Sex Differences in ICD Use

Abstract & Commentary

By John P. DiMarco, MD, PhD

Source: Lesley H et al. Sex Differences in the Use of Implantable Cardioverter-Defibrillators for Primary and Secondary Prevention of Sudden Cardiac Death. JAMA. 2007;298:1517-1524.

Lesley and colleagues analyzed a 5% national sample of Medicare inpatient, outpatient, and carrier files to examine the use of ICD therapy for both primary and secondary prevention of sudden cardiac death. Patients classified as having a primary prevention indication had a diagnosis of acute myocardial infarction and either heart failure or cardiomyopathy. Patients with a secondary indication had a prior diagnosis of cardiac arrest or ventricular tachycardia. Data on gender and comorbid conditions were collected and analyzed. The proportion of patients in each cohort who received ICD therapy was then analyzed

The analysis eventually included 136,420 individuals in the primary prevention cohort and 99,663 individuals in the secondary prevention cohort. The mean age was approximately 78 years, and approximately 9% of the total group was black. From 1999 through 2005, there was a 4-fold increase in the one year cumulative incidence of ICD use among men. A similar pattern was noted among women, but the absolute rates of ICD use were approximately 75% lower.

In the secondary prevention cohort, rates of ICD use among men more than doubled between 1999 and 2004. Absolute rates were lower among women and increased only slightly during the course of the study. When ICD use rates were controlled for comorbid conditions, geographic region, and year of cohort entry, men continued to be more likely to receive ICD therapy than women with a hazard ratio of 3.15. It was also noted that black patients were less likely than white patients to receive ICD therapy, with a hazard ratio of 0.85.

In the secondary prevention cohort, men were still more likely than women to receive ICD therapy, with a hazard ratio of 2.44, and black patients were again less likely than white patients to receive ICD therapy with a hazard ratio of 0.71. The presence of dementia, chronic renal disease, and metastatic solid tumor were independently and negatively associated with ICD use. When the group was analyzed according to age ≤ 75 years, men were still more likely to receive ICD therapy in both the primary and secondary prevention cohorts.

The relationship between ICD use and mortality were also examined. The hazard ratio for mortality was 17% lower in the first 180 days, but this difference was not statistically significant. Adjustment for comorbid conditions, year of cohort entry and probability of treatment, however, showed that the hazard of mortality at one year was not significantly lower. However, in the secondary prevention cohort, the hazard for mortality was 37% lower among patients who received an ICD within 30 days of cohort entry. After adjustment for age, comorbid conditions, years, and cohort entry and probability of treatment, the hazard of mortality remained significantly lower, with a hazard ratio of 0.62 for men and 0.68 for women.

Lesley et al concluded that in a representative sample of Medicare beneficiaries, men were 3.2 times more likely to receive ICD therapy for primary prevention and 2.4 times more likely than women to receive ICD therapy for secondary prevention. Thus, there may be factors unaccounted for in this study that explain the differences observed.

Commentary

This paper documents that among US Medicare recipients, men, particularly white men, are more likely than women to receive ICD therapy. In the primary prevention cohort, Lesley et al weren't able to use data concerning left ventricular ejection fractions since this information is not included in the National Medicare Database. Since women are more likely to have symptoms of congestive heart failure with preserved systolic function, this may account for much of the difference in ICD utilization in the primary prevention cohort. However, in the secondary prevention cohort, the reason for the gender discrepancy is less apparent. It may be possible that women may have more arrhythmias that were thought to be due to transient causes, but this can't be determined from this database. Another factor that may influence physicians is that women tend to have more technical complications with ICD implants. In thin or frail individuals, device erosion or pocket problems are more common, and many elderly women would fall into this category.