Antithrombotic therapy in patients with mechanical and biological prosthetic heart valves

[Anticoagulation after heart valve replacement]

In patients after mechanical heart valve replacement anticoagulation is required for the prevention of thrombotic and thromboembolic events. In this setting oral anticoagulation can only be performed with vitamin K antagonists (VKA), while currently all available non-vitamin K dependent oral anticoagulants (NOAC) are contraindicated in patients with mechanical heart valve replacement. This review deals with anticoagulation in patients with mechanical heart valve replacement as well as coagulation inhibition after bioprosthetic or percutaneous valve replacement. In addition, recommendations are given for antithrombotic medication in patients with mechanical heart valve replacement in various clinical scenarios.

A randomized clinical trial to evaluate the efficacy and safety of rivaroxaban in patients with bioprosthetic mitral valve and atrial fibrillation or flutter: Rationale and design of the RIVER trial

The efficacy and safety of rivaroxaban in patients with bioprosthetic mitral valves and atrial fibrillation or flutter remain uncertain. DESIGN: RIVER was an academic-led, multicenter, open-label, randomized, non-inferiority trial with blinded outcome adjudication that enrolled 1005 patients from 49 sites in Brazil. Patients with a bioprosthetic mitral valve and atrial fibrillation or flutter were randomly assigned (1:1) to rivaroxaban 20 mg once daily (15 mg in those with creatinine clearance <50 mL/min) or dose-adjusted warfarin (target international normalized ratio 2.0-30.); the follow-up period was 12 months. The primary outcome was a composite of all-cause mortality, stroke, transient ischemic attack, major bleeding, valve thrombosis, systemic embolism, or hospitalization for heart failure. Secondary outcomes included individual components of the primary composite outcome, bleeding events, and venous thromboembolism. SUMMARY: RIVER represents the largest trial specifically designed to assess the efficacy and safety of a direct oral anticoagulant in patients with bioprosthetic mitral valves and atrial fibrillation or flutter. The results of this trial can inform clinical practice and international guidelines.

"A Tale of Two Cities": Anticoagulation Management in Patients with Atrial Fibrillation and Prosthetic Valves in the Era of Direct Oral Anticoagulants

Valvular heart disease and atrial fibrillation often coexist. Oral vitamin K antagonists have represented the main anticoagulation management for antithrombotic prevention in this setting for decades. Novel direct oral anticoagulants (DOACs) are a new class of drugs and currently, due to their well-established efficacy and security, they represent the main therapeutic option in non-valvular atrial fibrillation. Some new evidences are exploring the role of DOACs in patients with valvular atrial fibrillation (mechanical and biological prosthetic valves). In this review we explore the data available in the medical literature to establish the actual role of DOACs in patients with valvular heart disease and atrial fibrillation.

The Prospective Randomized On-X Valve Anticoagulation Clinical Trial (PROACT): Lower is better, but is it good enough?

Due to their durability, mechanical prostheses are frequently used for aortic valve replacement (AVR) in young adults. However, these valves are thrombogenic and require lifelong anticoagulation. Over the last few decades, efforts have been made towards the lowering of INR targets in an effort to reduce bleeding events without influencing the thromboembolic risk. The Prospective Randomized On-X Valve Anticoagulation Clinical Trial (PROACT) was designed to compare standard versus low anticoagulation targets in high-risk patients undergoing mechanical AVR with the ON-X prosthesis.

Structural and mechanical characteristics of collagen tissue coated with chitosan in a liquid CO2/water system at different pressures

Chitosan coatings of biological heart-valve prostheses enhance their biocompatibility, resistance to pathogenic microflora and lifetime. Collagen tissues can be coated with chitosan in aqueous solution acidified, to make chitosan soluble, with H₂CO₃ formed from a coexisting liquid CO₂ phase under pressure. The advantage of H₂CO₃ is that it can be easily removed after the coating procedure. This study assessed the effects of 6-50 MPa CO₂ pressure during the coating procedure on the structure and mechanical properties of the resulting biocomposite matrices. The dependence of chitosan adsorption on CO₂ pressure was bell-shaped, reaching a maximum adsorption of 0.8 mass % at 40 MPa. Tissue surface became highly porous upon pressure treatment. At 50 MPa, the pores merged to form furrows with lengths of several hundred micrometers, accompanied by collagen fibril reorganisation. Chitosan coating did not affect tissue tensile strength in the axial direction, but increased it by 75% in the radial direction in the tissue coated at 50 MPa pressure. Strain at break, a measure of elasticity, increased in both directions by up to 100% upon coating with chitosan. CO₂ pressure of 30-50 MPa seems thus optimal in terms of chitosan incorporation and tissue mechanical properties.

