new diagnostic approaches for suspected pulmonary embolism
TRANSCRIPT
New Diagnostic Approaches
for Suspected Pulmonary Embolism
New Diagnostic Approaches for Suspected Pulmonary Embolism (PE) : Lecture Outline
ƒ Arterial blood gases (ABG's)ƒ D-Dimer assayƒ Plasma DNA assayƒ Spiral Computed Tomography
(CT)ƒ Electron Beam CTƒ Magnetic Resonance Imaging
(MRI)ƒ Transesophageal
echocardiography (TEE)
Utility of ABG's in PE Cases
ƒ Normal alveolar / arterial (A-a) gradient occurs in 10 to 23 % of PE cases–As high as 38 % in those without prior cardiopulmonary disease
ƒ Can have increased A-a gradient from pneumonia, COPD, etc.
ƒ Positive predictive value < 50 %ƒ So, ABG is really useless to rule in or
out PE–Don't obtain unless needed for other reasons
Use of D-Dimer Assay for PE Cases
ƒ Is specific degradation product of cross-linked fibrin
ƒ Found in acute thrombotic conditions :–PE, Deep Venous Thrombosis (DVT)–Hepatic insufficiency (cirrhosis)–Malignant neoplasms–Recent trauma or surgery–Preeclampsia–Sepsis
D-Dimer Assays
ƒ ELISA–Uses monoclonal antibodies against D-dimer– Colorimetric, quantitative result–Cumbersome, requires trained lab personnel, slow to get results–Sensitivity & neg. predictive value > 90 %–Poor specificity (30 to 50 %)–Lack of standardized calibration between different types of tests
D-Dimer Assays (cont.)
ƒ Latex Agglutination (LA)–4 commercially available types–Use latex particles coated with monoclonal antibodies to D-dimer, which agglutinate with plasma containing > a preset D-dimer level–Must be done in lab but are quick–Sensitivity poorer than ELISA (47 to 92 %)–Low specificity (48 to 60 %)–Negative predictive value (89 %) too low to be clinically useful
New Rapid D-Dimer Assays
ƒ SimpliRED–Can be done in 5 minutes at bedside–Sensitivity 94 % (similar to ELISA) in one study but later study showed higher miss rate
ƒ NYCO-CARD –Uses plasma so must be done in lab, but is quick–Sensitivity 88 to 92 %–Needs more study to decide if really as sensitive as ELISA
Conclusions About Use of D-Dimer Assays for PE Dx
ƒ Since levels decrease from event of onset, are not reliable if testing delayed
ƒ More specific in patients without comorbid conditions
ƒ If negative, may be used to avoid further testing (angio) in patients with low clinical suspicion and indeterminate screening radiologic tests (V/Q or spiral CT scan )
Use of Plasma DNA Assay to Dx PE
ƒ Uses counterimmunoelectrophoresis with serum from SLE patients containing antibodies to DNA
ƒ Circulating DNA found in PE patientsƒ Sensitivity for PE 82 % & specificity
85 % in one study of 49 casesƒ No standardized inter-lab kit
availableƒ Reduced sensitivity with time from
event (if Sx > 7 days)
Use of Plasma DNA Assay (cont.)
