Interpretation pitfalls of vascular laboratory testing

doi:10.1053/j.semvascsurg.2013.11.004

Seminars in Vascular Surgery

Volume 26, Issues 2–3, June–September 2013, Pages 67-71

https://doi.org/10.1053/j.semvascsurg.2013.11.004 Get rights and content

Abstract

Vascular laboratory testing of patients with arterial and venous disease requires a thorough understanding of the diagnostic instrumentation, anatomy, and blood flow hemodynamics. Diagnostic testing typically uses both Doppler ultrasound, especially duplex ultrasonography, alone or in combination with air plethysmography, to identify and classify vascular disease. In patients with symptomatic peripheral vascular disease, clinical evaluation is enhanced by noninvasive testing, and for many patients can provide sufficient information to proceed with medical treatment or intervention without additional confirmatory imaging studies. The diagnostic accuracy of vascular testing depends on the precision and reproducibility of the measurement (eg, pressure, pulse contour, blood flow velocity, or volume flow rate). For example, the measurement of ankle systolic blood pressure cannot always be assumed to be accurate because the test result can be affected by a number of factors, including biological variability, cuff size and placement, examiner skill, or the presence of tibial artery calcification preventing cuff occlusion. Interpretation of all vascular diagnostic testing requires an appreciation of the limitations, pitfalls, and artifacts of the testing modality. Interpretation errors can result in an incorrect diagnosis and subsequent decision making.

Section snippets

Classification of interpretation errors

Diagnostic errors associated with vascular laboratory testing can occur from procedural, interpretative, or statistical pitfalls. Procedural pitfalls result from deviation of the testing protocol, the instrumentation used, or variability of the biophysical property of the circulation measured. Interpretative pitfalls occur when the physicians does not correct apply appropriate diagnostic criteria or uses criteria that have not been correlated with a recognized gold standard, such as

Optimizing interpretation accuracy

Vascular laboratory testing, particularly duplex ultrasound, is a valuable clinical tool for the detection of common and uncommon vascular conditions. Diagnostic accuracy is dependent on examiner experience, use of testing protocols, and interpretation criteria applied appropriately. All testing should address the clinical indication and the examination tailored to provide the assessment of disease location, extent, and severity. The study interpretation should be relevant to the individual

Example questions:

1. The results of 180 carotid duplex studies correlated with cerebral angiography for the diagnosis of >70% ICA stenosis are shown in the table:

Carotid duplex	Arteriography
Carotid duplex	<70%	>70%
<70%	104	14
>70%	12	50

The correct measure of test accuracy is:

A. The positive predictive value is 104 / (104 + 12) = 89%

B. The sensitivity is 104 / (104+50) = 67%

C. The specificity is 50 / (50+12) = 81%

D. The accuracy is 154 / 180 = 86%

Answer:

2. An ultrasound study that produced no false-positive results compared with the

Answers to questions:

1. D

2. D

3. A

4. A

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D.J. Wright et al.
Pitfalls in lower extremity venous duplex testing
J Vasc Surg
(1990)
D.F. Leotta et al.
Physics and instrumentation for duplex scanning

There are more references available in the full text version of this article.

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In this high-risk and increasingly prevalent group, the loss of patency is often poorly tolerated and the window for successful limb preservation is more narrow. The assessment of anatomic patency using noninvasive imaging modalities, particularly for IP arteries, has known limitations.37,38 The accuracy of hemodynamic assessment using ABI and toe pressures may be impaired by vessel calcification or prior forefoot amputations.
In 2019, the Global Vascular Guidelines on chronic limb-threatening ischemia (CLTI) introduced the concept of limb-based patency (LBP) defined as maintained patency of a target artery pathway after intervention. The purpose of this study was to investigate the relationship between LBP and major adverse limb events (MALE) after infrainguinal revascularization for CLTI.
Consecutive patients undergoing revascularization for CLTI between 2016 and 2019 at a single tertiary institution with a dedicated limb preservation team were included. Subjects with aortoiliac disease, prior infrainguinal stents, or existing bypass grafts were excluded. Demographics, Global Limb Anatomic Staging System scores, Wound, Ischemia, foot Infection (WIfI) stages, revascularization details, and limb-specific outcomes were reviewed. LBP was defined by the absence of reintervention, occlusion, critical stenosis (>70%), or hemodynamic compromise with ongoing symptoms of CLTI. MALE included thrombectomy or thrombolysis, new bypass, open surgical graft revision and/or major amputation.
We analyzed 184 unique limbs in 163 patients. This cohort was composed of 66.9% male patients with a mean age of 72 years. Baseline characteristics included diabetes (66%), tissue loss (91%), and advanced WIfI stages (30% stage 3, 51% stage 4). Global Limb Anatomic Staging System stage 3 anatomic patterns were common (n = 119 [65%]). Sixty limbs were treated with open bypass (65% involving tibial targets) and 124 underwent endovascular intervention (70% including infrapopliteal targets). The 12-month freedom from MALE and loss of LBP were 74.0% ± 3.7% and 48.6% ± 4.2%, respectively. Diabetes (hazard ratio [HR], 2.56; 95% confidence interval [CI], 1.13-5.83; P = .025) and loss of LBP (HR, 4.12; 95% CI, 1.96-8.64; P < .001) were independent predictors of MALE in a Cox proportional hazard model. Loss of LBP was the sole independent predictor of major limb amputation after revascularization (HR, 4.97; 95% CI, 1.89-13.09; P = .001). Loss of LBP impacted both intermediate-risk limbs (HR, 2.85; 95% CI, 1.02-7.97; P = .047 in WIfI stages 1-3) and high-risk limbs (HR, 3.99; 95% CI, 1.32-12.11; P = .014 in WIfI stage 4). However, the loss of LBP had the greatest impact on patients presenting with WIfI stage 4 disease (31% vs 8% major limb amputation at 12 months in limbs without vs with maintained LBP).
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Acquiring knowledge in this area of vascular medicine is beyond that learned in medical school or general surgery training, and thus a core curriculum is required to ensure competency in the clinical application of vascular testing and its interpretation during a 2-year 5+2 fellowship or the integrated 0+5 residency. In the June–September 2013 issue of Seminars in Vascular Surgery [1], an in-depth discussion of interpretation criteria in the areas of arterial and venous testing was provided, as well as a review of ultrasound instrumentation and physics. Vascular surgery trainees can use this primer of vascular laboratory test interpretation to assess their competence by reviewing the questions that accompany each article.
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