Preventive and therapeutic approach to venous thromboembolic disease and pulmonary embolism--can death from pulmonary embolism be prevented?

Optimizing inferior vena cava filter design: A computational fluid dynamics study on strut configuration for enhanced hemodynamic performance and thrombosis reduction

Background and objective

Inferior vena cava filters have been shown to be effective in preventing deep vein thrombosis and its secondary complication, pulmonary embolism, thereby reducing the high mortality rate. Although inferior vena cava filters have evolved, specific complications like inferior vena cava thrombosis-induced deep vein thrombosis worsening and recurrent pulmonary embolism continue to pose challenges. This study analyzes the effects of geometric parameter variations of inferior vena cava filters, which have a significant impact on the thrombus formation inside the filter, the capture, dissolution, and hemodynamic flow of thrombus, as well as the shear stress on the filter and vascular wall.

Methods

This study used computational fluid dynamic simulations with the carreau model to investigate the impact of varying inferior vena cava filter design parameters (number of struts, strut arm length, and tilt angle) on hemodynamics.

Results

Recirculation and stagnation areas due to flow velocity and pressure, along with wall shear stress values, were identified as key factors. It is important to find a balance between wall shear stress high enough to aid thrombolysis and low enough to prevent platelet activation. The results of this paper show that the risk of platelet activation and thrombus filtration may be lowest when the wall shear stress of the filter ranges from 0 to 4 [Pa], minimizing stress concentration within the filter.

Conclusion

16 arm struts with a length of 20 mm and a tilt angle of 0° provide the best balance between thrombus capture and minimization of hemodynamic disturbance. This configuration minimizes the size of the stagnation and recirculation zones while maintaining sufficient wall shear stress for thrombus dissolution.

Venous Thromboembolism Prophylaxis in Major Orthopedic Surgeries and Factor XIa Inhibitors

Venous thromboembolism (VTE), comprising pulmonary embolism (PE) and deep vein thrombosis (DVT), poses a significant risk during and after hospitalization, particularly for surgical patients. Among various patient groups, those undergoing major orthopedic surgeries are considered to have a higher susceptibility to PE and DVT. Major lower-extremity orthopedic procedures carry a higher risk of symptomatic VTE compared to most other surgeries, with an estimated incidence of ~4%. The greatest risk period occurs within the first 7-14 days following surgery. Major bleeding is also more prevalent in these surgeries compared to others, with rates estimated between 2% and 4%. For patients undergoing major lower-extremity orthopedic surgery who have a low bleeding risk, it is recommended to use pharmacological thromboprophylaxis with or without mechanical devices. The choice of the initial agent depends on the specific surgery and patient comorbidities. First-line options include low-molecular-weight heparins (LMWHs), direct oral anticoagulants, and aspirin. Second-line options consist of unfractionated heparin (UFH), fondaparinux, and warfarin. For most patients undergoing knee or hip arthroplasty, the initial agents recommended for the early perioperative period are LMWHs (enoxaparin or dalteparin) or direct oral anticoagulants (rivaroxaban or apixaban). In the case of hip fracture surgery, LMWH is recommended as the preferred agent for the entire duration of prophylaxis. However, emerging factor XI(a) inhibitors, as revealed by a recent meta-analysis, have shown a substantial decrease in the occurrence of VTE and bleeding events among patients undergoing major orthopedic surgery. This discovery poses a challenge to the existing paradigm of anticoagulant therapy in this specific patient population and indicates that factor XI(a) inhibitors hold great promise as a potential strategy to be taken into serious consideration.

Thromboprophylaxis and thrombosis in medical, surgical, trauma, and obstetric/gynecologic patients

The International Consensus and the ACCP Sixth Consensus had a great impact on the clinical acceptance of LMWHs. These recommendations have been instrumental in initiating further clinical trial to answer key questions regarding thromboprophylaxis and in setting a new standard for patient care. Also, the key to cost containment in management of DVT/PE is to (1) define the etiology (blood coagulation protein or platelet defect), institute appropriate long-term therapy as indicated, and assess appropriate family members as indicated if a hereditary defect is found and (2) use LMWH as inpatient management. saving a minimum of 210,000.00 dollars per 1000 patients simply from cost savings of recurrence, saving 17 lives per 1000 patients, and saving exorbitant costs of care for patients with recurrence and development of chronic venous insufficiency. The use of outpatient LMWH will save 4,900,000.00 dollars per 1000 patients if applied to the 70% of patients with DVT who fit the criteria of no comorbid condition requiring hospitalization and who arrive early enough to allow a diagnosis to be sent home or hospitalized for 24 hours or less. The simple defining of defects leading to unexplained thrombosis will add another 3,000,000.00 dollars in savings per 1000 patients with DVT and approximately 350,000.00 dollars per 100 patients with thrombotic stroke. In those with transient ischemic attacks, defining the defect and instituting appropriate antithrombotic therapy, thereby potentially saving approximately 30% from developing a thrombotic stroke, amounts to approximately 350,500.00 dollars (= 30% of 1,168,500.00 dollars) in savings per 100 patients.

