Criteria for ICD Implantation
Criteria for ICD Implantation
Abstract & Commentary
By John P. DiMarco, MD, PhD Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.
Source: Goldenberg I, et al. Risk stratification for primary implantation of a cardioverter-defibrillator in patients with ischemic left ventricular dysfunction. J Am Coll Cardiol. 2008;51:288-296.
In this study, goldenberg and colleagues from the MADIT-II study analyzed risk factors for mortality in that trial. MADIT-II was a randomized trial of ICD versus conventional therapy, which included 1232 patients with documented previous myocardial infarctions who had an ejection fraction of ≤ 30%. Patients were excluded from the trial for the following reasons: New York Heart Association functional class IV; revascularization within the preceding three months; a myocardial infarction within the past month; advanced cerebrovascular disease; renal disease defined as a BUN greater than 70 mg/dL or a creatinine greater than 3 mg/dL; or any other non-cardiac disease associated with a high likelihood of early death. In this report, survival was analyzed for 2 groups. Outcome was analyzed separately in a prespecified very high-risk group defined by a BUN greater than 50 mg/dL or a serum creatinine greater than or equal to 2.5 mg/dL. A second multivariate analysis of predictors of outcome was carried out in the remaining patients.
There were 60 patients who were classified as very high risk based on their renal dysfunction. These patients had a BUN or creatinine in a narrow range, since patients with more severe renal dysfunction were excluded from the trial. However, the mortality for this group, with just moderately severe renal dysfunction, was 48% during the trial, and there was no difference between patients randomized to the ICD versus conventional therapy.
In the second part of the study, a proportional hazards regression model that initially looked at 17 prespecified variables was developed that identified five clinical risk factors: age > 70 years, New York Heart Association functional class > II, BUN > 26 mg/dL, atrial fibrillation at entry, and QRS duration > 120 m/sec. Each of these risk factors was assigned a single point and a risk score calculated. During the course of the trial, crude mortality was similar in the ICD and conventional therapy groups if none of the risk factors were present (9% and 8%, respectively). Among patients with either one or two risk factors, two-year mortality estimates between conventional and ICD therapy were 22% vs 9% and 32% vs 15%, respectively. Among patients with ³ three risk factors; however, the mortality estimate in the conventional group was 32%, with only a minor reduction to 29% in the ICD patients. When two-year mortality reduction was plotted as a function of the number of risk factors, a U-shaped curve was observed. No significant reduction was seen in patients with 0 risk factors or in the very high-risk group, and only a modest reduction was seen in patients with > three risk factors. However, large and clinically-significant reductions were seen in patients with one or two risk factors. Modes of death by risk group were also analyzed. In patients in the very high-risk group, the predominant mode of death was non-sudden death. In the other groups, sudden death, not non-sudden death, was attenuated by ICD therapy, with ICD therapy more beneficial when the proportion of deaths that were sudden was higher.
Goldenberg et al conclude that a simple risk score based on only five clinical risk factors can be used to identify subsets of patients who meet current criteria for ICD implantation who are either unlikely to benefit because of low risk or very high risk, even with defibrillator therapy.
Commentary
The paper by Goldenberg et al from the MADIT-II trial is quite important for clinicians. Current guidelines for insertion of implantable cardioverter defibrillators are based on ejection fraction, New York Heart Association classification, and diagnosis. The criteria for implantation are fairly broad but, as shown in this paper, within the group of patients currently indicated for ICD therapy, both low and high risk groups can be defined. However, the data presented here are for only a relatively short period of follow-up. I have reservations about excluding patients with no risk factors despite a low ejection fraction from ICD therapy based on only two-year data. It is very likely that as disease progresses in these patients a benefit of the ICD might be demonstrated, and its probably more appropriate to think in terms of five-year intervals. However, in patients with multiple risk factors or significant renal dysfunction, it is clear that the predominance of non-sudden causes for death largely negates, even in the short term, any benefit that might be gained by ICD implantation.
Physicians considering implanting an ICD should always consider each individual patient's clinical characteristics. The specific criteria used in ICD guidelines should probably be regarded as permissive rather than obligatory.
In this study, goldenberg and colleagues from the MADIT-II study analyzed risk factors for mortality in that trial. MADIT-II was a randomized trial of ICD versus conventional therapy, which included 1232 patients with documented previous myocardial infarctions who had an ejection fraction of ≤ 30%.Subscribe Now for Access
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