Follow-up and management of valvular heart disease patients with prosthetic valve: a clinical practice guideline for Indian scenario

PURPOSE

Valvular heart disease (VHD) patients after prosthetic valve implantation are at risk of thromboembolic events. Follow-up care of patients with prosthetic valve has a paramount role in reducing the morbidity and mortality. Currently, in India, there is quintessential need to stream line the follow-up care of prosthetic valve patients. This mandates the development of a consensus guideline for the antithrombotic therapy in VHD patients post prosthetic valve implantation.

METHODS

A national level panel was constituted comprising 13 leading cardio care experts in India who thoroughly reviewed the up to date literature, formulated the recommendations, and developed the consensus document. Later on, extensive discussions were held on this draft and the recommendations in 8 regional meetings involving 79 additional experts from the cardio care in India, to arrive at a consensus. The final consensus document is developed relying on the available evidence and/or majority consensus from all the meetings.

RESULTS

The panel recommended vitamin K antagonist (VKA) therapy with individualized target international normalized ratio (INR) in VHD patients after prosthetic valve implantation. The panel opined that management of prosthetic valve complications should be personalized on the basis of type of complications. In addition, the panel recommends to distinguish individuals with various co-morbidities and attend them appropriately.

CONCLUSIONS

Anticoagulant therapy with VKA seems to be an effective option post prosthetic valve implantation in VHD patients. However, the role for non-VKA oral therapy in prosthetic valve patients and the safety and efficacy of novel oral anticoagulants in patients with bioprosthetic valve need to be studied extensively.

Elevated International Normalized Ratio Is Not Associated With Increased Perioperative Morbidity in Podiatric Limb Salvage Surgery: A Retrospective Analysis

The risk of hemorrhage always exists in anticoagulated patients with an elevated international normalized ratio (INR), a risk that must be measured against the necessity for surgical procedures. The objective of the present retrospective medical record study was to assess the safety with which limb salvage procedures can be conducted in patients with an INR >1.4. The medical records of 231 patients who had undergone limb salvage procedures by 1 surgeon at the Yale New Haven Health System from November 2008 through July 2014 were reviewed. All patients were administered foot blocks with monitored intravenous sedation. The patients' demographic data, comorbidities, preoperative anticoagulant use, coagulation profile, intraoperative analgesic administration, estimated blood loss, total operating room time, total postanesthesia care unit time, intraoperative ankle tourniquet use, and postoperative complications within the initial 72 hours were reviewed. We found no differences in intraoperative bleeding, total intraoperative time, or recovery time between the INR <1.4 group (n = 212) and the INR >1.4 group (n = 19). None of the patients experienced any postoperative complications, defined as any cardiac or pulmonary event, the need for invasive monitoring, or admission to the intensive care unit within the initial 72-hour period. Our findings suggest that patients are suitable for undergoing peripheral procedures with foot blocks and monitored intravenous sedation even in the presence of an elevated INR.

Biomechanical and morphological stability of acellular scaffolds for tissue-engineered heart valves depends on different storage conditions

Currently available bioprosthetic heart valves have been successfully used clinically; however, they have several limitations. Alternatively, tissue-engineering techniques can be used. However, there are limited data concerning the impact of storage conditions of scaffolds on their biomechanics and morphology. The aim of this study was to determine the effect of different storage conditions on the biomechanics and morphology of pulmonary valve dedicated for the acellular scaffold preparation to achieve optimal conditions to obtain stable heart valve prostheses. Scaffold can then be used for the construction of tissue-engineered heart valve, for this reason evaluation of these parameters can determine the success of the clinical application this type of bioprosthesis. Pulmonary heart valves were collected from adult porcines. Materials were divided into five groups depending on the storage conditions. Biomechanical tests were performed, both the static tensile test, and examination of viscoelastic properties. Extracellular matrix morphology was evaluated using transmission electron microscopy and immunohistochemistry. Tissue stored at 4 °C exhibited a higher modulus of elasticity than the control (native) and fresh acellular, which indicated the stiffening of the tissue and changes of the viscoelastic properties. Such changes were not observed in the radial direction. Percent strain was not significantly different in the study groups. The storage conditions affected the acellularization efficiency and tissue morphology. To the best of our knowledge, this study is the first that attributes the mechanical properties of pulmonary valve tissue to the biomechanical changes in the collagen network due to different storage conditions. Storage conditions of scaffolds for tissue-engineered heart valves may have a significant impact on the haemodynamic and clinical effects of the used bioprostheses.

