Acute pulmonary thromboembolism: has its evolution been redefined?

Close concordance between pulmonary angiography and pathology in a canine model with chronic pulmonary thromboembolism and pathological mechanisms after lung ischemia reperfusion injury

To investigate the pulmonary angiography and pathology in a canine model with chronic pulmonary thromboembolism (PTE). The cylindrical blood clots were selectively introduced into the left (n = 10) or right (n = 20) lower pulmonary arteries of dogs. Pulmonary arteriography (PA) was performed before or after embolization. The values after embolization and baseline of mean pulmonary arterial pressure, pulmonary vascular resistance, cardiac output had changed. After 1 or 2 weeks' embolization, local PA demonstrated the abrupt cut-off perfusion defects or webs, bands, and abrupt vascular narrowing. 2 weeks after embolization, the pathology showed that the fibrin networks of the thrombi had multiple recanalization channels, and pulmonary artery had the concentric, lamellar (onion-like) intimal hyperplasia, multilayered, irregular arrangements of endothelial cells, and the infiltration of inflammatory cells. After embolectomy-mediated reperfusion, 2 weeks' subgroup showed destroyed and incomplete alveolar structures, and a large number of exudative cells, primarily neutrophils, and exudate. There close concordance between pulmonary angiography and pathology in a canine model with chronic PTE. The LIRI mechanisms after embolectomy-mediated reperfusion involve the destroyed, incomplete alveolar structures, and infiltration of inflammatory cells, primarily neutrophils.

Plasmin and Matrix Metalloproteinase System in Deep Venous Thrombosis Resolution

Deep venous thrombosis (DVT) is a common event in hospitalized medical and surgical patients. Outside of anticoagulation, few good options exist for decreasing the vein wall damage that results after natural thrombolysis. DVT resolution is complex and involves chemokines, leukocytes, and native vein wall cells. Herein some aspects of DVT resolution related to the intersection of inflammation, the plasminogen and matrix metalloproteinase systems, and their respective inhibitors are reviewed. Ultimately, better knowledge of these natural thrombolytic systems may allow local, directed, and specific acceleration of DVT resolution and decreased vein wall damage.

Absence of IFN-γ accelerates thrombus resolution through enhanced MMP-9 and VEGF expression in mice

Deep vein thrombosis (DVT) is a major cause of pulmonary thromboembolism, a leading cause of death in individuals with DVT. Several lines of evidence indicate proinflammatory cytokines such as TNF-α are involved in thrombus formation and resolution, but the roles of IFN-γ remain unclear. To address this issue, we performed ligation of the inferior vena cava to induce DVT in WT and IFN-γ-deficient (Ifng-/-) mice. In WT mice, intrathrombotic IFN-γ levels were elevated progressively as the postligation interval was extended. Thrombus size was substantially smaller at 10 and 14 days in Ifng-/- mice than in WT mice. Intrathrombotic collagen content was remarkably reduced at more than 10 days after the ligation in Ifng-/- mice compared with WT mice. The expression and activity of MMP-9, but not MMP-2, was higher at the late phase in Ifng-/- mice than in WT mice. Moreover, intrathrombotic recanalization was increased in Ifng-/- mice, with enhanced Vegf gene expression, compared with that in WT mice. Activation of the IFN-γ/Stat1 signal pathway suppressed PMA-induced Mmp9 and Vegf gene expression in peritoneal macrophages. Furthermore, administration of anti-IFN-γ mAbs accelerated thrombus resolution in WT mice. Collectively, these findings indicate that IFN-γ can have detrimental roles in thrombus resolution and may be a good molecular target for the acceleration of thrombus resolution in individuals with DVT.

Evaluation of right ventricle function in children with primary nephrotic syndrome

BACKGROUND

We aimed to evaluate right ventricle (RV) function in children with primary nephrotic syndrome (PNS).

METHODS

RV hemodynamics were evaluated by Doppler echocardiography in 50 children with PNS (aged 2.5-12 years), either at PNS onset (n = 37) or relapse (n = 13), and in 50 normal controls. Heart rate, stroke volume, cardiac output, RV enddiastolic and end-systolic volume, RV ejection fraction, RV end-diastolic pressure, RV peak systolic and end-systolic pressure were determined from pressure-volume loops. The maximal rates of RV pressure upstroke and fall (dP/d t(max) and dP/d t(min), respectively) were calculated. Effective pulmonary arterial elastance was calculated as end-systolic pressure divided by stroke volume. Plasma tumor necrosis factor-alpha (TNF-alpha) and insulin-like growth factor 1 (IGF-1) were also measured.

