Serial Impedance Plethysmography Research Articles

Diagnosis of recurrent deep vein thrombosis.

Long-term follow-up studies demonstrated that venous thromboembolism is a chronic disease, as the rate of recurrent deep vein thrombosis (DVT) continuously increases after the primitive thrombotic episode. Objective testing is mandatory to confirm or refute the presence of recurrent DVT, as only 30% of patients with suspected recurrence have a new documented thrombotic episode. There is no consensus on the preferred diagnostic procedure; furthermore, both invasive and noninvasive methods are limited in this context. Venography, the established gold standard, is invasive, costly, inconvenient and requires high technical skills. Among noninvasive techniques, serial impedance plethysmography, alone or in combination with leg scanning and venography, and serial compression ultrasound (CUS), were adequately investigated. At present, the recommended approach is represented by a quantitative CUS method that possesses an excellent reproducibility and accuracy. The safety of withholding anticoagulants from patients with a normal quantitative CUS work-up has been recently demonstrated in a prospective management study.

Withholding treatment in patients with acute pulmonary embolism who have a high risk of bleeding and negative serial noninvasive leg tests

PURPOSE: Patients who have nonmassive acute pulmonary embolism and a high risk of bleeding or contraindication to anticoagulants, such recent surgery or gastrointestinal bleeding, present a clinical dilemma. We sought to estimate whether such patients could be safely left untreated if serial compression ultrasound or serial impedance plethysmography were negative and cardiorespiratory reserve was adequate. SUBJECTS AND METHODS: The frequency of recurrent pulmonary embolism among patients with nonmassive acute pulmonary embolism and negative serial noninvasive leg tests who were not treated was estimated from two prospective studies of the noninvasive management of patients with suspected pulmonary embolism. One of the studies used serial impedance plethysmography of the lower extremities; the other used serial compression ultrasound. The prevalence of pulmonary embolism in patients with nondiagnostic ventilation/perfusion lung scans was determined from the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED). RESULTS: The estimated frequency of fatal recurrent pulmonary embolism was 1% [95% confidence interval (CI), 0% to 5%) among untreated patients with nonmassive pulmonary embolism who had negative serial impedance plethysmograms and 0% (95% CI, 0% to 4%) among those with negative serial compression ultrasonograms. The frequency of nonfatal recurrent pulmonary embolism among untreated patients was 3%, regardless of whether they had negative serial impedance plethysmograms or negative serial compression ultrasonograms. These results were comparable with the frequency of recurrent pulmonary embolism among patients treated with anticoagulants or with inferior vena cava filters. CONCLUSION: Withholding treatment of nonmassive acute pulmonary embolism, if serial impedance plethysmograms or serial venous ultrasonograms are negative and cardiopulmonary reserve is adequate, is a possible strategy for the management of patients with a high risk of bleeding or other contraindication to anticoagulants. This strategy may be associated with fewer adverse events than treatment with anticoagulants or an inferior vena cava filter. Prospective trials comparing alternative treatments are needed.

A simple clinical model for the diagnosis of deep-vein thrombosis combined with impedance plethysmography: potential for an improvement in the diagnostic process.

