Is prophylaxis the best use of the ICD?

When Michel Mirowski initially conceived of the implantable defibrillator the aim was to protect the patient at risk of sudden arrhythmic death. In the late 1960s, when Mirowski and co-workers projected the development of an automatic implantable defibrillator, out-of hospital resuscitation was a rare event. However, the out-of-hospital resuscitation initiatives led by investigators from Seattle and Miami started providing large groups of patients, thereby facilitating the clinical evaluation and acceptance of implantable cardioverter defibrillator (ICD) therapy, in the 1980s. The fact that patients resuscitated from cardiac arrest frequently develop recurrent potentially lethal arrhythmic episodes, combined with the development and increasing use of programmed ventricular stimulation, created the basis for their identification. Thus, during the first two decades, the ICD was used almost exclusively for secondary prevention of sudden death in patients who had already developed clinically documented sustained ventricular tachyarrhythmias. At the end of the first decade of ICD therapy — and in the spirit of ‘evidence-based medicine’ — four prospective randomized trials were begun, to evaluate the effectiveness of the ICD for secondary prevention, and three others for primary prevention. These studies were concluded within the 1990s, and demonstrated that patients enjoyed better survival with ICD therapy compared to conventional pharmacological alternatives. Furthermore, this benefit was evident both in patients with previous sustained ventricular tachyarrhythmias and without. The time has come to assess which patients benefit most from ICD therapy. The aforementioned trials provide strong and possibly surprising insights into this question, and are the focus of this article.