RESULTS

RV end-diastolic pressure was increased by an average of 20% in 39 of the patients with PNS, whereas RV ejection fraction was reduced by an average of 15% compared with controls (p < 0.05 for both). Cardiac output and stroke volume were maintained, indicating compensation at the expense of increased RV end-diastolic and end-systolic volumes and increased RV filling pressure (p < 0.05). Plasma TNF-alpha was elevated in patients with PNS (326 +/- 117 kU/L vs. 75 +/- 23 kU/L, p < 0.05); IGF-1 was similar in PNS patients and controls.

CONCLUSION

Right ventricle function was impaired in children with PNS. The characteristics were unrelated to blood pressure and IGF-1, but may be correlated with TNF-alpha and disease duration. Further studies are needed to evaluate the etiology and clinical implications of this abnormality.

Evaluation of Persistent Pulmonary Hypertension After Acute Pulmonary Embolism

BACKGROUND

Better knowledge of the evolution of persistent pulmonary hypertension after acute pulmonary embolism (PE) is required to optimize the indication and timing of pulmonary endarterectomy (PEA).

METHODS

We reviewed our experience with 17 consecutive patients demonstrated to have persistent pulmonary hypertension after acute massive (n = 1), submassive (n = 7), or recurrent PE (n = 9).

RESULTS

After a median of 18 weeks of anticoagulation (range, 12 to 30 weeks) since the last PE, 10 patients showed residual pulmonary artery systolic pressure (PAsP) > 50 mm Hg. These patients demonstrated a significant progression in PAsP over the ensuing 6 to 12 months, from 73 +/- 14 to 101 +/- 26 mm Hg (p = 0.005) [mean +/- SD], and eight patients were found to be suitable candidates for PEA. In contrast, among seven patients with residual PAsP from 35 to 40 mm Hg (n = 3) and 41 to 50 mm Hg (n = 4), six patients had evidence of residual perfusion defects on the ventilation/perfusion scan and CT. The PAsP did not change significantly over the ensuing 6 to 12 months, except in two patients who had new episodes of acute PE.

CONCLUSIONS

Two groups of patients can be identified based on the degree of residual pulmonary hypertension after acute PE. Patients with residual PAsP > 50 mm Hg should be evaluated for PEA since their pulmonary artery pressures will significantly progress over the ensuing 6 to 12 months despite the absence of recurrent PE. In contrast, patients with PAsP from 35 to 50 mm Hg are at risk for severe pulmonary hypertension if new PE occurs, and should therefore be closely monitored.

Natural History of Right Ventricular Dysfunction After Acute Pulmonary Embolism

BACKGROUND

Acute pulmonary embolism (PE) associated with right ventricular (RV) dysfunction has an adverse prognosis. We investigated individual parameters of RV dysfunction after acute PE, assessing their correlation with the PE extent and recovery during 6 months.

METHODS

In all, 35 patients (age 63 +/- 18 years) with acute PE were prospectively investigated for 6 months with serial echocardiography, incorporating longitudinal myocardial-velocity and strain imaging. The extent of PE was quantified on day 1 by ventilation/perfusion pulmonary scintigraphy with PE defined as large when there was greater than 30% lung involvement.

RESULTS

PE extent correlated strongly with a number of parameters of RV function, and the strongest univariate correlates were tricuspid annular motion (TAM) (r = -0.65, P < .0001) and the ratio of RV apical to RV basal systolic velocity (r = 0.66, P < .0001). Multivariate analysis identified TAM (P < .0001) and RV basal late-diastolic velocity (P = .01) as independently predicting PE extent, with a combined correlation (R2 = 0.52, P < .0001). A TAM of less than 2.0 cm had sensitivity, specificity, and positive- and negative-predictive values of 75%, 84%, 75%, and 79%, respectively, in predicting large PE. Prospective follow-up identified that RV:left ventricular end-diastolic area ratio returned to normal within 6 weeks, whereas TAM and ratio of RV apical to RV basal systolic velocity normalized after 3 to 6 months.

CONCLUSION

TAM and ratio of RV apical to RV basal systolic velocity are useful indicators of the extent of PE, and provide unique insights into the recovery of RV function after acute PE.

