It depends on the type of arrhythmia and requires a cardiologic evaluation. For all types of severe bradycardia with associated clinical symptoms, a pacemaker is necessary for protection; in other cases, for sudden fatal malignant arrhythmias, such as ventricular fibrillation and ventricular flutter, the patient will need to be implanted with an implantable cardioverter-defibrillator (ICD), an implantable medical device that has more features than a pacemaker.