Principal Developer: B. Geerts
Secondary Developers: C. Demers, C. Kearon

Suspected PE

Background

• Investigation of patients with suspected pulmonary emboli (PE) remains problematic and controversial – there are several ways to "rule in" and "rule out" the diagnosis (or, more importantly, to make a decision about anticoagulation or not)
• At least 70% of patients with suspected PE don’t have it
• PE is nearly always a complication of (proximal) DVT

Presentations of PE:

• Shortness of breath
• Chest pain (usually pleuritic)
• Hemoptysis
• Pre-syncope or syncope
• Shock
• Hypoxemia
• Arrhythmia especially atrial fibrillation
• Fever
• Right heart failure
• Pulmonary hypertension
• Sudden death

Clinical Priorities in the Investigation of Patients with Suspected PE

Not every PE can (or needs to) be diagnosed. However, among patients with suspected PE, the following clinical situations warrant investigation to prove or exclude this diagnosis:

1. Consideration of extensive PE
2. Consideration of PE in patients with severe symptoms and/or poor cardiopulmonary reserve
3. Diagnosis of any PE when associated with symptomatic or asymptomatic proximal DVT
4. Diagnosis in patients presenting with possible recurrent PE

Tests Generally NOT Helpful in the Diagnosis of Possible PE:

1. Arterial blood gases – usually abnormal in PE but of no diagnostic value
2. ECG and CXR – helpful for evaluation of differential diagnosis; often abnormal in PE but rarely helps to confirm or exclude PE

Tests That May be Helpful (but are not diagnostic on their own):

1. Clinical suspicion – Cannot prove or exclude PE but may assist with a decision for further testing. For example, if clinical suspicion strongly disagrees with non-invasive tests, further testing should be considered.
   
2. D-dimer – Although most patients with PE and DVT have an elevated D-dimer result, D-dimer is also elevated in many other conditions (such as recent injury or surgery, cancer, inflammatory diseases, healthy elderly, etc). Therefore, a positive test result is not helpful. A negative result, using a sensitive D-dimer assay, helps to rule out PE. However, the majority of D-dimer assays in current use are not sensitive enough to be used in the exclusion of PE/DVT on their own, and most centers have never standardized the use of and the testing for D-dimer.
   
3. Echocardiogram – Although the echocardiogram is often abnormal in the presence of major PE (and may have prognostic value), it has limited diagnostic value by itself

Perfusion/Ventilation Lung Scanning (V/Q scan)

There are 3 V/Q lung scan patterns:

1. A normal perfusion scan rules out PE.

2. Most patients with a high probability scan (defined as one or more, segmental or larger, perfusion defects with relatively preserved ventilation) have PE and they can generally be treated without further testing.

3. All other lung scan patterns (which, unfortunately, includes 60% of all the scans) are nondiagnostic.  These nondiagnostic patterns include “low probability”, “nonhigh probability”, “intermediate probability”, and “indeterminate probability”. Further testing is required in patients with this V/Q scan pattern.

·         Advantages of V/Q Lung Scans include:

1.   a normal V/Q scan rules out PE

2.   the radiation dose is low

3.   iodine-based contrast is not used

·         Limitations of V/Q Lung Scans include:

1.   the majority of V/Q scans are nondiagnostic

2.   V/Q scans do not help to identify an alternate diagnosis in the large proportion of patients who don’t have PE.

3. high cost

Spiral/Helical CT (SCT)

There are 3 SCT patterns:

1.      No PE seen and an alternate diagnosis is found. This group does not require any further investigation for VTE.

2.      Definite PE is detected in a segmental or larger pulmonary artery.

3.      Patients with normal SCT, technically inadequate scans, and scans that report “subsegmental PE” are all considered nondiagnostic. Further testing is required in patients with these SCT patterns.

·         SCT is rapidly replacing nuclear medicine lung scanning.

·         Advantages of SCT include:

1. ability to directly visualize emboli

2. high accuracy for large emboli (segmental or larger)

3. potential to provide the alternate diagnosis in patients who don’t have PE

·         Limitations of SCT include:

1. Filling defects confined to subsegmental vessels are not diagnostic

2. Contrast must be given (problematic in patients with renal insufficiency or a history of contrast allergy)

3. A normal SCT does not rule-out PE

4. Significant radiation

Since almost all pulmonary emboli arise from DVT, a useful strategy in some patients with suspected PE is to look for the presence of DVT using Duplex ultrasound (DUS).

