Pulmonary Embolism: Difference between revisions

The diagnosis of PE is based primarily on validated clinical criteria combined with selective testing because the typical clinical presentation ([[shortness of breath]], [[chest pain]]) cannot be definitively differentiated from other causes of chest pain and shortness of breath. The decision to do medical imaging is usually based on clinical grounds, i.e. the [[medical history]], symptoms and findings on [[physical examination]], followed by an assessment of clinical probability.<cite>Goldhaber</cite>

The most commonly used method to predict clinical probability, the Wells score, is a [[clinical prediction rule]], whose use is complicated by multiple versions being available. In 1995, Wells ''et al.'' initially developed a prediction rule (based on a literature search) to predict the likelihood of PE, based on clinical criteria.<cite>REFNAME1</cite> The prediction rule was revised in 1998 <cite>REFNAME2</cite> This prediction rule was further revised when simplified during a validation by Wells ''et al.'' in 2000. <cite>REFNAME3</cite> In the 2000 publication, Wells proposed two different scoring systems using cutoffs of 2 or 4 with the same prediction rule. <cite>REFNAME3</cite> In 2001, Wells published results using the more conservative cutoff of 2 to create three categories.<cite>REFNAME4</cite> An additional version, the "modified extended version", using the more recent cutoff of 2 but including findings from Wells's initial studies<cite>REFNAME5</cite> <cite>REFNAME6</cite> were proposed. <cite>REFNAME7</cite> Most recently, a further study reverted to Wells's earlier use of a cutoff of 4 points <cite>REFNAME3</cite> to create only two categories. <cite>REFNAME8</cite>

*clinically suspected [[DVT]] - 3.0 points

*[[tachycardia]] - 1.5 points

*history of [[DVT]] or PE - 1.5 points

*[[hemoptysis]] - 1.0 points

* Score 4 or less - PE unlikely. Consider [[D-dimer]] to rule out PE.

Early primary research has shown that in low/moderate suspicion of PE, a normal [[D-dimer]] level (shown in a [[blood test]]) is enough to exclude the possibility of thrombotic PE. <cite>REFNAME13</cite> This has been corroborated by a recent [[systematic review]] of studies of patients with low pre-test probability (PTP) of PE and negative [[D-dimer]] results that found the three month risk of thromboembolic events in patients excluded in this manner was 0.14%, with 95% confidence intervals from 0.05 to 0.41%, though this review was limited by its use of only one randomized-controlled clinical trial, the remainder of studies being prospective cohorts. <cite>REFNAME14</cite> D-dimer is highly sensitive but not very specific (specificity around 50%). In other words, a positive D-dimer is not synonymous with PE, but a negative D-dimer is, with a good degree of certainty, an indication of absence of a PE. <cite>REFNAME15</cite>

When a PE is being suspected, a number of [[blood test]]s are done, in order to exclude important secondary causes of PE. This includes a [[full blood count]], clotting status (PT, [[aPTT]], TT), and some screening tests ([[erythrocyte sedimentation rate]], [[renal function]], [[liver enzyme]]s, [[electrolyte]]s). If one of these is abnormal, further investigations might be warranted.

[[File:Pulmonary embolism selective angiogram.JPEG|thumb|Selective [[pulmonary angiogram]] revealing significant thrombus (labelled A) causing a central obstruction in the left main pulmonary artery. ECG tracing shown at bottom.]]

[[File:Pulmonary embolism CTPA.JPEG|thumb|[[CT pulmonary angiogram|CT pulmonary angiography]] (CTPA) showing a saddle embolus and substantial thrombus burden in the lobar branches of both main pulmonary arteries.]]

[[File:Pulmonary embolism scintigraphy PLoS.png|thumb|[[Ventilation-perfusion scintigraphy]] in a woman taking [[hormonal contraceptives]] and [[valdecoxib]].<br/>(A) After inhalation of 20.1 mCi of [[Xenon]]-133 gas, scintigraphic images were obtained in the [[Posterior (anatomy)|posterior]] projection, showing uniform ventilation to lungs.<br/>

(B) After intravenous injection of 4.1 mCi of [[Technetium]]-99m-labeled macroaggregated [[albumin]], scintigraphic images were obtained, shown here in the posterior projection. This and other views showed decreased activity in multiple regions.]]

The gold standard for diagnosing pulmonary embolism (PE) is ''[[pulmonary angiography]]''. Pulmonary angiography is used less often due to wider acceptance of CT scans, which are non-invasive. CT pulmonary angiography is the recommended first line diagnostic imaging test in most people.