Sudden cardiac arrest causes 325,000 adult deaths in the U.S. each year. That’s 50 percent of all of the deaths from heart disease. It can occur in the wake of a heart attack, or it can be a separate catastrophic cardiac event.

When it occurs outside a hospital setting, the death rate is 90 percent.

Sudden cardiac death occurs twice as often in men as in women, no matter the age group. At age 45, the lifetime risk for sudden cardiac death is 10.9 percent in men and 2.8 percent in women. The risk is 11.2 percent in men and 3.4 percent in women at age 55; 10.1 percent in men and 3.4 percent in women at age 65; and 6.7 percent in men and 2.4 percent in women at age 75, according to a study in the Journal of the American Medical Association.

High blood pressure was the best predictor of sudden cardiac arrest, though other factors include elevated cholesterol, obesity, a sedentary lifestyle, stress, and smoking.

Another study published in the Annals of Internal Medicine found that cardiac arrest may not be as unexpected as believed.

Researchers collected information about the four weeks before sudden cardiac arrests and found that about one-half of patients had warning signs during that period. Symptoms included chest pain, difficulty breathing, palpitations, sudden drop in blood pressure/ loss of consciousness, and other (including abdominal pain, nausea or vomiting, and back pain).