Acute Pulmonary Embolism: Focus on the Clinical Picture

Acute pulmonary embolism (APE) is characterized by numerous clinical manifestations which are the result of a complex interplay between different organs; the symptoms are therefore various and part of a complex clinical picture. For this reason, it may not be easy to make an immediate diagnosis. This is a comprehensive review of the literature on all the various clinical pictures in order to help physicians to promptly recognize this clinical condition, remembering that our leading role as cardiologists depends on and is influenced by our knowledge and working methods.

Deep venous thrombosis in spine surgery patients: incidence and hematoma formation

Deep venous thrombosis (DVT) is a significant health care problem; a variety of factors place spinal surgery patients at high risk for DVT. Our aim is to define the incidence of DVT occurrence in spite of prophylactic measures (mechanical and chemoprophylaxis), and the development of spinal epidural hematoma as a complication of chemoprophylaxis. In a single-center prospective study, 158 patients who underwent spinal surgical procedures were evaluated by clinical evaluation and lower limb Doppler ultrasonography imaging. Only one patient (0.6%) developed DVT; this patient was treated successfully without thrombus progression, with full recanalization. Three patients (1.8%) developed spinal epidural hematoma, but only one required surgical evacuation, and none sustained neurologic deficit. Careful evaluation for DVT risk on an individual basis and good prophylaxis helps to minimize the risk of DVT. The neurosurgeon is thus left to weigh the risks of postoperative hematoma formation against the benefits of protecting against DVT.

Interventional therapies for venous thromboembolism: vena caval interruption, surgical embolectomy, and catheter-directed interventions

Therapeutic strategies other than anticoagulation sometimes require consideration in the setting of acute venous thromboembolism. Vena caval filter placement is increasingly common, in part because of the availability of nonpermanent filter devices. Filter placement, surgical embolectomy, and catheter embolectomy have not been subjected to the same prospective, randomized clinical trial scrutiny as anticoagulation but seem appropriate in certain clinical settings. The indications, contraindications, and available data supporting these therapeutic methods are discussed.

Attenuation correction for lung SPECT: evidence of need and validation of an attenuation map derived from the emission data

PURPOSE

The aim of our study was to investigate the importance of attenuation correction (AC) in reconstructed and reprojected images on lung SPECT studies.

METHODS

Simulation studies were undertaken to evaluate the influence of AC on defect-to-normal ratios (D/N), to demonstrate the influence of errors in the correction map values and to detect lung boundaries used for AC. The use of a synthetic map (SM) for AC of the clinical data was also evaluated and the results compared with those obtained with data derived from CT (CTM). Additionally, the role of AC in reprojected SPECT data was assessed and level of noise on the 'planar-like' images was measured.

RESULTS

Phantom studies showed that AC markedly affects the D/N ratio. However, variations in micro values typical of those found in clinical studies resulted in relatively small changes in results. Eroded and dilated conditions did not cause any significant effect on D/N. The level of noise in the reprojected images is reduced in comparison with real planar data. Clinical SPECT/CT data reconstructed with AC using CTM and SM showed an excellent correlation between the two methods.

CONCLUSION

AC improves D/N in lung SPECT studies, thus potentially enhancing the diagnostic capability of the method. The use of a synthetic map for AC is feasible, avoiding the need for an additional procedure and the increased radiation dose involved. Planar-like images generated from reprojected SPECT data are well matched to normal planar images provided AC is performed and attenuation included in the reprojection.

Referent d-dimer enzyme-linked immunosorbent assay testing is of limited value in the exclusion of thromboembolic disease: result of a practical study in an ED

OBJECTIVE

The aim of this study was to assess in clinical practice the accuracy of a referent d-dimer enzyme-linked immunosorbent assay for the exclusion of venous thromboembolic disease (VTED).

PATIENTS AND METHODS

An observational prospective study took place in an emergency department; 205 consecutive outpatients suspected of having VTED were included. Blood samples were collected at admission for VIDAS DD measurement. Venous thromboembolic disease was confirmed by standard clinical imaging. All patients were followed up at 3 months.

RESULTS

Venous thromboembolic disease was confirmed in 57 patients (28%). The sensitivity and negative predictive value of a DD assay lower than 500 ng/mL were 78% (95% confidence interval = 67%-87%) and 84% (95% confidence interval = 73%-90%), respectively. Twelve patients had a false-negative DD with one or more of the following: (a) symptoms reported for more than 15 days (n = 2), (b) prior anticoagulation (n = 3), (c) distal VTED (n = 5), or (d) high clinical probability (n = 3).

CONCLUSION

In our cohort of patients, DD was less accurate than previously reported, with an upper estimate of the sensitivity of only 87%.

Diagnostic evaluation of planar and tomographic ventilation/perfusion lung images in patients with suspected pulmonary emboli

Planar lung ventilation/perfusion scintigraphy (V/P(PLANAR)) is a standard method for diagnosis of pulmonary embolism (PE). The goals of this study were to test whether the diagnostic information of ventilation/perfusion tomography (V/P(SPET)) applied in clinical routine might enhance information compared with V/P(PLANAR) and to streamline data processing for the demands of clinical routine. This prospective study includes 53 patients suspected for PE referred for lung scintigraphy. After inhalation of (99m)Tc-DTPA planar ventilation imaging was followed by tomography, using a dual-head gamma camera. (99m)Tc-MAA was injected i.v. for perfusion tomography followed by planar imaging. Patients were examined in supine position, unchanged during V/P tomography. Two reviewers evaluated V/P(PLANAR) and V/P(SPET) images separately and randomly. Mismatch points were calculated on the basis of extension of perfusion defects with preserved ventilation. Patients were followed up clinically for at least 6 months. With V/P(SPET) the number of patients with PE was higher and 53% more mismatch points were found. In V/P(SPET) interobserver variation was less compared with V/P(PLANAR). Ancillary findings were observed by both techniques in half of the patients but more precisely interpreted with V/P(SPET). V/P(SPET) shows more and better delineated mismatch defects, improved quantification and less interobserver variation compared with V/P(PLANAR). V/P(SPET) is amenable to implementation for clinical routine and suitable even when there is demand for a high patient throughput.

