Pulmonary embolism

In this presentation, diagnostic and treatment workup of pulmonary embolism have been explained. Major reference of the presentation is UPTODATE.

1. Pulmonary embolism Ramin Sadeghi , MD

2. Definition Pulmonary embolus (PE) refers to obstruction of the pulmonary artery or one of its branches by material ( eg , thrombus, tumor, air, or fat) that originated elsewhere in the body. This topic review focuses upon PE due to thrombus.

3. The temporal pattern of presentation •Acute – Patients with acute PE typically develop symptoms and signs immediately after obstruction of pulmonary vessels. • Subacute – Some patients with PE may also present subacutely within days or weeks following the initial event. •Chronic – Patients with chronic PE slowly develop symptoms of pulmonary hypertension over many years ( ie , chronic thromboembolic pulmonary hypertension; CTEPH).

4. The presence or absence of hemodynamic stability Hemodynamically unstable PE results in hypotension. Hypotension is defined as a systolic blood pressure <90 mmHg or a drop in systolic blood pressure of ≥40 mmHg from baseline for a period >15 minutes or hypotension that requires vasopressors or inotropic support and is not explained by other causes such as sepsis, arrhythmia, left ventricular dysfunction from acute myocardial ischemia or infarction, or hypovolemia . Hemodynamically stable PE is defined as PE that does not meet the definition of hemodynamically unstable PE. 

5. The anatomic location Saddle PE lodges at the bifurcation of the main pulmonary artery, often extending into the right and left main pulmonary arteries. Approximately 3 to 6 percent of patients with PE present with a saddle embolus retrospective studies suggest that among those diagnosed with a saddle embolus, only 22 percent are hemodynamically unstable, with an associated mortality of 5 percent Most PE move beyond the bifurcation of the main pulmonary artery to lodge distally in the main lobar, segmental, or subsegmental branches of a pulmonary artery. PE can be bilateral or unilateral, depending on whether they obstruct arteries in the right, left, or both lungs. Smaller thrombi that are located in the peripheral segmental or subsegmental branches are more likely to cause pulmonary infarction and pleuritis  

6. The presence or absence of symptoms Symptomatic PE refers to the presence of symptoms that usually leads to the radiologic confirmation of PE, whereas asymptomatic PE refers to the incidental finding of PE on imaging

7. Laboratory tests Complete blood count and serum chemistries  – Routine laboratory findings in patients with PE are nonspecific and include leukocytosis, an increased erythrocyte sedimentation rate (ESR), elevated serum lactate dehydrogenase (LDH) and aspartate aminotransferase (AST ). Arterial blood gas  (ABG) – For patients suspected of having a PE, an abnormal ABG is common, but is neither sensitive nor specific diagnostically since abnormal gas exchange in this population is often due to, and/or worsened by, underlying cardiopulmonary disease ABGs may be of prognostic value. As an example, patients with hypoxemia or room air pulse oximetry readings <95 percent at the time of diagnosis are at increased risk of in-hospital complications, including respiratory failure, obstructive shock, and death 

8. Laboratory tests Troponin In patients with suspected PE, serum troponin I and T levels are neither sensitive nor specific diagnostically. However , as markers of right ventricular dysfunction, troponin levels are elevated in 30 to 50 percent of patients who have a moderate to large PE D-dimer  – D-dimer is a sensitive but poorly specific diagnostic tool for patients with suspected PE. D-dimer levels are most useful when used in conjunction with clinical suspicion to facilitate for the decision to proceed with further testing.

9. Laboratory tests Electrocardiography The most common findings are tachycardia and nonspecific ST-segment and T-wave changes (70 percent ). Abnormalities historically considered to be suggestive of PE (S1Q3T3 pattern, right ventricular strain, new incomplete right bundle branch block) are infrequent (less than 10 percent ) ECG abnormalities that are associated with a poor prognosis in patients diagnosed with PE include[ ● Atrial arrhythmias ( eg , atrial fibrillation) ●Bradycardia (<50 beats per minute) or tachycardia (>100 beats per minute) ●New right bundle branch block ●Inferior Q-waves (leads II, III, and aVF ) ●Anterior ST-segment changes and T-wave inversion ●S1Q3T3 pattern

10. Chest radiograph A chest radiograph is typically performed in most patients suspected of PE to look for an alternative cause of the patient’s symptoms. It is also performed in those undergoing ventilation perfusion (V/Q) scanning for accurate interpretation of the scan. However, it is not necessary if a computed tomographic pulmonary angiogram (CTPA) is planned . Common findings include ●Atelectasis or pulmonary parenchymal abnormalities (18 to 69 percent) ●Pleural effusion (47 percent) ●Cardiomegaly (up to 50 percent) A normal chest radiograph can be seen in 12 to 22 percent of patients with PE.