Inhibitory effect of JTV-803, a new cyclic guanidine derivative, on factor Xa in vitro and in vivo

JTV-803, 4-[(2-amidino-1,2,3,4-tetrahydroisoquinolin-7-yloxy)methyl]-1-(4-pyridinyl)piperidine-4-carboxylic acid monomethanesulfonate trihydrate showed a competitive inhibitory effect on human factor Xa, with a K(i) value of 0.019 microM. This compound was 100 times more selective in inhibiting human factor Xa as compared to its inhibitory activity against thrombin, plasmin, and trypsin. JTV-803 was also examined for its inhibitory effect on activated factor Xa obtained from plasma of various animal species. JTV-803 exerted a potent inhibitory effect on human factor Xa (IC(50): 0.081 microM). JTV-803 prolonged activated partial thromboplastin time and prothrombin time in a dose-dependent manner. Oral anticoagulant efficacy of JTV-803 was examined ex vivo for its inhibition of human factor Xa in cynomolgus monkeys. JTV-803 produced more than 20% inhibition of human factor Xa for 8 h. Taken together, the results indicate JTV-803 is a long-acting oral anticoagulant which exerts its effect via specific inhibition of human factor Xa.

Isolated calf vein thrombosis: comparison of MR venography and conventional venography after initial sonography in symptomatic patients

RATIONALE AND OBJECTIVES

The authors performed this study to compare magnetic resonance (MR) venography and conventional venography in the diagnosis of deep venous thrombosis (DVT) in the calf after sonography.

MATERIALS AND METHODS

Sonography was performed in 595 patients who were suspected of having lower-extremity DVT. Patients with positive above-knee duplex sonograms, allergy to iodinated contrast material, renal insufficiency, or cardiac pacemakers and patients who were obese were excluded. The remaining 73 patients were asked to undergo MR venography and conventional venography. All studies were to be performed within 48 hours of the clinical diagnosis and according to standard clinical practice. Images were interpreted by radiologists who were blinded to the results of other modalities. Two separate analyses were performed: one in which conventional venography was used as the standard of reference, and one in which the presence of at least two positive studies for thrombus was considered diagnostic.

RESULTS

Although 36 patients agreed to participate in the study, only 14 underwent MR venography and conventional venography within 48 hours of the clinical diagnosis. With use of any two positive studies for confirmation, acute DVT was diagnosed in three patients. Conventional venography depicted two of the three cases, whereas sonography and MR venography each depicted all three. The findings were concordant in only five of the 14 patients.

CONCLUSION

Moderate discrepancy among modalities was demonstrated. This suggests radiologists should undertake comparisons among these three modalities for the detection of calf DVT. In patients with a high clinical suspicion, a second modality may be useful if the initial study is negative.

Proficient and cost-effective approaches for the prevention and treatment of venous thrombosis and thromboembolism

