Bileaflet Mechanical Aortic Valve Research Articles

Fluid dynamics and blood damage in the dilated ascending aorta after mechanical prosthetic valve implantation: an in vitro study

The implantation of aortic valve prostheses is often associated with the dilation of the ascending aorta. It is well known that the modification of the fluid dynamics induced by both the prosthetic valve and aortic dilation may, in turn, promote further vessel remodelling. Besides, when the prosthesis is mechanical, a major concern is the blood cell damage and platelet activation which requires a lifelong anticoagulant therapy, which in turn is an additional significant factor of comorbidity. We analysed in vitro the combined effect of the presence of a bileaflet mechanical aortic valve and the dilation of the aortic root in patient specific laboratory models. Three model aortas with increasing degree of dilation, hosted in a mock loop reproducing the heart flow pulsatility, were investigated. The measurement of the time-resolved velocity field allowed the analysis of the general structure of the flow and shear strain-rate distribution. Additionally, the Blood Damage Indexes (BDIs) for both haemolysis and platelet activation were computed along synthetic particle trajectories. Results suggest that a feedback process can be triggered since the aortic dilation tends to decrease the shear stresses at the walls and favour blood stasis: two factors that are known to promote vessel remodelling. Secondly, the analysis of BDIs shows that aortic dilation significantly increases the damage index for haemolysis, whereas a similar effect is not shown when focusing on platelet activation.Graphical abstract

Incidence and Risk Factors of Pannus after Mechanical Aortic Valve Replacement.

This study was conducted to evaluate the occurrence rate and risk factors of subaortic pannus (SAP) after bileaflet mechanical aortic valve (AV) replacement. Between 1990 and 2014, 862 patients underwent primary AV replacement with bileaflet mechanical prosthesis. SAP was defined as (1) gradual increase in mean pressure gradient through mechanical AV without any evidence of motion limitation of the leaflets on echocardiography and (2) AV mean pressure gradient >40 mm Hg or AV peak velocity >4 m/s on echocardiography, and (3) any visible subaortic tissue ingrowth beneath the mechanical AV on echocardiography or computed tomography. Clinical and echocardiographic follow-up durations were 13.8 ± 8.0 and 10.7 ± 7.9 years, respectively. Mean age was 51.1 ± 12.1 years and concomitant surgeries were performed in 503 patients (58.4%). Overall survival at 10 and 20 years was 84.2 and 67.1%, respectively. SAP occurred in 33 patients, and in only 2 patients during the first 10 years after surgery. The cumulative incidence of SAP formation at 10, 20, and 25 years were 0.3, 5.0, and 9.9%, respectively. The Fine and Gray model demonstrated that small prosthetic valve size (hazard ratio [HR] [95% confidence interval, CI] = 0.738 [0.575-0.946]), young age (HR [95% CI] = 0.944 [0.909-0.981]), and concomitant mitral valve replacement (MVR) (HR [95% CI] = 3.863 [1.358-10.988]) were significant risk factors for the SAP formation. SAP occurred gradually over time with 10- and 20-year cumulative incidence of 0.3 and 5.0%, respectively. Young age, small prosthetic valve size, and concomitant MVR were risk factors for SAP formation. Therefore, we recommend efforts to select large prostheses for young patients requiring concomitant MVR.

Proper Orthogonal Decomposition Analysis of the Flow Downstream of a Dysfunctional Bileaflet Mechanical Aortic Valve