Chronic thromboembolic pulmonary hypertension

The description of organized thrombus in major pulmonary arteries can be found in autopsy reports dating back to the late nineteenth and early twentieth centuries. Not until the 1950s was the antemortem diagnosis and clinical syndrome of chronic thrombotic obstruction of the major pulmonary arteries better characterized. The first surgical attempt to remove the adherent thrombus from the vessel wall occurred in 1958. This operation provided the conceptual foundation for the distinction between acute and chronic thromboembolic disease of the pulmonary vascular bed, and established that an endarterectomy, and not an embolectomy, would be necessary if a surgical remedy for this disease was to be successful.

Vascular endothelium summary statement V: Pulmonary hypertension and acute lung injury: public health implications

Although relatively rare, pulmonary hypertension can be devastating for those individuals who are affected and has significant societal implications. The 2003 WHO classification separates PAH (idiopathic, specific disease linked) from pulmonary hypertension related to lung disease, thromboembolic disease, and pulmonary venous hypertension. Another form of pulmonary hypertension, persistent pulmonary hypertension (PPHN), occurs in the newborn. In general, PPHN is thought to be responsible for approximately 10% of admissions to neonatal intensive care units and can be a complicating factor in 5 of 1000 live births. Acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) are complex disorders that pose a significant threat to critically ill patients. They are usually related to direct lung injury or indirect injury from sepsis, trauma, and other disorders. Although these pulmonary disorders reflect distinct pathophysiologic mechanisms, current evidence strongly suggests that a common denominator underlying many of the established molecular and cellular elements is endothelial cell activation and dysfunction. This summary statement briefly summarizes the state of the science and suggests future avenues of public health research.

Atrial and ventricular echocardiographic correlates of the extent of pulmonary embolism in the elderly

BACKGROUND

Acute pulmonary thromboembolism (PTE) can be associated with right ventricular (RV) dysfunction. The relative importance of individual echocardiographic parameters, including those suggesting interdependence between right and left heart chambers, in predicting thromboembolic burden in elderly patients with acute PTE is unknown.

METHODS

We retrospectively studied the transthoracic echocardiograms of 63 elderly patients (age 71 +/- 16 years) with acute PTE, and assessed which individual echocardiographic parameters identified more than 30% pulmonary artery obstruction on the basis of quantitative ventilation/perfusion pulmonary scintigraphy.

RESULTS

RV hypokinesis (visual grade 0-3, P = .02), and the quantitative parameters RV end-systolic area (P = .005) and RV ejection area (P = .01) were associated with more extensive pulmonary artery obstruction. Although right atrial end-systolic area and RV end-diastolic area did not correlate with extent of PTE, the ratio of RV:left ventricular end-diastolic area (P = .003), and ratio of right:left atrial end-systolic area (P = .004), were strongly associated with the extent of pulmonary artery obstruction. These transthoracic echocardiographic parameters were independent of clinical variables such as prior chronic lung disease, congestive cardiac failure, or prior PTE.

CONCLUSION

RV systolic dysfunction, RV end-systolic dilatation, right:left atrial end-systolic area ratio, and RV:left ventricular end-diastolic area ratio correlate with extent of PTE in the elderly.

The role of inflammation in early and late venous thrombosis: Are there clinical implications?

Venous thrombosis is associated with a significant inflammatory response. Inflammatory cells, adhesion molecules (especially selectins), cytokines, and procoagulant microparticles appear to be associated with the thrombogenic process. Once thrombus forms, inflammatory cells are important to thrombus resolution along with fibrinolytic agents and proinflammatory mediators. Collagen and elastin breakdown by the DVT renders the vein wall stiff and non-compliant. Rapid and complete thrombus resolution should lessen vein wall damage and lessen or prevent the development of chronic venous insufficiency. Understanding the basic biology of thrombogenesis and thrombus resolution is important, as novel therapies to both prevent and treat venous thrombosis and hasten thrombus resolution should result from a better understanding of the basic biological mechanisms.

Long-term effects of acute pulmonary embolism on echocardiographic Doppler indices and functional capacity

BACKGROUND AND HYPOTHESIS

Hemodynamic and functional consequences of acute pulmonary embolism (APE) are believed to be reversible with antithrombotic treatment. To verify this hypothesis, we reassessed our patients at least 1 year after an episode of APE.

METHODS

We compared echo Doppler indices and 6-min walking test parameters (6-MWT) of 36 patients (13 men, 23 women, age 66 +/- 11 years), studied on average 3.1 +/- 2.2 years after an acute episode of pharmacologically treated massive or submassive APE, with data of 30 age-matched subjects (12 men, 18 women, age 67 +/- 12 years).