We recently demonstrated the utility of a clinical model combined with ultrasonography to assist the diagnostic approach in patients with suspected deep-vein thrombosis (DVT). In this study we also sought to demonstrate that the model is useful with impedance plethysmography, a less accurate and less utilized diagnostic test. The original clinical model is slightly cumbersome to use; thus at the completion of the study we attempted to develop a simpler scoring system with a goal of maintaining accuracy. An open, nonrandomized, multicentre trial. Three centres, two in Canada, and one in Italy. Ambulatory patients with suspected deep-vein thrombosis. All patients were assessed clinically to determine the probability for deep-vein thrombosis prior to performing impedance plethysmography and venography. We compared the accuracy of impedance plethysmography between the three pretest probability categories of high, moderate and low. All of the above were performed and interpreted by independent observers. When the study was completed, we revised the clinical model by first performing a simple regression analysis then a multiple logistic regression analysis; a scoring system was devised using the latter. Impedance plethysmography is significantly more sensitive and less specific for all DVT in patients with high pretest probability for deep-vein thrombosis (P = 0.001). The post- test probability (positive predictive value) for deep-vein thrombosis with an abnormal impedance plethysmography result was significantly different (P = 0.0001) between the three pretest probability categories. Multiple regression analysis has provided a new model with only nine variables and a simple scoring system. The retrospective application of the revised clinical model, which is simpler to use, suggests it will provide similar results as the original clinical model when combined with impedance plethysmography. The combination of impedance plethysmography and the clinical model suggests patients are likely to have false positive results if they have a low or moderate pretest probability for deep-vein thrombosis and false negative results if the pretest probability is high. The combination of a low pretest probability and a normal impedance plethysmography result may exclude the need for serial testing, and represented more than 50% of our patient population. The use of the clinical model in conjunction with impedance plethysmography would decrease the number of false positive and negative diagnoses and could markedly decrease the need for serial impedance plethysmography. Combining the clinical model with impedance plethysmography could overcome the fact that impedance plethysmography is clearly less accurate than venous ultrasound imaging. The use of the revised clinical model may increase acceptability and utility, but prospective testing is required before widespread use.

Diagnostic strategies for the management of patients with clinically suspected deep-vein thrombosis.

Given the perceived inaccuracy of clinical diagnosis, patients with suspected deep vein thrombosis should have objective testing. Due to the inherent limitations of the reference method (contrast venography), several diagnostic strategies using noninvasive tests have been developed. These strategies share two components: anticoagulant therapy is initiated only in patients with an abnormal test, and serial testing is performed in patients with an initial normal test result. A thorough search of the literature was done to identify all studies that have evaluated the feasibility, accuracy, and safety of diagnostic strategies in patients with clinically suspected deep vein thrombosis. The safety of the individual diagnostic strategies was expressed as the total rate of venous thromboembolic complications. Feasibility was expressed as the mean number per patient of extra visits to the hospital and additional tests per patient. A total of 12 reports qualified for the analysis. The diagnostic strategies included venography, serial impedance plethysmography with and without 125I-fibrinogen leg scanning, serial ultrasound imaging with and without D-dimer determination, serial ultrasound imaging in combination with a clinical score, and a diagnostic work-up including ultrasound imaging, impedance plethysmography, D-dimer determination, and a clinical score. The observed venous thromboembolic complication rates varied between 0.4% and 2.6%. Feasibility was lowest for the initial serial impedance plethysmography strategy (mean number of extra hospital visits and mean number of additional tests, 4.1 per patient). Strategies that used the D-dimer test complimentary to ultrasound imaging or the combination of impedance plethysmography and a clinical score performed best (mean number of extra hospital visits and mean number of additional tests, approximately 0.3 per patient). All available noninvasive diagnostic strategies are as accurate and safe as contrast venography for the treatment of patients with clinically suspected deep vein thrombosis. The recently introduced simplified diagnostic strategies allow treatment decisions to be made on the day of presentation in most patients.

Blood coagulation during adjuvant epirubicin/cyclophosphamide chemotherapy in patients with primary operable breast cancer.

Influences of adjuvant epirubicin/cyclophosphamide (EC) chemotherapy on blood coagulation were investigated in patients with operable breast cancer and the incidence of thromboembolic events was recorded. In 50 consecutive node-positive breast cancer patients, serial coagulation studies (fibrinogen method of Clauss, antithrombin III, protein C amidolytic methods, D dimer enzyme-linked immunoadsorbent assay [ELISA] techniques, and plasminogen activator inhibitor [PAI] activity u-PA inhibition test) and impedance plethysmography (IPG) for screening of deep vein thrombosis (DVT) were performed preoperatively and postoperatively, before each of six cycles of adjuvant chemotherapy (60 mg/m2 epirubicin and 600 mg/m2 cyclophosphamide) and 3 months thereafter. Seventy-two healthy women served as controls. During chemotherapy, the phlebographically proven DVT incidence was 10% (n = 2 after second cycle; n = 3 after third cycle). Preoperative levels of D-dimer, fibrinogen, and the PAI activity were significantly higher than in healthy women and only mean levels of the D-dimer were significantly higher in patients with DVT compared with patients without DVT. Postoperatively, only D-dimer and fibrinogen levels significantly increased, while in the course of chemotherapy, these levels were significantly decreased. Mean D-dimer levels and PAI increased steadily in patients with DVT. Preoperatively and during chemotherapy, levels of antithrombin III and protein C were within the normal range. Only one patient with DVT had decreased protein C levels throughout chemotherapy. Monitoring with sophisticated coagulation tests during adjuvant EC chemotherapy for breast cancer does not identify patients at higher risk for DVT development. Preoperatively, in patients with later DVT, an imbalance of hemostasis is already present; thus, thrombosis might predominantly be initiated by malignancy-induced hypercoagulability and secondarily by the influence of EC chemotherapy. Prospective randomized trials must determine whether prophylactic anticoagulation during EC chemotherapy reduces the incidence of DVT.