Incidence of asymptomatic pulmonary embolism in moderately to severely injured trauma patients

BACKGROUND

Chest computed tomographic (CT) scanning is used frequently to evaluate symptomatic patients for pulmonary embolus (PE). The incidence of PE diagnosed by helical CT scanning in asymptomatic patients is unknown.

METHODS

Asymptomatic trauma patients with an Injury Severity Score > or = 9 were studied with contrast-enhanced helical CT images of the chest, pelvis, and lower extremities. Clot burden was assessed using an anatomic scoring system. Patients not receiving anticoagulation were followed.

RESULTS

Twenty-two of 90 patients had a PE. Four had major clot burden, including one patient with a saddle embolus. Risk factors for asymptomatic PE include age (odds ratio [OR], 1.04), head injury (OR, 6.78), chest injury (OR, 4.51), lower extremity injury (OR, 5.03), and transfusion (OR, 3.42). Thirty percent of patients receiving pharmacologic prophylaxis had a PE.

CONCLUSION

Asymptomatic PE occur in 24% of moderately to severely injured patients. Age, head, chest, and lower extremity injury are associated with an increased risk. Standard thromboembolic prophylaxis is not reliably protective.

Can We Rely on Computed Tomographic Scanning to Diagnose Pulmonary Embolism in Critically Ill Surgical Patients?

BACKGROUND

Spiral computed tomographic pulmonary angiography (CTPA) is gaining an increasing role in pulmonary embolism (PE) diagnosis because it is more convenient and less invasive than conventional pulmonary angiography (PA). Encouraging reports on the reliability of CTPA for medical patients have prompted widespread use despite the fact that its value in critically ill surgical patients has been inadequately explored. Hemodynamic and respiratory issues of critical illness may interfere with CTPA's diagnostic accuracy. The objective of this study was to compare CTPA with PA for the diagnosis of PE in critically ill surgical patients.

METHODS

Over 30 months (August 1999-February 2002), 37 critically ill surgical patients (28 trauma and 9 non-trauma patients) wiith clinical suspicion of PE were enrolled prospectively. CTPA and PA were independently interpreted by four radiologists (two for each test) blinded to each other's interpretation. Clinical suspicion for PE was classified as high, intermediate,or low on the basis of predetermined criteria. PA was considered as the standard of reference for the diagnosis of PE.

RESULTS

PE was found in 15 (40%) patients by: central PE in 8 and peripheral PE in 7. CTPA and PA findings were different in 11 patients (30%): CTPA was false-negative in 9 patients and false-positive in 2. Its sensitivity and specificity were PE 50% and 100%, respectively, for central PE; 28% and 93% for peripheral PE; and 40% and 91% for all PE. There were no differences in risk factors or clinical characteristics between patients with and without PE. The level of clinical suspicion was identical in the two groups. The independent reviewers disagreed on CTPA or PA interpretations in 11% and 16% of the readings, respectively.

CONCLUSION

PA remains the "gold standard" for diagnosis of PE in critically ill surgical patients. CTPA should be explored further before being universally accepted. Clinical criteria are unreliable for detecting PE in this population and therefore a high index of suspicion should be maintained.

Cost-effectiveness of ultrasound in preventing femoral venous catheter-associated pulmonary embolism

Femoral central venous catheter use is complicated by a high risk of deep venous thrombosis despite antithrombotic prophylaxis. Although some have recommended screening for femoral catheter-associated thrombosis to prevent pulmonary embolism (PE), this strategy's economic implications are unclear. Therefore, we used a decision model to evaluate the potential cost-effectiveness of a Doppler ultrasound-based screening strategy versus no ultrasound in averting thromboembolic complications associated with femoral catheters. The base-case analysis included a hypothetical cohort of 60-year-old medical patients treated for acute respiratory failure. The perspective was that of the health care payor, and the primary outcomes were quality-adjusted life expectancy, PE, and PE-associated deaths. The ultrasound strategy cost $8,688/quality-adjusted life-year (QALY) gained, $5,305/PE averted, and $99,286/PE death averted. The best- and worst-case scenarios, calculated in multiway sensitivity analyses by varying in-hospital mortality, deep venous thrombosis prevalence, and ultrasound accuracy, ranged from $1,170/QALY to $35,342/QALY, respectively. Probablistic analyses, in which variables with uncertain values were varied randomly within their ranges, demonstrated median costs of $12,793/QALY (interquartile range $8,176/QALY, $20,648/QALY). In summary, ultrasound screening may improve outcomes among the critically ill with femoral venous catheters at acceptable costs and could complement venous thrombosis primary prevention programs.

Selective venography versus nonselective venography before vena cava filter placement: evidence for more, not less

OBJECTIVE

We undertook this study to determine whether additional use of selective venography, compared with nonselective venography alone, reveals more abnormal anatomic venous findings that lead to changes in vena cava filter (VCF) position.

METHODS

From January 1998 to June 2002, 94 patients underwent VCF placement by vascular surgeons at a university tertiary care center. Indications, techniques, decision analysis, and complications were reviewed. Nonselective venography and selective venography of the inferior vena cava (IVC) were evaluated for image quality, abnormal findings, aberrant anatomy, and the anatomic relationship of vertebral bodies to major venous tributaries.

