Preventing Cardiac Emboli
Patients with cardiogenic sources of emboli are often treated with warfarin (Coumadin®). This is an anticoagulant that opposes the formation of fibrin by inhibiting the synthesis of vitamin K-dependent clotting factors. It therefore is particularly effective in preventing the extension of large, well-formed cardiac thrombi, which tend to contain a major component of fibrin with entrapped red blood cells as well as platelets.
Three of the major problems leading to thrombus formation in the heart are:
- Atrial fibrillation in which asynchronous contraction of the muscle of the left atrium results in failure to empty and formation of thrombus within the atrium.
- Valve abnormalities or prosthetic heart valves which are thrombogenic.
- Abnormally reduced motion of the heart wall, which may occur after a myocardial infarction or other damage to the heart muscle that decreases its ability to empty the ventricles with each cardiac cycle. Blood becomes stagnant, and thrombus tends to form. This is particularly a problem if the left ventricle is affected.
| Question: |
| Why is the formation of thrombus in the left ventricle more of a problem than in the right ventricle? |
| Answer: |
| Emboli from the left ventricle can travel in the systemic circulation to anywhere in the body, including the brain; however emboli from the right ventricle travel to the lungs first unless there is an abnormal right-left shunt in the heart. In the lung they often, although not always, are trapped without producing significant damage to lung tissue. |
In each of these situations, controlled clinical trials have shown that treatment with warfarin reduces the risk of cardioembolic stroke. Patients on warfarin therapy must be regularly monitored by tests of prothrombin time (a specific coagulation test). Because of the risk of hemorrhagic side effects, warfarin is contraindicated in people with bleeding disorders or a history of gastrointestinal bleeding, in people who are at risk for falls (unsteady walking, alcoholics, very elderly), and in people who are unreliable about taking their medications. These individuals are often given aspirin therapy as an alternative. Aspirin has considerably less efficacy for prevention of cardioembolic stroke than warfarin, because aspirin alters only platelet function and does not affect the humoral clotting system.