Thrombosis is clearly a common cause of death in the US. It is obviously of major importance to define the aetiology of deep vein thrombosis (DVT) as (i) many of these events are preventable if appropriate therapy, dependent upon the risk factors known is utilised; (ii) appropriate antithrombotic therapy will decrease risks of recurrence; (iii) the type of defect(s) and risk(s) will determine length of time the patient should remain on therapy for secondary prevention and (iv) if the defect is hereditary appropriate family members can be assessed. Aside from mortality, significant additional morbidity occurs from DVT including, but not limited to, stasis ulcers and other sequelae of post-phlebitic syndrome. Numerous studies have provided evidence that medical patients and patients undergoing surgery or trauma are at significant risk for developing DVT, including pulmonary embolism (PE). Thus, an important task for the clinician is to prevent DVT and its complications. It is important to define risk groups where prophylaxis must be considered. The attitudes and beliefs towards prophylaxis show great regional variations. This is true for the definition of risk groups, the proportion of patients receiving prophylaxis and prophylactic modalities used. For this reason, various 'consensus conference' groups have attempted to alleviate these problems; the primary mission of consensus guidelines is to provide optimal direction to the clinician in the setting of clinical practice. If the practice guidelines generated are successful they will assist clinicians in decision-making for their patients, and they will also provide protection against unjustified malpractice actions. Therapy may be complex, as clinical studies continue to identify more effective treatments. This review includes currently accepted approaches to the treatment of DVT. The clinical course of DVT is highly dynamic. When the response to therapy is not as expected, more than one cause of DVT may be present in a patient. Treatment must address the primary coagulopathy as well as any precipitating factors. The risk of pharmacological intervention must be balanced against potential benefit. If the incidence of DVT in a given disorder is low and if the mortality rate is similarly low, therapy with an agent known to be associated with a high risk for complications, such as warfarin, would not be indicated. If DVT is seen primarily after surgery or in other high-risk situations, therapy might be limited to a fixed time period. However, if the ongoing risk of DVT remains high or if a history of recurrent DVT dictates, lifelong therapy might be indicated. The recommendations presented are based upon published controlled trials; however, indications for therapy and therapeutic agents of choice will continually evolve. By applying the principles outlined in this review, substantial cost savings, reduction in morbidity and reductions in mortality should occur.

Prophylaxis of deep venous thrombosis and pulmonary embolism. Current recommendations

Pulmonary embolism is responsible for approximately 150,000 to 200,000 deaths per year in the United States. Venous thromboembolism usually occurs as a complication in patients who are sick and hospitalized, but it may also affect ambulant and otherwise healthy individuals. Many patients who die from pulmonary embolism succumb suddenly or within 2 hours after the acute event (i.e., before therapy can be initiated or take effect). Therefore, prevention is the key to reducing death and morbidity from venous thromboembolism. Effective and safe prophylactic measures against venous thromboembolism are now available for most high-risk patients. This article highlights practical approaches to the prevention of venous thromboembolism.

Prophylaxis of Deep Vein Thrombosis and Pulmonary Embolism: Current Recommendations

Pulmonary embolism remains a major cause of death in high-risk medical and surgical patients. This is unfor tunate as effective measures for prevention of venous throm boembolism in such patients are now available. Based on Level 1 evidence from clincial trials and systematic reviews, recom mendations can be made for the prevention of venous throm boembolism in most situations. If such information is not avail able, recommendations based on extrapolation from similar risk situations or from consensus opinions must be used. Additional clinical trials are required to fill in such gaps in our knowledge and permit adequate protection against fatal pulmonary embo lism in most if not all medical and surgical patients. Key Words: Heparin—Low molecular weight heparin—Oral anti coagulants—Intermittent pneumatic compression—Graduated compression stockings—Deep vein thrombosis—Pulmonary embolism.

Critical role of pulmonary angiography in the diagnosis of pulmonary emboli following cardiac surgery

This study was conducted to identify patients at high risk of the development of Pulmonary Embolism (PE) after open heart surgery, to evaluate pertinent diagnostic methods, and to assess the mortality associated with this complication. We evaluated the records of 2,551 consecutive patients who underwent open heart surgery over a 10-year period to identify those patients in whom PE developed. All surgical reports, ventilation/perfusion scans, pulmonary angiograms, and autopsies from the same period were also reviewed. Preoperative and postoperative risk factors for pulmonary embolism were also analyzed, as well as the outcome of this complication in each type of surgical procedure. Pulmonary embolism was identified in 69 (2.7%) patients after open heart surgery, in 43 (62.3%) of whom the diagnosis was established within the first week of surgery. Factors associated with high incidence for PE were hyperlipidemia, congestive heart failure and heparin-induced thrombocytopenia (P < 0.001); obesity and prolonged mechanical ventilation (P < 0.005); and prior right heart catheterization by the femoral approach and prior PE and/or deep vein thrombosis (P < 0.05). The diagnosis of PE was established by a high-probability ventilation/perfusion scan in 25 patients, by pulmonary angiography in 42 (29 of whom had prior V/Q scan read as intermediate or low probability for PE) and by autopsy in two patients. The mortality rate in patients who had PE was 7.2%, while in those without this complication it was 3.2%. These findings suggest that aggressive approach for the diagnosis of PE by pulmonary angiography whenever the V/Q scan is not read as high probability is crucial in patients with recent open heart surgery; such approach may identify patients with PE at an early stage and may have an impact in reducing mortality incurred by this complication. This diagnostic assessment should be emphasized in the perioperative period, especially in patients with multiple significant and identifiable risk factors for PE.

