TORONTO – A new study suggests women do not get the same level of benefit from implanted heart defibrillators as do men who have the devices.
The study findings suggest the criteria used to identify which women need the defibrillators may not be working as well as they should.
Lead author Dr. Douglas Lee says it seems clear that some of the women studied didn’t actually need the device, but that some women who should have defibrillators didn’t get them.
Lee says the problem may be a one-size-fits-all selection approach that works for men, but doesn’t take into account differences in the way the disease manifests itself in women.
The study was published in the Annals of Internal Medicine.
Lee, a cardiologist and cardiac epidemiologist, teaches at the University of Toronto’s medical school and is a scientist at the Institute for Clinical Evaluative Sciences.
He and colleagues followed a group of nearly 6,000 men and women from Ontario who were referred to an electrophysiologist for implantation of a ICD – implanted cardioverter-defibrillator – between February 2007 and July 2010.
The devices are small, implantable equivalents of the machines used on TV medical dramas to shock a heart back into rhythm. Slightly larger than a pacemaker, they are implanted on the chest, under the skin.
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ICDs are used in people who are at risk of dropping dead from a dangerous heart rhythm called ventricular tachycardia or ventricular fibrillation.
The research team wanted to see if there were gender differences in many aspects of the use of the devices. Were women diagnosed as needing them less frequently than men? Did the devices worked as well in women? Were complication rates similar between the genders?
It had been known that men were more likely to have ICDs implanted than women. And a previous meta-analysis – a study that analyzes data from a number of separate studies together – had suggested that while the devices help men with the condition to survive, the same benefit was not seen in women.
In Lee’s study, women were as likely to be given an ICD as men were – if they were referred to a cardiac specialist. But three times as many men as women received ICDs. This study can’t say why that is.
“It’s either some biological difference between men or women or they’re not being referred for implantation by their physician,” Lee says. “It’s something more upstream than the cardiologist who is implanting the device.”
The devices are computerized and gather data on all the times they fire in response to dangerous heart beats – as well as the times they fire inappropriately. Lee and his team analyzed that data and found women and men were equally likely to experience misfires, but women received about 30 per cent fewer appropriate shocks than men.
His conclusion: Some of the women didn’t need the devices in the first place.
“Based on our data, those women may not have needed a defibrillator. But they did get one. And the other thing is that we do know that from other studies that if we use these criteria, there may be some … women who we’re missing.”
“Our paper is suggesting that we may need to select women differently than we select men for the ICD,” Lee says. “If we use the same criteria for both men and women, what I think we’ll find is that fewer women will benefit.”
In addition, the study found the women were more likely to suffer complications, such as the lead – the wire connecting the device to the heart – detaching from the heart wall. Women were nearly twice as likely to have a major complication then men.
Lee says that may be the one-size-fits-all problem again. “I think it’s probably because these devices are not bio-engineered separately in men and women.”
He suggests the field needs to rethink the way these devices are used in women.
“I think we probably need randomized trials of just women. Before we do that, I think we need to go back to the drawing board to find better ways to risk stratify women for sudden cardiac death.”
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