Time to achieving therapeutic international normalized ratio increases hospital length of stay after heart valve replacement surgery

BACKGROUND

Achieving a therapeutic international normalized ratio (INR) before hospital discharge is an important inpatient goal for patients undergoing mechanical cardiac valve replacement (MCVR). The use of clinical algorithms has reduced the time to achieve therapeutic INR (TTI) with warfarin therapy. Whether TTI prolongs length of stay (LOS) is unknown.

METHODS

Patients who underwent MCVR over a consecutive 42-month period were included. Clinical data were obtained from the Society of Thoracic Surgeons Adult Cardiac Surgery database and electronic medical records. Therapeutic INR was defined as per standard guidelines. Warfarin dose was prescribed using an inpatient pharmacy-managed algorithm and computer-based dosing tool. International normalized ratio trajectory, procedural needs, and drug interactions were included in warfarin dose determination.

RESULTS

There were 708 patients who underwent MCVR, of which 159 were excluded for reasons that would preclude or interrupt warfarin use. Among the remainder of 549 patients, the average LOS was 6.4days and mean TTI was 3.5days. Landmark analysis showed that subjects in hospital on day 4 (n=542) who achieved therapeutic INR were more likely to be discharged by day 6 compared with those who did not achieve therapeutic INR (75% vs 59%, P<.001). Multivariable proportional hazards regression with TTI as a time-dependent effect showed a strong association with discharge (P=.0096, hazard ratio1.3) after adjustment for other significant clinical covariates.

CONCLUSIONS

Time to achieve therapeutic INR is an independent predictor of LOS in patients requiring anticoagulation with warfarin after MCVR surgery. Alternative dosing and anticoagulation strategies will need to be adopted to reduce LOS in these patients.

Validity of Criteria Used to Evaluate Fingerstick Devices That Assess International Normalized Ratio

Background . Investigators commonly rely on unvalidated, mainly arithmetic criteria to predict if point-of-care fingerstick devices that assess International Normalized Ratio (INR) lead to the same warfarin dosing decisions as a standard measure. Methods . Criteria that predict warfarin dosing agreement between 2 INR measurements were evaluated using clinicians’ actual dosing decisions as the standard. Bayesian hierarchical modeling was used to rank the criteria by the proportion of correct dosing predictions and the magnitude of difference between actual and predicted dosing agreement. Results . The prediction criteria misclassified dosing agreement for between 19% and 38% of paired INR values (x̄x: 27%). The magnitude of misclassification varied inconsistently throughout the INR scale. Conclusion . The unvalidated criteria used to predict warfarin dosing agreement between 2 INR measurements are associated with large error. Warfarin dosing decisions should be measured directly in such assessments.

Anticoagulation in Pregnant Women With Prosthetic Heart Valves

Background: Pregnancy is associated with an increased risk of thrombosis in women with mechanical prosthetic heart valves. Effective anticoagulation is therefore critical in such patients but remains problematic, since oral anticoagulation and both unfractionated and low-molecular-weight heparin may be associated with important fetal and maternal side effects.

Purpose: To review information related to the use of anticoagulation with both warfarin and heparin and reassess the safety and efficacy of these therapies in pregnant women with mechanical prosthetic heart valves.

Data source and selection: A MEDLINE search from 1966 to October 2003 for English and non-English language articles that reported the use of anticoagulation in pregnancy was conducted. Articles were included if they reported use of anticoagulation in pregnancy with emphasis on those that included women with mechanical prosthetic heart valves.

