Diagnosis of Pulmonary Embolus Edited

8/8/2019 Diagnosis of Pulmonary Embolus Edited

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DIAGNOSIS OF PULMONARYDIAGNOSIS OF PULMONARYEMBOLUSEMBOLUS

Adapted from source


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INTRODUCTIONINTRODUCTIONy No single non invasive test is both sensitive and

specific enoughy Test: ruling in PE, e.g. helical CT or ruling out

e.g. D-dimer, others do both, often non-diagnostic

e.g. VQ scansy Choice of initial diagnostic test guided by clinical

assessment of probability & patientcharacteristics that may influence test accuracy

y Clinical assessment alone unreliable, objectivetesting crucial

y Failure to Dx PE high mortality, incorrect Dx of PE exposes patient risks of anticoagulation.


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OBJECTIVES OF THIS REVIEWOBJECTIVES OF THIS REVIEWy Outline approach to Dx of PE that minimises

the use of Pulmonary Angiography (PA)y Based on 2 guiding principlesy Accurate test/combination of tests should have

a positive predictive value 85% & a negativepredictive value of 95% OR

y Be associated with no more than 2% VTE duringF/U if it is the basis of withholding treatment


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CLINICAL ASSESSMENTCLINICAL ASSESSMENTy 2 Categories of clinical assessment

Empirical clinical assessment: Hx, Examination,CXR, ECG, ABG low, intermediate & highprobability categoriesx PIOPED & McMaster studies, prevalence of PE

established by PA was 15%, 38%, 79%Standardized clinical model (or prediction rules):x Wells & colleagues used S&S, alternative Dx

possible & presence of risk factors for VTE- low,intermediate & high probability categories


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CLINICAL ASSESSMENTCLINICAL ASSESSMENTy Wells Score

Variable Pointsx S&S of DVT 3.0x Alternative Dx less likely than PE 3.0x HR>100 b/min 1.5x Immobilization/Sx past 4/52 1.5x Previous DVT/PE 1.5x Haemoptysis 1.0x Malignancy(on Rx/in past 6/12) 1.0

High >6, Moderate 2-6, Low


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Clinical assessment SUMMARYClinical assessment SUMMARYy Wells scoring, prevalence of PE 2% low

probability group, 19% intermediate & 50% inhigh probability group

y Evidence shows that clinical assessment( empirical/standardised) can stratify patientsprobability of having PE

y Prevalence expected: 60% high probabilitycategory


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NATURAL HX OF VTENATURAL HX OF VTEy Most cases DVT (~90%) start in the calf y Isolated calf DVT rarely causes leg symptoms or PEy 25% unRxd calf DVT will extend to proximal veins, do so

within a week of presentationy 75% of pts with PE have DVTy Most pts with symptomatic PE have incr D-dimery ~50% symptomatic PE involve lobar or main pulmonary

arteriesy Without Rx,1/2 pts symptomatic DVT/PE have recurrence

within 3/12y With Rx of PE, ~50% resolution of perfusion defects in 2-

4/52. Complete resolution occur in 2/3 of ptsy With Rx of proximal DVT, residual thrombus is seen on USS

in of pts at 1 yr


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DD--DIMER TESTINGDIMER TESTINGy D-dimer cross-linked fibrin lysed by plasminy Elevations are non-specific: infection, inflammation,

ageing, cancer, cardiac ischemiay Wide variety of assaysy

Valid assays for PE Dx: 2 CategoriesVery Highly sensitive D-dimer testx Sensitivity >98%; Usu low specificity ~40%- high false

positivesx Used to rule out PE

Moderate-Highly sensitive D-dimer testx Sensitivity 85-98%, not high enough to rule out PE, needsto be combined with another assessment

HBH: Simple D-dimer assay: 100% sensitive, ~50%specific


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OTHER DIAGNOSTIC TESTSOTHER DIAGNOSTIC TESTSy VQ SCAN

Normal scan excludes PEPerfusion defects are non-specific-1/3 pts withdefects have PEProbability increases with increase in number andsize of perfusion defects & presence of normalventilation scan

y CT

Spiral/Helical scans with contrast (CT-PA)y MRIy Tests for DVT: USS, Venography: indirect way

of Dx PE


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OTHER DIAGNOSTIC TESTSOTHER DIAGNOSTIC TESTSy Pulmonary Angiography: Requires more

expertise & support staff; invasive, timeconsuming, more expensive, and less available

y Echocardiography: Transthoracic/TEEdirectly visualise thrombi in right heartchamber or central pulmonary arteriesshow right heart hemodynamic changes thatindirectly suggest PETEE visualise thrombi in central pulmonaryarteries with a specificity of >90%


