Recent studies led by Sumeet Chugh, MD, associate director of the Smidt Heart Institute and the Pauline and Harold Price Chair in Cardiac Electrophysiology Research, unveil clues to factors that heighten the danger of sudden cardiac arrest.

Heart experts have long believed weekday mornings—especially Mondays—to be the peak danger zone for sudden cardiac arrest, but Chugh’s research shows this is no longer the case. However, the news is not necessarily good, as cardiac arrests are now considered equally possible at any time. “Stress is likely a major factor,” he says. “We now live in a fast-paced, ‘always on’ era.”

Other findings are more positive, including promising outcomes from new treatment strategies in high-risk patients as well as corrections for how past studies inadequately measured time of death.

Read: A Better Way to Predict Who Is at Risk for Cardiac Arrest

Smidt Heart Institute investigators discovered that patients with the most common type of heart failure are twice as likely to have an untreatable form of lethal heart rhythm responsible for sudden cardiac arrest—heart failure with preserved ejection fraction (HFpEF). HFpEF is not only responsible for about half of all cases of heart failure, but also is more likely to strike women than men. The findings suggest that surgically implanted defibrillators are less effective against HFpEF than other types of heart failure. Additional studies are needed to determine which high-risk patients are most likely to benefit from defibrillator implantation.

Patients with multiple sclerosis (MS) face five times the risk of sudden cardiac arrest compared to the general public, according to Chugh. While the reasons for the disparity need further investigation, the brain’s established links with cardiac function could be influencing the heart’s electrical function in MS patients.

In another study, Chugh and his team found that patients with left ventricular hypertrophy (LVH)—an enlargement and thickening of the walls of the heart’s main pumping chamber—are also at elevated risk of sudden cardiac arrest. However, diagnosing those in the most danger had proved elusive.

Now, using an electrocardiography risk score, clinicians can better identify patients with intermediate or high-risk LVH. Another of Chugh’s projects found that obesity and LVH are each independent predictors of sudden cardiac arrest.

The data for these studies came from the Oregon Sudden Unexpected Death Study—a comprehensive project headed by Chugh that is now in its 16th year.

“Because sudden cardiac arrest is usually fatal, we have to prevent it before it strikes,” he says.

Read: Study: Sex Unlikely to Trigger Cardiac Arrest