Aortic valve replacement remains the only viable solution for symptomatic patients with severe aortic valve stenosis. Despite their improved design and long history of successful operation, bileaflet mechanical heart valves are still associated with post-operative complications leading to valve dysfunction. Thus, the flow dynamics can be highly disturbed downstream of the dysfunctional valve. In this in vitro study, the flow dynamics downstream of healthy and dysfunctional bileaflet mechanical heart valves have been investigated using particle image velocimetry measurements. Proper orthogonal decomposition of the velocity field has been performed in order to explore the coherent flow features in the ascending aorta in the presence of a dysfunctional bileaflet mechanical heart valve. The ability of proper orthogonal decomposition derived metrics to differentiate between heathy and dysfunctional cases is reported. Moreover, reduced-order modeling using proper orthogonal decomposition is thoroughly investigated not only for the velocity field but also for higher order flow characteristics such as time average wall shear stress, oscillatory shear index and viscous energy dissipation. Considering these results, proper orthogonal decomposition can provide a rapid binary classifier to evaluate if the bileaflet mechanical valve deviates from its normal operating conditions. Moreover, the study shows that the size of the reduced-order model depends on which flow parameter is required to be reconstructed.

In vitro characterization of Lagrangian fluid transport downstream of a dysfunctional bileaflet mechanical aortic valve

This experimental study aims to explore the Lagrangian nature of fluid transport downstream of a bileaflet mechanical aortic valve under different malfunction scenarios that might be encountered clinically. Time-resolved planar particle image velocimetry measurements are performed to extract instantaneous velocity fields downstream of the bileaflet mechanical valve implanted in an elastic aortic model. The results show an increase in particle residence time with the severity of malfunction. This is attributed to the expansion of the recirculation regions downstream of the valve. The time-evolution of Lagrangian coherent structures over one cardiac cycle (using finite-time Lyapunov exponent fields) shows the effect of valve dysfunction on the material transport and its barriers inside the aorta. The unbalanced flow through the dysfunctional leaflets leads to a significant redistribution of the LCS, thus the fluid transport along the ascending aorta. Moreover, a new technique for the evaluation of the highest accumulated shear stresses is applied along the Lagrangian trajectory of particles being released from the extracted Lagrangian coherent structures where the highest stretching occurs. Finally, the induced non-laminar flow behavior by the valve dysfunction is analyzed using the time-frequency spectra of velocity signals at selected points in the ascending aorta.

Safety of low intensity oral anticoagulant therapy in patients with bileaflet mechanical aortic valve prosthesis: A propensity weighted study

BackgroundScarce data are available on the long-term outcomes of different regimens of oral anticoagulation in an all comer population of patients undergoing aortic valve replacement with a bileaflet mechanical heart valve. MethodsOutcomes of 88 patients discharged with a target INR of 2.0 (LOW-INR) were compared to 147 contemporary patients who have been recommended a target INR of 2.5 (CONV). Primary outcome was the composite of any thromboembolic or haemorrhagic events. Secondary outcomes were the individual components of the primary outcome, cardiovascular mortality and stroke. To reduce selection bias, a propensity weighted analysis was performed. ResultsAfter inverse probability of treatment weighting, the primary endpoint occurred in 0.7% of patient in the LOW-INR group and in 7.0% in the CONV group (p = .0255). Linearized event rate were significantly lower in the LOW-INR group (primary endpoint: rate difference − 12.0 per 1000 patient/years, p = .0052; haemorrhage: −5.8 per 1000 patient/years, p = .0330; neurological events: −7.6 per 1000 patient/years, p = .0140). Conventional target INR was associated with an increased hazard of the composite endpoint (HR 11.193, 95% CI 1.424–88.003, p = .0217). ConclusionsLowering the intensity of oral anticoagulation resulted in a relevant clinical benefit of reduced rates of haemorrhagic and neurological adverse events in the mid-term follow-up. This report confirms the safety profile of the low INR regimen in an all comer population undergoing aortic valve replacement with an Abbott mechanical valve.

Experimental investigation of the flow downstream of a dysfunctional bileaflet mechanical aortic valve.

