Complex sentence: An implantable cardioverter-defibrillator (ICD) is a small battery-powered electrical impulse generator that is implanted in patients who are at risk of sudden cardiac death due to ventricular fibrillation and ventricular tachycardia.
Split into simpler sentences: An implantable cardioverter-defibrillator (ICD) is a device combining a cardioverter and a defibrillator into one implantable unit. It is thus a small battery-powered electrical impulse generator that is implanted in patients who are at risk of sudden cardiac death due to ventricular fibrillation and ventricular tachycardia.