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Blood is carried to the heart via the veins. Pulmonary arteries then route the blood through the right side of the heart and into the lungs, prior to flowing through the left side of the heart. Arteries then serve to carry the blood away to the body. A paradoxical embolism occurs when a blood clot breaks off in a vein, typically from the legs, arms and pelvis, and instead of moving through the right side of the heart and into the lungs it passes through a small defect in the upper chamber septum and directly into the left side of the heart. The clot, or embolus, is now able to travel directly to the brain without getting lodged in the lungs.
Once the blood clot is flowing within the arterial circulation it can reach the brain and create a blockage in one of the vessels. This creates the circumstance for a stroke, or embolism. If the clot were to have lodged in the lungs it would result in a pulmonary embolism. The hole that the clot travels through to create the paradoxical embolism is called an atrial septal defect, or patent foramen ovale. Surgeons will usually recommend repairing even the smallest defect.
Julius Friedrich Cohnheim, a German pathologist, coined the term "paradoxical embolism" in 1877. In 1885, during an autopsy, a doctor reported a blood clot that had passed through a patent foramen ovale. In general, paradoxical embolisms are hard to diagnose and have been found in up to 35 percent of the healthy population during autopsy. Emboli can come in several forms, such as solids, liquids and gas. These can include fat, tumors and even amniotic fluid. Although extremely rare, paradoxical embolism can be caused by foreign bodies such as a bullet or residue from a gunshot.
Paradoxical embolism is very often found in young patients that have experienced cerebral ischemia. This is a condition where there is not enough blood flow to the brain and can lead to cerebral hypoxia and stroke. Treatment for paradoxical embolism includes both medical and surgical options. Anticoagulation treatment is employed as a first step to stop the progression of the clot. Echocardiography is used prior to surgery as a tool to locate any potential emboli.
These events are rare, accounting for only two percent of arterial emboli. When paradoxical embolism does occur, however, it tends to be very dangerous, with early death rates of up to 21 percent.