Pharmacodynamics, clinical indications, and adverse effects of heparin

Heparins are a heterogenous group of naturally occurring glycosaminoglycans characterized by anticoagulant activity and a wide range of molecular weights (low molecular weight or fractionated heparins evolving within the past two decades). Cofactors for endogenous inhibitors of coagulation (antithrombin III and heparin cofactor II), heparin administration results in a hypocoagulable state. Various platelet activities, including inhibition of activity induced by platelet-derived growth factors on vascular smooth muscle, also have been noted. Divorced of anticoagulant nature, novel applications may include a role in atherosclerosis prevention, acceleration of collateral coronary as well as peripheral circulation (i.e., angiogenesis), and continued (chronic) post-myocardial infarction therapy. Established indications include treatment of various thrombotic diseases, unstable angina, and thrombosis chemoprophylaxis in medical/surgical patients. The antithrombotic potential of the heparins is used also in thrombosis management related to extracorporeal circulatory assistance or dialysis devices. Heparin's therapeutic potential in the postphlebitic syndrome as well as in acute treatment of myocardial infarction (primarily and adjunctively with various thrombolytic agents) continues to undergo evaluation; however, early data review shows favorable trends for its inclusion in situations that favor thrombus generation (e.g., anterior myocardial infarction). Although associated with thrombocytopenia or hypertransaminasemia, the heparins are relatively well tolerated. In a small subset of patients, a severe thrombocytopenia may ensue, which generally resolves on medication withdrawal. As this class of glycosaminoglycans becomes better characterized, new indications may emerge for both native and the newer fractionated heparins.

Pulmonary embolism in the cardiac surgical patient

Pulmonary embolism (PE) is thought to occur infrequently after cardiac operations, possibly because systemic heparinization during cardiopulmonary bypass prevents deep vein thrombosis. This retrospective study was undertaken to determine the actual incidence of PE after cardiac operations and to identify risk factors. Between January 1, 1985, and December 31, 1989, 5,694 adult patients (greater than 18 years old) had open heart operations at the Johns Hopkins Hospital. Thirty-two patients (20 men and 12 women) had PE within 60 days of operation, an overall PE incidence of 0.56%. The diagnosis of PE was established by ventilation/perfusion scan, pulmonary angiogram, or autopsy. Mortality among patients with PE was 34%. Using a case-control method, preoperative and postoperative risk factors for PE were identified by multivariate and multiple logistic regression analyses. Preoperative risk factors included bed rest (p less than 0.003), prolonged hospitalization before operation (p less than 0.004), and cardiac catheterization performed through the groin within 15 days before operation (p less than 0.01). Post-operative risk factors were congestive heart failure (p less than 0.008), prolonged bed rest (p less than 0.05), and deep vein thrombosis (p less than 0.03). This study demonstrates that PE is an unusual complication after cardiac operations, has a high mortality rate, and is often related to perioperative immobility and recent groin catheterization. These results also suggest that minimizing preoperative hospital stay may be important in PE prophylaxis.

Heparin pharmacokinetics and pharmacodynamics

Heparin was discovered approximately 75 years ago and has been used extensively for the last 50 years to treat thromboembolic disorders. An endogenous glycosaminoglycan, heparin is found largely in the liver, lung and intestine. It is available for exogenous administration both as unfractionated and low molecular weight heparin. Unfractionated heparin is a heterogenous mixture of polysaccharide chains of varying length resulting in a range of molecular weights from 3000 to 30,000D while low molecular weight heparin ranges from 3000 to 6000D. Heparin produces its antithrombotic effect by binding to antithrombin III and this complex then binds to thrombin. In order to accomplish this a total of 18 to 22 monosaccharide units is necessary including a specific pentasaccharide binding site for antithrombin III. After either subcutaneous or intravenous injection heparin is distributed primarily within the intravascular space. A short distribution phase is seen which is thought to correspond to endothelial cell binding and internalisation. The disposition curve for unfractionated heparin has a unique concave-convex shape which is the result of combined saturable and nonsaturable elimination mechanisms. The nonsaturable elimination mechanism is renal and is the primary route of elimination for low molecular weight heparins. For this reason, the concave-convex pattern is not seen with low molecular weight preparations. Both forms of heparin are useful antithrombotic agents; however, the correlation between the antithrombotic effect and an in vitro laboratory test for either type still needs further clarification.

