An implanted cardiac defibrillator (ICD) is a small device that can be considered the ultimate insurance policy for a patient with severe heart disease. If a patient suffers a heart attack that injures the muscle and reduces the pump function (ejection fraction, or EF) they have a higher chance of death in the next 5 to 10 years. The risk can be reduced with medications such as beta-blockers, ace inhibitors, statins and anti-platelet agents. The most common cause of death in patients with congestive heart failure is a ventricular arrhythmia. An ICD prevents sudden death due to ventricular arrhythmias.
After a heart attack, the injured muscle develops a scarred area. In this scar, the electrical impulses are conducted improperly and the result is a chaotic pattern of electrical conduction. This breakdown in the normal electrical conduction can easily develop into ventricular tachycardia or ventricular fibrillation. Both rhythms are fatal if treatment is not promptly instituted. The ICD has a sensor that is always watching the heart rhythm. After implantation, the physician programs the device, telling it what to watch for. After identifying a life-threatening arrhythmia, the device often starts by trying to change the rate by using its pacemaker mode. If that is unsuccessful the device charges its system up to deliver an electrical shock that will restore normal heart rhythm. ICD's are often evaluated at least every 6 months and more frequently if there are shocks delivered.
An ICD is implanted exactly like a pacemaker, and has a fully functioning pacemaker if needed. A small incision is made in the chest wall and wire leads are implanted into the upper and lower heart chambers on the right side of the heart. The most common indication for an ICD is a history of heart attack with an EF of less than 35 percent. The data supports the use of an ICD in all patients with an EF less than 35 percent regardless of cause, in addition to maximal medial therapy to improve symptoms and survival. In specific cases of depressed ejection fraction and Left Bundle Branch Block, a specialized defibrillator with a third lead can be implanted. This extra lead is implanted in the heart's venous drainage system (coronary sinus) and stimulates more contractile force. This type of ICD, know as a Biventricular ICD, can be adjusted to improve the EF and improve symptoms. An ICD is not always the right choice for every patient, but patients who meet the criteria should have a discussion with their cardiologist. The standard of care mandates that patients who have an EF below 35 percent be considered for an ICD. The devices are expensive, and in some cases may not give a patient a better quality of life if they have end stage heart disease, as the shocks delivered are quite painful. There is no specific age cutoff for an ICD, but it is generally accepted that the cost-effectiveness of the devices may be somewhat lower in the very elderly.
