A pulmonary embolism (thromboembolism) occurs when a blood clot, generally a venous thrombus, becomes dislodged from its site of formation and embolizes to the arterial blood supply of one of the lungs. Symptoms may include difficulty breathing, pain during breathing, and more rarely circulatory instability and death. Treatment is with anticoagulant medication, such as warfarin.
Clinical presentation
Signs of PE are sudden-onset dyspnea (shortness of breath, 73%), tachypnea (rapid breathing, 70%), chest pain of "pleuritic" nature (worsened by breathing, 66%), cough (37%), hemoptysis (coughing up blood, 13%), and in severe cases, cyanosis, tachycardia (rapid heart rate), hypotension, shock, loss of consciousness, and death. Simply put, marked decreased oxygen saturation, tachycardia and/or hypotension. Although most cases have no clinical evidence of deep venous thrombosis in the legs, findings that indicate this may aid in the diagnosis.
Confirming pulmonary embolism
The gold standard for diagnosing pulmonary embolism (PE) is pulmonary angiography. In most cases, however, when PE is suspected on the basis of shortness of breath and chest pain, the following studies may confirm the presence of an embolus. Pulmonary angiography is used less often because of wider acceptance of CT scans which are non-invasive.
- Computed tomography with radiocontrast, effectively a pulmonary angiogram imaged by CT, is increasingly used as the mainstay in diagnosis. Advantages are clinical equivalence, better access for patients and the possibility of picking up other lung disorders from the differential diagnosis in case there is no pulmonary embolism.
- "Ventilation-perfusion scan" (or V/Q scan), which shows that some areas of the lung are being ventilated but not perfused with blood (due to obstruction by a clot). It is a type of scintigraphy. This study is used less often because of CT technology, however, it may be useful in patients who have an allergy to iodinated contrast
In low/moderate suspicion of PE, a normal D-dimer level (shown in a blood test) is enough to exclude the possibility of PE (Bounameaux et al 1994).
An electrocardiogram may show signs of right heart strain or acute cor pulmonale in cases of large PEs - the classic signs are a large S wave in lead I, a large Q wave in lead III and an inverted T wave in lead III ("S1Q3T3", as described by McGinn & White 1935). This is occasionally (up to 20%) present, but may also occur in other acute lung conditions and has therefore limited diagnostic value; The most commonly seen sign in the ECG is sinus tachycardia.
In massive PE, dysfunction of the right side of the heart can be seen on echocardiography, an indication that the pulmonary artery is severely obstructed and the heart is unable to match the pressure. In the United States, many physicians see this as an adequate indication for thrombolysis (see below).
The presence of deep venous thrombosis is in itself enough to warrant anticoagulation, without requiring the V/Q or spiral CT scans, and leg ultrasound can be used as a surrogate. This may be valid approach in pregnancy, in which the other modalities would increase the risk of birth defects in the unborn child. However, a negative scan does not rule out PE, and low-radiation dose scanning may be required if the mother is deemed at high risk of having pulmonary embolism.