Cost-effectiveness of Pulmonary Embolism Diagnosis

I read with interest the recent article Cost-effectiveness of Pulmonary Embolism Diagnosis by Hull et al. 1 The authors claim that a strategy using serial impedance plethysmography in patients with non-diagnostic lung scans and adequate cardiopulmonary reserve is the most cost-effective approach to the diagnosis and management of suspected pulmonary embolism. Their approach may actually be even less costly than they report, if the strategy is sufficiently supported by validating data documenting effectiveness. In their cost calculations, Hull and colleagues include expenses for 5 serial noninvasive lower extremity studies. While 5 leg tests were performed in their initial 1989 study of this strategy, 2 the findings of a more recent investigation involving patients with suspected deep vein thrombosis suggested that a total of 3 examinations yields similar results. 3 If this theory is true, the proposed approach would save an additional $300 to $600 per patient. The cost savings projected

Cost-effectiveness of Pulmonary Embolism Diagnosis

In recent years, improvements in the methods of clinical trials and the use of objective tests to detect venous thrombosis have enhanced the clinician's ability to diagnose pulmonary embolism. To perform a cost-effectiveness analysis of the commonly recommended strategies for pulmonary embolism diagnosis and management. Two criteria of effectiveness were used: correct identification of pulmonary embolism and correct identification of patients in whom treatment was unnecessary. The cost of each diagnostic alternative was defined as the direct cost of administering the diagnostic test plus the treatment cost associated with a positive test result. Data derived from a decision analysis published separately on 662 patients were used for this study. A strategy based on the use of ventilation-perfusion lung scans, serial impedance plethysmography, and pulmonary angiography was the most cost-effective. It remained so under all possible variations within the sensitivity analysis. The strategy that requires pulmonary angiography in the fewest patients is a combination of ventilation-perfusion lung scans and serial impedance plethysmography. This strategy also proved to be the most cost-effective.

A Noninvasive Approach for the Treatment of Patients with Suspected Pulmonary Embolism.

The diagnosis of pulmonary embolism is challenging because the signs and symptoms are nonspecific, the findings on ventilation-perfusion lung scans are often nondiagnostic, and pulmonary angiography, although definitive, is not always available. We previously reported that serial noninvasive leg testing provided a practical, noninvasive alternative to pulmonary angiography in patients who had nondiagnostic lung scans and adequate cardiorespiratory reserve. In this prospective cohort study of 1564 patients with suspected pulmonary embolism, ventilation-perfusion lung scanning and serial impedance plethysmography were used to objectively assess prognosis. Only 12 of 627 patients (1.9%) with nondiagnostic lung scans but normal serial leg testing results who were not given anticoagulants had venous thromboembolism during long-term follow-up. Noninvasive serial leg testing can avoid the need for pulmonary angiography for the majority of patients, identify those with proximal vein thrombosis who require anticoagulant treatment, and avert treatment and further investigation of patients who have adequate cardiorespiratory reserve.

