Lower rates of sudden death among women may be related to gender differences in heart arrhythmias, rather than to other heart disease factors or treatments, hypertension, diabetes or other measured variables, according to a new study in the June 16, 2004 issue of the Journal of the American College of Cardiology.
"Even after we controlled for all those potential explanatory factors, women still had fewer arrhythmias; suggesting there may be something intrinsic about being a woman that makes you less prone to arrhythmias," said Rachel Lampert, MD, FACC from the Yale University School of Medicine in New Haven, Conn.
The researchers reviewed data on 340 men and 59 women with coronary artery disease who received implantable cardioverter-defibrillators that automatically trigger electrical shocks to treat dangerous abnormal heart rhythms. The devices in these patients recorded the heart rhythms each time a treatment shock was administered, so researchers could document that a dangerous arrhythmia had occurred.
"These findings are very different than the epidemiologic studies of sudden death, because in epidemiologic studies, you don't know what pathophysiologic process was actually responsible for the death. In this study we could very easily see whether these women are or are not having fewer arrhythmias. This had never been looked at before in this way in a large, homogeneous group of patients with coronary artery disease," Dr. Lampert said.
Sustained dangerous arrhythmias (either ventricular tachycardia or ventricular fibrillation) occurred in 52 percent of the men in the study, but only 34 percent of the women (p < 0.01). Although some other studies have not reported this gender difference in arrhythmias, Dr. Lampert noted that those studies included patients with a variety of underlying heart diseases, while this study looked at only patients with coronary artery disease.
Although this study was not designed to investigate the mechanisms that might explain a gender difference in heart arrhythmias, Dr. Lampert says other research suggests two leading suspects.
"There are data from laboratory experiments that electrical properties in isolated cells do differ between cells from male versus female animals, so there are intrinsic electrical differences," she said. "Also, there may be differences in the autonomic nervous system between men and women. For example, there are some studies that suggest women have a lower sympathetic nervous system response to acute stress, so it may be they are less prone to have arrhythmias in response to triggers."
Although the women in this study were less likely to have episodes of dangerous arrhythmias than the men, Dr. Lampert said that doesn't mean they had less need for the implantable cardioverter-defibrillator (ICD) devices.
"No, absolutely not," she said. "The women in this study had fewer arrhythmic events than men, but significant numbers had potentially life-threatening arrhythmias treated by the device, implying a significant benefit from ICD implantation. Our purpose was to explore the question of why women have less sudden death."
Dr. Lampert noted that other studies have demonstrated the benefits of implantable cardioverter-defibrillator devices for female patients.
L. Brent Mitchell, MD, FACC from the Libin Cardiovascular Institute in Calgary, Alberta, Canada, who was not part of this research effort, said this study makes an important contribution to our understanding of who is affected by ventricular tachycardia. He noted the advantages of studying people with ICD devices, because they continuously and accurately record occurrences of potentially dangerous arrhythmias.
"This analysis identified gender as the most powerful independent predictor of ventricular tachyarrhythmias in this patient population. This observation is noteworthy for the challenge that it provides to identify a mechanism for the interaction between gender and ventricular tachyarrhythmia incidence. Identification of the mechanism for this relationship has the potential for providing important rationale for the further development of preventative therapies for this critical health care problem," Dr. Mitchell said.
Dr. Mitchell said the results suggest that clinicians may need to reconsider the typical standards used to decide which patients are likely to receive the most benefit from ICDs.
The American College of Cardiology, a 29,000-member nonprofit professional medical society and teaching institution, is dedicated to fostering optimal cardiovascular care and disease prevention through professional education, promotion of research, leadership in the development of standards and guidelines, and the formulation of health care policy.