Conclusions: Anticoagulation prophylaxis with both warfarin and heparin (unfractionated heparin and low-molecular-weight heparin) may be associated with important fetal and maternal side effects. Optional regimens for the treatment of low-risk and high-risk patients are proposed to minimize potential complications.

Detecting nonvalvular atrial fibrillation and anticoagulant therapy in cardioembolic ischemic stroke

Nonvalvular Atrial fibrillation (NVAF) is the most common cardiac arrhythmia associated with an increase in risk of stroke and systemic thromboembolism. Strokes related to AF are associated with higher mortality, greater disability, longer hospital stays, and lower chance of being discharged home. The present review will focus on the current status of detecting NVAF and stroke prevention when there is AF. The CHA2DS2-VASc risk stratification scheme is discussed for the identification of patients who are at risk for thromboembolic stroke related to NVAF. Patient with a CHA2DS2-VASc score of 2 or greater are candidates for warfarin or a novel oral anticoagulant, irrespective of whether the strategy is for rate or rhythm control. Finally, guidelines and landmark clinical trials in NVAF patients with primary or secondary stroke prevention are discussed.

Early Results of a Novel Mitral Valve Repair Procedure: The Interpapillary Polytetrafluoroethylene Bridge Formation

BACKGROUND

Surgical repair of ischemic mitral regurgitation (IMR) associated with chordal rupture in patients with ischemic cardiomyopathy is challenging as it aims to correct several structural pathologies at once. There are ongoing studies evaluating multiple approaches, however long term results are still scarce.

METHODS AND RESULTS

19 patients with IMR underwent mitral valve repair with interpapillary polytetrafluoroethylene (PTFE) bridge and neochordae formation at the Zala County Teaching Hospital. Concomitant coronary artery bypass grafting was performed in all patients. Post-procedural Transesophageal Echocardiogram (TEE) showed no mitral regurgitation (MR) in eighteen (94.7%) patients, with a leaflet coaptation mean height of 8 ± 3 mm. No operative mortality was observed. At the follow up (mean 17.7 ± 4.6 months; range 9 to 24 months), 17 (89%) patients showed no leakage and 2 had regurgitation grade ≤1, with documented NYHA functional class I or II in all patients.

CONCLUSION

This retrospective study presents the first results of a novel surgical approach to treating ischemic mitral regurgitation. The interpapillary PTFE bridge formation is a safe and feasible surgical procedure that is reproducible, time sparing and effectively eliminates mitral valve regurgitation with promising long-term results.

Efficacy and safety of novel oral anticoagulants in patients with bioprosthetic valves

PURPOSE

Prosthetic valve replacement is performed in several hundred thousand patients worldwide annually, and many of these patients have or will ultimately develop atrial fibrillation or flutter (AF). Novel oral anticoagulants (NOACs) are not recommended in patients with AF and mechanical valves but have not been evaluated in patients with bioprosthetic valves. This study sought to evaluate the efficacy and safety of NOACs in patients with AF and bioprosthetic valves.

METHODS

A retrospective single-center cohort study was performed on all patients with bioprosthetic valve implantation, for whom a NOAC was prescribed for the indication of AF. Patients were evaluated for thromboembolic events including imaging confirmed ischemic stroke, clinically suspected transient ischemic attack, and major bleeding events (according to International Society on Thrombosis and Hemostasis definition).

RESULTS

In total, 73 patients (26 female, 35.6 %) were identified. NOAC therapy began, on average, 990.0 ± 1029.1 days after bioprosthetic valve implantation for an average duration of 511.8 ± 400.8 days. Aspirin was used concomitantly in a majority of patients (72.6 %). There were no ischemic strokes identified (0.0 %) and one possible TIA (1.4 %). There were 6 (8.2 %) minor and 5 (6.9 %) major bleeding events.

CONCLUSION

The use of NOAC therapy for AF in patients with bioprosthetic valves appears safe and effective in the occurrence of thromboembolic events, however, at the expense of increased bleeding. Larger studies are necessary to confirm these findings.

Prevention of Venous Thromboembolism After Stroke

Venous thromboembolism (VTE) is a common complication following acute ischemic and hemorrhagic stroke. Pulmonary embolism (PE), the most serious consequence of deep vein thrombosis (DVT), can result in significant morbidity and death. Patients with stroke are at particular risk because of limb paralysis, prolonged bed rest, and increased prothrombotic activity. Preventive measures should be taken at all levels of care and can include mechanical calf compression, antiplatelet agents, and the use of anticoagulants such as heparin and low molecular weight heparin. Prevention of VTE should be incorporated into all stroke care pathways.

