The implantable cardioverter defibrillator (ICD) is a small battery-powered medical device that detects deadly cardiac arrhythmia and acts as an electrical impulse generator in order to deliver a dose of electrical energy to the affected heart.
Implantable cardioverter defibrillators most commonly detect ventricular fibrillation and ventricular tachycardia. The ICD began its development in 1969 at the reins of cardiologists Michael Murowski and Morton Mower. A few years later these two teamed up with M. Stephen Heilman who offered more funding and research and also helped develop the wearable cardioverter defibrillator. They researched ways that they could deliver an electrical shock to the heart within 15 to 20 seconds of detecting ventricular fibrillation. In 1980, their research and perseverance paid off and the first implantable cardioverter defibrillator was implanted in a patient at Johns Hopkins Hospital by Dr. Levi Watkins, Jr.
In the past, implantable cardioverter defibrillators required more than one sensing lead to be connected to the heart in order to be effective. However, ICD’s have since progressed to allow for only one sensing lead to be needed — although more than one lead being connected to the heart is not uncommon. Implantable cardioverter defibrillators are often implanted in the left pectoral region of the chest. Many modern ICD’s also act as a pacemaker and can treat less significant forms of cardiac arrhythmia in addition to more deadly arrhythmias. Modern implantable defibrillators have evolved to detect not just ventricular fibrillation, but also ventricular tachycardia which is often a precursor to VF. ICDs are able to accomplish this by the method of anti-tachycardia pacing (ATP), which essentially tries to pace the heart at a faster rate than the ventricular tachycardia in order to terminate the abnormal rhythm. However, this is not always applicable and most ICD’s will calculate the most effective form of treatment for the patient at the time. An implantable cardioverter defibrillator uses rate discrimination, rhythm discrimination, and morphology discrimination in order to effectively treat an abnormal heartbeat.
There have been numerous clinical studies/trials surrounding various elements of implantable cardioverter defibrillators such as general effectiveness and patient quality-of-life. Patients who have experienced myocardial infarction, otherwise known as a heart attack, are much more susceptible to ventricular arrhythmia. If a patient who is actively experiencing arrhythmia has suffered from myocardial infarction in the past, they are at a high risk of developing ventricular tachycardia and/or ventricular fibrillation, often leading to death.
According to the Antiarrhythmics Versus Implantable Defibrillators (AVID) medical study that was administered in 1999, patients who had defibrillator implants experienced a significantly lower risk of death compared to patients who were being treated with either a placebo or anti-arrhythmic drugs. This is why the ICD is a life-saving medical device. An implantable cardioverter defibrillator is often seen as a better treatment for ventricular arrhythmia than anti-arrhythmic drug therapy.
The psychosocial impact of implantable cardioverter defibrillators has been the case of intense study in recent years. A study conducted in 1999 headed by Samuel Frazier Sears, Jr., found that patients outfitted with an ICD may experience anxiety and depression. It was found that 13% to 38% of those who participated in the study had been diagnosed with anxiety. These psychological symptoms of anxiety and depression in patients who have an implantable cardioverter defibrillator can to some degree be attributed to their ICD. It is common for patients with heart problems to express concern or fear about a complex medical device that is implanted right next to their heart. Fear of shock and fear of device malfunction were identified in the study as two ICD specific concerns. Patient anxiety and depression was not overwhelming enough to reduce the effectiveness and life-saving benefits that implantable cardioverter defibrillators provide. If you are concerned about receiving an implantable cardioverter defibrillator, or if you already have one, please read our article on the precautions that should be taken to minimize interference with an ICD. An ICD may be referred to as an implantable cardioverter, automatic defibrillator implantation, automatic implantable cardioverter defibrillator, single chamber ICD, AICD, or dual chamber ICD.