RESULTS

At least 1 year after APE, right ventricular (RV) diameter remained increased in patients compared with controls (27 +/- 2 vs. 23 +/- 2 mm, p<0.001). Also, acceleration time of pulmonary ejection (AcT) was markedly shorter (97 +/- 19 vs. 123 +/- 19 ms, p<0.001) and the diameter of the pulmonary trunk was significantly larger in patients than in controls (21 +/- 2.6 vs. 18 +/- 2.2, p<0.001). Although the mean value of the tricuspid valve peak systolic gradient (TVPG) in the APE group at follow-up was similar to that in controls, TVPG>30 mmHg was recorded in three patients with APE (8.3%). There was no difference in the distance of 6-MWT between both groups; however, the mean desaturation after 6-MWT was higher in the APE group than in controls (3.04 +/- 2.08 vs. 1.45 +/- 0.69%, p=0.0005).

CONCLUSIONS

Pharmacologic treatment of acute pulmonary embolism does not prevent mild persistent changes in morphology and function of the cardiovascular system. Despite normalization of pulmonary artery systolic pressure and similar exercise capacity, survivors of APE present signs suggesting RV dysfunction and/or its disturbed coupling to the pulmonary arterial bed, as well as ventilation to perfusion mismatch at exertion persisting long after the acute embolic episode.

Pulmonary Hypertension Among End-Stage Renal Failure Patients Following Hemodialysis Access Thrombectomy

PURPOSE

Percutaneous hemodialysis thrombectomy causes subclinical pulmonary emboli without short-term clinical consequence; the long-term effects on the pulmonary arterial vasculature are unknown. We compared the prevalence of pulmonary hypertension between patients who underwent one or more hemodialysis access thrombectomy procedures with controls without prior thrombectomy.

METHODS

A retrospective case-control study was performed. Cases (n = 88) had undergone one or more hemodialysis graft thrombectomy procedures, with subsequent echocardiography during routine investigation of comorbid cardiovascular disease. Cases were compared with controls without end-stage renal disease (ESRD) (n = 100, group 1), and controls with ESRD but no prior thrombectomy procedures (n = 117, group 2). The presence and velocity of tricuspid regurgitation on echocardiography was used to determine the prevalence and grade of pulmonary hypertension; these were compared between cases and controls using the chi-square test and logistic regression.

RESULTS

The prevalence of pulmonary hypertension among cases was 52% (46/88), consisting of mild, moderate and severe in 26% (n = 23), 10% (n = 9) and 16% (n = 14), respectively. Prevalence of pulmonary hypertension among group 1 controls was 26% (26/100), consisting of mild, moderate and severe pulmonary hypertension in 14%, 5% and 7%, respectively. Cases had 2.7 times greater odds of having pulmonary hypertension than group 1 controls (p = 0.002). The prevalence of pulmonary hypertension among group 2 controls was 42% (49/117), consisting of mild, moderate and severe pulmonary arterial hypertension in 25% (n = 49), 10% (n = 12) and 4% (n = 5), respectively. Cases were slightly more likely to have pulmonary hypertension than group 2 controls (OR = 1.5), although this failed to reach statistical significance (p = 0.14).

CONCLUSION

Prior hemodialysis access thrombectomy does not appear to be a risk factor for pulmonary arterial hypertension. Patients with ESRD are more likely to have pulmonary hypertension.

Increased pulmonary arterial pressure in children with nephrotic syndrome

AIMS

To evaluate the pulmonary arterial pressure in children with nephrotic syndrome (NS).

METHODS

Doppler echocardiography was performed in 40 children with NS (aged 1.5-13 years) at NS onset (n = 28) or relapse (n = 12), and 40 normal controls. Pulmonary pressure was estimated by: (1) measuring the systolic transtricuspid gradient from tricuspid regurgitation; and (2) measuring the time to peak velocity of pulmonary flow.

RESULTS

Thirty five of the 40 patients with NS had measurable tricuspid regurgitation with a pulmonary systolic pressure ranging from 21 to 48 mm Hg. Pulmonary systolic pressure was >40 mm Hg in seven patients. The pulmonary time to peak velocity was shortened and the ratio of time to peak velocity and right ventricular ejection time decreased compared with controls. The patients with increased pulmonary pressure had a longer time since onset of NS. One patient developed thrombus in the inferior vena cava during hospitalisation.