Long-term bleeding events after mechanical aortic valve replacement in patients under the age of 60

BACKGROUND

Although younger patients are supposed to be less susceptible to bleeding complications of mechanical aortic valve replacement (mAVR) than older patients, there is a relative paucity of data on this subject. Therefore, it remains uncertain whether younger patients are really at a lower risk of these complications than older patients.

METHODS

Incidence rates of bleeding events during 15 years of follow-up after mAVR were compared between 163 patients under 60 (group I), 122 patients between 60 and 65 (group II), and 145 patients over 65 (group III) years of age at operation. The target international normalised ratio (INR) was 3.0-4.0.

RESULTS

During 15 years of follow-up, the annual incidence rate of major bleeding events (excluding haemorrhagic stroke) was lower in the youngest as compared with the oldest group (3.0 versus 4.7 %, respectively; p = 0.030). However, the annual incidence rate of haemorrhagic stroke was as high in the youngest as in the two older groups (0.6 versus 0.7 % and 0.7 %, respectively; p = 0.928).

CONCLUSIONS

With a target INR of 3.0-4.0, patients under 60 years of age are at equally high risk of haemorrhagic stroke after mAVR as older patients. This finding confirms the relevance of a lower target INR as used in international guidelines.

Age-related changes in biomechanical properties of transgenic porcine pulmonary and aortic conduits

The limitations associated with conventional valve prosthesis have led to a search for alternatives. One potential approach is tissue engineering. Most tissue engineering studies have described the biomechanical properties of heart valves derived from adult pigs. However, because one of the factors affecting the function of valve prosthesis after implantation is appropriate sizing for a given patient, it is important to evaluate the usefulness of a heart valve given the donor animal's weight and age. The aim of this study was to evaluate how the age of a pig can influence the biomechanical and hemodynamical properties of porcine heart valve prosthesis after acellularization. Acellular porcine aortic and pulmonary valve conduits were used. Hearts were harvested from animals differing in weight and age. The biomechanical properties of the valves were then characterized using a uniaxial tensile test. Moreover, computer simulations based on the finite element method (FEM) were used to study the influence of biomechanical properties on the hemodynamic conditions. Studying biomechanical and morphological changes in porcine heart valve conduits according to the weight and age of the animals can be valuable for developing age-targeted therapy using tissue engineering techniques.

Management of Anticoagulant Therapy for Patients with Prosthetic Heart Valves or Atrial Fibrillation

There is a wide array of recommendations for the management of anticoagulant therapy in patients with mechanical heart valves. Especially the optimal intensity of vitamin K antagonists (VKA) is a ongoing matter of debate. On the basis of several studies, recommendations for daily clinical practice can be made. In this review, we discussed the studies and the different guidelines. Guidelines for the prevention of thromboembolic complications in patients with atrial fibrillation are more stringent. VKA with a target INR between 2.0 and 3.0 is more effective in the prevention of stroke than aspirin, especially in the presence of riskfactors for thromboembolism (age above 65, previous thromboembolism, history of hypertension and diabetes, enlarged left atrial diameter and left ventricular dysfunction). In the absence of clinical or echocardiographical riskfactors for thromboembolism, patients may be safely treated with aspirin.

Antiplatelet and anticoagulation for patients with prosthetic heart valves

BACKGROUND

Patients with prosthetic heart valves are at increased risk for valve thrombosis and arterial thromboembolism. Oral anticoagulation alone, or the addition of antiplatelet drugs, has been used to minimise this risk. An important issue is the effectiveness and safety of the latter strategy.

OBJECTIVES

This is an update of our previous review; the goal was to create a valid synthesis of all available, methodologically sound data to further assess the safety and efficacy of combined oral anticoagulant and antiplatelet therapy versus oral anticoagulant monotherapy in patients with prosthetic heart valves.

