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Women are at greater risk of complications and are less likely to receive appropriate shocks from their implantable cardioverter-defibrillators (ICDs) than men, Canadian researchers found.

In a prospective study, women were significantly more likely to have both early and late major complications (P=0.002 and P<0.001, respectively), Douglas Lee, MD, PhD, of the Institute for Clinical Evaluative Sciences in Toronto, and colleagues reported in the Annals of Internal Medicine.

They were also significantly less likely to receive appropriate shocks and therapy via antitachycardia pacing (P=0.015 and P=0.003), Lee and colleagues reported.

Mortality rates, however, were similar between men and women, they found.

Clinicians have been concerned about potential gender differences in ICD complication rates, and have raised concerns about a potential lack of benefit for the devices in women, but sex differences associated with ICDs haven't been fully studied, the researchers said.

So Lee and colleagues conducted a prospective trial of ICD patients at 18 implantation centers throughout Ontario, Canada; 6,021 patients -- 4,733 of whom were men -- were referred for implantation between February 2007 and July 2010.

A total of 5,450 patients received an ICD, and implantation rates were similar between men and women, the researchers found.

In adjusted analyses, however, women were significantly more likely to have major complications within both 45 days and one year (OR 1.78, 95% CI 1.24 to 2.58, P=0.002 and HR 1.91, 95% CI 1.48 to 2.47, P<0.001, respectively).

The most common early, major complications were lead repositioning for men and lead replacement for women, and late complications for both genders also included pocket infection and electrical storm, the researchers reported.

"Although most of the sex differences in complications were lead-related, the underlying reasons may be more complex and multifactorial and may be related to differences in body size, delayed presentation in women, or innate differences in response to disease," they wrote.

The combined occurrence of any major or minor complication was also higher in women at both time points, the researchers found (OR 1.5, 95% CI 1.12 to 2.00, P=0.006 and HR 1.55, 95% CI 1.25 to 1.93, P<0.001, respectively).

Women were also less likely to receive appropriate shocks or appropriate therapy via shock or antitachycardia pacing (HR 0.69, 95% CI 0.51 to 0.93, P=0.015 and HR 0.73, 95% CI 0.59 to 0.90, P=0.003, respectively).

Though they didn't evaluate the mechanisms for this relationship, Lee and colleagues wrote that women may have less left ventricular systolic dysfunction or other differences in cardiac electrical physiology.

They noted that total mortality, however, didn't differ between men and women.

Overall, the findings confirm data from the randomized, controlled DEFINITE and SCD-HeFT trials that pointed to the existence of gender differences in ICD outcomes, and imply that physicians and patients should consider the lower rate of appropriate therapy and higher complication rates in women when making decisions about ICD implantation, Lee and colleagues wrote.

They said future ICD studies should consider reporting their results by gender, and more work should focus on improving risk stratification for sudden cardiac death in women.

The study was limited because it only included patients referred for consultation by an electrophysiologist and thus could not identify upstream referral patterns and how those would affect outcomes.

In an accompanying editorial, Pamela Douglas, MD, and Lesley Curtis, PhD, of Duke University, wrote that the findings raise questions about "whether known differences in the underlying biology of cardiac arrhythmias between men and women, such as the higher prevalence of nonischemic cardiomyopathy as a cause of sudden death and the greater use of concomitant cardiac resynchronization therapy, might contribute to the problem."

If so, they wrote, the question would then be whether "sex-specific approaches to ICD use, programming, or other factors might maximize benefit and minimize harms in women."

Another critical question, they added, is whether ICDs are more effective than pharmaceutical treatment alone in preventing sudden death in women, noting that pivotal trials have been inconclusive.

From the American Heart Association:

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