CONCLUSION

Pulmonary arterial pressure was increased in children with NS. Further work is needed to evaluate the aetiology and clinical implications of this abnormality.

Chronic thromboembolic pulmonary hypertension

During the past 2 decades, there has been a steady rise in the number of patients with chronic thromboembolic pulmonary hypertension (CTEPH) undergoing surgery and in the number of programs worldwide dedicated to the diagnosis and management of this patient population. This article discusses the natural history and clinical presentation of CTEPH, the evaluation of patients for pulmonary thromboendarterectomy, and the outcomes following surgery, along with a brief review of the procedure as performed at the University of California, San Diego.

Echocardiography in pulmonary vascular disease

The assessment of pulmonary artery pressure, right ventricular function, right ventricular filling pressure, and tricuspid regurgitation provides invaluable information in the care of patients with pulmonary vascular disease. Echocardiography provides a rapid, noninvasive, portable, and accurate method to evaluate these parameters and also provides information on left ventricular and valvular function. Echocardiography has therefore become one of the most commonly performed diagnostic studies in patients with pulmonary vascular disease, and the technique's applications in this area are likely to grow. This article presents an overview of the current uses of echocardiography in pulmonary vascular disease and pulmonary hypertension.

Cellular IL-10 is more effective than viral IL-10 in decreasing venous thrombosis

BACKGROUND

Systemic administration of cellular interleukin-10 (cIL-10) and gene transfection of viral interleukin-10 (vIL-10) at thrombus induction decreases vein wall inflammation. Only cIL-10, despite sharing an 84% amino acid sequence homology with vIL-10, decreases thrombosis through mechanisms yet to be determined.

METHODS

C57BL/6 mice (Mus musculus, n99) were studied. Inferior vena caval thrombosis was created by inferior vena caval ligation and the animals were sacrificed and evaluated at days 2 and 6 after ligation. At thrombus induction groups received intravenous 0.25 microg of cIL-10, 0.25 microg of vIL-10, or saline (untreated controls). Evaluations included thrombus mass and vein wall leukocyte counts, protein levels, and reverse-transcription polymerase chain reaction mRNA levels of P- and E-selectin, monocyte chemotactic protein-1, and IL-10. Groups were compared by analysis of variance and t tests.

RESULTS

Less thrombus was noted at both days 2 and 6 in animals treated with cIL-10. At day 2 only, vein wall leukocyte counts revealed a significant decrease in neutrophils in cIL-10 animals versus controls, with no significant differences for vIL-10 animals. In cIL-10-treated animals, P-selectin protein levels were decreased at day 6, along with a decreased thrombus mass, without significant differences in E-selectin, monocyte chemotactic protein-1, or IL-10 protein levels. vIL-10 treated animals showed increased E-selectin mRNA and thrombus mass versus controls on day 6.

CONCLUSIONS

cIL-10 is more antithrombotic/anti-inflammatory than vIL-10. This may be the result of cIL-10 decreasing P-selectin protein expression and vIL-10 increasing E-selectin mRNA levels.

Evaluation of the deep venous system in patients with suspected pulmonary embolism with multi-detector CT: a prospective study in comparison to Doppler sonography

OBJECTIVE

This prospective study was done to evaluate the ability of indirect multidetector row CT venography (CTV) in detecting deep venous thrombosis of the pelvis and the thighs in comparison with Doppler sonography in patients with suspected pulmonary embolism (PE).

METHODS

Forty-one patients with suspected PE were included, and CTV (collimation 4 x 2.5 mm, table feed 12.5 mm, 120 kV, eff. mAs 165) from the iliac crest to the knees was done after CT angiography (CTA) of the pulmonary arteries. Doppler sonography was performed within 24 hours. Applied radiation doses were estimated using the PC program WinDose.

RESULTS

PE was diagnosed in 20 patients with additional DVT in 11 patients. The CTV has a sensitivity of 100%, specificity of 96.6%, a positive and negative predictive value of 91.7% and 100%, respectively. The median cumulative effective dose for CTV was 8.26 mSv with a gonadal dose of 3.87 mSv. Changing the CTV protocol to a collimation of 4 x 5 mm with a 25 mm table feed could reduce the dose by approximately 11% (p < 0.05) to 7.25 mSv and 3.35 mSv, respectively.