RESULTS

Absolute and relative indications for VCF placement were 44% and 56%, respectively. Jugular, femoral, and subclavian vein approach was used in 47%, 47%, and 6% of patients, respectively. Seventy-three percent of VCFs were placed in the catheterization laboratory, 21% in the operating room, and 5% at the bedside. Nonselective venography was performed in 80 patients (85%), of whom 44% had undergone selective venography. At nonselective venography plus selective venography 7.5% of patients had an abnormal finding (IVC compression, n = 3; IVC thrombus, n = 2; tortuosity, n = 1). Similarly, 17.5% of patients had aberrant anatomy (accessory renal vein, n = 8; IVC duplication, n = 3; large low right gonadal vein, n = 2; megacava, n = 2). Nonselective venography plus selective venography demonstrated that 16% of VCFs required a major change in position, 10% of which were placed above the renal veins. Compared with nonselective venography alone, selective venography enabled detection of significantly more abnormal and aberrant findings (9% vs 49%; P <.001). Changes in VCF placement were necessary significantly more often in patients undergoing additional selective venography compared with nonselective venography alone (31% vs 4%; P =.003). In one patient in the series, a VCF was malpositioned in the iliac vein with intravascular ultrasound visualization.

CONCLUSION

When nonselective venography plus selective venography were performed, 23% of patients had either an abnormal finding or aberrant anatomy, and most of these required a major change in VCF position. Nonselective venography plus selective venography redefines the criterion standard and, because of limitations of other methods of vena cava visualization for VCF deployment, should be performed in most patients.

The Utility of Plasma D-dimer to Identify Thromboembolic Disease in Dogs

This prospective study was designed to investigate D-dimer concentrations in clinically healthy dogs, clinically ill dogs without thromboembolic disease (TE), and dogs with TE. The goals of this study were to determine whether the coagulation cascade is activated in nonembolic metabolic and inflammatory conditions and whether differentiation from TE is possible. Group 1 consisted of 30 clinically healthy dogs presented for routine care. Group 2 consisted of 67 clinically ill dogs without TE. This group was subdivided into the following categories: postoperative surgical procedures, congestive heart failure, renal failure, hepatic disease, and neoplastic disease. Group 3 consisted of 20 dogs diagnosed with TE. A CBC and a measurement of prothrombin time (PT), activated partial thromboplastin time (PTT), fibrinogen degradation product (FDP) concentration, and plasma D-dimer concentration was performed on dogs in all groups. D-dimer concentrations were highest in dogs with TE; next highest was the hepatic disease group. Only these 2 groups had median D-dimer concentrations markedly different from clinically healthy dogs. The frequency of platelet abnormalities was markedly greater for the TE and neoplastic disease groups. The sensitivity of D-dimer concentrations >500 ng/mL for predicting TE was 100%; however, the specificity of D-dimer for TE at that concentration was 70%. The specificity of D-dimer concentrations >1,000 ng/mL to predict TE was 94% (sensitivity, 80%), and the specificity of D-dimer concentrations >2,000 ng/mL was 98.5% (sensitivity, 36%). FDPs were not high in any TE patient; thus, they may be an insensitive indicator of thromboembolism, with or without overt disseminated intravascular coagulation (DIC).

Radionuclide imaging of acute pulmonary embolism

Pulmonary embolism (PE) is a potentially fatal condition for which treatment is highly effective. The diagnosis of PE can be challenging and often requires diagnostic imaging. For many years, chest radiographs and ventilation-perfusion (V/Q) scintigraphy have been the primary imaging modalities used in the evaluation of patients with suspected acute PE. The combination of clinical assessment, plus results of V/Q scintigraphy and a noninvasive venous study of the lower extremities can provide clinicians with the information needed to direct treatment in the majority of patients with suspected PE. More recently, advances in computerized tomography (CT) angiography have allowed for the direct visualization of PE, and this technique has emerged as an important diagnostic test in the evaluation of patients with suspected PE. Proponents suggest that CT angiography should be used as the first line imaging test in patients with suspected PE. Others suggest that V/Q scanning should remain as the first line diagnostic imaging test and that CT angiography should be used in patient's in whom the diagnosis remains uncertain. The combination of CT angiography and CT venography has the potential to provide a single comprehensive study of patients with suspected venous thromboembolism.

Diagnosis of pulmonary embolism with spiral CT as a second procedure following scintigraphy

Our objective was to evaluate, in a routine clinical setting, the role of spiral CT as a second procedure in patients with clinically suspected pulmonary embolism (PE) and abnormal perfusion scan. We prospectively studied the role of spiral CT in 279 patients suspected of PE. All patients started their diagnostic algorithm with chest radiographs and perfusion scintigraphy. Depending on the results of perfusion scintigraphy, patients proceeded to subsequent levels in the algorithm: stop if perfusion scintigraphy was normal; CT and pulmonary angiography if subsegmental perfusion defects were seen; ventilation scintigraphy followed by CT when segmental perfusion defects were seen; and pulmonary angiography in this last group when results of ventilation/perfusion scintigraphy and CT were incongruent. Reference diagnosis was based on normal perfusion scintigraphy, high probability perfusion/ventilation scintigraphy in combination with abnormal CT, or pulmonary angiography. If PE was present, the largest involved branch was noted on pulmonary angiography, or on spiral CT scan in case of a high-probability ventilation/perfusion scan and a positive CT scan. A distinction was made between embolism in a segmental branch or larger, or subsegmental embolism. Two hundred seventy-nine patients had abnormal scintigraphy. In 27 patients spiral CT and/or pulmonary angiography were non-diagnostic and these were excluded for image analysis. Using spiral CT we correctly identified 117 of 135 patients with PE, and 106 of 117 patients without PE. Sensitivity and specificity was therefore 87 and 91%, respectively. Prevalence of PE was 53%. Positive and negative predictive values were, respectively, 91 and 86%. In the high-probability group, sensitivity and specificity increased to 97 and 100%, respectively, with a prevalence of 90%. In the non-high probability-group sensitivity and specificity decreased to 61 and 89%, respectively, with a prevalence of 25%. In a routine clinical setting single-detector spiral CT technology has limited value as a second diagnostic test because of low added value in patients with a high-probability lung scan and low sensitivity in patients with non-high-probability lung scan result.