Deep venous thrombosis in the surgical intensive care unit

The ICU patient population is at a high risk for the development of deep venous thrombosis leading to a potentially fatal pulmonary embolism. It is vital to appreciate this risk and apply appropriate prophylaxis. Constant vigilance is required, as deep venous thrombosis and pulmonary emboli can develop and progress despite standard prophylactic measures. In unstable patients, more aggressive prophylaxis may be warranted, including the use of inferior vena cava filters. A high index of suspicion and a low threshold for screening and diagnostic testing will allow earlier recognition and treatment of this lifethreatening condition. Treatment decisions are based on clinical suspicion, diagnostic examination results, and the potential complications of difficult treatment modalities.

Prophylaxis of venous thromboembolism

The objective of prophylaxis in venous thromboembolism is, first, to prevent fatal pulmonary embolism and, second, to reduce the morbidity associated with deep vein thrombosis (DVT) and the postphlebitic limb. This should now be standard practice for most patients over 40 years of age undergoing major surgery and for younger patients with a history of venous thromboembolism. Particularly high-risk groups include patients over 60 years of age undergoing major surgery, those with malignancy, and those requiring hip operations. Low-dose subcutaneous heparin 5,000 IU commencing 2 hours preoperatively and continuing 12 hourly until the patient is fully mobile is unequivocally effective in preventing DVT in medical and surgical patients and, most importantly, significantly reduces the incidence of fatal postoperative pulmonary embolism and total mortality. Such prophylaxis, in the presence of established DVT, also limits proximal clot propagation, which is the precursor of major pulmonary embolism. Low-dose heparin prophylaxis is associated with a small risk of bleeding complications, evidenced mostly by an increased frequency of wound hematoma rather than major clinical hemorrhage. Low molecular weight heparin fragments (e.g., Fragmin, Choay, Enoxaparine) are emerging as useful alternative agents, having the advantage of once daily administration and yet providing similar efficacy in the prevention of DVT. Mechanical methods of prevention which counteract venous stasis, such as graduated elastic compression stockings, are also useful in protecting against DVT but have not been shown to prevent fatal postoperative pulmonary embolism. They are recommended particularly for patients in whom heparin prophylaxis is best avoided (e.g., neurosurgery) and possibly in combination with heparin in very high-risk patients.

Contrast venography: from gold standard to 'golden backup' in clinically suspected deep vein thrombosis

In a series of 180 patients, clinically suspected of having deep venous thrombosis (DVT), contrast venography was compared with radionuclide phlebography, duplex ultrasonography and strain gauge plethysmography. In most patients lung scintigraphy was also performed to detect pulmonary embolism (PE). Venography was performed on a routine basis. All venograms were read by at least two observers (radiologists or radiologist/resident) and an inter-observer agreement was reached of 96% with a kappa value of 0.935. In six patients venography was technically impossible or inadequate, 58% of the patients actually had DVT and 26% developed pulmonary embolism (PE). Of the patients with proven DVT, 43% developed PE. Of the three other methods duplex scanning scored the best for the detection of proximal thrombosis, with 92%, 90% and 9.2, and strain gauge plethysmography the worst, with values of 72%, 78% and 3.2 for, respectively, sensitivity, specificity and positive likelihood ratio's. On the basis of the presented material and the current literature it is concluded that the choice for a screening test for proximal thrombosis could best be made on the basis of (local) availability, cost-effectiveness and patient comfort. Duplex ultra-sonography is tipped as the most promising method, accepting that distal thrombosis (calf veins) does not play an important role in PE. Contrast venography should be used as a 'golden backup' in any case of doubt.

Prophylaxis against venous thromboembolism

Death from venous thromboembolism occurs in the perioperative period at a rate varying between 0.1% and 7.0%. The risk factors and methods of prophylaxis are reviewed and current recommendations presented.

Autopsy proven pulmonary embolism in hospital patients: are we detecting enough deep vein thrombosis?

To investigate the present status of pulmonary embolism as a cause of death in a general hospital patient population, a 5-year retrospective study of all autopsy reports and associated hospital records was undertaken. Pulmonary embolism was thought to be the cause of death in 239 of 2388 autopsies performed (10%): 15% of these patients were aged less than 60 years and 68% did not have cancer. Of these patients, 83% had deep-vein thrombosis (DVT) in the legs at autopsy, of whom only 19% had symptoms of DVT before death. Only 3% of patients who had DVT at autopsy had undergone an investigation for such before death. Twenty-four per cent of patients who died from pulmonary embolism had undergone surgery a mean of 6.9 days before. Screening tests for DVT should be applied widely in the hospital population.

