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An embolus, is described as a free-floating mass, located inside blood vessels that can travel from one site in the blood stream to another. An embolus can be made up of solid (like a blood clot), liquid (like amniotic fluid), or gas (like air). Once these masses get "stuck" in a different blood vessel, it is then known as an "embolism." An embolism can cause ischemia—damage to an organ from lack of oxygen. A paradoxical embolism is a specific type of embolism in which the embolus travels from the right side of the heart (venous circulation) to the left side of the heart (arterial circulation) and lodges itself in a blood vessel known as an artery. It is termed "paradoxical" because venous emboli will usually be lodged in pulmonary artery in an event called pulmonary embolism, instead of systemic circulation.
Once an embolus enters arterial circulation it continually travels down arteries to smaller vessels before lodging itself in vessels and stopping blood flow to the tissues supplied by those blood vessels. Often, the embolus will reach the brain and cause permanent stoppage of blood flow to a region of the brain, a feared complication of paradoxical embolism. This stoppage of blood flow in the brain, or ischemia, is called a cerebral infarct, also known as a stroke.
Additional findings in a patient with a paradoxical embolism will be dependent upon where the emboli lodges and disrupts blood flow. Three important clinical manifestations that may be caused by paradoxical embolism include a stroke, migraine, and acute myocardial infarction, also known as a heart attack. A stroke and migraine in the setting of a paradoxical embolism are caused by the emboli disrupting blood flow in a cerebral artery. A myocardial infarction in the setting of a paradoxical embolism are caused by the emboli disrupting blood flow in a coronary artery. Physical findings that should be evaluated include a comprehensive neurological examination for evaluation of stroke symptoms such as weakness, gait changes, slurred speech, and facial droop.
Additionally, if a paradoxical embolism is suspected in a patient, findings consistent with a congenital heart defect that may lead to right-to-left shunting can be evaluated. These include Nail clubbing due to chronic hypoxemia in distal extremities or a widely-split S2, a pathological heartbeat pattern where the second heart sound has two components.
Ultrasound, MRI imaging, or CT scans of the lower extremities help to identify a possible DVT, which provides evidence that an emboli may have come from venous circulation. Although these imaging modalities are used to evaluate for venous thromboembolism, their use in detecting heart defects is limited. The use of MRI to detect cardiac shunts is "controversial" and that the use of CT is not recommended due to exposure to ionizing radiation and lack of functional imaging.
It is reported that transesophageal echocardiography or TEE, is the best non-invasive option for diagnosing intracardiac shunts like a patent foramen ovale. Additionally, there is a need for a color flow Doppler study or the injection of agitated saline/contrast medium followed by a Valsalva maneuver to visualize flow of blood from the lower pressure venous system to the higher pressure arterial system.
Similar to a TEE, a transcranial Doppler sonography study is also described as helping to evaluate for right-to-left shunts of the heart. However, it can also be used to detect other forms of right-to-left shunts including pulmonary arteriovenous malformations because it too needs agitated saline/contrast injected, but rather than imaging the heart, observes if any microemboli appear in the middle cerebral artery, an artery or the brain, following a valsalva maneuver.
Ear oximetry is also described as a fairly accurate screening tool for a shunt. It measures the oxygen saturation of blood as it passes through the ear. Following a valsalva maneuver, pressure increases in the right heart, deoxygenated blood is shunted into arterial circulation, and a decrease in oxygen saturation can then be measured in the capillaries of the ear.
A paradoxical emboli should be medically managed similar to any other thromboembolism with medical anticoagulation. This is to prevent new or worsening blood clot formation that may occlude vessels and cause organ ischemia. Some sources suggest anticoagulation with heparin be performed, while others give a list of reasonable drug options including anticoagulants like heparin and warfarin, anti-platelet therapy like aspirin and clopidogrel, and thrombolytic therapy like alteplase and streptokinase. If an embolus is causing life or limb-threatening ischemia, is located in a reasonable location, and is first visualized with fluoroscopy, catheter embolectomy can be performed to retrieve the clot as well.
Surgical closure of a patent foramen ovale or other atrial septal defects is often done through an out-patient, percutaneous, surgery that has few complications. Although closure of a patent foramen ovale or atrial septal defect theoretically removes the pathway for an arterial embolus to enter venous circulation and cause a paradoxical embolism, data suggests that closing intracardiac shunts is no more effective than medical management alone in preventing strokes.
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