Effectiveness of Implantable Cardioverter Defibrillators for Primary Prevention of Sudden Cardiac Death in Subgroups: A Systematic Review
The following are 10 points to remember about the effectiveness of implantable cardioverter-defibrillators (ICDs) for primary prevention of sudden cardiac death:
1. Although ICDs have been shown to prolong survival in multiple primary prevention studies, whether certain subgroups are less or more likely to benefit is not clear.
2. In this meta-analysis of 14 studies, the superiority of ICDs in reducing sudden cardiac death and overall mortality was confirmed.
3. Meta-analyses of the relative odds ratio of death (ROR, OR for one subgroup divided by the other) for subgroups of gender, age, and QRS interval failed to show any statistical differences.
4. For other subgroups, such as New York Heart Association (NYHA) class, ejection fraction, bundle branch block, time since myocardial infarction (MI), renal dysfunction, and diabetes, the evidence was indeterminate because only a few studies included them.
5. Even if a difference had been found in the outcome of various subgroups in this review, it would have to be verified in a randomized fashion before it could be used to determine ICD candidacy.
6. An ICD is indicated for primary prevention of sudden death for patients with ischemic (at least 40 days post-MI) or nonischemic heart disease, ejection fraction ≤35%, and NYHA class II or III symptoms. An ICD is also indicated for primary prevention for patients with ischemic heart disease who are at least 40 days post-MI, ejection fraction ≤30%, and NYHA class I symptoms.
7. Since the primary studies and the meta-analyses have in general failed to show any difference in outcomes with respect to various subgroups, an ICD should be offered to patients with evidence-based indications, as specified in points 6 and 7.
8. Despite the fact that the mortality benefit is sustained to up to 8 years (MADIT II trial), we need a better method of risk stratification to identity patients who are most likely to benefit from an ICD.
9. Whether an ICD is beneficial in the very elderly (>85 years) or those with severe comorbid conditions (e.g., patients on hemodialysis) is unknown.
10. A completely subcutaneous ICD is now available, which has the potential to reduce sudden cardiac death without the morbidity related to conventional transvenous systems.
Keywords: Risk, Myocardial Ischemia, Myocardial Infarction, Kidney Failure, Chronic, New York, Primary Prevention, Renal Dialysis, Tachycardia, Ventricular, Heart Block, Bundle-Branch Block, Diabetes Mellitus, Defibrillators, Implantable, Death, Sudden, Cardiac
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