Tissue plasminogen activator plasma levels as a potential diagnostic aid in acute pulmonary embolism

CONTEXT

Pulmonary embolism (PE) is a potentially fatal and frequent complication of deep venous thrombosis, and the most reliable techniques for the diagnosis of PE are not universally available and have other limitations.

OBJECTIVE

To determine the efficacy of 4 different fibrinolysis system parameters, namely, tissue plasminogen activator (tPA), tissue plasminogen activator inhibitor type 1 (PAI-1), plasmin-antiplasmin complexes (PAP), and D-dimer, in the diagnosis of acute PE.

SETTING

A 350-bed university hospital serving an area with 280,000 inhabitants.

PATIENTS

Sixty-six consecutive outpatients with clinically suspected PE. The diagnosis of PE was based on ventilation-perfusion (V/Q) lung scan in combination with clinical assessment, lower limb study, and (when required) pulmonary angiography.

MAIN OUTCOME MEASURES

At the moment of clinical suspicion, a sample of venous blood was obtained to measure levels of tPA, PAI-1, PAP, and D-dimer using an enzyme-linked immunosorbent assay method.

RESULTS

Twenty-seven patients (41%) were classified as PE positive (high clinical probability and V/Q lung scan [n = 12], nondiagnostic V/Q lung scan and high clinical probability [n = 1], inconclusive V/Q lung scan and positive lower limb examination for deep venous thrombosis [n = 11], and positive pulmonary angiography [n = 3]), and 39 patients (59%) were classified PE negative. The sensitivity/negative predictive value for tPA, using a cutoff of 8.5 ng/mL, and PAI-1, using a cutoff of 15 ng/mL, were 100%/100% and 100%/100%, respectively. A tPA level lower than 8.5 ng/mL occurred in 13 (19.7%; all PE negative) of 66 patients with suspected PE, and PAI-1 levels were lower than 15 ng/mL in 9 (13.6%; all PE negative) of 66 patients with suspected PE. The D-dimer, using a cutoff of 500 ng/mL, showed a sensitivity and negative predictive value of 92.6% and 87.5%, respectively.

CONCLUSIONS

Our data indicate that tPA and PAI-1 levels are potentially useful in ruling out PE, although tPA seems to be the better parameter. The sensitivity levels and negative predictive values for the rapid enzyme-linked immunosorbent assay for D-dimer used in this investigation were low compared with previous studies using the same test.

Use of computed tomography pulmonary angiography in the diagnosis of pulmonary embolismin patients with an intermediate probability ventilation/perfusion scan

BACKGROUND

Computed tomography pulmonary -angiography (CTPA) plays an increasingly important role in the diagnosis of pulmonary embolism (PE). Although accurate in the detection of large PE, its accuracy in other patient groups is yet to be defined.

AIM

To compare CTPA with pulmonary angiography as a second-line investigation in patients with a ventilation/perfusion (VQ) scan indicating an intermediate probability of PE.

METHODS

We recruited 25 patients over a 17-month period. Subjects were eligible if they: (i). had clinically suspected PE, (ii). had a VQ scan indicating an intermediate probability of PE and (iii). were referred for pulmonary angiography. Subjects underwent CTPA within 36 h of the VQ scan. CTPA was interpreted without knowledge of the results of the pulmonary angiogram by two of the authors.

RESULTS

PE was prevalent (i.e. embolus detected at pulmonary angiography) in seven of 25 subjects (28%). The sensitivity of CTPA was 57% and the specificity was 94%.

CONCLUSIONS

In the setting of intermediate-probability VQ scanning, CTPA may be used to clarify the diagnosis of PE. However, a negative CTPA cannot -definitely exclude PE. Conventional pulmonary angiography may be necessary to determine the presence of PE if CTPA is negative.

Clinical policy: critical issues in the evaluation and management of adult patients presenting with suspected pulmonary embolism

This clinical policy focuses on critical issues in the evaluation and management of patients with signs or symptoms of pulmonary embolism (PE). A MEDLINE search for clinical trials published from January 1995 through April 2001 was performed using the key words "pulmonary embolus" with limits of "clinical investigations" and "clinical policies." Subcommittee members and expert peer reviewers also supplied articles with direct bearing on the policy. This policy focuses on 2 major areas of current interest and/or controversy: (1) diagnostic: utility of D -dimer, ventilation-perfusion scanning, and spiral computed tomography angiogram in the evaluation of PE; and (2) therapeutic: indications for fibrinolytic therapy. Recommendations for patient management are provided for each 1 of these topics based on strength of evidence (Level A, B, or C). Level A recommendations represent patient management principles that reflect a high degree of clinical certainty; Level B recommendations represent patient management principles that reflect moderate clinical certainty; and Level C recommendations represent other patient management strategies based on preliminary, inconclusive, or conflicting evidence, or based on panel consensus. This guideline is intended for physicians working in emergency departments or chest pain evaluation units.

Comparison of ventilation/perfusion scintigraphy and helical CT for diagnosis of pulmonary embolism; strategy using clinical data and ancillary findings

STUDY OBJECTIVE

To address the question whether ventilation/perfusion scintigraphy (SCINT) or helical computed tomography (CT) should be the first hand method for diagnosis of pulmonary embolism (PE).

SETTING

Departments of radiology, nuclear medicine and internal medicine of a large university hospital.