Pulmonary embolism. Strategy for evaluation and treatment of patients at increased risk

Pulmonary embolism is a common clinical problem, particularly in hospitalized patients. Its recognition is difficult because no single sign, symptom, or laboratory test is diagnostic for its presence. A high index of suspicion must be maintained for predisposed patients. The diagnostic algorithm presented here suggests an approach to definitive assessment. Anticoagulation, the management of choice, is highly effective in reducing thromboembolic deaths and in preventing recurrent pulmonary embolism. Low-dose anticoagulant therapy may also be preventive.

Prevalence and prevention of deep venous thrombosis of the lower extremities in high-risk pulmonary patients

Information is lacking about the prevalence of, and the best method of preventing deep venous thrombosis (DVT) of the lower extremities in patients forty years or older with pulmonary disease that keeps them in bed for three consecutive days or more and who are thus at high risk of developing DVT or pulmonary embolism (PE). In this study, 192 high-risk patients, aged forty to ninety-two, received 125I fibrinogen and had daily radioactive scans, venous Doppler, and strain gauge plethysmography. Four preventive methods were used until patients became ambulatory: graded compression stockings (GCS) in 39, elastic bandages (EB) in 33, subcutaneous administration of 5,000 USP units of heparin (HEP) bid in 39, and oral administration of 0.5 g of acetylsalicyclic acid (ASA) bid in 35. Results were compared with those in 46 patients in a control group (CG). Twelve patients in CG, none in GCS, 4 in EB, 1 in HEP, and 2 in ASA developed DVT proved by contrast venography. There was a statistically significant difference between GCS and CG (P less than 0.0003), HEP and CG (P less than 0.0022), and ASA and CG (P less than 0.0148) but not between EB and CG (P greater than 0.10); no significant differences were found between any pair of prophylaxis groups. The significant differences could not be attributed to differences in age, sex, or length of stay in bed. PE occurred in 3 patients in CG and 1 in EB. Hemorrhagic complications occurred in 7 patients in HEP and 4 in ASA, requiring exclusion of 2 patients and 1 patient, respectively, from the study.(ABSTRACT TRUNCATED AT 250 WORDS)

Thrombosis and embolism from cardiac chambers and infected valves

In a number of cardiac conditions (acute myocardial infarction, chronic left ventricular aneurysm, dilated cardiomyopathy, infective endocarditis and atrial fibrillation in the absence of valvular disease), the risk of embolism gives cause for concern. Although anticoagulation with warfarin (Coumadin)-derivatives has been shown to be effective in some of these situations, there is no evidence regarding the role of antiplatelet agents. The common factor in the thromboembolic potential of acute myocardial infarction, chronic left ventricular aneurysm and dilated cardiomyopathy is mural thrombus. This can be detected by two-dimensional echocardiography and indium-111 platelet scintigraphy. Although of value in elucidating the natural history of mural thrombus, in most cases, management is not substantially aided by these investigations. In patients with extensive myocardial infarction, particularly anterior infarction, moderate intensity anticoagulation started soon after hospital admission reduces the rate of embolism. After 8 to 12 weeks, embolic risk is low so that anticoagulants can usually be discontinued. Patients with chronic left ventricular aneurysm have a low incidence of embolism; anticoagulation is, therefore, inappropriate. Dilated cardiomyopathy is associated with a high risk of embolism; moderate intensity anticoagulation may be advisable in many such cases. Little information is available regarding the incidence of thromboembolism or the role of antithrombotic therapy in the patient with a diffusely dilated left ventricle due to ischemic heart disease. In native valve infective endocarditis, the risk of hemorrhage is high, and the efficacy of conventional anticoagulants unclear; thus, anticoagulation should not be instituted for the cardiac condition as such. However, in prosthetic valve endocarditis, the risk of embolism seems to be very high, and anticoagulant therapy should be continued, but with great care because there is a substantial risk of cerebral hemorrhage. Atrial fibrillation in patients with valvular heart disease is dealt with in a previous review. Patients with nonvalvular atrial fibrillation are at varying risk of embolism, depending on the etiology of the arrhythmia; trials of antithrombotic therapy are needed for the various subsets of patients. In most elderly patients, the etiology is not known, and their stroke risk is high. The risk of embolism in younger patients with idiopathic atrial fibrillation is so low as to make any antithrombotic therapy unnecessary.(ABSTRACT TRUNCATED AT 400 WORDS)