Blood clots are usually harmless. They form whenever we cut or scrape our skin or bump into something and get a bruise. However, when blood clots form within blood vessels they can obstruct blood flow, a condition called thrombosis. That could mean trouble. If a clot in an artery breaks free and travels through the circulatory system, it can cause blockages affecting the heart, lungs, and other organs—potentially shutting them down.

The results can be deadly. Thrombosis affects up to 900,000 people in the United States per year and kills up to 100,000.

“At Yale Medicine, patients with suspected thrombosis get evaluated very quickly,” says Michael Remetz, MD, a Yale Medicine interventional cardiologist. For blood clots that affect the heart: “That is precious time when the heart is being damaged. If a large part of the heart is affected, permanent heart damage results, or it can be fatal.”

There are three types—venous thromboembolism, pulmonary embolism, and coronary thrombosis. Venous thromboembolism occurs in veins or arteries, most commonly in the legs. When a blood clot travels to the lungs and causes a blockage of an artery, it’s called a pulmonary embolism. Coronary thrombosis is a blockage of an artery in the heart, which can lead to a heart attack.

Normal blood clots happen whenever there’s an injury to the cells lining blood vessels. However, abnormal blood clots can form if there are unusual variations in blood flow, such as those caused by conditions including valvulitis and aneurysm, or because of conditions that cause blood to clot unnecessarily, such as leukemia or Factor V mutation.

Coronary thrombosis can occur when arteries become clogged with cholesterol and fat, making it difficult for blood to flow through.

Additional risk factors for blood clots include:

• Obesity
• Pregnancy
• Sitting for extended periods of time
• Smoking
• Oral contraceptives
• Injury or surgery
• Age (increased risk for people over age 60)
• A family history of blood clots
• Chronic inflammatory diseases

Symptoms of thrombosis in veins (which usually affect the legs) include: swelling, pain,, and cramping.

Symptoms of pulmonary embolism (a blood clot that has traveled into the lungs) include shortness of breath, chest pain, and coughing.

Symptoms of coronary thrombosis (a blood clot that forms in the heart) include severe pain in the chest and arm, sweating and trouble breathing.

The blood clots can be treated with a combination of medical and surgical procedures. The first line of defense is blood-thinning medications, such as warfarin, which can prevent new clots from forming while the body works to break up existing clots. Aspirin, a blood thinner, is also used. A class of medications called thrombolytics can dissolve clots even more quickly, but can increase the risk of bleeding.

Doctors may also opt to perform surgery to remove the blood clot.

At Yale Medicine, our cardiology team is comprised of leading researchers in the field. They conduct clinical trials for medications that might not yet be available on the market and use their knowledge to better diagnose and treat blood clots.

In addition, for blood clots affecting the heart, our cardiologists work closely with the emergency departments of area hospitals to treat patients as quickly as possible. They rush patients to our catheterization lab either by ambulance or helicopter, where our expert clinicians perform diagnostic procedures, such as state-of-the art blood tests and cardiac catheterization. The latter is a procedure where a catheter is threaded into the affected veins and arteries to clear them.

“The first two hours of a heart problem is when there is most damage to the heart,” says Dr. Remetz.