Impedance Plethysmography for Suspected Deep-Vein Thrombosis-Reply

In reply We agree with Raskob and associates that the use of serial impedance plethysmography (IPG) is generally a safe approach in patients with suspected venous thromboembolism. Our recommendation that patients with a high pretest probability of deep-vein thrombosis (DVT) and a normal IPG undergo further testing is based on several considerations. First, Raskob and associates fail to cite one study 1 in which the use of serial IPG in 381 consecutive patients with suspected DVT was associated with an unacceptably high rate of venous thromboembolism (10 patients [3.2%]), including four episodes of fatal pulmonary embolism, in follow-up. Although a novel IPG machine was used, its sensitivity for proximal DVT in a preliminary study was 91%, a rate consistent with those reported earlier. 2 Fatal pulmonary embolism has also been reported in high-risk patients on the day of normal IPG testing. 3 Second, our study showed that the sensitivity of

Application of a Novel and Rapid Whole Blood Assay for D-Dimer in Patients with Clinically Suspected Pulmonary Embolism

To determine the clinical utility of a novel whole blood assay for D-dimer (SimpliRED) in patients with clinically suspected pulmonary embolism (PE). Prospective cohort. Eighty-six consecutive patients with clinically suspected PE. All patients had the SimpliRED D-dimer assay performed and underwent ventilation/perfusion (V/Q) lung scanning and bilateral impedance plethysmography (IPG); pulmonary angiography was performed in two patients. Patients were classified as: 1) PE-positive; positive pulmonary angiography or high probability V/Q scan or non-high probability V/Q scan and either abnormal IPG (either at presentation or upon serial testing and confirmed by contrast venography) or symptomatic thromboembolic event within three months of presentation or 2) PE-negative; normal V/Q scan or normal pulmonary angiography or non-high probability V/Q scan and normal serial IPG and absence of symptomatic venous thromboembolism within three months of follow up. Sixteen (19%) patients were classified as PE-positive and 70 (81%) patients were classified as PE-negative. MEASUREMENTS AND RESULT: The sensitivities, specificities, positive predictive values, and negative predictive values of the D-dimer assay were calculated for all patients and for the subgroup of patients without comorbid conditions that independently can cause elevated D-dimer levels. The D-dimer showed a sensitivity of 94%, a negative predictive value of 98%, a specificity of 66%, and a positive predictive value of 38%. In the subgroup of patients without comorbid conditions, the specificity increased to 98% and the positive predictive value to 83%, but because only six patients had an abnormal D-dimer level, the 95% confidence interval on the observed positive predictive value is wide (36-100%). This study demonstrates that the SimpliRED D-dimer assay, which can be performed and interpreted at the bedside within five minutes, has potential clinical utility as an exclusionary test in patients with clinically suspected PE. The assay should be evaluated in large clinical management studies.

A prospective study of venous thromboembolism after major trauma.

Although deep-vein thrombosis and pulmonary embolism are considered common complications after major trauma, their frequency and the associated risk factors have not been carefully quantified. We performed serial impedance plethysmography and lower-extremity contrast venography to detect deep-vein thrombosis in a cohort of 716 patients admitted to a regional trauma unit. Prophylaxis against thromboembolism was not used. Deep-vein thrombosis in the lower extremities was found in 201 of the 349 patients (58 percent) with adequate venographic studies, and proximal-vein thrombosis was found in 63 (18 percent). Three patients died of massive pulmonary embolism before venography could be performed. Before venography, only three of the patients with deep-vein thrombosis had clinical features suggestive of the condition. Deep-vein thrombosis was found in 65 of the 129 patients with major injuries involving the face, chest, or abdomen (50 percent); in 49 of the 91 patients with major head injuries (53.8 percent); in 41 of the 66 with spinal injuries (62 percent); and in 126 of the 182 with lower-extremity orthopedic injuries (69 percent). Thrombi were detected in 61 of the 100 patients with pelvic fractures (61 percent), in 59 of the 74 with femoral fractures (80 percent), and in 66 of the 86 with tibial fractures (77 percent). A multivariate analysis identified five independent risk factors for deep-vein thrombosis: older age (odds ratio, 1.05 per year of age; 95 percent confidence interval, 1.03 to 1.06), blood transfusion (odds ratio, 1.74; 95 percent confidence interval, 1.03 to 2.93), surgery (odds ratio, 2.30; 95 percent confidence interval, 1.08 to 4.89), fracture of the femur or tibia (odds ratio, 4.82; 95 percent confidence interval, 2.79 to 8.33), and spinal cord injury (odds ratio, 8.59; 95 percent confidence interval, 2.92 to 25.28). Venous thromboembolism is a common complication in patients with major trauma, and effective, safe prophylactic regimens are needed.