SEARCH METHODS

We updated the previous searches from 2003 and 2010 on 16 January 2013 and searched the Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library (2012, Issue 12), MEDLINE (OVID, 1946 to January Week 1 2013), and EMBASE (OVID, 1980 to 2013 Week 02). We have also looked at reference lists of individual reports, review articles, meta-analyses, and consensus statements. We included reports published in any language or in abstract form.

SELECTION CRITERIA

All reports of randomised controlled trials comparing standard-dose oral anticoagulation to standard-dose oral anticoagulation and antiplatelet therapy in patients with one or more prosthetic heart valves.

DATA COLLECTION AND ANALYSIS

Two review authors independently performed the search strategy, assessed trials for inclusion and study quality, and extracted data. We collected adverse effects information from the trials.

MAIN RESULTS

One new study has been identified and included in this update. In total, 13 studies involving 4122 participants were included in this review update. Years of publication ranged from 1971 to 2011. Compared with anticoagulation alone, the addition of an antiplatelet agent reduced the risk of thromboembolic events (odds ratio (OR) 0.43, 95% confidence interval (CI) 0.32 to 0.59; P < 0.00001) and total mortality (OR 0.57, 95% CI 0.42 to 0.78; P = 0.0004). Aspirin and dipyridamole reduced these events similarly. The risk of major bleeding was increased when antiplatelet agents were added to oral anticoagulants (OR 1.58, 95% CI 1.14 to 2.18; P = 0.006).For major bleeding, there was no evidence of heterogeneity between aspirin and dipyridamole and in the comparison of trials performed before and after 1990, around the time when anticoagulation standardisation with the international normalised ratio was being implemented. A lower daily dose of aspirin (< 100 mg) may be associated with a lower major bleeding risk than higher doses.

AUTHORS' CONCLUSIONS

Adding antiplatelet therapy, either dipyridamole or low-dose aspirin, to oral anticoagulation decreases the risk of systemic embolism or death among patients with prosthetic heart valves. The risk of major bleeding is increased with antiplatelet therapy. These results apply to patients with mechanical prosthetic valves or those with biological valves and indicators of high risk such as atrial fibrillation or prior thromboembolic events. The effectiveness and safety of low-dose aspirin (100 mg daily) appears to be similar to higher-dose aspirin and dipyridamole. In general, the quality of the included trials tended to be low, possibly reflecting the era when the majority of the trials were conducted (1970s and 1980s when trial methodology was less advanced).

Plasminogen activators and ischemic stroke: conditions for acute delivery

Appropriate acute treatment with plasminogen activators (PAs) can significantly increase the probability of minimal or no disability in selected ischemic stroke patients. There is a great deal of evidence showing that intravenous recombinant tissue PAs (rt-PA) infusion accomplishes this goal, recanalization with other PAs has also been demonstrated in the development of this treatment. Recanalization of symptomatic, documented carotid or vertebrobasilar arterial territory occlusions have also been achieved by local intra-arterial PA delivery, although only a single prospective double-blinded randomized placebo-controlled study has been reported. The increase in intracerebral hemorrhage with these agents by either delivery approach underscores the need for careful patient selection, dose-appropriate safety and efficacy, proper clinical trial design, and an understanding of the evolution of cerebral tissue injury due to focal ischemia. Principles underlying the evolution of focal ischemia have been expanded by experience with acute PA intervention. Several questions remain open that concern the manner in which PAs can be applied acutely in ischemic stroke and how injury development can be limited.

Cerebral microembolization after bioprosthetic aortic valve replacement: comparison of warfarin plus aspirin versus aspirin only

BACKGROUND

No human physiological data exists on whether aspirin only is as effective as warfarin plus aspirin in preventing cerebral microembolization in the early postoperative period after bioprosthetic aortic valve replacement (bAVR).

METHODS AND RESULTS

We prospectively enrolled 56 patients who had no other indication for oral anticoagulation, who underwent bAVR and received, in an open-label fashion, either daily warfarin (for INR 2.0-3.0) plus 81 mg of aspirin (n=28) or 325 mg of aspirin only (n=28). Cerebral microembolization was quantified at 4 hours (baseline) and at 1 month postoperatively, by recording 1-hour bilateral middle cerebral artery (MCA) microembolic signals (MES). Platelet-function analysis (PFA) of closure times (CT) on collagen was also used as a marker of platelet-dependent activation. Follow-up to 1 year was complete. Preoperative demographics and baseline platelet function were equivalent in both groups. There was no mortality, stroke, or transient ischemic attack at 1 year in either group. No significant differences were found in the proportion of patients with MES among those receiving warfarin plus aspirin versus aspirin only, at baseline (68% versus 82%, respectively; P=0.4) and at 1 month (46% versus 43%; P=1.0) after bAVR. The total MES and PFA were also equivalent between groups, at baseline and follow-up.