CONCLUSION

CTV is a safe and quick diagnostic tool for detecting DVT in patients with suspected PE. Due to the relevant increase in radiation dose, the indication has to be considered very carefully.

Selectins influence thrombosis in a mouse model of experimental deep venous thrombosis

BACKGROUND

This study characterizes venous thrombosis in the mouse and examines the important role that the adhesion molecules P-selectin and E-selectin and the anti-inflammatory cytokine interleukin-10 (IL-10) play in the thrombotic process.

MATERIALS AND METHODS

C57BL/6 (wild-type) mice in a natural history protocol (Phase I) and gene-targeted (KO) mice for P-selectin, E-selectin, P/E-selectin, and IL-10 in a follow-up protocol (Phase II) were studied. Inferior vena caval thrombosis was produced by ligation just below the renal veins, and mice were sacrificed and evaluated at various time points up to 12 days later.

RESULTS

Phase I: A significant increase in neutrophils on day 2 and in monocytes on day 6 postthrombosis was found in ligated vs sham animals. An associated significant increase in vein wall P-selectin mRNA (6 h, day 2) and an increase in protein (6 h through day 6) were found, while E-selectin mRNA was significantly increased (day 2 through day 6), with a smaller increase in E-selectin protein. IL-10 mRNA increased significantly later (day 2 through day 9), with the values increasing progressively. A positive correlation existed (r = 0.77) between neutrophils and thrombosis at day 2.

PHASE II

The E-selectin and P/E-selectin double-KO mice showed the least thrombus at day 2 vs wild-type clotted mice, P < 0.01. Additionally, P/E-KO mice demonstrated the lowest inflammatory cell extravasation into the vein wall at day 2.

CONCLUSIONS

This study demonstrates an acute to chronic inflammatory response in the vein wall associated with venous thrombosis. Inhibition of selectins decreased thrombus formation.

Electron beam tomography of interpulmonary saddle embolism: extent and vascular distribution

PURPOSE

The purpose of this work was to assess morphology and secondary signs of interpulmonary emboli extending across the bifurcation of the main pulmonary artery (PA).

METHOD

Retrospective evaluation of 780 electron beam tomographic studies of the chest yielded 17 cases of interpulmonary saddle embolism. Length, diameter, vascular distribution of the emboli, and secondary findings were prospectively assessed by two blinded reviewers. Follow-up studies were carried out in 12 of 17 patients (71%).

RESULT

Mean total length of the emboli was 46.6 cm (range 20.9-81.5 cm). The mean diameter of the saddle embolus was significantly smaller at the level of the bifurcation than in the left or right PA (4.5, 7.7, and 7.4 mm, respectively; p < 0.01). Dilatation of the right heart was found in 10 of 17 cases (59%). At follow-up, the saddle state was no longer present in 8 of 12 patients (67%).

CONCLUSION

Interpulmonary saddle emboli appear to be a transient form of acute pulmonary embolism, the site of predilection for rupture of the embolus being the level of the bifurcation. Their frequency may therefore be underestimated.

Development of oral heparin therapy for prophylaxis and treatment of deep venous thrombosis

OBJECTIVE

To review the current research and published literature regarding the development of oral heparin therapy for the prophylaxis and treatment of deep venous thrombosis.

BACKGROUND

Currently, the accepted practice of prophylaxis and/or treatment of acute deep venous thrombosis (DVT) is intravenous or subcutaneous (SQ) heparin followed by oral warfarin or SC low molecular weight heparin (LMWH) therapy followed by warfarin. Both of which are less than ideal. More recently, advances have been made towards an effective oral heparin preparation that would resolve many of the drawbacks to the current therapies.

METHODS

A review of the current and relevant English literature identified via a search of the Medline database from January 1990 to present.

RESULTS

Initial oral heparin therapy for DVT was unsuccessful due to presumed inadequate intestinal absorption as a result of heparin's molecular and structural characteristics. The development of oral heparin therapy, based on combining heparin with the carrier molecule Sodium N-(8[2-hydroxybenzoyl]amino) caprylate (SNAC) to enhance its intestinal absorption and bioavailability for the prophylaxis and treatment of DVT has been demonstrated to be effective in animal models. More recent efforts have been aimed at human trials.

CONCLUSION

Recent advances in prophylaxis and treatment of DVT have stimulated great interest among researchers to develop an effective, convenient, and well tolerated oral therapy. An effective oral heparin therapy may represent an ideal method of prophylaxis and treatment of DVT.