AIM: Women fare worse than men for ICD implants

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Rates of implantable cardioverter-defibrillator (ICD) implantation are similar among the sexes; however, women suffer from a greater risk of both major and minor complications, according to a study published in the Feb. 7 issue of the Annals of Internal Medicine. Researchers found that women were also less likely to receive appropriate ICD-delivered therapies when compared with men.

“Implantable cardioverter-defibrillators (ICDs) have been shown to reduce mortality as primary prevention among persons with myocardial infarction or heart failure and as secondary prevention after cardiac arrest,” Derek R. MacFadden, MD, of the University of Toronto and Institute for Clinical Evaluative Sciences, Toronto, and colleagues wrote. However, previous studies have alluded to the fact that women may be less likely to receive ICDs compared with men. While sex differences in ICD implants have emerged in the literature, differences in outcomes between the sexes remain understudied.

To better outline sex differences in the use of ICD implantation, MacFadden et al designed a health payor-mandated, prospective study of patients undergoing ICD implantation at 18 follow-up centers throughout Ontario, Canada, between February 2007 and July 2010. The researchers identified 6,021 patients and evaluated the 45-day complication rates, device outcomes and death at one-year follow-up.

Of the total cohort, 4,733 patients were male. Men were older, had a higher prevalence of atrial fibrillation, dyslipidemia and hypertension, while women had lower creatinine and hemoglobin concentrations.

Researchers reported ICD implantation rates to be similar for both women and men, but women saw more complications 45 days post-device implantation and one-year after implantation. Major early complications occurred in 3.3 percent of men and 5.4 percent of women. The most common complications were due to lead replacements for women and lead repositioning for men.

Minor complications also occurred more frequently in women compared with men at 45 days follow-up, 5.8 percent in women and 3.8 percent in men, respectively. At one-year follow-up, 227 major complications occurred in 4,106 men and 111 events occurred in 1,106 women. This equated to rates of 7.4 and 13.9 major complications per 100 person-years. In an extended follow up, major or minor complication rates remained higher in women compared with men.

“Women and men were equally likely to receive an ICD after referral to a cardiac electrophysiologist; however, women who received an ICD were 31 percent less likely than men to receive an appropriate shock and 27 percent less likely to receive appropriate antitachycardia therapy from the device,” the authors wrote. Men and women were equally likely to receive inappropriate shocks.

The researchers also reported that therapeutic interventions were less likely to occur among women, but women had a higher risk of developing device complications. In fact, women saw a 1.7-fold higher risk of developing complications at 45 days.

“To our knowledge, ours is the first population-based study to demonstrate that women are less likely than men to receive appropriate shock or antitachycardia therapy,” the authors noted. Previous studies have shown that women are less likely to have left ventricular systolic dysfunction compared with men, which means that the underlying cardiac function may affect arrhythmogenicity in women differently. “[S]electing for ICD candidacy on this basis may have contributed to sex difference in baseline risk for ventricular arrhythmia,” the authors wrote.

Additionally, MacFadden et al said:

  • Both physicians and patients should consider the lower rate of appropriate ICD-delivered therapy and higher complication rates in women when deciding whether defibrillator therapy is beneficial. The reduction in appropriate therapies in women could suggest a decreased anticipated benefit of ICDs, the authors wrote; and
  • Arrhythmic risk stratification may differ for men and women and baseline risk for ventricular tachyarrhythmia suggested that the threshold for defibrillator use may vary by sex.
The authors noted that future studies need to examine ICD benefits in women.

“Women were less likely to experience appropriate ICD-delivered shocks and therapies, which suggests that their baseline arrhythmic risk is lower under current primary and secondary prevention eligibility criteria,” the authors summed. “Mortality did not differ and no evidence of differential use of ICDs by sex was found in a cohort referred to a cardiac electrophysiologist for device consideration.”

In an accompanied editorial, Pamela S. Douglas, MD, of the Duke University Medical Center and Lesley H. Curtis, PhD, of the Duke Clinical Research Institute, both in Durham, N.C., explored whether care can be optimized for all patients, despite gender differences.

“A one-size-fits-all approach ignores the underlying biological differences between men and women and sometimes results in excess mortality for female patients,” the editorialists noted. “In such cases, the lack of generalizable data on treatment efficacy makes the practice of evidence-based medicine in individual patients more challenging.”

Douglas and Curtis questioned whether patients would benefit from sex-specific approaches to ICD implantation, due to MacFadden et al’s findings. “A higher complication rate and a lower rate of receiving appropriate therapies do not mean that ICDs are not effective in women; it may simply means that the number needed to treat is higher for women than for men,” they noted. These results may point to the fact that clinicians might need to tailor selection criteria in women and develop better technologies.