D-Dimer in Patients With Clinically Suspected Pulmonary Embolism

To determine whether measurement of D-dimer, using an enzyme-linked immunosorbent assay (ELISA) with a cutoff of 300 ng/ml, and a latex agglutination assay with a cutoff of 500 ng/ml, is clinically useful in patients with suspected pulmonary embolism (PE). Prospective cohort. Tertiary care referral center, university-affiliated hospital. Two hundred twenty-one consecutive patients with clinically suspected PE. All patients had blood drawn to measure levels of D-dimer and underwent ventilation/perfusion (V/Q) lung scanning and bilateral impedance plethysmography (IPG); pulmonary angiography was performed in nine patients. Patients were classified as follows: (1) PE-positive; positive pulmonary angiography or high probability V/Q scan or non-high-probability V/Q scan and either abnormal IPG (either at presentation or on serial testing and confirmed by contrast venography) or symptomatic thromboembolic event within 3 months of presentation; or (2) PE-negative; normal V/Q scan or normal pulmonary angiography or non-high-probability V/Q scan and either normal serial IPG or abnormal IPG with normal venography and absence of symptomatic venous thromboembolism within 3 months of followup. Forty-three patients were classified as PE positive and 178 patients were classified as PE negative. The sensitivities, specificities, positive predictive values, and negative predictive values of the ELISA and latex agglutination assay were calculated for all patients and for the subgroup of patients with non-high-probability V/Q scans. The ELISA D-dimer, using a cutoff of 300 ng/ml, showed a sensitivity and negative predictive value of 100 percent in all patients and patients with non-high-probability V/Q scans, but the corresponding specificities were only 26 percent and 13 percent, respectively. The latex agglutination assay for D-dimer using a cutoff of 500 ng/ml showed the following: sensitivities of 84 percent in all patients and 90 percent in patients with non-high-probability scans, negative predictive values of 93 percent in all patients, and 98 percent in patients with non-high-probability scans and specificities of 56 percent in all patients and 55 percent in patients with non-high-probability scans. This study demonstrates that an ELISA D-dimer result of less than 300 ng/ml excludes PE but occurs in a small proportion of patients with clinically suspected PE. The latex agglutination assay, using a cutoff of 500 ng/ml, has potential clinical utility in excluding PE in the subgroup of patients with clinically suspected PE and non-high-probability V/Q scans. However, the 95 percent confidence interval on the observed sensitivity of the latex agglutination assay in patients with non-high-probability V/Q scans is wide. Therefore, these promising results should be confirmed in a large clinical trial before the latex agglutination assay is used to make management decisions.

Deep Vein Thrombosis in Obstetric Patients: Diagnosis and Risk Factors

This study was performed to assess the prevalence of deep vein thrombosis (DVT) in consecutive obstetric patients with clinical symptoms of DVT, using impedance plethysmography (IPG) as the diagnostic method and to establish the safety of withholding anticoagulant therapy in patients with a repeatedly normal IPG. In addition, in patients with DVT the prevalence of coagulation and fibrinolytic disorders, which may explain the occurrence of venous thrombosis was investigated. Of the 77 obstetric patients with symptoms of DVT, 32 (42%) had an abnormal IPG. The remaining 45 patients had a repeatedly normal IPG and showed no venous thromboembolism during a 6 months follow-up period. Twenty percent (six patients) of the patients with an abnormal IPG had a coagulation or fibrinolytic abnormality. These observations suggest that serial IPG can be used effectively in the management of obstetric patients with clinically suspected DVT and that hemostatic abnormalities are frequently found in those patients with DVT.

