An implantable cardioverter defibrillator (ICD) is a different kind of device that's placed in the chest that we use to help treat your arrhythmia, depending on its type. An ICD uses high-energy electrical pulses (shocks) to help control life-threatening arrhythmias that occur in the ventricles (the heart's lower chambers). Some can also work as a pacemaker.
We consider ICDs for patients who are at risk for ventricular tachycardia or ventricular fibrillation, who have cardiomyopathy and an ejection fraction of <35%, or are otherwise at risk for sudden cardiac death.
Types of Cardioverter Defibrillators
There are two types of cardioverter defibrillators:
These ICDs work as pacemakers as well as when necessary. Transvenous (through the vein) ICDs can have one, two, or three wires. The ICDs stop a potentially life-threatening ventricular tachyarrhyhtmias if they occur. Ventricular arrhythmias like ventricular tachycardia and ventricular fibrillation are medical emergencies that must be treated with defibrillation (delivering an energy shock to the heart muscle) as soon as possible, if they do not terminate spontaneously, to reset the heart’s electricity and prevent death.
Transvenous is the classic type of ICD and has been used for over 50 years. It is implanted under the skin in the left pectoral area under the clavicle and the wires are threaded through the vein into the heart. The ICD will monitor your heart rhythm, and if the device detects an irregular rhythm in your ventricles, it will use either low-energy electrical pulses to restore a normal rhythm or if the low-energy pulses fail, then the ICD will switch to shock for defibrillation.
These ICDs act defibrillators solely, they cannot pace the heart, the device itself is larger than the transvenous type and it is placed in the axilla (underarm) with the lead tunneled under skin outside of the chest cavity. Subcutaneous ICDs have been in use for close to 10 years. The advantage is that there is no invasion of the vascular system – no wiring inside the veins or heart.
Finally, the majority of implantable cardioverter defibrillators used currently are MRI-compatible – if you have any questions regarding this, just ask.