Table of Contents
Pulmonary embolism diagnosis
A normal D-dimer test result is useful in excluding pulmonary embolism in patients with a low pretest probability of pulmonary embolism or a nondiagnostic lung scan 1).
A negative D-dimer test reliably excludes PE in patients with a low clinical probability of PE 2) or in those with nondiagnostic VQ scan 3).
Alternatively, one can check for Deep-vein thrombosis utilizing IPG, Doppler, or venography. If positive, this indicates a possible source of PE, and since the treatment is similar for both, no further search for PE need be made and treatment is started. If negative, further testing may be needed (e.g.VQ scan).
Laboratory tests
General diagnostic tests
None are very sensitive or specific.
● EKG: “classic” S1Q3T3 is rare. Usually just nonspecific-ST & T changes occur. Tachycardia may be the only finding.
● CXR: normal in 25–30%. When abnormal, usually shows infiltrate and elevated hemidiaphragm
● ABG: not very sensitive. pO2 > 90 on room air virtually excludes massive PE
Specific radiographic evaluation
● Test of choice: contrast enhanced chest CT. Occasion ally chest CTA may be employed. Can provide insight into alternate diagnoses
● pulmonary angiogram: historically, the “gold standard.” Invasive, expensive, and labor intensive. 3–4% risk of significant complications. Not indicated in most cases
● ventilation-perfusion scan (V/Q scan)
● thin-section contrast-enhanced chest CT: more accurate in patients with COPD who often have an indeterminate VQ scan.
Transthoracic echocardiogram
A study analyzed the regional pattern of right ventricular (RV) dysfunction on transthoracic echocardiograms in patients with and without acute pulmonary embolism. Quantitative (centerline) and qualitative (wall motion score) analyses of segmental RV free wall motion were performed on a “training” cohort of 41 patients (group 1), including 14 patients with acute pulmonary embolism, 9 patients with primary pulmonary hypertension, and 18 normal subjects. Patients with acute pulmonary embolism had a distinct regional pattern of RV dysfunction, with akinesia of the mid-free wall (centerline excursion: -0.2 +/- 0.8 mm, p = 0.0001 vs normal) but normal motion at the apex (centerline excursion: 5.7 +/- 0.8 mm, p = NS vs normal). In contrast, patients with primary pulmonary hypertension had abnormal wall motion in all regions (p <0.03 vs normal). This echocardiographic finding of normal wall motion at the apex and abnormal wall motion in the mid-free wall in acute pulmonary embolism was then tested in a “validation” cohort of 85 patients (group 2), consisting of hospitalized patients with RV dysfunction from any cause, including 13 patients with acute pulmonary embolism. The finding had a 77% sensitivity and a 94% specificity for the diagnosis of acute pulmonary embolism, with a positive predictive value of 71% and a negative predictive value of 96%. Thus, a distinct echocardiographic pattern of regional RV dysfunction, in which the apex is spared occurs in acute pulmonary embolism. This finding should raise the level of clinical suspicion for the diagnosis of acute pulmonary embolism 4).
In 1239 inpatients and outpatients with suspected pulmonary embolism.
A clinical model categorized pretest probability of pulmonary embolism as low, moderate, or high, and ventilation-perfusion scanning and bilateral deep venous ultrasonography were done. Testing by serial ultrasonography, venography, or angiography depended on pretest probability and lung scans.
Patients were considered positive for pulmonary embolism if they had an abnormal pulmonary angiogram, abnormal ultrasonogram or venogram, high-probability ventilation-perfusion scan plus moderate or high pretest probability, or venous thromboembolic event during the 3-month follow-up. All other patients were considered negative for pulmonary embolism. Rates of pulmonary embolism during follow-up in patients who had a normal lung scan and those with a non-high-probability scan and normal serial ultrasonogram were compared.
Pretest probability was low in 734 patients (3.4% with pulmonary embolism), moderate in 403 (27.8% with pulmonary embolism), and high in 102 (78.4% with pulmonary embolism). Three of the 665 patients (0.5% [95% CI, 0.1% to 1.3%]) with low or moderate pretest probability and a non-high-probability scan who were considered negative for pulmonary embolism had pulmonary embolism or deep venous thrombosis during 90-day follow-up; this rate did not differ from that in patients with a normal scan (0.6% [CI, 0.1% to 1.8%]; P > 0.2).
Management of patients with suspected pulmonary embolism on the basis of pretest probability and results of ventilation-perfusion scanning is safe 5).
To determine the sensitivities and specificities of ventilation/perfusion lung scans for acute pulmonary embolism, a random sample of 933 of 1493 patients was studied prospectively. Nine hundred thirty-one underwent scintigraphy and 755 underwent pulmonary angiography; 251 (33%) of 755 demonstrated pulmonary embolism. Almost all patients with pulmonary embolism had abnormal scans of high, intermediate, or low probability, but so did most without pulmonary embolism (sensitivity, 98%; specificity, 10%). Of 116 patients with high-probability scans and definitive angiograms, 102 (88%) had pulmonary embolism, but only a minority with pulmonary embolism had high-probability scans (sensitivity, 41%; specificity, 97%). Of 322 with intermediate-probability scans and definitive angiograms, 105 (33%) had pulmonary embolism. Follow-up and angiography together suggest pulmonary embolism occurred among 12% of patients with low-probability scans. Clinical assessment combined with the ventilation/perfusion scan established the diagnosis or exclusion of pulmonary embolism only for a minority of patients–those with clear and concordant clinical and ventilation/perfusion scan findings 6).