimulation, or if the ventricles start to fibrillate. Cardioversion (which means converting the heart’s rhythm) is a weak electroshock that stresses you less than a defibrillation shock would.

3. Defibrillation

The ICD delivers a strong electroshock in case of ventricular fibrillation, or if the other therapy levels remained unsuccessful. This usually ends the tachyarrhythmia reliably. The energy for this strong shock is ready in less than ten seconds after ventricular fibrillation has begun. Should the life-threatening situation continue after the first shock, the ICD delivers additional shocks. Before delivering a therapy, the ICD always checks whether the tachyarrhythmia still exists.

Do I Feel the Shocks?

You barely feel the antitachycardia and antibradycardia stimulation at all (level 1), but you do notice that your heart rhythm stabilizes if this therapy was successful. Cardioversion and defibrillation (levels 2 and 3) are briefly painful. Due to the ventricular fibrillation, however, many patients lose consciousness before the shock is delivered, so they do not feel anything at all. Those who are conscious as the electroshock is delivered find it to be like a strong blow to the chest, but the pain immediately subsides.
The chest and arm muscles on the side of the body where the implant is located tense up, so the patient has muscle aches for one to two days after the episode. Statistically speaking, the strong electroshocks are most frequently delivered in the first few months after implantation. After this period, many ICD patients live without any cardioversion or defibrillation for years to come.




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