The first ICD was approved for implantation in the United States in 1985. At that time, it was indicated only for patients who had a documented cardiac arrest or life-threatening arrhythmia. The implantation of these devices was difficult and required electrodes to be placed directly on the surface of the heart. The device itself had to be placed in the wall of the upper abdomen as it was too large to be placed in the chest.
By the early 1990's, the devices no longer required wiring directly on the heart, but allowed for wiring that went through the vein to the inside surface of the heart. This made the implant procedure much easier and the recovery much quicker (just overnight).
The technology further improved to allow the devices to be smaller, which allowed implantation of the device in the upper chest, like a pacemaker, rather in the abdomen.
Around this time, the first seminal studies of defibrillators were complete. These studies evaluated ICDs for patients who had not yet had a life-threatening arrhythmia, but were statistically likely to develop one. The first such study, MADIT, took patients with a weakened heart from coronary artery disease. All patients received best medical therapy. Half the patients received a defibrillator and half did not. The group that implanted a defibrillator lived longer. The second major study, called SCD-HeFT, took patients with a weakened heart from any cause. Again, the group that received a defibrillator lived longer. Since that time, CMS approved the ICD for use in patients at high risk for a cardiac arrest.
Over time, the technology of ICDs has improved. They are essentially implantable computers that keep track of a patient's heart rhythm by pacing (protect from slow heart rates) as well as treating fast rhythms. They can pace-terminated a fast rhythm called ventricular tachycardia without resorting to a shock. In fact, a patient could have a life-threatening arrhythmia, the device could detect and treat it, without the patient even knowing it. They last longer than they did a decade ago. They can pace and also pace both sides of the heart for those patients with conduction problems and would benefits from bi-ventricular pacing.