The Use of the D-Dimer Test in Combination with Non-Invasive Testing Versus Serial Non-Invasive Testing Alone for the Diagnosis of Deep-Vein Thrombosis

We studied the usefulness of the determination of plasma D-dimer levels (using an ELISA) in combination with non-invasive testing with impedance plethysmography (IPG) or real-time ultrasonography (US) for the diagnosis of deep-vein thrombosis (DVT), in outpatients with clinically suspected DVT. This combined approach was compared to serial non-invasive testing alone in these patients. The sensitivity of a positive D-dimer test (greater than 300 micrograms/l) for the presence of DVT was 100% (70/70 patients; 95% C.I.: 95-100%), whereas the specificity was 29% (69/239 patients; 95% C.I.: 23-34%). The proportion of patients in which a definitive decision about the presence or absence of DVT could be made on the day of referral, was calculated for both approaches. When applying the combined approach, in 42% of all referred patients the diagnosis of DVT could either be established or refuted on entry, as opposed to only 19% of patients using serial non-invasive testing alone. Also, the costs per DVT diagnosed were calculated for the two diagnostic approaches. For the diagnosis of DVT the costs using serial IPG were comparable to the costs using the combination of IPG and the D-dimer test. The same conclusion holds for the comparison of serial US with the combination of US and D-dimer testing. We conclude that for the diagnosis of DVT in symptomatic outpatients the combination of non-invasive testing with the D-dimer test might be preferred over serial non-invasive testing alone, although the safety of such an approach remains to be established in future management studies.

D-Dimer and Thrombin-Antithrombin III Complexes in Patients with Clinically Suspected Pulmonary Embolism

One hundred and fifty-six consecutive patients with clinically suspected pulmonary embolism (PE) had blood drawn to measure levels of D-dimer and thrombin-antithrombin (TAT) complexes and underwent ventilation/perfusion (V/Q) lung scanning and bilateral impedance plethysmography (IPG); pulmonary angiography was performed in 10 patients. Patients were classified as: PE-positive (positive pulmonary angiography or high probability lung scan or non-high probability lung scan and abnormal IPG) or, PE-negative (normal lung scan or normal pulmonary angiography) or PE-unlikely (non-high probability lung scan and normal serial IPG and absence of venous thromboembolism in follow-up). Thirty patients were classified as PE-positive, 64 as PE-negative and 62 patients as PE-unlikely. PE-positive patients were treated with anticoagulants, whereas PE-negative and PE-unlikely patients were not. PE-unlikely patients were followed for 3 months with repeat IPG and clinical evaluation for the occurrence of venous thromboembolism. The sensitivities, specificities, positive predictive values and negative predictive values of the D-dimer and TAT complex assays were calculated for patients classified as PE-positive and PE-negative. In addition, the prevalences of normal D-dimer and TAT complex assays were calculated for PE-unlikely patients. Cutoffs of 300 ng/ml for D-dimer and 3.5 micrograms/ml for TAT complexes provided sensitivities of 96% for both assays, negative predictive values of 97% for D-dimer and 96% for TAT complexes and specificities of 52% for D-dimer and 51% for TAT complexes. The specificities of the assays were higher in patients without comorbid conditions and in outpatients.(ABSTRACT TRUNCATED AT 250 WORDS)

Management of clinically suspected acute venous thrombosis in outpatients with serial impedance plethysmography in a community hospital setting: Huisman MV, Buller HR, ten Cate JW, et al. Arch Int Med 1989:149:511-3

Management of clinically suspected acute venous thrombosis in outpatients with serial impedance plethysmography in a community hospital setting: Huisman MV, Buller HR, ten Cate JW, et al. Arch Int Med 1989:149:511-3

Diagnosing Pulmonary Embolism: New Facts and Strategies

To provide a clinical approach to the diagnosis of pulmonary embolism. An English-language literature search using MEDLINE (1982 to 1990) and bibliographic reviews of textbooks and review articles. In addition to several reviews, studies that evaluated the diagnostic technology of pulmonary embolism were selected. Preference was given to studies with a prospective design, particularly those done within the past decade. Studies were assessed independently by three unblinded observers. Data were chosen to describe the efficacy of diagnostic technology on the basis of disease prevalence, sensitivity and specificity, and predictive value. A normal lung scan or pulmonary angiogram rules out the diagnosis of clinically important pulmonary embolism with at least 95% certainty. Lung scan interpretations indicating high or low probability have approximately a 15% error in diagnosing or ruling out pulmonary embolism. The accuracy of either scan result improves when the clinical suspicion of pulmonary embolism matches the lung scan result. Serial impedance plethysmography of the lower extremities may exclude thromboembolism with 95% certainty in patients without high-probability lung scan results or cardiopulmonary disease. The combination of clinical suspicion and the results of the lung scan and impedance plethysmography appear to offer acceptable diagnostic accuracy in evaluating many patients suspected of having pulmonary embolism. The usefulness of this approach for patients with cardiopulmonary disease is still unknown.

