High Estradiol Levels Linked to Sudden Cardiac Arrest

Ob/Gyns may not think of themselves as well-positioned to help prevent sudden cardiac arrest, but new research suggests you just may be quite well placed to help identify women at risk.

Researchers reported in Heart Rhythm that measuring the levels of sex hormones in patients' blood may identify those at risk for a sudden cardiac arrest, a heart rhythm disorder that is fatal in 95% of patients.

The new findings show that higher levels of estradiol, the major female sex hormone, were strongly associated with greater chances of having a sudden cardiac arrest in both women and men. And unique to men, lower levels of testosterone, the predominant male sex hormone, were found in men who had sudden cardiac arrest.

"Because sudden cardiac arrest is usually fatal, we are constantly looking for ways to predict which patients are susceptible so we can concentrate on prevention," said Sumeet Chugh, MD, director of the Heart Rhythm Center in the Cedars-Sinai Heart Institute and the Pauline and Harold Price Chair in Cardiac Electrophysiology Research. "If we wait until someone has a sudden cardiac arrest, it is usually too late for treatment."

Unlike heart attacks, which typically result from clogged arteries, sudden cardiac arrest is caused by defective electrical impulses and patients may have little or no warning of the event, which usually causes nearly instantaneous death. Every year, 250,000 to 300,000 people in the United States and up to 5 million worldwide die from sudden cardiac arrest.

Despite years of significant advances in emergency medicine and resuscitation, just 5% of those who have a sudden cardiac arrest survive. For patients at known risk for this or other heart rhythm abnormalities, an implantable cardioverter-defibrillator (ICD) may be appropriate.

The sex hormone findings are a result of the Oregon Sudden Unexpected Death Study, a comprehensive, 16-hospital, multiyear assessment of cardiac deaths in the 1 million population Portland, Ore, metropolitan area. Led by Chugh and funded in part by the National Heart, Lung, and Blood Institute, the study's goal is to shed light on the risk factors, triggers, and genetic defects associated with sudden cardiac death.

"This is the first time it has been reported that there is an association between sex hormone levels and sudden cardiac arrest," said Chugh. "While these findings need to be confirmed by other studies, they suggest that higher testosterone levels in men may offer protection from sudden cardiac arrest and lower levels of estrogen may protect both men and women."

Researchers measured blood hormone levels in 149 patients who had a sudden cardiac arrest, comparing them with levels in 149 patients who had coronary artery disease but did not have sudden cardiac arrest. The average patient age was 64.1 years.

Women who had sudden cardiac arrest had estradiol levels of 54 pg/mL, compared with 36 pg/mL for the female control group.

In men, those with sudden cardiac arrests had testosterone levels averaging 4.4 ng/mL and estradiol levels averaging 68 pg/mL, compared with an average testosterone level of 5.4 ng/mL and average estradiol level of 52 pg/mL for male controls.