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DX OF PE IN PREGNANCYDX OF PE IN PREGNANCYy MODIFICATIONS IN MXM

1ST: USS of proximal veins initial test2nd : Amount of radio-isotope used for VQSreduced & duration of scanning extended3rd: If PA performed, brachial approach usedwith abdominal screening

4th

: In the absence of safety data, helical CT isdiscouraged


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CLINICAL SITUATIONS ALTERCLINICAL SITUATIONS ALTERDIAGNOSTIC APPROACH/ TESTDIAGNOSTIC APPROACH/ TESTINTERPRETATIONINTERPRETATIONy In-hospital patients

Inpatients, especially after surgery, oftenhave increased D-dimer levels thatmarkedly reduce the value of D-dimertesting (e.g., specificity of 7% in

inpatients versus 47% in outpatients).


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y Tr eatment of p r esumptivepulmona ry embolism

D-dimer levels are estimated to decreaseabout 25% after 24 hours of heparintherapy, and this is expected to reducethe sensitivity of D-dimer testing (e.g.,from 96% to 89%)


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y H igh clinical p r obabilit yD-dimer testing has little clinical utility in patientswith a high clinical probability of pulmonary

embolism, because specificity is lower in thisgroup (e.g., 28% compared with 54% with lowclinical probability)The combination of a lower specificity and highprevalence of embolism results in a lowfrequency of negative D-dimer results (e.g., 17%compared with 51% with low probability), whichhave a lower negative predictive value(e.g., 77%compared with 100% with low probability).


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y P r evious venous th r ombo-embolism

Imaging abnormalities associated with previous

DVT or PE may persist and be misdiagnosed asrecurrent VTE(e.g., decrease in positivepredictive value of a high probability lung scanfrom 91% to 74% with a history of PE).In about half of patients with recently diagnosedDVT who present with suspected PE and have ahigh-probability lung scan, the abnormalitiespredate the onset of chest symptoms


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y Influence of age on accu r ac y of diagnostic tests

The specificity of D-dimer testing and lungscanning decreases with age (e.g., D-dimerspecificity: 67% at 50 years versus 10% at 80 years

Proportion of lung scans that are non-diagnostic: 32% at 40 years versus 58% at 80 years)


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y C a r diopulmona ry diseaseCardiopulmonary disease (particularlylung disease) is associated with a highproportion of non-diagnostic lung scans(e.g., 78% [91% with COPD] versus 64%)and a lower positive predictive value with

a high-probability defect (e.g., 83% versus93%)


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y M alignant diseaseMalignancy reduces the specificity of manytests for PE(e.g., D-dimer: 48% versus82%) & may also result in false-positiveresults (e.g., high-probability lung scans orabnormal helical CT with intra-thoracic

malignancy).


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y C ent r al venous cathete r sThe arms and central veins should beconsidered as a source for emboli & as atarget for diagnostic testing in patientswith central venous catheters who aresuspected of having PE


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y P r egnanc yAs compared with non-pregnant patients,the prevalence of PE among pregnantpatients who are investigated for PE islow (about 5% versus about 20%) and theprevalence of normal perfusion scans is

high (about 70% versus about 25%)


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SUMMARYSUMMARYy PE IS CONF IRMED BY :

Pulmonary angiography: intra-luminal fillingdefect

Helical CT: intra-luminal filling defect in alobar or main pulmonary arteryVentilationperfusion scan: high-probabilityscan and moderate/high clinical probabilityDiagnostic tests for DVT: evidence of acuteDVT with non-diagnostic ventilation perfusion scan or helical CT


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SUMMARYSUMMARYy PE IS EXCLUDED BY:

Pulmonary angiogram: normalPerfusion scan: normalD-dimer test: normal test with a very high

sensitivity( 98%) & at least moderate specificity (40%)Normal D-dimer that has at least moderately highsensitivity ( 85%) and specificity ( 70%) ANDx (a) low clinical suspicion for PE ORx (b) normal alveolar dead space fractionNon-diagnostic VQS or normal helical CT, and normalproximal venous ultrasound scans ANDx (a) low clinical suspicion for PE ORx (b) normal D-dimer test that has at least moderately high

sensitivity ( 85%) and specificity ( 70%)


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QUESTIONSQUESTIONS


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TAKETAKE HOME MESSAGEHOME MESSAGEy When individual tests are non-

diagnostic, it is possible to

combine their results to confirmor exclude pulmonary embolism

y Assessment of clinical probabilityis of vital importance

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Diagnosis of Pulmonary Embolus Edited