Coronary artery disease (CAD) is when one or more arteries in the heart are obstructed or narrowed by plaque deposits forming along artery walls. CAD is the major risk factor for a heart attack.

Less common but no less dangerous is non-obstructive coronary artery disease. This is when the heart’s arteries are compressed by surrounding heart muscle tissue or are compromised by something other than blockage in the blood vessels.

The causes of non-obstructive coronary artery disease aren’t always known, though it has many of the same risk factors that contribute to obstructive CAD.

Diagnosing non-obstructive CAD can be challenging because there isn’t plaque buildup to identify in imaging tests. Treatment usually involves lifestyle changes and medications. Surgery may be necessary when medications aren’t effective.

Non-obstructive CAD differs from obstructive CAD — what most people think of when discussing coronary artery disease — in some important ways. To better understand the distinctions, it’s important to understand traditional CAD and its complications.

Obstructive CAD

The clinical term for blocked or narrowed arteries is atherosclerosis, which causes obstructive CAD. The arterial plaque deposits that cause atherosclerosis comprise cholesterol, fats, white blood cells, and other substances.

About half of all older Americans are unaware they have atherosclerosis.

In atherosclerosis, the coronary arteries can become so narrow that the heart muscle can starve of oxygen-rich blood, resulting in a heart attack.

Another common complication of atherosclerosis is that a plaque ruptures. This can cause a blood clot to form, blocking blood flow and triggering a heart attack.

A significant decrease in blood flow through the coronary arteries can also cause angina, chest pain brought on by poor blood supply to the heart.

Non-obstructive CAD

Non-obstructive CAD, while seemingly less severe, is also a major risk factor for heart attack.

A 2014 study in JAMA suggests that non-obstructive CAD patients are two to four times more likely to experience a heart attack than patients with no apparent CAD.

Non-obstructive CAD can also cause angina, along with the following symptoms, which people with obstructive CAD often exhibit:

Non-obstructive CAD is not the result of atherosclerosis but refers to other types of coronary artery dysfunction, including:

  • damage to the endothelium (inner lining) of one or more coronary arteries
  • abnormal constriction of the coronary arteries (coronary vasospasm)
  • problems with the smaller blood vessels that branch off the main coronary arteries (microvascular dysfunction)
  • pressure from nearby heart muscle tissue (myocardial bridging)

Because non-obstructive CAD can present in several forms, it has various potential causes.

A 2021 study, for example, suggests that about two-thirds of people with non-obstructive CAD have coronary microvascular dysfunction — a condition likely triggered by common heart disease risk factors such as:

These risk factors may also cause endothelial dysfunction. The cause of coronary vasospasm, the overly active constriction of the heart’s arteries, isn’t well understood. The other common form of non-obstructive CAD —myocardial bridging — is the result of a congenital abnormality of the heart’s anatomical structure.

Diagnosing non-obstructive CAD usually begins with:

  • a review of the person’s symptoms and medical history
  • a review of family medical history
  • a physical examination

A 2018 review of numerous studies also suggests that receiving an accurate diagnosis requires your healthcare professional to exclude other potential causes of your symptoms. Other non-cardiac conditions that could cause similar symptoms include:

A combination of invasive and noninvasive imaging tests should be used to reach a diagnosis. A stress test to gauge blood flow and heart function can be helpful but wouldn’t reveal the presence of non-obstructive CAD.

Other screenings include:

  • cardiac MRI
  • echocardiogram
  • electrocardiogram

But the most definitive test for non-obstructive CAD, according to a 2019 study, is angiography.

Angiography uses special X-ray equipment and a dye that can be easily identifiable as it travels through the bloodstream in the heart. This method can show whether a blockage in a coronary artery or something else is affecting circulation within the heart.

Treatment is determined by the nature of your non-obstructive coronary artery disease. Typically, managing the condition is done through lifestyle and clinical approaches.

Lifestyle changes

Mild cases of non-obstructive CAD that present no symptoms may not need treatment other than maintaining a healthy lifestyle.

If you’re experiencing angina or other symptoms, and your doctor determines that you may have endothelial or microvascular dysfunction, you may need to adopt more specific heart-healthy behaviors, including:

  • exercising for 30 to 40 minutes most days of the week
  • following a balanced diet, such as the Mediterranean or DASH diets
  • getting sufficient sleep
  • limiting alcohol intake
  • managing stress
  • no smoking

Clinical treatments

Even though non-obstructive CAD is not the result of cholesterol-fueled plaque formation in the arteries, some underlying atherosclerosis may likely be present.

To lower cholesterol levels and reduce the risk of atherosclerosis, a statin prescription is often used to manage non-obstructive CAD and lower future cardiac risks, according to researchers published in the Journal of the American College of Cardiology.

Additional preventive therapies and medications may also be used to manage risk.

Other medications that may be appropriate for non-obstructive CAD include antihypertensive medications to lower blood pressure, including ACE inhibitors, beta-blockers, and calcium channel blockers.

If myocardial bridging is diagnosed and causes serious non-obstructive CAD, surgery may be needed to reshape the heart. “Unroofing” involves the removal of heart muscle tissue pressing against the artery.

Non-obstructive coronary artery disease may not be as common as obstructive CAD, but it is a serious risk factor for heart attack.

The condition is not caused by plaques forming in the heart’s arteries but rather by arterial dysfunction or anatomical abnormalities. It may require several tests to get an accurate diagnosis.

If you have symptoms, such as angina or other signs of CAD, it’s important to work with your cardiologist to reach a diagnosis and put together a treatment plan.

Having non-obstructive CAD puts you at a higher risk of developing obstructive CAD, so that you may require both medications and lifestyle changes.