PATIENTS

During 3 years all 128 patients examined for PE with both methods were analysed. The strategy of interpretation behind original clinical reports, i.e. clinical CT and clinical SCINT, was based upon basic criteria for PE, ancillary findings and information from the referring doctor and from previous examinations. Reviewed SCINT and CT reports were obtained from experts in each field blinded to clinical and laboratory data. The findings with respect to PE were classified as no PE, PE or non-diagnostic. Other pathology than PE was described. A final diagnosis serving as reference was based upon CT, SCINT and other information including clinical follow for 6-24 months.

METHODS

Planar SCINT was made with ventilation always preceding perfusion. CT was made with contrast injection using 3 mm collimation and table feed of 3 mm s-1.

RESULTS

PE was diagnosed in 32 patients. For clinical and reviewed SCINT sensitivity was 91 and 97%, specificity 96 and 100% and rate of non-diagnostic findings 10 and 9%, respectively. For clinical and reviewed CT sensitivity was 81 and 78%, specificity 99 and 100% and non-diagnostic findings was observed in 8 and 1%, respectively. In patients with PE, concordant positive results were obtained with both modalities in 23 of 32 patients (72%).

CONCLUSION

SCINT remains the first hand method because its high sensitivity, general feasibility, low radiation burden and low rate of non-diagnostic findings in our setting. CT is indispensable when SCINT is not available or its result non-diagnostic.

Detection of pelvic vein thrombosis by magnetic resonance angiography in patients with acute pulmonary embolism and normal lower limb compression ultrasonography

STUDY OBJECTIVE

In patients with proven acute pulmonary embolism (PE), a systematic search for "residual" deep vein thrombosis (DVT) using venography or compression duplex ultrasonography (CDUS) of the lower limbs is negative in 20 to 50% of patients. We hypothesized that undetectable pelvic vein thrombosis (from the external iliac vein to the inferior vena cava) could account for a substantial proportion of patients with negative CDUS findings. Using a noninvasive test, magnetic resonance angiography (MRA), the objective of the study was to assess the prevalence of pelvic DVT in patients with acute PEs and normal findings on lower limb CDUS.

DESIGN

Prospective study.

SETTING

A 35-bed respiratory unit in a 680-bed Parisian teaching hospital.

PATIENTS

From June 1995 to October 1996, 24 patients (mean age, 49 years; age range, 18 to 83 years) with acute PEs and normal findings on lower limb CDUS underwent pelvic MRA.

MEASUREMENTS AND RESULTS

MRA disclosed pelvic DVT in seven patients (29%). The common iliac vein was involved in five patients. Internal iliac vein (hypogastric) thrombosis was imaged in two patients, but no patients had DVT limited to this vein. Three patients underwent subsequent venography studies that confirmed the MRA findings. In three other patients, a new MRA at the end of anticoagulant therapy showed the resolution of the DVT.

CONCLUSIONS

Our data support the view that, among patients with negative findings on CDUS, a substantial proportion of the DVTs that are responsible for PE originates in the pelvic veins. This study provides additional arguments to suggest that MRA might become the reference test for the exploration of pelvic DVT.

MRA of the lower extremities in patients with pulmonary embolism using a blood pool contrast agent: initial experience

PURPOSE

To evaluate the feasibility of blood pool contrast-enhanced magnetic resonance angiography (MRA) to visualize the arterial and venous vessel tree and to detect deep venous thrombosis (DVT) of the lower extremities.

MATERIALS AND METHODS

Nine consecutive patients with pulmonary embolism (mean age = 46 +/- 9) were randomized to various doses of NC100150 (between 0.75 and 6 mg of Fe/kg of body weight). A T1-weighted (T1W) 3D gradient recalled echo (GRE) sequence (TE = 2.0 msec, TR = 5.0 msec) was used. Two observers blinded to the dose of contrast agent assessed image quality, contrast attenuation, and appearance of thrombi.

RESULTS

Qualitative assessment of overall MRA image quality and semiquantitative vessel scoring revealed good to excellent delineation of venous and arterial vessel segments independent of the dose of NC100150. However, quantitative region of interest analysis revealed a significantly higher signal-to-noise ratio (SNR) in the high-dose group than in the mid- and low-dose groups of NC100150 (P < 0.01). Between dose groups, the SNR was independent of vessel type (artery or vein) and vessel segment localization (proximal or distal). All seven venous thrombi (mean length = 7.2 +/- 0.95 cm) were characterized by a very low signal intensity (SI), which was only 16.6 +/- 7% of the SI in adjacent venous segments (P < 0.0001).

CONCLUSION

High-quality MR angiograms of the lower extremities can be obtained using low concentrations of NC100150 in combination with a strong T1W 3D GRE sequence. The obvious delineation of venous thrombi suggests that this technique may be potentially used as a noninvasive "one-stop shopping" tool in the evaluation of thromboembolic disease.

Outcomes after withholding anticoagulation from patients with suspected acute pulmonary embolism and negative computed tomographic findings: a cohort study

OBJECTIVE

To determine the outcome of withholding anticoagulation from patients with suspected acute pulmonary embolism in whom computed tomographic (CT) findings are interpreted as negative for pulmonary embolism.

PATIENTS AND METHODS

This retrospective cohort study included 1512 consecutive patients referred from August 7, 1997, to November 30, 1998, for CT because of clinically suspected acute pulmonary embolism. All patients were examined by electron beam CT, and scanning was performed in a cephalocaudad direction from the top of the aortic arch to the base of the heart with 3-mm collimation, 2-mm table incrementation, and an exposure time of 0.2 second (130 peak kV, 620 mA, and standard reconstruction algorithm). Contrast material was infused at a rate of 3 to 4 mL/s through an antecubital vein with an automated injector. Findings on CT were interpreted as either positive or negative. The main outcome measures were deep venous thrombosis, pulmonary embolism, and vital status within 3 months after the CT scan and the cause of death based on medical record review, mailed patient questionnaires, and telephone interviews.

