New research finds that chronic obstructive pulmonary disease (COPD) increases the risk for sudden cardiac death, even among patients without major heart problems.

About 735,000 Americans have a heart attack each year, and not all of them have heart disease.

For some, heart failure can strike without warning. When these unexpected heart attacks are fatal, it’s called sudden cardiac death (SCD), which claims as many as 250,000 lives in the United States every year.

A new study has concluded that a major risk factor for these killer heart attacks is chronic obstructive pulmonary disease (COPD), an ailment that damages the lungs and reduces their ability to exchange oxygen for carbon dioxide.

Existing studies have linked COPD with SCD among people with major heart problems, such as those who have experienced a heart attack or have needed heart surgery.

However, research published in the European Heart Journal found that even among people without such heart problems, people with COPD still have a substantially elevated risk for sudden cardiac death.

Learn More About Chronic Obstructive Pulmonary Disease (COPD) »

Researchers examined data from 13,471 people over the age of 45, following them from 1990 to 2014. They found that after five years of living with COPD, patients had a twofold increase in their chances of experiencing SCD, even after the researchers took into account age, sex, and cigarette smoking. Among people with frequent complications from their COPD, such as coughing or shortness of breath, the risk increased threefold.

“This is the first study to show that COPD is associated with an increased risk of SCD in the general population and that this remains the case even when taking into account the fact that COPD is known to increase the risk of death from any cause,” explained Lies Lahousse, first author on the paper and post-doctoral researcher in respiratory medicine at Ghent University, Belgium, and the Erasmus Medical Center, Netherlands, in an interview with Healthline.

Although the exact nature of the connection between COPD and SCD isn’t yet fully understood, Lahousse pointed to some likely culprits. COPD and its complications can increase heart rate, cause systemic inflammation, and most importantly, progressively starve the heart of life-giving oxygen. As the lungs slowly fail, the available oxygen supply in the blood drops further and further, while poisonous carbon dioxide builds up. This weakens the heart and boosts the likelihood that it will spontaneously stop.

“I think this paper adds to the body of evidence that COPD, and likely the severity of the COPD and exacerbation frequency, have systemic effects that make the cardiac system more susceptible to SCD,” said Dr. Albert A. Rizzo, senior medical advisor to the American Lung Association and section chief of pulmonary/critical care medicine in the Christiana Care Health System, in an interview with Healthline. “This study may help raise the awareness of the importance of early diagnosis of COPD, both on the patient’s part as well as the health care provider.”

Read More: People with COPD Face Increased Heart Failure Risk »

Chronic lung disease, including COPD, is the third leading cause of death in the United States. About 13 million Americans have been diagnosed with COPD, although due to underdiagnosis, the actual number afflicted may be as high as 24 million.

Lahousse hopes that COPD will be added to the list of warning signs for SCD risk.

“Doctors should be aware of this increased risk of SCD in COPD patients, and should add COPD to other risk factors, including high blood pressure, high blood cholesterol, smoking, obesity, diabetes, and a unhealthy lifestyle to optimize the individual risk stratification for cardiovascular screening,” she said. “If a patient with COPD has a high risk of SCD, preventive measures can be applied.”

“Once diagnosed, there can be more concerted efforts at improving lifestyles and the use of appropriate medications to help the COPD condition,” Rizzo explained. “These efforts should decrease the symptoms and decrease the rates of exacerbation and based on this study’s findings, decrease the risk of SCD.”

While medications like beta-blockers may help reduce the risk, Rizzo and Lahousse agree that quitting smoking is one of the most important ways that people with COPD can decrease their risk for SCD.

“Smoking cessation is paramount and participating in a form of regular exercise such as a formal pulmonary rehabilitation program is key to improve the quality of life of individuals with COPD,” concluded Rizzo.

Learn More: A Short Walk a Day Helps COPD Patients Stay Out of the Hospital »