“What Determines What Part Of The Body Gets A Blood Clot?  Why Do Some Blood Clots Go To The Heart, Whereas Others Go To The Brain Or To The Pulmonary Arteries?”

The ability to form blood clots is critical for the body to prevent excessive bleeding.  When a blood vessel is damaged, cells in the blood called platelets interact with various clotting proteins to form a clot.  This effectively “plugs up the hole” to stop the bleeding.  Over time, the clot typically dissolves as the body repairs the blood vessel damage.  However, in some cases, blood clots may develop inappropriately and become deadly.

Blood clots play a major role in myocardial infarction (MI), or heart attack.  Over time, the coronary arteries can develop a buildup of cholesterol, fibrous tissue, and inflammatory cells in a process called atherosclerosis.  Important risk factors for this include smoking, hypertension, high cholesterol, and diabetes.

This buildup coalesces in various segments of the arteries in structures called plaques.  In some cases, these plaques become unstable and fracture, which triggers the body to form a blood clot at that site.  The blood clot may block the coronary artery and starve a portion of the heart muscle of oxygen and nutrients, thus causing an MI.

In deep vein thrombosis (DVT), blood clots develop in the leg or pelvis veins in the absence of obvious damage to the vessel.  Within the vessel, a combination of microscopic injury to the vein wall along with abnormal blood flow and a propensity for blood clots all contribute to DVT formation.  Inflammation and underlying genetic factors likely predispose people to DVT, and other risk factors such as cancer or immobility also increase risk for DVT.  If a portion of the DVT dislodges, it can travel through the veins and relocate in the pulmonary arteries, thereby becoming a pulmonary embolism (PE).

Finally, blood clots also play a role in stroke.  When the heart is in normal rhythm, blood flows briskly through each chamber.  However, in atrial fibrillation, blood has more opportunity to stagnate in the atria, or top chambers of the heart.  With less movement, blood is more prone to clotting, and blood clots may develop in the left atrium of patients with atrial fibrillation.  Once they form, they can be pumped out of the heart and into the body’s arterial system.  Some of the first arteries blood reaches once it leaves the heart are the arteries to the brain, and a blood clot passing out of the heart and into these arteries can cause a stroke.

Aaron W. Aday, MD
Cardiovascular Medicine Fellow,
Brigham and Womens Hospital
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