RESULTS

In 1010 patients (67%) CT scans were interpreted as negative for acute pulmonary embolism. Seventeen patients were excluded because they received anticoagulation. Of the remaining 993 patients, deep venous thrombosis or pulmonary embolism developed in 8; 118 patients died, 3 of pulmonary embolism. Nineteen patients were known to be alive, but additional clinical information could not be obtained. The 3-month cumulative incidence of overall deep venous thrombosis or pulmonary embolism was 0.5% (95% confidence interval, 0.1%-1.0%) and of fatal pulmonary embolism, 0.3% (95% confidence interval, 0.0%-0.7%).

CONCLUSIONS

The incidence of (1) overall deep venous thrombosis or pulmonary embolism or (2) fatal pulmonary embolism among patients with suspected acute pulmonary embolism, negative CT results, and no other evidence of venous thromboembolism is low. Withholding anticoagulation in these patients appears to be safe.

Current strategies for the diagnosis of pulmonary embolus

Venous thromboembolic disease (VTD), comprising venous thrombosis and pulmonary embolus, is responsible for innumerable deaths every day. Wide variance in its presentation and clinical manifestations and the resultant difficulties in achieving its diagnosis have confounded attempts to define optimal diagnostic and treatment strategies. Those strategies should be predicated on the understanding of the manifestations of VTD and of the attributes and interrelationship of the various modalities available for its diagnosis. This review will present an overview of the literature describing those modalities, their strengths and deficiencies, and their current value in algorithms for the diagnosis of VTD.

The use of a D-dimer assay in patients undergoing CT pulmonary angiography for suspected pulmonary embolus

PURPOSE

To assess the ability of a semi-quantitative latex agglutination D-dimer test Accuclot with bedside measurements of arterial oxygen saturation, respiratory and cardiac rates to exclude pulmonary embolism (PE) on computed tomographic pulmonary angiography (CTPA).

MATERIALS AND METHODS

All patients referred to our CT unit for investigation of suspected acute pulmonary embolism were enrolled. Pulse oximetery, respiratory rate, heart rate and blood sampling for D-dimer testing were carried out just before CT. A high resolution CT (HRCT) of the chest was followed by a CT pulmonary angiogram (CTPA). The images were independently interpreted at a workstation with cine-paging and 2D reformation facilities by three consultant radiologists blinded to the clinical and laboratory data. If positive, the level of the most proximal embolus was recorded. Discordant imaging results were re-read collectively and consensus achieved.

RESULTS

A total of 101 patients were enrolled. The CTPA was positive for PE in 28/101 (28%). The D-dimer was positive in 65/101 (65%). Twenty-six patients had a positive CT and positive D-dimer, two a positive CT but negative D-dimer, 39 a negative CT and positive D-dimer, and 34 a negative CT and negative D-dimer. The negative predictive value of the Accuclot D-dimer test for excluding a pulmonary embolus on spiral CT was 0.94. Combining the D-dimer result with pulse oximetry (normal SaO2 > or = 90%) improved the negative predictive value to 0.97.

CONCLUSION

A negative Accuclot D-dimer assay proved highly predictive for a negative CT pulmonary angiogram in suspected acute pulmonary embolus. If this D-dimer assay were included in the diagnostic algorithm of these patients a negative D-dimer would have unnecessary CTPA rendered in 36% of patients.

Estudo experimental comparativo da eficácia antitrombótica da heparina convencional e da heparina de baixo peso molecular

Em estudo randomizado e cego comparou-se a eficácia antitrombótica (redução do peso do trombo) de duas heparinas; uma de baixo peso molecular (HBPM) e outra não fracionada - heparina convencional (HC). Foram utilizados dois procedimentos de trombose venosa experimental: no grupo I a trombose venosa foi induzida injetando-se oleato de etanolamina na veia jugular de 30 coelhos e glicose a 50% em mais 30, todos da raça New Zealand. No Grupo II a trombose venosa foi induzida por estase mediante a ligadura da veia cava de 30 ratos da raça Wistar. Não se encontrou diferenças estatisticamente significantes com relação à redução do peso do trombo em ambos os grupos. Também concluiu-se que a eficácia antitrombótica das drogas estudadas não variou conforme o tipo de estímulo indutor da trombose nos modelos testados, e que o oleato de etanolamina induziu de forma mais significante a formação de trombos no grupo I.

Radionuclide imaging of acute pulmonary embolism

From the prospective and outcome-based studies that have been carried out in the past few years, the following conclusions regarding the diagnostic evaluation of patients with suspected PE can be made: 1. A normal V/Q scan interpretation excludes the diagnosis of clinically significant PE. 2. Patients with a very-low- or low-probability V/Q scan interpretation and a low clinical likelihood of PE do not require angiography or anticoagulation. 3. Patients with a very-low- or low-probability V/Q scan interpretation, an intermediate or high clinical likelihood of PE, and negative serial noninvasive venous studies of the lower extremities do not require anticoagulation or angiography. If serial noninvasive venous studies of the lower extremities are positive, patients should be treated. 4. Clinically stable patients with an intermediate-probability V/Q scan interpretation require noninvasive venous studies of the legs and, if negative, require CT angiography or pulmonary angiography for a definite diagnosis. 5. Clinically stable patients with a high-probability V/Q scan interpretation and a high clinical likelihood of PE require treatment and need no further diagnostic tests to confirm the diagnosis. 6. Clinically stable patients with a high-probability V/Q scan interpretation and a low or intermediate clinical likelihood of PE require noninvasive venous studies of the legs and, if negative, often require CT angiography or pulmonary CT for a definitive diagnosis.

