The comparative value of noninvasive testing for diagnosis and surveillance of deep vein thrombosis

Meta-analysis of plethysmography and rheography in the diagnosis of deep vein thrombosis

BACKGROUND

Plethysmography and rheography techniques have been widely studied as diagnostic tests for deep vein thrombosis (DVT). This study aimed to systematically review the accuracy of these tests for diagnosing clinically suspected DVT.

METHODS

The following databases were searched: Medline, EMBASE, CINAHL, Web of Science, Cochrane Database of Systematic Reviews, Cochrane Controlled Trials Register, Database of Reviews of Effectiveness, the ACP Journal Club (1966 to 2004), and citation lists of retrieved articles. Studies that compared plethysmography or rheography to a reference standard of ultrasound or contrast venography were selected. Standardised data were extracted and study quality determined against validated criteria. Data were analysed by random effects meta-analysis and meta-regression.

RESULTS

The meta-analysis included 78 studies, reporting 82 patient cohorts. Sensitivity and specificity (95% CI) were: 75% (73% to 77%) and 90% (89% to 91%) for impedance plethysmography, 83% (81% to 85%) and 81% (79% to 82%) for strain-gauge plethysmography, 85% (79% to 90%) and 91% (81% to 95%) for air plethysmography, 91% (87% to 94%) and 71% (66% to 75%) for light-reflex rheography, and 86% (83% to 89%) and 93% (91% to 95%) for phleborheography. Meta-regression was limited by poor reporting of studies. There was some evidence that diagnostic performance depended on the proportion of males in the cohort and reporting of study setting.

CONCLUSIONS

Although plethysmography and rheography techniques add diagnostic value, they have inadequate diagnostic performance to act as a stand-alone test in DVT diagnosis. Evaluation of their role in combination with other tests, or standardised clinical assessment, is required.

The relationship between acute ischaemic stroke and plasma D-dimer levels in patients developing neither venous thromboembolism nor major intercurrent illness

The true relationship between plasma D-dimers and acute ischaemic stroke (AIS) is uncertain as previous studies investigating this have not screened for subclinical deep vein thrombosis. We addressed this as part of a study in which we screened AIS patients for venous thromboembolism (VTE). We also assessed the performance characteristics of two D-dimer assays as exclusionary tests for VTE in these patients. One hundred and two unselected AIS patients were screened for VTE using magnetic resonance direct thrombus imaging. D-dimers were analysed on days 2, 9, 14 and 21 using the VIDAS immunofluorescent assay (cut-off >or= 500 ng/ml) and the IL test D-dimer immunoturbidimetric assay (cut-off >or= 255 ng/ml). The relationship between D-dimers and AIS was examined in 52 patients neither developing VTE nor intercurrent illness. D-dimers were elevated throughout the study. Median values at the four time points were 652, 692, 737 and 686 ng/ml (VIDAS assay) and 260.5, 268.5, 273 and 283 ng/ml (IL assay). D-dimers were higher in patients aged older than 70 years, with severe stroke or with total anterior circulation infarcts: only age older than 70 years was significantly associated with D-dimer values greater than the median on univariate and multivariable analysis. Both assays were 100% sensitive for VTE. Specificities were 30% (VIDAS assay) and 34% (IL assay). Specificity was adversely affected by age older than 70 and severe versus non-severe stroke. D-dimers are elevated in the first 3 weeks post-AIS after eliminating the confounding effect of subclinical deep vein thrombosis. The VIDAS and IL assays remained sensitive tests for VTE but the specificity was low, limiting their exclusionary efficiency in these patients.

Do anticoagulants improve survival in patients presenting with venous thromboembolism?

Anticoagulants have been available since around 1940 and have become the standard of treatment for venous thromboembolism (VTE) for over four decades. However, as with other treatments which became established before the evidence-based era, there is a paucity of evidence from randomized controlled trials validating their effectiveness in preventing the most feared complication of VTE, recurrent fatal pulmonary embolism (PE). Only two such trials have been performed, the results of which conflict. The bulk of data supporting their use are derived from three sources. First, studies of thromboprophylaxis, and comparisons of shorter and longer courses of anticoagulants in high-risk patients with established VTE have clearly demonstrated their effectiveness in primary and late secondary prevention. Given that heparin has an immediate onset of action, anticoagulants should therefore also be effective in early secondary prevention, the proposed mechanism of action in the acute treatment of VTE. Secondly, studies of inadequately treated patients have consistently shown higher recurrence rates than in those adequately treated. Finally, comparisons of outcomes in untreated and treated historical series, and of untreated historical series to treated series in the modern era have shown substantially lower rates of fatal PE in anticoagulated patients. Because these differences are so marked, harmonize with our current understanding of the mechanism of action of anticoagulants and are supported by other evidence, it is much more likely that they at least partly reflect the effectiveness of anticoagulants as opposed to being explicable purely in terms of accumulated biases and a changing distribution of disease severity.

Developments in diagnosis and classification of venous disorders: non-invasive diagnosis

PURPOSE

This review examines the many techniques that have been used for the non-invasive diagnosis of acute and chronic venous disease and was conducted by members of the Committee on Research of the American Venous Forum. It proposes to identify those techniques with the greatest clinical potential, to suggest algorithms for the clinical application of non-invasive techniques in the identification of acute deep venous thrombosis and chronic venous insufficiency, and to identify areas of deficient knowledge and potential areas for future research initiatives.