Mechanical heart valve replacement is the preferred alternative in younger patients with severe symptomatic aortic valve disease. However, thrombus and pannus formations are common complications associated with bileaflet mechanical heart valves. This leads to risks of valve leaflet dysfunction, a life-threatening event. In this experimental study, we investigate, using time-resolved planar particle image velocimetry, the flow characteristics in the ascending aorta in the presence of a dysfunctional bileaflet mechanical heart valve. Several configurations of leaflet dysfunction are investigated and the induced flow disturbances in terms of velocity fields, viscous energy dissipation, wall shear stress, and accumulation of viscous shear stresses are evaluated. We also explore the ability of a new set of parameters, solely based on the analysis of the normalized axial velocity profiles in the ascending aorta, to detect bileaflet mechanical heart valve dysfunction and differentiate between the different configurations tested in this study. Our results show that a bileaflet mechanical heart valve dysfunction leads to a complex spectrum of flow disturbances with each flow characteristic evaluated having its own worst case scenario in terms of dysfunction configuration. We also show that the suggested approach based on the analysis of the normalized axial velocity profiles in the ascending aorta has the potential to clearly discriminate not only between normal and dysfunctional bilealfet heart valves but also between the different leaflet dysfunction configurations. This approach could be easily implemented using phase-contrast MRI to follow up patients with bileaflet mechanical heart valves.

Bileaflet mechanical aortic valves do not alter ascending aortic wall shear stress

Progressive ascending aortic dilatation has been observed after mechanical aortic valve replacement (mAVR), possibly due to altered blood flow and wall shear stress (WSS) patterns induced by their bileaflet design. We examined the effect of mAVR on WSS in the ascending aorta using time-resolved 4D flow MRI. Fifteen patients with mechanical aortic valve prostheses, 10 patients with bicuspid aortic valve disease and 10 healthy individuals underwent thoracic 4D flow MRI. Peak systolic hemodynamic parameters (velocity and WSS) and vessel diameters were assessed in the ascending aorta. In addition, three-dimensional per-voxel analysis was used to compare velocity and WSS between patient groups and healthy controls. Peak aortic diameters were significantly higher in mAVR and BAV patients compared to healthy controls (p = 0.011). Mean aortic diameters were comparable between mAVR and BAV patients. No differences in 4D flow MRI-derived mean blood flow velocity and peak WSS were found between the three groups. Compared to healthy controls, mean WSS was significantly lower in mAVR patients (p = 0.031). Per-voxel analysis revealed no increased WSS in the ascending aortic wall and significantly lower velocity and WSS values in mAVR patients compared to healthy controls. In contrast, regions of significantly increased outer lumen velocities and WSS in BAV patients compared to healthy controls were found. This study shows that there is no increased ascending aortic WSS after mAVR. Our results suggest that, in contrast to BAV patients, there is no indication for intensified follow-up of the ascending aorta after mAVR.

Possible interaction of warfarin with peppermint herbal tea: a case report

Herbal medicine is usually safe and popular in Iranian communities. Peppermint herbal products may interact with warfarin, which is an essential lifelong drug used in patients with prosthetic heart valves. Herein, we report a case of possible interaction between warfarin and peppermint herbal tea.We described a 68-year-old woman who was on warfarin treatment due to bileaflet mechanical aortic valve, and mitral valve replacement presented with severe dyspnea in the setting of large obstructive prosthetic mitral valve thrombosis diagnosed by echocardiography. Therefore, cardiac surgery was conducted in the emergent setting. Warfarin was started the day after the procedure. She developed melena with a volatile and elevated international normalized ratio (INR) of 4.8 and prothrombin time > 30 s on the 7th post-operation day. She reported no changes in drug or dietary habits except for drinking high amounts of peppermint tea the day before. After the discontinuation of warfarin and medical consultation for gastrointestinal bleeding, the INR level decreased to 1.8 within two days.Consumption of peppermint herbal products are usually safe; however, caution should be taken with patients under warfarin treatment. Full disclosure for patients on anticoagulant treatment is necessary before discharge and during clinical follow-up

Apixaban Versus Warfarin for Mechanical Heart Valve Thromboprophylaxis in a Swine Aortic Heterotopic Valve Model