CONCLUSIONS

Early after bAVR, the effects of these 2 antithrombotic regimens on cerebral microembolization and platelet function are equivalent. These data bring new mechanistic support to the premise that aspirin only may safely be used early after bAVR in patients who have no other indication for oral anticoagulation.

Optimal thromboprophylaxis following bioprosthetic aortic valve replacement: still a matter of debate?

Optimal thromboprophylaxis following bioprosthetic aortic valve replacement (AVR) remains controversial. The main objective, which is the effective prevention of central nervous or peripheral embolic events, especially in the early postoperative period, will have to be weighed against the haemorrhagic risk that is associated with the utilization of different antithrombotic regimes. Most governing bodies in cardiovascular medicine have issued recommendations on thromboprophylaxis after the surgical implantation of aortic bioprostheses. However, the level of evidence to support these recommendations remains low, largely due to the inherent limitations of conducting appropriately randomized and adequately powered clinical research in this area. It is apparent from the recent surveys and large registries that there is a great variability in antithrombotic practice at an institutional or individual-clinician level reflecting this controversy and the lack of robust evidence. While organizational, financial or conceptual limitations could hinder the conduct and availability of conclusive research on optimal thromboprophylaxis after aortic bioprosthesis, it is imperative that all evidence is presented in a systematic way in order to assist the decision-making for the modern clinician. In this review, we provide an outline of the current recommendations for thromboprophylaxis, followed by a comprehensive and analytical presentation of all comparative studies examining anticoagulation vs. antiplatelet therapy after bioprosthetic AVR.

Antithrombotic and thrombolytic therapy for valvular disease: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

Antithrombotic therapy in valvular disease is important to mitigate thromboembolism, but the hemorrhagic risk imposed must be considered.

METHODS

The methods of this guideline follow those described in Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines. Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines in this supplement.

RESULTS

In rheumatic mitral disease, we recommend vitamin K antagonist (VKA) therapy when the left atrial diameter is > 55 mm (Grade 2C) or when complicated by left atrial thrombus (Grade 1A). In candidates for percutaneous mitral valvotomy with left atrial thrombus, we recommend VKA therapy until thrombus resolution, and we recommend abandoning valvotomy if the thrombus fails to resolve (Grade 1A). In patients with patent foramen ovale (PFO) and stroke or transient ischemic attack, we recommend initial aspirin therapy (Grade 1B) and suggest substitution of VKA if recurrence (Grade 2C). In patients with cryptogenic stroke and DVT and a PFO, we recommend VKA therapy for 3 months (Grade 1B) and consideration of PFO closure (Grade 2C). We recommend against the use of anticoagulant (Grade 1C) and antiplatelet therapy (Grade 1B) for native valve endocarditis. We suggest holding VKA therapy until the patient is stabilized without neurologic complications for infective endocarditis of a prosthetic valve (Grade 2C). In the first 3 months after bioprosthetic valve implantation, we recommend aspirin for aortic valves (Grade 2C), the addition of clopidogrel to aspirin if the aortic valve is transcatheter (Grade 2C), and VKA therapy with a target international normalized ratio (INR) of 2.5 for mitral valves (Grade 2C). After 3 months, we suggest aspirin therapy (Grade 2C). We recommend early bridging of mechanical valve patients to VKA therapy with unfractionated heparin (DVT dosing) or low-molecular-weight heparin (Grade 2C). We recommend long-term VKA therapy for all mechanical valves (Grade 1B): target INR 2.5 for aortic (Grade 1B) and 3.0 for mitral or double valve (Grade 2C). In patients with mechanical valves at low bleeding risk, we suggest the addition of low-dose aspirin (50-100 mg/d) (Grade 1B). In valve repair patients, we suggest aspirin therapy (Grade 2C). In patients with thrombosed prosthetic valve, we recommend fibrinolysis for right-sided valves and left-sided valves with thrombus area < 0.8 cm(2) (Grade 2C). For patients with left-sided prosthetic valve thrombosis and thrombus area ≥ 0.8 cm(2), we recommend early surgery (Grade 2C).