METHODS

Review of pertinent clinical and research material.

RESULTS

Impedance plethysmography and ultrasonic imaging are the primary non-invasive tools used in the diagnosis of acute deep venous thrombosis. At present, ultrasonic imaging techniques are recommended on the basis of greater diagnostic accuracy in recent comparative clinical trials. Data would suggest that serial evaluation should probably be viewed as the preferred option for symptomatic patients with a negative initial examination and the presence of risk factors or physical findings suggesting a proximal deep venous obstruction/thrombosis. Chronic venous disease is the result of valvular incompetence, with or without associated venous obstruction. Duplex imaging can be used to determine the location and extent of reflux; however, there are reported procedural variations in the performance and interpretation of such studies. Recent innovations in air plethysmography may provide a means of quantifying volume changes, and permit an objective characterization of venous reflux and calf pump efficiency.

CONCLUSIONS

There are still significant questions that need to be answered by well-designed research initiatives. Research applications that incorporate non-invasive diagnostic techniques may involve the diagnosis, treatment and natural history of acute deep venous obstruction/thrombosis and chronic venous insufficiency, assessment prior to and following venous reconstruction, and the basic science aspects of acute and chronic venous disease. At present, a lack of common standards is, by far, the greatest impediment to an organized research approach to venous disease.

The diagnosis of deep vein thrombosis in the multiply injured patient with pelvic ring or acetabular fractures

Thirty-one patients with unstable displaced pelvic or acetabular fractures were admitted and underwent an open reduction and internal fixation of their fracture. All patients were studied prospectively for the incidence of proximal deep vein thrombosis (DVT) utilizing venous duplex ultrasound. Duplex scans were repeated at 1 week postoperatively in all patients. Additional scans were performed when clinically indicated. A total of 61 scans were completed. DVT developed in three patients (approximately 10%). Two of the three positive scans were noted only on postoperative examination. The third scan was positive on the preoperative phase. Duplex ultrasound was easily applied and well tolerated by the multiply injured patient.

A comparison of subcutaneous low-molecular-weight heparin with warfarin sodium for prophylaxis against deep-vein thrombosis after hip or knee implantation

BACKGROUND

Deep-vein thrombosis is a potentially life-threatening complication of total hip or knee replacement. There are few data on the effectiveness and safety of warfarin as compared with low-molecular-weight heparin as prophylaxis against this problem.

METHODS

We therefore performed a randomized, double-blind trial in 1436 patients to evaluate the effectiveness and safety of low-molecular-weight heparin (given subcutaneously once daily) as compared with adjusted-dose warfarin to prevent venous thrombosis after hip or knee replacement. Treatment with the drugs was started postoperatively. The primary end point was deep-vein thrombosis as detected by contrast venography (performed a mean of 9.4 days after surgery in each group).

RESULTS

Among the 1207 patients with interpretable venograms, 231 of 617 patients (37.4 percent) in the warfarin group and 185 of 590 patients (31.4 percent) in the low-molecular-weight-heparin group had deep-vein thrombosis (P = 0.03). The reduction in risk with low-molecular-weight heparin as compared with warfarin was 16 percent, and the absolute difference in the incidence of venous thrombosis was 6 percent in favor of low-molecular-weight heparin (95 percent confidence interval, 0.8 to 11.4 percent). The incidence of major bleeding was 1.2 percent (9 of 721 patients) in the warfarin group and 2.8 percent (20 of 715 patients) in the low-molecular-weight-heparin group (P = 0.04), and the absolute difference was 1.5 percent in favor of warfarin (95 percent confidence interval, 0.1 to 3.0 percent).

CONCLUSIONS

Our data demonstrate that the small reduction in the incidence of venous thrombosis with low-molecular-weight heparin, as compared with warfarin, was offset by an increase in bleeding complications. Although the use of low-molecular-weight heparin is simpler, because it is administered subcutaneously without the need for monitoring, it may be more costly than warfarin. Warfarin is inexpensive, but the overall cost of its use is increased by the need to monitor the intensity of anticoagulation. At this time it is unclear which of these approaches is the most cost effective.

Noninvasive vascular laboratory in clinical practice

Noninvasive vascular testing methods have validated application in the evaluation of patients with suspected peripheral arterial, cerebrovascular, or peripheral venous disease. Accurate and reproducible testing requires the use of appropriate instrumentation by experienced technologists, and interpretation of data with verified diagnostic criteria. Noninvasive testing can facilitate clinical decision-making by providing quantitative anatomical and hemodynamic data, thereby quantifying functional severity of disease. Duplex ultrasonography is essential instrumentation for cerebrovascular testing to localize and grade occlusive lesions. In peripheral arterial testing, the combination of segmental pressure measurements and waveform (velocity, pulse pressure) analysis should be the initial diagnostic method, with duplex scanning reserved for characterizing hemodynamically abnormal arterial segments. A number of techniques (duplex scanning, B-mode imaging supplemented by Doppler, venous outflow plethysmography) are appropriate for assessing the venous system for thrombosis, structural abnormalities, and venous valve function. Physicians should be aware of the pitfalls of noninvasive vascular testing and confirm equivocal studies using "gold standard" diagnostic methods such as arteriography and contrast venography.