11. DIAGNOSTIC ALGORITHMS FOR HEMODYNAMICALLY STABLE PATIENTS Several diagnostic algorithms for hemodynamically stable patients with suspected pulmonary embolus (PE) have been proposed, none of which are foolproof Their purpose is to efficiently diagnose PE while simultaneously avoiding unnecessary testing and minimizing the risk of missing clinically important cases.

12. Determining the clinical probability of pulmonary embolism For nonpregnant patients in whom PE is suspected, following clinical and laboratory assessment, the pretest probability (PTP) for PE should be estimated by gestalt or calculated using the Modified Wells or Modified Geneva score

13. Unlikely probability of pulmonary embolism Patients in this group should undergo sensitive D-dimer testing, or, alternatively , the PE rule-out criteria (PERC) can be applied  When D-dimer is chosen, the following applies: ●For patients in whom PE is unlikely and the D-dimer level is <500  ng /mL (fibrinogen equivalent units), no further testing is required ●For patients in whom PE is unlikely and the D-dimer is ≥500  ng /mL (fibrinogen equivalent units), diagnostic imaging should be performed When the PERC rule is chosen, the following applies: ●For patients in whom PE is unlikely who fulfill all eight PERC rule criteria, no further testing is required ●For patients in whom PE is unlikely who do not fulfill all eight criteria, further testing with sensitive D-dimer measurement or imaging should be performed

14. PERC rule The PE rule-out criteria ("PERC rule") is an alternate to sensitive D-dimer testing in patients with a low-probability assessment for PE

15. Likely probability of pulmonary embolism This population of patients includes those with a likely clinical probability of PE as well as those with an unlikely clinical probability who have a D-dimer level ≥500  ng /mL (fibrinogen equivalent units) or who do not fulfill all eight PERC rule criteria.

16. Computed tomographic pulmonary angiography-based algorithms   For most patients with suspected PE, CTPA is the first-choice diagnostic imaging modality because it is sensitive and specific for the diagnosis of PE. 

17. Christopher study TI Effectiveness of managing suspected pulmonary embolism using an algorithm combining clinical probability, D-dimer testing, and computed tomography. AU van Belle A, Büller HR, Huisman MV, Huisman PM, Kaasjager K, Kamphuisen PW, Kramer MH, Kruip MJ, Kwakkel -van Erp JM, Leebeek FW, Nijkeuter M, Prins MH, Sohne M, Tick LW, Christopher Study Investigators SO JAMA. 2006;295(2):172.

18. Ventilation/perfusion scan   For most nonpregnant patients V/Q scanning is reserved for those with suspected PE in whom CTPA is contraindicated ( eg , renal insufficiency [estimated glomerular filtration rate <60 mL/min/1.73 m 2 ], contrast allergy, or morbid obesity), is inconclusive, or is negative but discordant with a high clinical suspicion  V/Q scanning is often the test of choice for the diagnosis of PE in pregnancy

19. SPECT Technological advances in CT scanning have resulted in the development of three-dimensional SPECT (also known as noncontrast perfusion SPECT and Q-SPECT). The advantages of SPECT are the avoidance of contrast, and it may allow the clearer depiction, and therefore increased detection of, smaller subsegmental pulmonary emboli. Preliminary studies suggest that SPECT is as sensitive as CTPA and more sensitive than V/Q scanning

20. Other imaging Contrast-enhanced pulmonary angiography Magnetic resonance pulmonary angiography Lower-extremity ultrasound Echocardiography

21. PE in pregnancy

22. Pulmonary hypertension Patients with pulmonary hypertension (PH) initially present with exertional dyspnea and fatigue, that progress to develop the signs and symptoms of severe PH or right ventricular failure ( eg , exertional chest pain or syncope, and congestion including peripheral edema, ascites, and pleural effusion). The diagnosis is often delayed because the presenting features of PH are frequently attributed incorrectly to age, deconditioning, or a coexisting or alternate medical condition. 

23. Diagnostic testing Diagnostic testing is indicated whenever PH is suspected. The purpose of the diagnostic testing is to confirm that PH exists, determine its severity, and identify its cause.

24. V/Q scanning Although falling out of favor as a diagnostic technique for acute pulmonary embolism, ventilation-perfusion (V/Q) lung scanning represents the initial imaging procedure of choice in patients presenting with newly diagnosed pulmonary hypertension. It can differentiate proximal large vessel types of pulmonary hypertension ( eg , CTEPH, pulmonary artery sarcoma) from distal small vessel types ( eg , group 1 pulmonary arterial hypertension), which are the most common competing diagnostic possibilities V/Q lung scanning is preferred over computed tomographic pulmonary angiography (CT-PA) as the initial test because it detects CTEPH with greater sensitivity . For those patients whose V/Q lung scanning suggests CTEPH, an additional imaging study is required.