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What are the Parts of a Defibrillator?

An internal cardioverter defibrillator (ICD) is an implantable device that monitors the natural electrical activity of the heart for abnormalities that are not compatible with life. Internal defibrillators are very sophisticated computers that process data through sensing leads placed in one or more chambers of the heart. The main components of a defibrillator are the can, one or more sensing leads and a special lead that is referred to as a shocking coil.

  1. The Can

    • The largest part of the device is the housing for the circuitry and battery unit. The name for this housing is the can, as in a soda or sardine can. Some misidentify the can as just a battery pack. While the battery is located in the can, so are the components that enable programming of therapies specifically for the reason patient has the implantation. The can also stores information for analysis of the device's overall function.

    The Lead Wires

    • A lead is the more common name for any of the wires that sprout from the can. The leads are maneuvered into the heart and placed in the appropriate chamber where the patient needs therapy. Most defibrillators have the ability to accommodate up to three different leads. Depending on the reason for implantation, a lead can be placed in the right atrium and both right and left ventricles. For all defibrillators, the surgeon places one lead in the right ventricle.

    Atrial Lead Function

    • The surgeon places an atrial lead the right atrium if the patient needs to utilize both the pacemaker and defibrillator functions of the device. The atrial lead allows this configuration to artificially pace the heart by two methods. The first is a constant setting in which the pacing lead initiates every electrical impulse that causes the heart to contract. The second is an intermittent setting that allows the heart's own electrical rhythm to trigger contraction, yet will also make up for any beats the heart does not signal on its own.

    Ventricular Lead Function

    • An ICD can accommodate two ventricular leads. The right ventricular lead is standard on all internal cardioverter defibrillators. Physicians commonly refer to this lead as the shocking coil because it conducts the energy from the defibrillator. The surgeon can also place a left ventricular lead to help assist a heart with a low ejection fraction, or poor stroke volume, to compensate for structural weaknesses that impair health due to cardiomyopathic-related asynchronous contractility.

    Specific Information Related to the Right Ventricular Lead

    • In patients who have an otherwise normally functioning heart without electrophysical impairment, an ICD with only a right ventricular lead can be placed as a precaution concerning a decreased ejection fraction. In these instances, the defibrillator may function only as a sensing device. If the ICD detects a terminal cardiac dysrhythmia, it charges the internal battery supply and discharges the energy through the shocking coil, in an attempt to return the heart to a viable heart rhythm.

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