Implantable Cardioverter-Defibrillator Therapy for Primary Prevention of Sudden Cardiac Death

摘要

Primary prevention trials have focused on differing sub-groups of patients at high-risk of sudden cardiac death (SCD) and this includes patients with coronary artery disease (CAD), a history of myocardial infarction, congestive heart failure (CHF), and ventricular arrhythmias on electrophysiology study or with a non-sustained episode of ventricular tachycardia on Holter and/or in hospital monitoring, and syncope from unidentified causes and patients with differing forms of cardiomyopathy. The purpose of this article is to provide an up-to-date review of the use of an implantable cardioverter-defibrillator (ICD) in the primary prevention of SCD based on information obtained from randomised clinical trials, particularly in those focusing on high-risk patients with CAD. Introduction Sudden cardiac death (SCD) resulting from fatal ventricular arrhythmias is one of the most common causes of death in the developed world. Patients suffering from a potentially fatal arrhythmia are at risk of death before they even reach medical intervention and out-of-hospital survival rates are as low as 2-15% (1). Immediate defibrillation treatment is the only remedy for arrhythmic sudden death caused by hemodynamically compromising ventricular tachycardia (VT) and ventricular fibrillation (VF) (2). The implantable cardioverter-defibrillator (ICD) has seen dramatic changes in design to accommodate its role in preventing sudden cardiac death, particularly given the fact that anti-arrhythmic drug therapy has proven to be of limited use and in some instances increased the risk of death (3). This said, it is still universally accepted that treatment with beta-blockers and ACE-inhibitors reduce the risk of sudden cardiac death and should therefore be administered to those patients that are not contraindicated (4, 5).Of those patients who do survive a potentially fatal arrhythmia, the implantation of an ICD has proved invaluable to their continued survival as these patients are at an especially high-risk of ventricular arrhythmia recurrence. A number of randomised trials, the Antiarrhythmics Versus Implantable Defibrillators (AVID), Cardiac Arrest Study Hamburg (CASH), and the Canadian Implantable Defibrillator Study (CIDS) have been conducted to assess the role of ICDs in the secondary prevention of SCD and have proven to be effective with a reduction in all-cause mortality of 20-30% (6,7,8). Given the large battery of trials supporting the use of the ICD in the secondary prevention of SCD, further trials have been envisioned to assess the use of an ICD in the primary prevention of SCD to address the large number of patients who have not experienced fatal arrhythmias before ICD therapy. Addressing the question of who should be prophylactically implanted with an ICD in order to prevent SCD is one that can not be answered easily, and ethical considerations should not be overlooked when contemplating the use of such a device for treatment. Indications for ICD therapy The American College of Cardiology/American Heart Association and North American Society for Pacing and Electrophysiology (ACC/AHA/NASPE) recognises that there are a number of conditions for which there is evidence and/or general agreement that a given procedure or treatment is useful and effective (Class 1) (9). Table 1 lists the ACC/AHA/NASPE class 1 indications for ICD therapy. Further to this, ICD has also been commonly used in the prophylactic prevention of SCD for conditions such as long QT syndrome, Brugada syndrome, idiopathic VF, arrhythmogenic right ventricular dysplasia and hypertonic cardiomyopathy (1).