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Three Part Question

In [patients who have undergone ventilation-perfusions scans for possible pulmonary embolus] does [combining clinical probability of pulmonary embolism and [ventilation–perfusion scan result] increase the [diagnostic utility]?

Clinical Scenario

A 20 year old woman presents to the emergency department with shortness of breath and chest pain. Her D-dimer level is abnormal and you have sent her for a ventilation-perfusion scan. The scan result is reported as "low probability for pulmonary embolic disease, however this does not rule out pulmonary embolism". You have assigned her a low clinical probability of pulmonary embolism score and wonder if this helps interpret the scan.

Search Strategy

Medline 1966–07/03 using the OVID interface.
[exp pulmonary embolism/ OR pulmonary embol$.mp. OR PE.mp. OR exp thromboembolism/ OR pulmonary infarct$.mp.] AND [exp nuclear medicine/ OR exp ventilation-perfusion ratio/ OR ventilation-perfusion.mp. OR ventilation perfusion.mp. OR VQ.mp. OR lung scan.mp.] AND [exp Risk Assessment/ OR risk assessment.mp. OR risk stratification.mp. OR probability.mp] LIMIT to human AND English.

Search Outcome

387 papers found of which 6 addressed the question and are shown in the table below.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
PIOPED investigators, 1990, USA	931 ?PE patients at 6 centres. All underwent clinical probability scoring, VQ scan and pulmonary angiogram. 69 patients with normal VQs and 106 others did not undergo the pulmonary angiogram All followed up clinically for a year	Prospective diagnostic study	Accuracy of combining clinical probability with VQ scan results	High probability VQ scans -with high clinical probability 28/29 had PE -with moderate clinical probability 70/80 had PE Normal VQ scans - 5/128 PEs regardless of clinical probability Low probability VQ scan -with low clinical probability 4/90 had PE No other combination was diagnostic	Only 30% patients were from the emergency department Subjective clinical probability score assigned by clinicians Radiologists not blinded to VQ scan results when interpreting pulmonary angiograms
Miniati M et al, 1996, Italy	890 patients ?PE had a perfusion scan. 413 of 670 patients with abnormal perfusion scan had a pulmonary angiogram. All abnormal perfusion scan patients were followed up for 1 year	Prospective diagnostic study	Accuracy of combining clinical probability with Q scan results	Q scans compatible with PE -with high clinical probability 222/225 had PE -with moderate clinical probability 70/75 had PE Abnormal Q scans not compatible with PE -with low clinical probability 4/127 had PE No other combination was diagnostic	Only 13% patients were from the emergency department Patients with normal/near normal perfusion scans were not followed up after discharge Physicians rated clinical probability of PE subjectively
Wells PS et al, 1998, Canada	1239 patients ?PE underwent a clinical probability assessment, VQ scan +/- serial Doppler scans All patients negative for PE were followed up clinically for 3 months	Management study	Accuracy of combining clinical probability with VQ scan results	Normal VQ scans - 4/334 had PE/DVT regardless of clinical probability Low/intermediate probability VQ scan - 13/454 with low clinical probability had PE/DVT No other combination was diagnostic	Complex clinical probabiliry scoring system
Perrier A et al, 2000, Quebec and Geneva	180 patients from 2 centres with nondiagnsotic (low and intermediate probability) lung scan and low clinical probability, followed up for 3 months	Prospective management study	3 month outcome of patients with low clinical probability and non-diagnostic VQ scan	8/175 patients had DVT/PE diagnosed.4.4% false negative rate False negative rate lowered to 1.7% when serial Doppler ultrasound carried out on all patients	Physicians rated clinical probability of PE subjectively Patients presenting with symptoms of DVT were excluded
Barghouth G et al, 2000, Switzerland	143 consecutive ?PE patients in acute medical ward. 9 lost to follow up excluded Decision algorhythm used to isolate those requiring pulmonary angiogram, based on VQ scan result and clinical probability score	Retrospective mangement study	Number of pulmonary angiograms ordered	20% patients	Subjective clinical probability score assigned by clinicians Decision algrhythm not detailed 8 patients were anticoagulated for reasons other than DVT/PE during follow up Follow up not robust and carried out retrospectively
			Number of recurrenct thromboembolic events in next 2 years	4 DVTs diagnosed in patients without diagnosis of PE (101 total) - ?false negatives. No further events
Nilsson T et al, 2001, Sweden	170 ?PE patients 1991-1994 All had clinical probability score, Q or VQ scan, pulmonary angiogram, and 6 month follow up	Prospective diagnostic study	Accuracy of combining clinical probability with Q or VQ scan results	High probability VQ scans -with high clinical probability 17/17 had PE -with moderate clinical probability 10/10 had PE Normal VQ scans -0/27 PEs regardless of clinical probability Low probability VQ scan -with low clinical probability 1/34 had PE No other combination was diagnostic	Physicians used a visual analogue scale (VAS) rather than objective clinical probability score Nuclear physicians used PIOPED criteria to report VQ scans but then went on to give subjective VAS result as probability PE No description of follow up methodology or completion

Clinical Bottom Line

All ventilation-perfusion scans must be interpreted with an independent clinical probability score.

References

1. The Pioped Investigators. Value of the Ventilation/Perfusion Scan In Acute Pulmonary Embolism JAMA 1990;263(20):2753-59.
2. Miniati M, Pistolesi M, Marini C, et al. Value of perfusion lung scan in the diagnosis of pulmonary embolism: results of the Prospective Investigative Study of Acute Pulmonary Embolism Diagnosis (PISA-PED) Am J Respir Crit Care Med 1996;154:1387-93.
3. Wells PS, Ginsberg JS, Anderson DR, et al. Use of a Clinical Model for Safe Management of Patients with Suspected Pulmonary Embolism. Ann Intern Med 1998;129(12):997-1005.
4. Perrier A, Miron MJ, Desmarais S, et al. Using clinical evaluation and lung scan to rule out suspected pulmonary embolism: Is it a valid option in patients with normal results of lower-limb venous compression ultrasonography? Arch Intern Med 2000;160:512-6.
5. Barghouth G, Yersin B, Boubaker A, et al. Combination of clinical and V/Q scan assessment for the diagnosis of pulmonary embolism: a 2-year outcome prospective study. Eur J Nucl Med 2000;27:1280-5.
6. Nilsson T, Mare K, Carlsson A. Value of structured clinical and scintigraphic protocols in acute pulmonary embolism. J Intern Med 2001;250:213-8.