In the U.S., sudden cardiac arrest claims around 250,000 lives each year, which is about 30% of the total deaths from cardiovascular disease.
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In a heart attack, blood flow to the heart muscle is restricted, causing damage to the muscle. A severe enough heart attack can also cause sudden cardiac arrest, and heart muscle damage from previous heart attacks increases the risk of sudden cardiac arrest as well. Having coronary artery disease is the biggest risk factor for heart attacks and sudden cardiac arrest; a weak pumping ability of the heart muscle further increases the chances of having sudden cardiac arrest.
Men are more likely to suffer sudden cardiac arrest. Now researchers are finding that their underlying heart structures may be a reason.
In a study of more than 1,500 of these events that occurred in Portland, Ore., Dr. Sumeet Chugh, associate director of the Cedars-Sinai Heart Institute in Los Angeles, established that about two-thirds of the cases were men and about one-third were women. That wasn't surprising, but they also found a significant difference in the structures of men's and women's hearts.
The women were much less likely to have the classic signs of structural damage that predict a sudden cardiac arrest. And with an almost-always fatal disorder, prediction and prevention are everything, Chugh notes.
Currently, to determine who is at risk, doctors look for severe left-ventricular dysfunction, a condition in which the left ventricle (or chamber) of the heart does not pump blood efficiently to the rest of the body. This failure is a sign that the heart muscle has become weakened from damage, which can cause the disrupted electrical activity in sudden cardiac arrest.
Patients with an irregular heart rhythm or other suspicious symptoms are screened with an echocardiogram, or ultrasound of the heart, to measure left-ventricular function. Using this and other tests, doctors determine which patients should get an implantable defibrillator, a "souped-up version of a pacemaker," which detects electrical disturbances and sends an internal electrical shock to try to fix the arrythmia.
Of the 485 patients in Chugh's study who had previously had their left-ventricle function measured, only 20% of the women had severe dysfunction. Twice the proportion of men had a severe left-ventricle problem, but at 40% that's still not a great predictor, says Chugh. "The only major criteria we have is LV dysfunction, and that's not good enough for men or women, but especially not for women."
He says the other women who succumb to a sudden cardiac arrest without signs of structural damage may in fact have microvessel disease that increases their risk, but there is no concrete evidence linking the two, yet. Chugh's study, which is ongoing, is tracking all of the sudden cardiac arrests that occur in Portland. He hopes to find better ways to predict who is at risk of sudden cardiac arrest.
"If you have chest pain you cannot explain, shortness of breath, you are severely dizzy, you pass out, have palpitations or irregularity of your heart rhythm, these are all warning symptoms, and you need to be looked at," Chugh says.