Women Less Likely than Men to Get ICDs

DURHAM, N.C., Oct. 2 -- Women at risk of sudden cardiac death are two to three times less likely to receive an implantable cardioverter-defibrillator (ICD) than men who are at risk, investigators here have found.

Three times as many men as women receive ICDs for primary prevention and a two-fold gender disparity exists in use of ICDs for secondary prevention, Lesley Curtis, Ph.D., of Duke University Medical Center here, and colleagues reported in the Oct. 3 issue of JAMA.

The findings "highlight the need for an improved understanding of sex differences in patterns of care," the authors concluded. "Moreover," they said, "it is essential that these findings be verified in data sets that include left ventricular ejection fraction and robust measures of comorbidity."

Beginning with the Multicenter Automatic Defibrillator Implantation Trials (MADIT I and II), evidence from multiple investigators supported the use of ICDs for primary prevention of sudden cardiac death in patients with left ventricular systolic dysfunction. Since the late 1990s, the benefits of ICD implantation have been extended to secondary prevention, the authors stated.

Several studies have also documented gender disparities in use of ICDs. However, those studies were conducted before Medicare started covering the devices, the authors noted. So the current study focused on gender differences in the use of ICD therapy for primary and secondary prevention in a more contemporary sample of Medicare beneficiaries.

The study involved a 5% sample of Medicare beneficiaries from 1991 through 2005. From that sample, investigators identified 65,917 men and 70,504 women who had diagnoses of acute myocardial infarction and either heart failure or cardiomyopathy but no history of cardiac arrest or ventricular tachycardia. They made up the primary prevention cohort. A secondary prevention cohort comprised 52,252 men and 47,411 women with a history of cardiac arrest or ventricular tachycardia. All the patients had been treated from 1999 through 2005.

The primary outcomes were ICD use and one-year mortality. In the primary prevention cohort, the rate of ICD use was 32.3 per 1,000 men versus 8.6 per 1,000 women, which translated into a statistically significant hazard ratio of 3.15 for ICD therapy among men (95% CI 2.86 to 3.47).

In the secondary prevention cohort, the implantation rates were 102.2 per 1,000 men and 38.4 per 1,000 women, resulting in a statistically significant hazard ratio of 2.44 in favor of men (95% CI 2.30 to 2.59).

Among primary prevention patients alive at 180 days after cohort entry, the one-year mortality hazard ratio did not differ between patients who received ICDs and those who did not (HR 1.01).

However, ICD therapy had a significant impact on mortality in the secondary prevention group. Among patients alive at 30 days after cohort entry, the one-year mortality hazard ratio was 0.65 in favor of ICD therapy (95% CI 0.60 to 0.71).

Addressing the lack of mortality benefit in the primary prevention cohort, Dr. Curtis and colleagues noted that patients were not randomized to therapy and that no information was available on LVEF, a key influence on patient selection and mortality.

"To the extent that ICDs are implanted selectively in patients who have low ejection fraction (and are therefore at high risk of mortality), the results may suggest that ICDs have improved the survival of high-risk patients so that their survival is now similar to that of low-risk patients," the authors stated. "Without key clinical data, however, we cannot test that hypothesis."

In an editorial that accompanied the article, Rita Redberg, M.D., of the University of California, San Francisco, called the lack of mortality benefit in the primary prevention group "discomforting." She also noted that the study did not consider the impact of ICDs on quality of life.

Investigators in MADIT II concluded that the "adverse effects of ICD on health-related quality of life, together with lower quality of life among survivors, may offset the 3-year survival benefits of ICDs," Dr. Redberg said.

She concluded that the "multibillion-dollar question" is whether too few women receive ICDs for primary prevention or are too many of the devices being implanted in men. The report by Curtis et al provides insights into better understanding of how to optimize delivery of cardiovascular health care, she noted.

Dr. Curtis reported receiving research and salary support from Allergan Pharmaceuticals, GlaxoSmithKline, Lilly, Medtronic, Novartis, Ortho Biotech, OSI Eyetech, Pfizer, and Sanofi-Aventis. Dr. Redberg disclosed honoraria for lectures at symposia from Guidant and Medtronic.