ƒ Positive in many other conditions :–Major surgery or burns–Corticosteroid Rx–Hemodialysis–Chemotherapy–Active SLE–Sickle cell crisis–Liver failure
Conclusions About Use of DNA Assays for Dx of PE
ƒ Not as sensitive as D-Dimerƒ Same confounding false positive
factors as D-dimerƒ Not generally clinically useful at
this time
Use of Spiral CT for Dx of PE
ƒ First reported in 1992ƒ Most studies done so far show
sensitivity for central pulmonary artery clots > 90 %
ƒ Less sensitive for subsegmental clots (63 to 80 %)
ƒ Can make alternative Dx in some patients
ƒ Requires alteration of CT technique for most accurate (sensitive) results
Changes in CT Technique Needed for Accuracy in Dx of PE by Spiral CT
ƒ Must first get noncontrast scan of thoraxƒ Contrast must be scanned at first pass
thru pulm. arteryƒ Must use rapid power injection of contrastƒ 20 second breath hold allows best
visualization of segmental arteriesƒ Must be careful not to misinterpret hilar
nodes as intraluminal clot
Spiral computed tomography scan showing clots in the anterior
segmental artery of the right upper lobe
Embolus in the right pulmonary artery ; curved arrows show a previously known esophageal cancer
Filling defects (clots) in the interlobar pulmonary arteries
“Saddle” pulmonary embolus
Embolus in anterior left upper lobe segmental artery
Scan of same patient 5 weeks later (on Coumadin) showing complete clot resolution
Spiral CT showing distal clot in the left lower lobe
Advantages of Spiral CT to Dx PE
ƒ Less expensive than angiographyƒ Short time for scanƒ Can be done on relatively unstable
patientsƒ Uses less contrast than angioƒ Can find other thoracic Dx'sƒ No mortalities reported from
procedureƒ Close to 100 % sensitivity for
clinically significant PE's
Electron Beam CT for Dx of PE
ƒ Studies so far show about same sensitivity as for spiral CT (> 90 %)
ƒ False negative for some peripheral subsegmental clots (same as for spiral CT)
ƒ No cross comparison reports versus spiral CT yet
Magnetic Resonance Imaging (MRI) for Dx of PE
ƒ About same sensitivity as spiral CT
ƒ May also miss subsegmental clots
ƒ Does not require iodine based contrast
ƒ MRI has high accuracy for leg DVT, so combined leg and chest scan may prove useful for some patients
ƒ Currently usually more expensive than spiral CT
Transesophageal Echocardiography (TEE) for Dx of PE
ƒ Sensitivity is 58 to > 80 % for central clots
ƒ May miss clot on one side when bilateral
ƒ Can be done even during CPRƒ Can be done on patients who
cannot be moved for other studiesƒ Dependent on operator skill
Transesophageal echo showing snake-like pulmonary embolus (TH)
Comments on Pulmonary Angiographyƒ PIOPED study reported :
–Mortality 0.5 %–Major complications in 1.0 %–Minor complications in 5 %
ƒ However, current use of smaller catheters (5F instead of 6 to 7 F) and nonionic contrast may be making this safer than previously reported
ƒ Low agreement (k = 0.4 to 0.5) between different radiologists in interpretation of subsegmental clots
Proposed Diagnosis Sequence for Suspected PE
First, Spiral CT
Positive
Treat for PE
Negative
Doppler US of legs
D-Dimer
PositiveNegative
Indeterminate
Positive
Negative
Stop
StopConsider MRI or angio
Another proposed workup algorithm
Conclusions About Spiral CT Use in Suspected PE
ƒ Fewer indeterminate results than V/ Q scan
ƒ Because of the lack of interobserver consistency in interpreting peripheral clots on pulmonary angios, accuracy of spiral CT may be close to that of angio
ƒ Spiral CT is cheaper, faster, and has less complications than angio
ƒ Combination scheme of spiral CT and leg US shown cost-effective
Conclusions About Use of Other Modalities in Dx of PE
ƒ D-Dimer only helpful if negative–Then may help exclude PE & obviate further testing in low suspicion patients already screened by V/Q or spiral CT
ƒ DNA assay not useful yetƒ TEE may be tried first in the unstable patient
–Will need additional study if negativeƒ Electron beam CT technique probably equivalent
to spiral CTƒ Some false negatives relative to angio in prior
reports may reflect the often extended time period between the 2 studies compared
Further Studies Needed on Dx of PE
ƒ Determine sensitivity of newer D-Dimer tests in larger groups of patients with proven PE
ƒ Followup studies to determine safety of schemes involving stopping workup short of angio
ƒ Redetermine current complication rates for angio