Computed tomography scan versus ventilation-perfusion lung scan in the detection of pulmonary embolism

This study compared the sensitivity and specificity of computed tomography (CT) scan and ventilation-perfusion (V-P) scan in detecting pulmonary embolism (PE) with pulmonary angiogram (AG) as the reference standard. Following a comprehensive search of the indexed medical literature, CT scan studies related to PE diagnosis were systematically evaluated to select those using AG as the reference standard and meeting specified methodologic criteria. Studies were further grouped by those reporting results for central PE findings only versus central and peripheral PE combined. A composite analysis of data derived from seven selected publications yielded sensitivity and specificity estimates for CT scan in detecting PE, which were statistically compared to the published results of a multi-center study reporting the sensitivity and specificity of the V-P scan with pulmonary AG as the reference standard. The calculated CT scan sensitivity was 77% for central PE only data and 81% for central and peripheral PE combined data, and the CT scan specificity was 91% and 98%, respectively. High-probability V-P scan sensitivity was 41% and specificity 97%; high- and intermediate-probability V-P scans combined yielded sensitivity 83% and specificity 52%. The sensitivity for PE detection was significantly greater for CT scan than for high-probability V-P scan; CT scan sensitivity was equivalent to V-P when high- and intermediate-probability scans were considered together. CT scan specificity for central and peripheral PE combined was equivalent to that of the high-probability V-P scan, but significantly greater than that of high- and intermediate-probability V-P scans considered together. Considering that only a small proportion of patients with suspected PE yield high-probability V-P scan results (which are usually indicative of PE), while as many as one-half of patients may yield intermediate-probability results (which are commonly not useful in PE diagnosis), our results suggest the CT scan may be an appropriate study for use by Emergency Physicians in the clinical evaluation of suspected PE.

Prevention, diagnosis, and treatment of venous thromboembolic complications of gynecologic surgery

Deep vein thrombosis and pulmonary embolism, collectively referred to as venous thromboembolic events, are a source of significant morbidity and mortality after gynecologic surgical procedures. In this literature review the advantages and disadvantages of various preventive measures for deep venous thrombosis, including low-molecular-weight heparins, are discussed. The most appropriate prophylactic methods for patients in varying risk categories are recommended. Current methods of diagnosing deep venous thrombosis and pulmonary embolism, including ultrasonography, venography, ventilation-perfusion scan, helical computed tomographic scan, and D -dimer measurement are then discussed. Finally, treatment modalities for deep venous thrombosis and pulmonary embolism, including heparin, low-molecular-weight heparin, warfarin, and thrombolytic therapy, are detailed.

Systematic study of occult pulmonary thromboembolism in patients with deep venous thrombosis

PURPOSE

This study was carried out to evaluate the prevalence and extension of pulmonary thromboembolism (PTE) in symptom-free patients with symptomatic deep venous thrombosis (DVT) of lower limbs and to evaluate their possible implication in the adequate treatment of thromboembolic disease.

MATERIALS AND METHODS

We prospectively studied, using noninvasive examination (pulmonary spiral computed tomography [CT] angiography), 159 consecutive patients with acute DVT confirmed by duplex scanning without symptoms of PTE. CT was repeated at 30 days to study evolution of these clinically occult PTE.

RESULTS

We observed silent PTE in 65 patients (41%) in all levels of lower limb venous thrombosis. Prevalence of PTE showed significant association with male sex (P =.001) and previously diagnosed heart disease (P =.023). There was no significant association between the level of DVT and the presence of PTE nor the DVT side and thromboembolic pulmonary localization. Of the 65 patients with positive CT exploration results for PTE, 52 had characteristics of acute PTE, 10 had chronic PTE, and 3 patients had both. Chronic PTE was found more frequently in patients with previous episodes of DVT (P =.024). A total of 165 pulmonary artery-affected segments were found at several locations: 5 main, 35 lobar, 58 interlobar, and 67 segmental. Multiple segments were affected in 59% of patients. Repeat CT examinations were performed at 30 days in 53 of 65 patients with positive CT scanning results. In 48 cases (90.6%) PTE had completely disappeared.

CONCLUSIONS

Silent PTE occurred frequently in association with clots of lower limbs. The CT scan had a good availability and cost-effectiveness to detect clinically underestimated PTE. The incorporation of this exploration in the systematic diagnostic strategy of most patients with DVT to establish the extension of thromboembolic disease at diagnosis may be useful in the evaluation of added pulmonary artery symptoms and treatment strategies.

Direct and indirect antithrombins. Heparins, low molecular weight heparins, heparinoids, and hirudin

With the eclipse of UH by newer anticoagulants, the field has opened up to search for new and better drugs. Hirulog or bivalirudin is another direct antithrombin that has been used in initial trials. It is smaller than hirudin, at 20 amino acids. Currently under investigation, it seems to have a short half-life, a narrow therapeutic window, and a reverse dose effect, with lower levels achieving better cardiac post-thrombolysis patency than higher doses. Other antithrombins being examined are the hirudisins, where four amino acids of hirudin have been replaced by the RGDS integrin-binding sequence and thrombin receptor antagonist peptides. In addition, many other inhibitors of activated clotting factors are being studied for future therapeutic value. Tick anticoagulant protein studies are underway, as are studies on a group of benzamidine isoxazoline derivates, which are direct Xa inhibitors. We are truly at an age of discovery with the newer anticoagulants and it may take many years until we can distinguish the advantages and disadvantages of all the newer therapies. It looks like an ever more real possibility that medicine may find an antithrombotic regimen that is highly effective, highly reversible, and nontoxic.

