Diagnosis of VTE

Question 1

What is the Wells Score?

Answer 1

A clinical model for predicting the pre-test probability (ultrasound) of a DVT
Generates a score: >2 likely, <2 unlikely
e.g Active cancer, immobility, surgery, tenderness, swelling, pitting oedema, superficial veins, previous DVT, alternative diagnosis likely (-2)

Question 2

What is the evidence for the Wells score?

Answer 2

Wells et al, 1997
600 patients assessed, given a wells score and then given ultrasonography
-Showed that SIGNIFICANT numbers of patients with high Wells score DID have a DVT (75%)
-very few patients with low wells scores had DVT (3%)
*shows wells score has a LOW false negative
*Showed a significant decrease in the amount of imaging required was feasible and safe using the wells score

Question 3

Why are only certain clinical features included in the Wells Score?

Answer 3

Wells et al, 1995:
Was found that extra clinical features such as age, sex, symptom duration, erythema, hospital admission etc were NOT significantly associated with DVT upon stepwise logistic regression

Question 4

What is modern day practice for DVT diagnosis?

Answer 4

1. Assessment
2. Wells Score
3. D-Dimer test dependent on the results of the Wells Score-a D-dimer test is performed if the wells score <2
4. If wells score is >2, Ultrasound or parenteral anticoagulation until ultrasound is performed

Question 5

What is D-Dimer?

Answer 5

D-dimers are specific degradation products of cross-linked fibrin that released when endogenous fibrinolytic systems attack the fibrin mesh of a VTE
-The absence of a raised concentration of D-dimer implies there is no fresh thromboembolic material undergoing dissolution in the deep veins or pulmonary tree

Question 6

What is the evidence for the D-dimer test?

Answer 6

Wells et al, 2003:
1000 patients with suspected DVT
-Patients given a Wells score, >2 likely, <2 unlikely
-Split into two arms:
1. control
2. Received D-dimer test

Very low numbers of patients who received d-dimer but were ruled out of DVT due to negative result actually had a DVT = high negative predictive value 96.1%
Shows that D-dimer is a safe and feasible way of selecting patients for ultrasound
A low wells score and negative D-dimer can safely exclude DVTs

Question 7

What are some restrictions of the D-dimer test?

Answer 7

Has high sensitivity but low specificity
Can be falsely raised because of:
-pregnancy
-liver disease
-recent trauma/surgery

Question 8

What is the protocol for leg vein ultrasound?

Answer 8

Only the proximal veins are surveyed.
If a calf vein DVT is suspected, Wells and D-Dimer should be repeated
If a DVT is present on Ultrasound, the vein will not compress and it will not be pulsatile which differentiates it from an artery. *Sonographic material of a DVT may not develop until 5/6 days

Question 9

What is the protocol for P.E diagnosis?

Answer 9

1. History and examination
2. CXR-to rule out other causes of breathlessness
   -but 40% of P.E x-rays are normal
3. 2-level wells score
   -Signs and symptoms of DVT
   -Alternative diagnosis likely (-2)
   -HR >100
   -Immobilisation
   -Previous DVT/P.E
   -Haemoptysis
   -Malignancy
   >4 likely, <4 unlikely

> 4= CTPA, <4 = D-dimer

Question 10

What is CTPA?

Answer 10

Visualisation of the pulmonary arteries using radiocontrast and CT-highlights any defects in vasculature filling

Question 11

What is the evidence for using CTPA?

Answer 11

PIOPEDII Trial, 2006:
800 patients-CTPA versus standard VQ/CXR
-Sensitivity and specificity of CTPA shown to be very high
-But the study showed that the high accuracies of CTPA only occurred with high clinical probability, so for low scores CTPA is less useful (probably related to size of thrombus and how easy it is to visualise)

Question 12

What is VQ Scanning?

Answer 12

Ventilation Perfusion Mismatch Scanning

• radioisotope contrast and aerosols so perfusion and ventilation can be assessed
• Any areas ventilated but not perfused = P.E

Question 13

CTPA versus VQ:

Answer 13

CTPA has wider availability and can show other causes of symptoms

• Easier to detect smaller clots in smaller vessels on CTPA
• VQ useful in renal failure or contrast allergy
• BOTH tests have SIMILAR DIAGNOSTIC ACCURACIES
• VQ = 65 CXR, CTPA = 400 CXR

Question 14

Evidence for favouring CTPA:

Answer 14

Anderson et al, 2007:
demonstrated that CTPA, Wells Score clinical probability and D-dimer was NOT inferior to VQ scanning
-CTPA produced a greater number of diagnoses than VQ
-But PIOPEDII showed that CTPA had lots of false negatives in the peripheral lung fields so this may explain the higher number of CTPA diagnoses in the anderson study

Question 15

Other tests used in P.E diagnosis:

Answer 15

ECG = S1Q3T3 - but not very specific as only seen in 20%, sinus tachycardia is much more common
ABG = hypoxia and hypocapnoea
ECHO = right heart strain-useful in haemodynamically unstable patients to do at the bedside