Implantable cardioverter-defibrillators: expanding indications and technologies

Sudden cardiac death (SCD) is a major challenge facing contemporary cardiology. For an increasing number of patients, the current standard of care for the treatment and prevention of SCD is the implantable cardioverter-defibrillator (ICD). Since its introduction, there have been numerous advances in ICD technology, and indications for its use have expanded greatly in the past year.

To highlight the evolving indications for and the numerous advances in ICD technology, with emphasis on primary and secondary prophylaxis of SCD.

Electronic literature search of the Pubmed and MEDLINE databases from January 1996 to July 2005, using the Medical Subject Heading implantable defibrillator. Abstracts and titles were reviewed to identify English-language randomized controlled trials that included an ICD group and a non-ICD group and that had end points of all-cause mortality, cardiac death, and/or arrhythmic mortality as the main outcome. A further MEDLINE search was conducted to identify randomized controlled trials of cardiac resynchronization therapy (CRT) with a CRT and a non-CRT group (including both mortality and other end points). Other studies were included that clarify aspects of device function and other relevant issues. A total of 22 trials were identified.

ICD implantation improves survival in patients with a history of life-threatening ventricular arrhythmia. More recent evidence shows that ICD implantation also improves survival as primary prophylaxis against SCD in patients at high risk for ventricular arrhythmias, including those with left ventricular ejection fraction (LVEF) of 35% or less and New York Heart Association class II or III heart failure and those with a history of myocardial infarction and LVEF of 30% or less. Cardiac resynchronization improves symptoms, quality of life, and survival for patients with advanced heart failure and intraventricular conduction delays and ventricular dyssynchrony.

ICDs have been shown to improve survival as both primary and secondary prophylaxis in an expanding population of patients. Ongoing ICD research may continue to delineate groups with survival benefit from ICDs, and the use and indications of these devices in clinical practice will continue to expand.