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Cover of Assessment on Implantable Defibrillators and the Evidence for Primary Prevention of Sudden Cardiac Death

Assessment on Implantable Defibrillators and the Evidence for Primary Prevention of Sudden Cardiac Death

Technology Assessment Report

, MD, MS, , MD, MPH, , BS, , BA, , MD, , MD, MPH, , MS, , MD, and , BA.

Author Information and Affiliations

Structured Abstract

Background:

Implantable cardioverter–defibrillators (ICDs) are battery-powered implantable devices that monitor heart rhythm and deliver therapy in the form of either electric shock or antitachycardia pacing (ATP) when a life-threatening ventricular arrhythmia is detected. ICDs have been used in patients who survived sustained ventricular arrhythmias to prevent sudden cardiac death (SCD). In recent years, ICDs have also been implanted for primary prevention (prevention of SCD in a patient who has not had yet had sustained ventricular tachyarrhythmia but has risk factors for it). ICDs may also include cardiac resynchronization therapy (CRT) for additional treatment of heart failure in patients with dyssynchronous ventricles.

Objectives:

We aimed to examine the clinical effectiveness of ICD use for primary prevention of SCD. Key Question 1 examined ICD versus no ICD, ICD with ATP versus ICD alone, or ICD with CRT versus ICD alone, and differences among subgroups. Key Question 2 examined early and late adverse events and inappropriate shocks after ICD implantation, and differences among subgroups. Key Question 3 examined eligibility criteria and evaluation methods for patients included in comparative studies and the risk of SCD.

Data Sources:

MEDLINE® (through December 4, 2012) and the Cochrane Central Trials Registry (through the third quarter of 2012), with no language exclusion.

Review Methods:

For Key Questions 1 and 3, we included comparative studies of ICDs for primary prevention. For Key Question 2, we examined reports from ICD registries or other cohort studies with at least 500 patients with ICDs for primary or secondary prevention. Details on design, patients, interventions, outcomes and quality were extracted into standard forms.

Results:

There were 14 studies comparing ICD versus no ICD, 3 studies comparing ICD with CRT (CRT-D) versus ICD, and 59 articles contributing data on adverse events after ICD implantation. There is a high strength of evidence for benefit from ICD treatment compared to control treatment without an ICD for reducing all cause mortality. Meta-analysis of seven RCTs comparing ICD versus control yielded a summary hazard ratio (HR) of 0.69 (95% confidence interval [CI] 0.60, 0.79) for death favoring ICD treatment. Across RCTs, the number needed to treat (NNT) to prevent one death ranged from 6.2 (95% CI 4.0, 18) to 22 (95% CI 2.3, infinite) at the longest durations of followup (3 to 7 years). There is a high strength of evidence for benefit from ICD treatment compared to control treatment without an ICD for reducing SCD. Meta-analysis of five studies comparing ICD versus control showed benefit from ICD use for reducing SCD (HR 0.37; 95% CI 0.26, 0.52). Across RCTs, the NNT to prevent one arrhythmic death ranged from about 2 to 3 (approximate 95% CI 1.3, 16) to 11 (95% CI 1.3, infinite).Three other trials in which ICDs were implanted immediately after myocardial infarction (MI) or at the time of coronary artery bypass grafting did not show a benefit for all-cause mortality, but two of the trials did show a reduction in SCD. Three RCTs of ICD versus no ICD provided low strength of evidence that failed to show a consistent effect of ICD placement on quality of life.

Analyses failed to show statistically significant differences for all-cause mortality or SCD across subgroups by age, sex, and other patient characteristics; however, there may be an indication that ICDs are more effective in patients with more distant coronary revascularization compared with recent surgery. Studies of patients with recent MIs (within 31 or 40 days) had no reduction in all-cause mortality in contrast with studies in patients with more distant MIs. Due to discordant findings among studies, there is insufficient evidence from four RCTs regarding the relative effect on all-cause mortality among patients who receive CRT-D compared to those who receive ICD alone. Heart failure outcomes and related quality of life measures were not reviewed.

