The likely cause for the mortality of middle aged women is______. [originaltext]

Atrial fibrillation, or AF happens when electrical impulses in two of the four chambers of the heart go into an irregular or chaotic pattern. Doctors often diagnose it when patients come in with symptoms of heart palpitations. It is a condition not commonly seen in middle aged women.
    An international group of researchers wanted to know why, so they looked at results of the Women’s Health Study, conducted from 1993 to 2010. Data was collected from 35,000 women whose average age was 53. No one in the group had previous heart problems. But surprisingly, the women with sustained atrial fibrillation had a twofold greater risk of death than others.
    Dr. David Conen of the University Hospital in Basel, Switzerland and other researchers wanted to know what the risk factors were for these women, especially those who appeared to be healthy.
    Cardiologist Christine Albert of Brigham and Women’s Hospital in Boston, Massachusetts was one of the researchers. She says the key is whether the AF is constant.
    Patients are often treated with medication to reduce high blood pressure and are urged to reduce their cholesterol levels and not to smoke.
    Women, and men, who feel they have symptoms of atrial fibrillation are advised to see their doctor for appropriate treatment.