"There is some fundamental difference between the genders and we have to be sensitive to that," said Andrew Kao, M.D., F.A.C.C. Dr. Kao was at the University of Pennsylvania School of Medicine in Philadelphia at the time of this study. He is now with Cardiovascular Consultants, PA, which manages the Mid-America Heart Institute in Kansas City, Missouri.
Peak oxygen consumption (VO2) is a powerful and reliable predictor of survival in patients with advanced heart failure. If a patient who is working hard on the treadmill is consuming less than about 12 milliliters of oxygen per kilogram of body weight per minute (ml/kg/min), then the odds of long-term survival may be poor and it is generally thought to be appropriate to consider heart transplantation, Dr. Kao said.
However, the VO2 standards are based on the experiences of patients who were almost all men.
"Most of us in tertiary referral centers end up seeing mostly men, and so the reports that come out are mostly on men. We took this opportunity to go back and look at all of our heart failure patients, both men and women." Dr. Kao said. The researchers, including first author Sammy Elmariah, M.D., from the University of Pennsylvania School of Medicine, reviewed the records of 594 heart failure patients who took treadmill exercise tests at the University of Pennsylvania's Heart Failure and Transplant Ambulatory Care Center between July 2000 and December 2003. They found that on average women had significantly lower peak VO2 compared to men, despite adjusting for their body size. However, women had better survival rates than men. The researchers correlated the peak VO2 results from those tests with the survival and heart transplant data for the patients up until June 30, 2004. They wanted to determine what VO2 test results predicted an 85 percent chance of surviving at least one year without needing a heart transplant. This survival rate would be equivalent to the expected one-year survival after heart transplantation.
"When we did that, we found that for men, the VO2 result was 11.5, which is really very close to the 12 that has been reported in the literature recently; but surprisingly, in women, because they do have both lower exercise capacity as well as better survival, we found that they would not have benefited from transplant until their VO2 level was less than 10," he said.
To put it another way, the women in this study had better one-year survival rates than men for any given VO2 level, so over-reliance on VO2 test results might lead clinicians to think their female heart failure patients are sicker than they really are, perhaps leading them to consider heart transplantation earlier than necessary.
Dr. Kao noted that women are smaller and have less muscle mass on average than men, but that difference did not fully explain why the relationship between exercise test results and one-year survival is different for female and male heart failure patients.
"At this time we don't have a really good answer. What we do want people to be aware of is that they shouldn't just use the same criteria for everyone, because you may end up transplanting women too early," he said.
Dr. Kao stressed that the results of this initial study need to be confirmed in a larger study. Also, he pointed out that physicians look at many factors other than VO2 test results before deciding whether a patient would benefit from a heart transplant.
He cautioned physicians against changing their clinical practice based on this single report.
"We're not trying to do that. We're just trying to raise awareness that men and women heart failure patients may have different outcomes. If physicians see someone who has a low VO2 value, but the clinical judgment is that they are stable clinically, they should perhaps use this new information to help them say that maybe their initial impression was right," Dr. Kao said.
David Feldman, M.D., Ph.D., F.A.C.C. from Ohio State University in Columbus, Ohio, wrote an editorial in the journal that said this study brings forward "a provocative and potentially contentious idea--that men and women are not the same and should be treated differently." He cautioned that the characteristics of this study and the lack of an explanation for such gender differences make the results "an observation, not an irrefutable fact."
"I would make the following points: one, for any level of functional capacity, women with heart failure may survive longer then men and, two, this study is not definitive and until confirmatory evidence is available, women and men should be treated the same," Dr. Feldman said.
Sources quoted in this news release do not report any potential conflicts of interest regarding this topic.