Clinical aspects of pulmonary embolism

1. Pulmonary Embolic Disease: An Overview Venous thrombolembolic disease, including deep venous thrombosis (DVT) and pulmonary embolism (PE), is an important medical condition. It is estimated that there are approximately 5 million cases of deep venous thrombosis annually in the US. At least 10% of these lead to PE, and approximately 10% of these result in death (50,000). PE is the sole or major cause of death in 10-15% of adults dying in the acute care wards of general hospitals. Therapy for thromboembolic disease exists in the form of anticoagulation medication. The majority of deaths arise not from failure of therapy, but rather from failure to diagnosis the disease or from prophylactic failure. Unfortunately the diagnosis of PE can be challenging. Approximately 90% of PEs that achieve clinical attention arise in the deep venous system of the legs, with the remainder arising in the deep venous system of the upper extremities, or rarely within the right heart or the pulmonary arteries. Thrombi limited to the calf veins rarely embolize, whereas those that extend or originate more proximally (popliteal, ileofemoral veins) may embolize in up to 50%. The initiating event is typically platelet aggregation at venous valves due to turbulence, or at sites of intimal injury. This results in release of mediators which initiate the coagulation cascade, and development of a red fibrin thrombus. Fibrinolysis is subsequently initiated, resulting in break down of the clot, which can occur at varying rates and to various degrees. At any point in the process some or all of the thrombus may detach and travel to the lungs as an embolism, although the risk is greatest early on. Most emboli lodge in branches of the pulmonary arteries, a few straddle the bifurcation, and a very few lodge in the right heart. Major physiologic consequences include compromise of respiratory function, and cardiac complications due to elevated pulmonary arterial pressures. The patient’s ability to cope with these processes is significantly compromised by the presence of pre-existing cardiopulmonary disease. In patients with impaired cardiopulmonary function, severe pulmonary arterial hypertension can result from pulmonary embolic disease involving a relatively small portion of the pulmonary vascular bed. As mentioned, the diagnosis of PE can be challenging. Patient presentation falls into one of three syndromes: isolated dyspnea, pleuritic pain or hemoptysis, and circulatory collapse. The most common presenting symptom is dyspnea, and the most common sign is tachycardia. However, the clinical presentation is not specific and cannot be relied upon to make the diagnosis of PE. Rather it merely raises the suspicion, leading to diagnostic testing, including imaging.