CONCLUSIONS

These antithrombotic guidelines provide recommendations based on the optimal balance of thrombotic and hemorrhagic risk.

Anti-platelet therapy: phosphodiesterase inhibitors

Inhibition of platelet aggregation can be achieved either by the blockade of membrane receptors or by interaction with intracellular signalling pathways. Cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) are two critical intracellular second messengers provided with strong inhibitory activity on fundamental platelet functions. Phosphodiesterases (PDEs), by catalysing the hydrolysis of cAMP and cGMP, limit the intracellular levels of cyclic nucleotides, thus regulating platelet function. The inhibition of PDEs may therefore exert a strong platelet inhibitory effect. Platelets possess three PDE isoforms (PDE2, PDE3 and PDE5), with different selectivity for cAMP and cGMP. Several nonselective or isoenzyme-selective PDE inhibitors have been developed, and some of them have entered clinical use as antiplatelet agents. This review focuses on the effect of PDE2, PDE3 and PDE5 inhibitors on platelet function and on the evidence for an antithrombotic action of some of them, and in particular of dipyridamole and cilostazol.

Antithrombotic medication for cardioembolic stroke prevention

Embolism of cardiac origin accounts for about 20% of ischemic strokes. Nonvalvular atrial fibrillation is the most frequent cause of cardioembolic stroke. Approximately 1% of population is affected by atrial fibrillation, and its prevalence is growing with ageing in the modern world. Strokes due to cardioembolism are in general severe and prone to early recurrence and have a higher long-term risk of recurrence and mortality. Despite its enormous preventive potential, continuous oral anticoagulation is prescribed for less than half of patients with atrial fibrillation who have risk factors for cardioembolism and no contraindications for anticoagulation. Available evidence does not support routine immediate anticoagulation of acute cardioembolic stroke. Anticoagulation therapy's associated risk of hemorrhage and monitoring requirements have encouraged the investigation of alternative therapies for individuals with atrial fibrillation. New anticoagulants being tested for prevention of stroke are low-molecular-weight heparins (LMWH), unfractionated heparin, factor Xa inhibitors, or direct thrombin inhibitors like dabigatran etexilate and rivaroxaban. The later exhibit stable pharmacokinetics obviating the need for coagulation monitoring or dose titration, and they lack clinically significant food or drug interaction. Moreover, they offer another potential that includes fixed dosing, oral administration, and rapid onset of action. There are several concerns regarding potential harm, including an increased risk for hepatotoxicity, clinically significant bleeding, and acute coronary events. Therefore, additional trials and postmarketing surveillance will be needed.

Peri-operative management of ophthalmic patients taking antithrombotic therapy

Increasing number of patients presenting for ophthalmic surgery are using oral anti-coagulant and anti-platelet therapy. The current practice of discontinuing these drugs preoperatively because of a presumed increased risk of bleeding may not be evidence-based and could pose a significant risk to the patient's health. To provide an evidence-based review on the peri-operative management of ophthalmic patients who are taking anti-thrombotic therapy. In addition, we briefly discuss the underlying conditions that necessitate the use of these drugs as well as management of the operative field in anti-coagulated patients. A semi-systematic review of literature was performed. The databases searched included MEDLINE, EMBASE, database of abstracts of reviews of effects (DARE), Cochrane controlled trial register and Cochrane systematic reviews. In addition, the bibliographies of the included papers were also scanned for evidence. The published data suggests that aspirin did not appear to increase the risk of serious postoperative bleeding in any type of ophthalmic surgery. Topical, sub-tenon, peri-bulbar and retrobulbar anaesthesia appear to be safe in patients on anti-thrombotic (warfarin and aspirin) therapy. Warfarin does not increase the risk of significant bleeding in most types of ophthalmic surgery when the INR was within the therapeutic range. Current evidence supports the continued use of aspirin and with some exceptions, warfarin in the peri-operative period. The risk of thrombosis-related complications on disruption of anticoagulation may be higher than the risk of significant bleeding by continuing its use for most types of ophthalmic surgery.