Eligibility criteria were reviewed to assess applicability. Comparative studies included individuals with ischemic or nonischemic dilated cardiomyopathy, and left ventricular ejection fraction was ≤35 percent in all but one study. Eligibility criteria regarding heart failure class were variable. The trials of CRT-D used QRS interval data for eligibility; most other trials did not. Most of the RCTs of ICD tested all patients for nonsustained VT, but with different diagnostic tools. Only one RCT reported performing electrophysiology testing in all patients. Only 4 of the 13 RCTs explicitly tested for coronary stenosis, mostly with coronary angiography or exercise testing. Most studies excluded older adults over 70 to 80 years. SCD occurred in 4 to 13 percent of control patients during the 2 to 5 years after randomization.

A high strength of evidence shows early (in-hospital) adverse event rates of approximately 3 percent and serious adverse event rates of approximately 1 percent. Low strength of evidence shows variable, late (out of hospital) rates for device- and lead-related adverse events. Moderate strength evidence shows 3 to 21 percent of patients experience at least one inappropriate shock over 1 to 5 years of followup.

Limitations of the evidence base in some RCTs include lack of blinding of outcome assessors of arrhythmia outcomes or SCD, high attrition rates (>20%), or differential rates of attrition or crossover between study groups and differences in the control treatments or in the rates of concomitant use of beta blockers between the study groups. Nonsignificant findings in subgroup analyses need to be interpreted in the context of studies likely being underpowered to explore differences in effects across subgroups of interest. The quality of the long-term adverse events suffered from a lack of harmonized definitions and systematic ascertainment.

Future research is needed to address comparative effectiveness for quality of life and other patient reported outcomes and to explore treatment heterogeneity according to baseline risk. Consistent reporting of rates of SCD in the non-ICD trial arms would facilitate an assessment of how the mortality benefit may be correlated with the baseline risk.

Conclusions:

There is a high strength of evidence that ICD therapy for primary prevention of SCD, versus no ICD therapy, shows benefit with regard to all cause mortality and SCD in patients with reduced left ventricular ejection fraction and ischemic or nonischemic cardiomyopathy beyond the immediate post-MI or coronary revascularization periods. Studies failed to show statistically significant differences for all-cause mortality across subgroups. There is insufficient evidence for all-cause mortality for patients who receive CRT-Ds versus ICD alone for primary prevention. There is high strength of evidence that in-hospital adverse events are infrequent (1-3%) and moderate strength of evidence that up to one-fifth of patients receive inappropriate shocks from the ICDs.

Contents

Suggested citation:

Uhlig K, Balk EM, Earley A, Persson R, Garlitski AC, Chen M, Lamont JL, Miligkos M, Avendano EE. Assessment on Implantable Defibrillators and the Evidence for Primary Prevention of Sudden Cardiac Death. Evidence Report/Technology Assessment. No. <#>. (Prepared by the Tufts Evidence-based Practice Center under Contract No. 290-2007-10055-I.) Rockville, MD: Agency for Healthcare Research and Quality. June 2013. www.effectivehealthcare.gov/reports/final.cfm.

This report is based on research conducted by the Tufts Evidence-based Practice Center under contract to the Agency for Healthcare Research and Quality (AHRQ), Rockville, MD (Contract No. 290 2007 10055 I). The findings and conclusions in this document are those of the author(s) who are responsible for its contents; the findings and conclusions do not necessarily represent the views of AHRQ. No statement in this article should be construed as an official position of the Agency for Healthcare Research and Quality or of the U.S. Department of Health and Human Services.

The information in this report is intended to help health care decision-makers; patients and clinicians, health system leaders, and policymakers, make well-informed decisions and thereby improve the quality of health care services. This report is not intended to be a substitute for the application of clinical judgment. Decisions concerning the provision of clinical care should consider this report in the same way as any medical reference and in conjunction with all other pertinent information, i.e., in the context of available resources and circumstances presented by individual patients.

This report may be used, in whole or in part, as the basis for development of clinical practice guidelines and other quality enhancement tools, or as a basis for reimbursement and coverage policies. AHRQ or U.S. Department of Health and Human Services endorsement of such derivative products may not be stated or implied.

None of the investigators has any affiliations or financial involvement related to the material presented in this report.

Bookshelf ID: NBK248310PMID: 25356453

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