• If the DUS of the proximal veins is positive, the patient requires treatment (the treatment of proximal DVT and PE is the same).
• If the DUS is negative, the risk of recurrent PE in the short term is very low.
• Repeating the DUS testing in 5-7 days  is a safe strategy in suspected PE with nondiagnostic lung imaging.

1. Should I start with lung imaging (V/Q scan, SCT) or with DUS?

2. If I start with lung imaging, should it be a P/V scan or spiral CT?

• There are very few indications do both a V/Q scan and a SCT.

A number of diagnostic algorithms for the investigation of patients with suspected PE have been studied.  Three algorithms are presented here – the first is based on imaging tests alone (Figure 1) and the remaining two incorporate a formal clinical probability assessment and a sensitive D-dimer assay along with either V/Q lung scanning (Figure 2) or spiral CT (Figure 3). For patients who have PE excluded by one of these algorithms, the chance of DVT/PE in the next 3 months is less than 1%.

Figure 1: Investigation of Suspected PE Based on Imaging Tests Alone

Figure 2: Investigation of Suspected PE Using Clinical Probability Assessment, Sensitive D-dimer, and P/V Lung Scanning

Figure 3: Investigation of Suspected PE Using Clinical Probability Assessment, Sensitive D-dimer, and Spiral CT

Clinical Probability Assessment for Pulmonary Embolism*

* Wells PS, et al. Ann Intern Med 2001;135:98

• Anticoagulate patients with suspected PE when:

1. DUS shows proximal DVT
2. V/Q lung scan is "high probability"
3. Spiral CT shows segmental or larger filling defect
4. Pulmonary angiogram is positive
5. There is another indication for anticoagulation (such as atrial fibrillation)

• Do not anticoagulate patients with:

1. Perfusion lung scan normal
2. Spiral CT that does not show PE and demonstrates an alternate Dx
3. Spiral CT does not show PE and there is no proximal DVT on DUS and clinical probability of PE is low or moderate
4. Pulmonary angiogram that is normal
5. A nondiagnostic lung scan with normal serial DUS
6. A low clinical probability of PE combined with a negative sensitive D-dimer assay

References:

1. Kearon C. Diagnosis of pulmonary embolism. CMAJ 2003;168:183-194
2. Fedullo PF, Tapson VF. The evaluation of suspected pulmonary embolism. N Engl J Med 2003;349:1247-1256
3. Kearon C, et al. Noninvasive diagnosis of deep venous thrombosis. Ann Intern Med 1998;128:663-677
4. Rathbun SW, et al. Sensitivity and specificity of helical computed tomography in the diagnosis of pulmonary embolism: a systematic review. Ann Intern Med 2000;132:227-232
5. Perrier A, et al. Performance of helical computed tomogaphy in unselected outpatients with suspected pulmonary embolism. Ann Intern Med 2001;135:88-97
6. van Strijen MJL, et al. Single-detector helical computed tomography as the primary diagnostic test in suspected pulmonary embolism: a multicenter clinical management study of 510 patients. Ann Intern Med 2003;138:307
7. Kruip MJHA, et al. Diagnostic strategies for excluding pulmonary embolism in clinical outcome studies: a systematic review. Ann Intern Med 2003;138:941-951
8. Musset D, et al. Diagnostic strategy for patients with suspected pulmonary embolism: a prospective multicentre outcome study. Lancet 2002;360:1914-1920
9. Perrier A, et al. Diagnosing pulmonary embolism in outpatients with clinical assessment, D-dimer measurement, venous ultrasound, and helical computed tomography: a multicenter management study. Am J Med 2004;291-299
10. Chunilal SD , et al. Does this patient have pulmonary embolism? JAMA 2003;290:2849-2858
11. Stein PD, et al. D-dimer for the exclusion of acute venous thrombosis and pulmonary embolism: a systematic review. Ann Intern Med 2004;140:589-602