One of the greatest inventions of the modern era has been the implantable cardioverter-defibrillator (ICD). Envisioned by Michel Mirowski and Morton Mower in the late 1970s and early 1980s, this device was initially very large, requiring an open-chest implant and a 10-day hospital stay. The device can now be used to treat life-threatening ventricular tachycardias with a simple transvenous approach.
A single-chamber ICD consists of a pulse generator and lead. Dual-chamber and three-chamber (biventricular) devices also exist. In the most simplistic terms, the ICD determines the heart rate of the patient. When the heart rate exceeds a predetermined number (165 beats per minute, for example), the device is programmed to diagnose a ventricular tachycardia and give a correcting impulse (up to 42 joules). ICDs have additional features that can determine the nature of the tachycardia and try to differentiate it from other types of supraventricular tachycardias. These features can be useful in trying to discriminate atrial fibrillation with a rapid ventricular response from ventricular tachycardia. In addition, these devices can be programmed to deliver rapid, paced beats in order to terminate ventricular tachycardia and minimize the number of delivered shocks. Finally, bradycardia pacing is also available.