Implantable Cardioverter Defibrillators in Primary and Secondary Prevention: A Systematic Review of Randomized Controlled Trials

Annals of Internal Medicine, 2003;138:445-452.

Justin A. Ezekowitz, MB, BCh; Paul W. Armstrong, MD, FRCPC; Finlay A. McAlister, MD, MSc, FRCPC

Purpose: To assess the efficacy of ICDs in persons at increased risk for SCD.

Conclusion: ICDs prevent sudden cardiac death regardless of baseline risk. However, their impact on total mortality is sensitive to baseline risk for arrhythmic death. Decisions about resource allocation for ICDs depend on accurate stratification of patients according to risk.

Summary:

· A systematic review of trials of primary and secondary prevention with ICDs to examine the effects of this therapy on rates of SCD and all-cause mortality. (AVID, CASH, CIDS, MADIT, CABG Patch, MUSTT, MADIT II, CAT) (8 trials=4909 patients)

· ICDs reduce the relative risk for SCD by approximately 50% regardless of baseline risk

· The effect of ICD therapy on all-cause mortality varies according to baseline risk

v ICDs reduced all-cause mortality by approximately 1/3 in survivors of cardiac arrest and in high-risk patients who had not yet had an arrest (CAD and severe LV systolic dysfunction)

v ICDs did not create a significant impact on total mortality rates in patients at lower risk for SCD (LV systolic dysfunction but no CAD or inducible ventricular arrhythmias)

v Challenge: to accurately stratify patients by baseline risk to identify those most likely to benefit from ICD therapy

v Data supports the policy of considering ICD therapy for secondary prevention (survivors of cardiac arrest) or for primary prevention in high-risk patients

· The benefits of ICDs on total mortality are sensitive to baseline risk for SCD.

v Analysis suggests, given the variability in baseline risks among patient subgroups, incremental cost-effectiveness ratios for ICD placement compared with drug therapy estimates a range from $17,700 to $138,800 per year of life saved.

v The wide variability in cost-effectiveness ratios emphasizes the importance of accurate risk stratification tools to assist in determining who should receive ICD therapy.

v Further research is needed to develop accurate risk stratification tools, to determine the economic impact of ICD therapy in different subgroups of patients, and to evaluate quality-of-life issues.

This meta-analysis concludes that the benefits of ICDs on total mortality are sensitive to baseline risk for SCD and therefore accurate risk stratification should be done to identify the most appropriate high-risk patients for EP referral and subsequent ICD therapy.

www.alternans.org Editor comment: Microvolt T-Wave Alternans is a risk stratifier that will identify the high-risk patients who are most qualified to be referred to EP study and most likely benefit from an ICD. It will also identify the patients who are at minimal risk and spare them the discomfort of an unnecessary EP study and ICD placement.