Implantable Defibrillator and a Pacemaker

The illustration compares an implantable defibrillator and a pacemaker. Figure A shows the location and general size of an implantable cardiac defibrillator in the upper chest. The wires with electrodes on the ends are inserted into the heart through a vein in the upper chest. Figure B shows the location and general size of a double-electrode pacemaker in the upper chest. The wires with electrodes on the ends are inserted into the heart through a vein in the upper chest.

What is a Defibrillator?

An implantable defibrillator is a small medical device implanted in the upper chest that monitors your heart and can deliver defibrillation therapy in the event of a dangerously fast heart rhythm. Many implantable defibrillators also have a built in pacemakers as well so they can regulate an abnormal heart rhythm such as; ventricular tachycardia/ VT and ventricular fibrillation/ VF. An implantable defibrillator may also be called an ICD. The abbreviation "ICD" stands for "Implantable Cardioverter Defibrillator".

The main portion of the defibrillator is also known to clinicians as a "pulse generator" because it generates electrical energy. The pulse generator contains electronic circuitry, a battery, capacitors to store the electrical charge, and a mini-computer to evaluate the heart rate, store it in memory, and help the defibrillator know when

to deliver therapy and when to stand by.

The top of the implantable defibrillator consists of a clear header with several ports. One or more insulated wires are plugged into the ports in the header. These insulated wires are called "leads." They deliver small electrical pacing pulse to the heart (for the pacemaker) and larger electrical outputs for defibrillation therapy. Most of the time the defibrillator simply monitors the hearts activity. The defibrillator has a built-in computer that not only evaluates the heart's actions, but can also store these cardiac events into the devices memory so your cardiologist can access them. In the event that a dangerously fast heart rhythm is detected, the defibrillator quickly delivers therapy in the form of electrical energy.

Your cardiologist/electrophysiologist will choose the type of implantable defibrillator that's best for you. A defibrillator with a single chamber pacemaker is called a single- chamber defibrillator, or single chamber ICD. A single chamber ICD paces in one chamber of the heart only (the right ventricle). A dual -chamber ICD has a dual-chamber pacemaker and paces in both the upper and lower chambers of the heart (the right atrium and the right ventricle).

Defibrillators offer therapy to stop dangerously fast heart rhythms, such as ventricular tachycardia and ventricular fibrillation, by delivering electrical energy to the right ventricle. The primary function is defibrillation whether the ICD is a single-chamber or a dual-chamber defibrillator

An implantable defibrillator is very effective in detecting and stopping certain deadly heart rhythms such as; ventricular tachycardia and ventricular fibrillation. An ICD can be more effective than drug therapy in preventing sudden cardiac arrest, depending on the cause of the arrest. Although a defibrillator can't cure heart disease, it can lower the risk of dying by up to 50 percent in some patients who have heart disease.

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