1. electrocardiogram
More than 70% PE patients have abnormal ECG, but there is no specificity. Most of them appear immediately after the onset and show dynamic changes. About 50% patients showed ST-T changes of V 1 ~ V4, while others showed right bundle branch block, pulmonary P wave, right deviation of electric axis, clockwise transposition, etc. The classic SIQ Ⅲ T Ⅲ only appears in 10% acute PE. No abnormality in ECG only means that PE is unlikely, but PE cannot be ruled out.
2. Arterial blood gas
When the pulmonary vascular bed is blocked by 15% ~ 20%, the oxygen partial pressure will decrease, which is often manifested as hypoxemia, hypocapnia and increased alveolar-arterial oxygen partial pressure difference, but these changes can also be seen in other cardiopulmonary diseases. These indexes can be normal in PE patients with 10% ~ 15%, so the change of arterial blood gas is only of reference value for the diagnosis of PE.
3. chest x-ray plain film
X-ray changes of PE usually occur within 12 ~ 36 hours or days after onset. According to the data of the Prospective Study of PE Diagnosis (PIOPED), 80% of PE patients had abnormal chest radiographs, of which 65% showed pulmonary consolidation or atelectasis, and 48% showed pleural effusion. Regional pulmonary blood decrease, central pulmonary artery protrusion, right lower pulmonary trunk widening with truncation sign, pulmonary artery segment swelling, right ventricular dilatation sign and involved diaphragm elevation may also occur. The most typical sign is the wedge-shaped dense shadow (Hampton sign) above the diaphragm, but it is rare. Although these changes can not be used as the diagnostic criteria of PE. But it is still helpful for the differential diagnosis of other cardiopulmonary diseases with similar symptoms to PE.
4.D- dimer detection.
As the preferred screening test for PE, it has been recognized. At present, the main methods to detect D-D are latex agglutination and enzyme-linked immunosorbent assay (ELISA). Most scholars believe that the sensitivity and specificity of ELISA are better than latex agglutination method. The diagnosis and treatment guidelines of acute pulmonary embolism in Europe and China all use ELISA to detect D-D in plasma. The result of ELISA method is >: 500μ g/L. The sensitivity to acute PE is 92% ~ 100%, but the specificity is low, only 40% ~ 43%. Tumor, trauma, infection, cardiovascular and cerebrovascular diseases, age and other factors can increase D-D. It is reported that the specificity of D-D increase in the age group of 30-39 years old is 72%, and it drops to 9% in the age group over 80 years old. So, D-D > The positive predictive value of 500μg/L for pulmonary embolism is low, so it cannot be used for the diagnosis of pulmonary embolism. Plasma D-D negative results can basically exclude PE.
5. Echocardiography (UCG)
We can find the changes of the right heart caused by PE, which is of great value to prompt the diagnosis and exclusion of other cardiovascular diseases. Conventional chest ultrasound examination can find that the local motion amplitude of the right ventricular wall decreases and the right ventricle and/or right atrium increases. The ventricular septum moves to the left and abnormally, the proximal pulmonary artery dilates, and the tricuspid regurgitation velocity increases. These signs only indicate that the right ventricle is overloaded and cannot be used as a clear diagnostic index of PE. PE can only be diagnosed if embolus is found in the proximal pulmonary artery. Recent studies have proved that transesophageal ultrasound (TEE) is of great value in the diagnosis of PE, and it is considered that TEE is clearer than the former. In about 80% of PE patients, signs of embolus and right ventricular overload in the heart or central pulmonary artery can be seen. Comparing the sensitivity and specificity of TEE and spiral CT(SCT) in the diagnosis of PE, it was found that the sensitivity of SCT was higher than that of TEE (97.5%: 70%), but their specificity was similar (100%: 90%).
