ICDs in the Real World

Researchers answer the question: Does the impact of primary implantable cardioverter defibrillators on the prevention of sudden cardiac death translate from research trials to real-world patients?


The U.S. is the world’s largest user of implantable cardioverter defibrillators (ICDs), according to researchers from Brigham and Women’s Hospital and Harvard Medical School, both in Boston, Massachusetts; Stanford University School of Medicine in Palo Alto, California; and Duke Clinical Research Institute in Durham, North Carolina. Reviews have shown that real-world recipients of ICDs are typically older than those in research trials, with more noncardiac comorbidities. Moreover, primary ICD trials were conducted in outpatients with stable mild-to-moderate heart failure (HF), the researchers note. But about a third of older patients who get ICDs have undergone the implantation during a hospital admission for exacerbation of HF or other acute comorbidities—and the early postdischarge period for these patients carries a high risk of death, usually from progressive HF.

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Does the impact of primary ICDs on the prevention of sudden cardiac death translate to overall survival benefits for these patients? To help answer this question, the researchers analyzed data from 23,111 patients with HF (5,258 with an ICD and 17,853 without). Patients with ICDs were more likely to have ischemic HF. They were younger and more likely to be men, and they had a lower ejection fraction, more previous admissions for cardiac diseases, and more physician visits. They also had a higher prevalence of comorbidities, such as chronic kidney disease and metastatic cancer.

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During the average 2.8 years of follow-up, 12,293 (53%) patients died. The crude mortality risk for patients admitted to the hospital was 34% at 1 year and 56% at 3 years. The mortality curves for patients with and without ICDs began to diverge immediately after ICD implantation, the researchers say. At 1 year, crude mortality was lower, compared with eligible patients without an ICD (18% vs 39%); at 3 years, the difference was 40% vs 60%. The researchers note, however, that the crude mortality among hospitalized Medicare patients with an ICD at 1 year was similar to that seen at 3 years in trials of ICDs in ambulatory recipients.

The researchers conclude that the benefits of primary ICD therapy previously shown in ambulatory patients with HF thus “do not seem to translate” to the elderly patients in their study group. After adjustment, the apparent impact of ICD therapy was a 5% reduction in sudden cardiac death and a 9% reduction in all-cause mortality, both not significant.

The researchers did find a trend toward benefits for patients who had nonrecent myocardial infarction (> 40 days prior to the implantation), left bundle branch block, or lower serum B-type natriuretic peptide, although these, too, did not reach significance.

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This is the first study to use latency analysis to adjust for healthy candidate bias, a bias that can lead to overestimation of the net benefits of ICDs, the researchers say. This method, they add, “allows a less biased evaluation by focusing on a time period more likely to reflect true ICD effectiveness rather than preferential selection of ICDs for and by healthier patients.”

The researchers emphasize that the lack of benefit was only for those older patients receiving ICDs during an urgent admission for exacerbation of HF or other acute causes. They found no reason to restrict access to ICDs for older patients with HF who otherwise seem similar to patients in pivotal ICD trials.

Chen C-Y, Stevenson LW, Stewart GC, et al. BMJ. 2015;351:h3529.
doi: 10.1136/bmj.h3529.

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