What is pulmonary embolism (PE)?
A very large PE can block the entire trunk of the pulmonary artery (before it branches into the right and left pulmonary arteries) and cause death instantly. Pulmonary emboli that are not quite so large may block an entire right or left pulmonary artery, stopping the blood flow to an entire lung and—especially if the person already has lung or heart disease—causing death. Smaller emboli may block smaller branches of the pulmonary artery with varying consequences. When the blood supply to a small “end-artery” at the edge of the lung is blocked, oxygen to that part of the lung is cut off, and the cells in that part of the lung begin to die, resulting in pulmonary infarction (that is, death of lung tissue). When blood flow is blocked within a larger branch of the pulmonary artery, the normal exchange of oxygen for carbon dioxide does not take place and the entire body is affected. Pulmonary infarctions usually result from smaller clots and are unlikely to be fatal.
The likelihood of death from PE depends largely on the size of the PE. If the main pulmonary artery is completely blocked, the right ventricle (the chamber of the heart that pumps blood into the lungs) cannot get the blood into the lungs; this “right ventricular failure” then leads to death from PE. The age and health of the affected individual are also critical factors. When the person already has lung or heart disease, PE may have a more dramatic impact. While the death rate from PE may be as high as 25 percent in sick, hospitalized patients, the death rate in young healthy individuals is closer to 1 percent.