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How do blood clots affect your heart?

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Blood clotting is a natural process that allows the blood to thicken and form a clot of blood cells and fibrin, to stop the bleeding when a blood vessel is severed or damaged. If your body didn't have the ability to clot blood, you would bleed to death after even a minor cut.

However, when a blood clot (thrombus) forms in an artery, blocking the blood flow to the heart muscle or the brain, a heart attack or stroke can follow. Or when blood lingers in one of the heart’s chambers (from certain heart conditions), a clot may form and a piece of the blood clot can be pumped from the heart, travel through the bloodstream, and lodge in either an organ or an artery, cutting off the blood supply from that point. This travelling clot is called an "embolus".

There are many other conditions related to blood clots, for example:

  • Coronary thrombosis that involves a blood clot in coronary arteries leading to a heart attack.
  • Deep-vein thrombosis that involves a blood clot in the leg veins.
  • Pulmonary embolism that involves a blood clot lodged in the pulmonary artery (lungs).
  • Retinal vein occlusion that involves a blood clot in a vein of the eye.

To prevent excess clot formation, the body has a system where clot formation ceases once the clot has served its purpose, and the formed clot is then gradually dissolved. If this controlling system fails, clots may form excessively and persist, causing complications.

Causes
There are certain conditions necessary for the formation of blood clots:

  • Platelets are special blood cells which clump together to form a "plug"' helping to stop bleeding from a site.
  • Clotting factors are proteins in the blood that are involved, along with the platelets, in clot formation.
  • Endothelial damage – damage to the lining of the blood vessels and heart may determine where the clots are formed.
  • Slow flow or turbulence of blood flow will predispose towards clot formation.

How are clots formed?
The inner lining (endothelium) of blood vessels or of the heart itself may be damaged by, for example, cholesterol plaques, turbulence in blood flow or infection; all of which can expose the collagen fibres underneath the endothelium. The exposed collagen acts as a trigger, attracting platelets to the site and activating the clotting factors in the blood. A thrombus forms exactly where it's needed.

Once the thrombus seals off the damaged site, the process stops, and when the damaged endothelium is healed, the thrombus is slowly dissolved and removed. The thrombus that forms may be large enough to partially or even completely obstruct the blood vessel, shutting off the normal blood supply.

If this happens in a coronary artery, the heart muscle is totally deprived of oxygenated blood, and the result is a heart attack. If this happens in an artery to the brain, the result is a stroke. Patients with atrial fibrillation have a sluggish flow in their atria, and are at high risk for thrombus formation inside the heart. These also have a high risk of embolising to the lungs or brain.

After a heart attack, portions of the heart may no longer contract normally, causing slow flow of blood and permitting thrombus formation within the heart. The same applies in any aneurysm. Damage to heart valves, especially the mitral valve, can also cause thrombus formation because of endothelial damage and slow flow.

Other risk factors:

  • Smoking.
  • Obesity (more than 10kg overweight).
  • Lack of exercise.
  • Oral contraceptives, especially high-dose types.
  • High dosages of oestrogen or hormone-replacement therapy (HRT).
  • Sitting in one position for a prolonged time (as in an aeroplane).

Symptoms and signs
Blood clot is lodged:

Long (pulmonary embolism): Sharp chest pain, rapid heart rate, blood-tinged coughing, shortness of breath and low-grade fever.

Arm or leg (e.g. deep-vein thrombosis): Sudden pain, swelling and a slight blue colouration. If it's in a vein, it could cause swelling and tenderness.

Brain (stroke): Visual disturbances, weakness, seizure, speech impairment. Artherosclerotic plaques in the carotid artery can lead to blood clots lodging in the carotid artery or deep in the brain.

Heart (heart attack): Chest pain. Blood clots in the heart can also travel to any organ or artery. Conditions that can lead to blood clots forming in the heart include heart-valve disease, previous heart attack, atrial fibrillation and heart failure.

Abdomen: Severe abdominal pain, vomiting and/or diarrhoea.

When to see your doctor
If you have or suspect you have any of the symptoms or risk factors, see your doctor as soon as possible. Patients with known heart disease are at special risk.

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