6. Examination of deep vein thrombosis
It is two manifestations of the same disease, collectively referred to as venous thromboembolism. PE can occur in 50% ~ 60% lower extremity DVT, and autopsy data show that 80 ~ 90% PE embolus comes from lower extremity DVT. Therefore, it is necessary to check DVT in the diagnosis of PE. Venography is still the gold standard of DVT, and its sensitivity and specificity are close to 100. Other examinations include ultrasound, impedance plethysmography and radionuclide venography. Ultrasound is still the most widely used diagnostic method in clinic. For symptomatic proximal DVT, the sensitivity and specificity of ultrasound diagnosis are 95% and 98% respectively, but the sensitivity and specificity of venous and asymptomatic DVT are 35% and 99% respectively.
7. Pulmonary ventilation/perfusion (V/Q) imaging
The standard of V/Q imaging in the diagnosis of PE is that lung lobe, lung segment or multiple subpulmonary segments show perfusion defects. Ventilation imaging is normal. PIOPED data showed that the sensitivity of V/Q imaging in the diagnosis of pulmonary embolism was 92%. The specificity was 87%. In order to better explain the results of V/Q imaging, the imaging results are divided into three categories recently: ① High probability, that is, perfusion imaging shows two or more perfusion defects, while ventilation imaging is normal, and the probability of diagnosing PE is 88%; ② Normal or close to normal, that is, there is no perfusion defect in lung perfusion imaging, except PE, and the probability of PE is only 0.2%. ③ Non-diagnostic abnormality, that is, perfusion defect and ventilation defect coexist in V/Q imaging, and its symptoms are between high possibility and normal, including low possibility and medium possibility. About 50 suspected PE patients are V/Q imaging without diagnostic significance, and the probability of PE at this time is 16 ~ 33%, which needs further examination.
8. spiral CT
Embolus located in pulmonary artery trunk, lobe and segment can be clearly detected. It is characterized by pulmonary artery filling defect and vascular truncation. According to this, PE diagnosis can be made. However, its sensitivity to subsegmental and peripheral pulmonary embolism is limited. The overall sensitivity and specificity of spiral CT in diagnosing pulmonary embolism were 72% and 95%, respectively. The diagnostic sensitivity and specificity of pulmonary embolism above segmental level are 75 ~ 100% and 78 ~ 100% respectively, while the diagnostic sensitivity and specificity of pulmonary embolism below segmental level are obviously reduced, which are 63% and 89% respectively, but these peripheral emboli only account for 6 ~ 10% of PE, and their clinical significance is not important. Computed tomography angiography (CTA) is a new imaging technique, which uses enhanced spiral CT scanning to obtain the original image, and can display the pulmonary vessels in three dimensions after reconstruction. The data showed that CTA had a sensitivity of 53% ~ 100% and a specificity of 75 ~ 100%.
9. Magnetic resonance imaging (MRI)
Ordinary MRI can show pulmonary embolism above segmental level, which has high sensitivity and specificity in diagnosing PE, but peripheral pulmonary artery dysplasia has similar clinical diagnostic value to spiral CT. Magnetic resonance angiography (MRA) is similar to CTA in imaging principle, and can display peripheral pulmonary artery. The recent MRA study showed that its sensitivity to segmental pulmonary embolism was 75 ~ 100%, and its specificity was 42 ~ 100%. Compared with spiral CT, MRI has three advantages: ① it does not need contrast agent and is suitable for iodine allergy and the elderly; ② At the same time, we can visualize the blood vessels of lower limbs and find the evidence of DVT. ③ It has the potential ability to identify old and new thrombus, and provides the basis for determining thrombolytic therapy.
10. Pulmonary angiography
This is the current gold standard for diagnosing PE. The direct sign is pulmonary artery cavity filling defect or complete occlusion, and the indirect sign is slow flow of contrast agent, local hypoperfusion and delayed venous return. Pulmonary embolism cannot be diagnosed without its direct symptoms. The sensitivity of PA is above 98%, and the specificity is 90 ~ 98%. However, with the decrease of blood vessel diameter, its accuracy decreases, and the blood vessels below the segment are only 66%. PA is an invasive examination, and its mortality and incidence of serious complications are 0. 1% and 1.5% respectively. It is generally believed that all patients who cannot be diagnosed by non-invasive examination can choose PA.