The negative predictive value of spiral computed tomography for the diagnosis of pulmonary embolism in patients with nondiagnostic ventilation-perfusion scans

BACKGROUND

There is no noninvasive method to rule out pulmonary embolism when the clinical suspicion for pulmonary embolism is high. We did a prospective observational study to determine the negative predictive value of spiral computed tomography (CT) in this situation.

METHODS

We performed spiral CT scans of the thorax in consecutive patients with high clinical suspicion of pulmonary embolism with intermediate or low probability ventilation-perfusion scans. Patients with negative or indeterminate spiral CT results had conventional angiography at the discretion of the attending physician. Only patients with positive spiral CT results or positive conventional angiograms were treated. All patients were observed for 6 months for evidence of venous thromboembolic disease. Clinical outcome without treatment or the results of conventional angiography were used as reference standards. False-negative results were defined as a negative spiral CT with a positive conventional angiogram or any diagnosis of venous thromboembolism within 6 months.

RESULTS

Among the 103 patients who were studied, spiral CT scans were positive in 22 patients, indeterminate in 10 patients, and negative in 71 patients. Twenty-seven (26%) patients had pulmonary embolism by clinical outcome, including 3 of the 71 patients with negative spiral CT scans and 2 of the 10 patients with indeterminate scans. A negative spiral CT result had a likelihood ratio of 0.12 (95% confidence interval [CI]: 0.04 to 0.35) with a negative predictive value of 96% (95% CI: 88% to 99%). Using conventional angiography only as the reference standard, a negative spiral CT result had a likelihood ratio of 0.08 (95% CI: 0.02 to 0.31) and a negative predictive value of 93% (95% CI: 77% to 98%).

CONCLUSIONS

Spiral CT has a high negative predictive value for pulmonary embolism and may replace conventional angiography in the workup of pulmonary embolism. Patients with indeterminate spiral CT results should be considered for conventional angiography.

Diagnosis of venous thromboembolism. Step-by-step approach to a still lethal disease

Rapid diagnosis of VTE is vital in reducing the significant morbidity and mortality rates associated with this disease. Although angiographic studies remain the "gold standard" for diagnosis, many noninvasive diagnostic procedures are available and are appropriate for evaluation in clinically stable patients. The algorithm presented in this article facilitates the practical and efficient use of available resources in diagnosing and treating VTE.

Subsequent pulmonary embolism: risk after a negative helical CT pulmonary angiogram--prospective comparison with scintigraphy

PURPOSE

To determine whether a helical computed tomographic (CT) scan that is negative for pulmonary embolism (PE) is a sufficiently reliable criterion to safely withhold anticoagulation therapy.

MATERIALS AND METHODS

Patients with negative helical CT scans were prospectively compared with patients with negative or low-probability scintigrams. In a 460-bed university hospital and clinic, 1,015 adult patients underwent either scintigraphy or helical CT for possible PE for 25 months. Five hundred forty-eight patients who had negative images and were not receiving anticoagulation therapy were prospectively followed up for 3 months for clinical, new imaging, death certificate, or autopsy evidence of subsequent PE. Ninety-seven patients were lost to follow-up.

RESULTS

Subsequent PE was found in two (1.0%) of 198 patients with negative CT scans, none of 188 patients with negative ventilation-perfusion (V-P) scans, and five (3.1%) of 162 patients with low-probability V-P scans (not statistically significant). Patients in the helical CT group were hospitalized more often, had more severe disease, had more substantial PE risk factors, and had a higher death rate. No deaths were attributed to PE in either group.

CONCLUSION

The frequency of clinical diagnoses of PE after a negative CT scan was low and similar to that after a negative or low-probability V-P scan. Helical CT is a reliable imaging tool for excluding clinically important PE.

Efficient lung scintigraphy

Lung scintigraphy is a first-choice method to diagnose lung embolism. The clinical routine in most centres is a perfusion study complemented with a ventilation study when judged necessary. We describe a routine with ventilation scintigraphy preceding perfusion scintigraphy, which is completed within one hour. Furthermore, the data acquired allow the determination of lung clearance of the tracer 99mTc-DTPA (diethylene triamine penta-acetate) used for the ventilation scintigraphy. An aerosol generator charged once a day with 99mTc-DTPA solution is used for all inhalations during the day. Inhalation is monitored with a counter and interrupted when the count rate corresponds to about 20 MBq. The ventilation imaging starts and ends with posterior projections. This allows calculation of lung clearance of 99mTc-DTPA. Perfusion scintigraphy is performed in a standard fashion with 100 MBq of 99mTc-MAA (macro-aggregated albumin). The ventilation study was considered to give some diagnostic information in the majority of the patients. The clearance determination allows detection of inflammatory lung disease. The background activity caused by the ventilation study comprised only 13% of the activity in the perfusion scintigraphy and did not significantly interfere with interpretation of the perfusion scan. The cost for the investigation is low because of the rational system for aerosol administration and the short time for a complete study.

New diagnostic tests for pulmonary embolism

In 1990, the multicenter Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED), sponsored by the National Institutes of Health, compared the diagnostic value of the radioisotopic ventilation-perfusion lung scan (V/Q scan) with that of pulmonary angiography for the diagnosis of pulmonary embolism (PE). Despite the endurance of the radioisotopic V/Q scan as the most widely used test for evaluation of pulmonary embolism (PE), a better screening tool is clearly needed for use in the emergency department. During the past decade, several new modalities have emerged for evaluation of patients with suspected PE. We evaluate the diagnostic utility of the D-dimer test and the alveolar dead space determination as potential screening tests and of spiral computed tomography, magnetic resonance imaging, transthoracic echocardiography, and transesophageal echocardiography as potential confirmatory tests for PE. For comparison, recent data on the diagnostic utility of the alveolar-arterial oxygen gradient and the V/Q scan are included. The potential application of these new tests to a hypothetical ED population is described.