Women who have defibrillators implanted for heart problems are more likely to develop complications than men, a Canadian study suggests.

Men and women were equally likely to have cardioverter-defibrillators or ICDs implanted. But women were nearly twice as likely to have major complications within a year of getting the devices, according to the study in Monday's issue of the Annals of Internal Medicine.

Defibrillators were not designed with body size in mind. (Michael Conroy/Associated Press)

The defibrillators are implanted in people who are at risk of sudden cardiac death because of heart rhythm disorders. The devices work by recognizing serious heart rhythm problems and treating them automatically such as by giving an electrical shock.

Women were a third less likely to receive an appropriate shock than men, the researchers found.

"We had thought complication rates were fairly low," said Dr. Douglas Lee, a cardiologist at the Peter Munk Cardiac Centre in Toronto and a scientist at the Institute for Clinical Evaluative Sciences.

"In fact, it was a lot higher than anticipated."

The findings suggest women should be aware of the potential risk of early complications after the surgery and see their doctor if these occur.

Such symptoms may include:

• Swelling or tenderness at the surgical site.
• Difficulty breathing.

Other complications can only be detected during regular checks of the defibrillator at a clinic, which is why regular follow-up is so important, the authors said.

Women-only trials needed

In the study, a major complication was lead dislodgement. When a lead or wire connecting the heart to the defibrillator is dislodged then the device can't sense any abnormal electrical activity or deliver shocks. The patient has to go back into the operating room to have the lead repositioned or replaced, Lee said.

To obtain the data, researchers analyzed Ontario's ICD database, focusing on 6,021 patients including 1,288 women from February 2007 to July 2010.

The researchers did not find any differences in mortality rates between men and women who received the defibrillators. But discovering the differences in complication rates adds to what is known about sex differences in heart patients.

The devices were not designed with body size in mind, which may be part of the reason for the lead-related problems in women, Lee speculated.

"The results reported by the investigators emphasize the ongoing need for inclusion of large numbers of women in randomized prospective clinical trials," said Dr. Stephanie Brister, a cardiac surgeon at the Peter Munk Cardiac Centre.

"Indeed these results suggest that in certain circumstances 'women only' clinical trials may be required," she added in a release.

The researchers noted there were drawbacks to the study, such as not following up on all potential ICD candidates.

They also did not look into potential reasons for the differences between men and women.

The study was funded by the Canadian Institutes of Health Research and the Ontario Ministry of Health and Long-Term Care.

With files from CBC's Amina Zafar