Serial impedance plethysmography in pregnant patients with clinically suspected deep-vein thrombosis. Clinical validity of negative findings

STUDY OBJECTIVE To determine the safety of withholding anticoagulant therapy in pregnant patients with clinically suspected deep-vein thrombosis who have negative results by serial impedance plethysmography. DESIGN Prospective study evaluating prognosis by long-term follow-up to 3 months postpartum in all patients. SETTING University-affiliated community hospital and referral center. PATIENTS One hundred fifty-two consecutive pregnant patients referred with clinically suspected deep-vein thrombosis. All patients completed the study. INTERVENTIONS Anticoagulant therapy was withheld in 139 patients negative by serial impedance plethysmography, and the patients were followed long term. MEASUREMENTS AND MAIN RESULTS None of 139 patients (0%; 95% CI, 0% to 2.6%) had symptomatic pulmonary embolism or recurrent venous thrombosis. CONCLUSIONS The findings establish the safety of withholding anticoagulant therapy in pregnant patients who have negative results after serial impedance plethysmography. Sufficient patients were entered to provide narrow confidence intervals on the outcomes observed in patients with negative findings by impedance plethysmography. These findings are similar to those seen after venography in symptomatic patients. These data extend the role of non-invasive testing in patients with clinically suspected deep-vein thrombosis to the pregnant symptomatic patient.

Randomized controlled study of heparin and low molecular weight heparin for prevention of deep-vein thrombosis in medical patients

166 patients aged 40–80 years were included in a controlled, randomized, double-blind study to determine the efficacy and safety of a single daily injection of a low molecular weight (LMW) heparin for prevention of deep-vein thrombosis compared to low dose conventional heparin. Patients received 1 × 1.500 aPTT units of a LMW heparin fraction (plus 2 × placebo injection) or 3 × 5.000 IU of an unfractionated heparin. During 10 days of treatment, patients underwent repeated clinical investigation, serial impedance plethysmography, and Doppler sonography for detection of thrombosis of the lower limbs. Combined application of these methods revealed evidence of thrombosis in 4.5 % of patients on unfractionated heparin and 3.6 % of patients on LMW heparin. Subcutaneous hematomas were significantly smaller in diameter upon treatment with LMW heparin (p<0.001). Antithrombin III levels were significantly higher at the end of the observation period in the LMW heparin group (p<0.005). Thrombocyte count, transaminases, creatinine, and haemoglobin did not change in either group. The results indicate that LMW heparin administered by a single s.c. dose daily may be as effective as low dose heparin in prevention of deep venous thrombosis in medical inpatients.

Serial Impedance Plethysmography in Pregnant Patients with Clinically Suspected Deep-Vein Thrombosis

To determine the safety of withholding anticoagulant therapy in pregnant patients with clinically suspected deep-vein thrombosis who have negative results by serial impedance plethysmography. Prospective study evaluating prognosis by long-term follow-up to 3 months postpartum in all patients. University-affiliated community hospital and referral center. One hundred fifty-two consecutive pregnant patients referred with clinically suspected deep-vein thrombosis. All patients completed the study. Anticoagulant therapy was withheld in 139 patients negative by serial impedance plethysmography, and the patients were followed long term. None of 139 patients (0%; 95% CI, 0% to 2.6%) had symptomatic pulmonary embolism or recurrent venous thrombosis. The findings establish the safety of withholding anticoagulant therapy in pregnant patients who have negative results after serial impedance plethysmography. Sufficient patients were entered to provide narrow confidence intervals on the outcomes observed in patients with negative findings by impedance plethysmography. These findings are similar to those seen after venography in symptomatic patients. These data extend the role of non-invasive testing in patients with clinically suspected deep-vein thrombosis to the pregnant symptomatic patient.