Understand which patients with heart failure should be considered for a primary prevention implantable cardioverter defibrillator (ICD).

Appreciate which ICD system is most appropriate (eg, transvenous, subcutaneous), and how should it be programmed.

Understand how to troubleshoot a range of practical issues for the ICD recipient.

Four decades ago, Mirowski et al reported on the first three humans treated with an automatic implantable defibrillator.1 These devices have evolved from high-voltage defibrillation-only ‘shock boxes’ to the modern implantable cardioverter defibrillator (ICD), replete with superior longevity, reliability, footprint, diagnostic accuracy and new therapeutic functions. A parallel clinico-scientific process has sought to identify the patients most likely to benefit from an ICD. This article reviews the historical trial evidence as a route to understanding contemporary ICD decision making. Practical considerations and potential future developments are discussed. Although obviously associated issues, secondary prevention ICDs and cardiac resynchronisation therapy (CRT) are beyond the scope of this article.

Primary prevention ICD trials initially focused on patients with left ventricular systolic dysfunction (LVSD) and coronary artery disease (CAD) or prior myocardial infarction (MI) (see table 1). Despite invariably requiring a reduced left ventricular ejection fraction (LVEF), these populations were more accurately defined by ischaemic pathology than symptomatic heart failure (HF). Seminal among early primary prevention randomised controlled trials (RCTs) was the Multicentre Automatic Defibrillator Implantation Trial II (MADIT II).2 Reported in 2002, MADIT II enrolled 1232 patients with prior MI and LVEF ≤30%, assigning them to optimal medical therapy (OMT) with or without a primary prevention ICD. During an average follow-up of 20 months, an ICD reduced all-cause mortality (ACM) by 31%. Where predecessor trials had used relatively exclusive participation criteria based on electrophysiology studies (EPS),3 4 the uncomplicated MADIT II inclusion criteria translated into a newly broadened clinical applicability of primary prevention ICDs. …