Warfarin is the current standard for oral anticoagulation therapy in patients with mechanical heart valves, yet optimal therapy to maximize anticoagulation and minimize bleeding complications requires routine coagulation monitoring, possible dietary restrictions, and drug interaction monitoring. As alternatives to warfarin, oral direct acting factor Xa inhibitors are currently approved for the prophylaxis and treatment of venous thromboembolism and reduction of stroke and systemic embolization. However, no in vivo preclinical or clinical studies have been performed directly comparing oral factor Xa inhibitors such as apixaban to warfarin, the current standard of therapy. A well-documented heterotopic aortic valve porcine model was used to test the hypothesis that apixaban has comparable efficacy to warfarin for thromboprophylaxis of mechanical heart valves. Sixteen swine were implanted with a bileaflet mechanical aortic valve that bypassed the ligated descending thoracic aorta. Animals were randomized to 4 groups: control (no anticoagulation; n=4), apixaban oral 1 mg/kg twice a day (n=5), warfarin oral 0.04 to 0.08 mg/kg daily (international normalized ratio 2-3; n=3), and apixaban infusion (n=4). Postmortem valve thrombus was measured 30 days post-surgery for control-oral groups and 14 days post-surgery for the apixaban infusion group. Control thrombus weight (mean) was significantly different (1422.9 mg) compared with apixaban oral (357.5 mg), warfarin (247.1 mg), and apixiban 14-day infusion (61.1 mg; P<0.05). Apixaban is a promising candidate and may be a useful alternative to warfarin for thromboprophylaxis of mechanical heart valves. Unlike warfarin, no adverse bleeding events were observed in any apixaban groups.

Integrated strategy for in vitro characterization of a bileaflet mechanical aortic valve

BackgroundHaemodynamic performance of heart valve prosthesis can be defined as its ability to fully open and completely close during the cardiac cycle, neither overloading heart work nor damaging blood particles when passing through the valve. In this perspective, global and local flow parameters, valve dynamics and blood damage safety of the prosthesis, as well as their mutual interactions, have all to be accounted for when assessing the device functionality. Even though all these issues have been and continue to be widely investigated, they are not usually studied through an integrated approach yet, i.e. by analyzing them simultaneously and highlighting their connections.ResultsAn in vitro test campaign of flow through a bileaflet mechanical heart valve (Sorin Slimline 25 mm) was performed in a suitably arranged pulsatile mock loop able to reproduce human systemic pressure and flow curves. The valve was placed in an elastic, transparent, and anatomically accurate model of healthy aorta, and tested under several pulsatile flow conditions. Global and local hydrodynamics measurements and leaflet dynamics were analysed focusing on correlations between flow characteristics and valve motion. The haemolysis index due to the valve was estimated according to a literature power law model and related to hydrodynamic conditions, and a correlation between the spatial distribution of experimental shear stress and pannus/thrombotic deposits on mechanical valves was suggested. As main and general result, this study validates the potential of the integrated strategy for performance assessment of any prosthetic valve thanks to its capability of highlighting the complex interaction between the different physical mechanisms that govern transvalvular haemodynamics.ConclusionsWe have defined an in vitro procedure for a comprehensive analysis of aortic valve prosthesis performance; the rationale for this study was the belief that a proper and overall characterization of the device should be based on the simultaneous measurement of all different quantities of interest for haemodynamic performance and the analysis of their mutual interactions.

Advancing a Guiding Catheter Across a Mechanical Aortic Valve.

Postoperative mitral paravalvular leaks (MPVLs) occur in approximately 5% of patients undergoing mitral valve replacement and are associated with substantial morbidity. Although surgical repair is the gold standard, it carries a significant risk of morbidity and death, which makes percutaneous closure guided by transesophageal echocardiography a viable and attractive approach in high-risk patients.1 Most case reports discuss an antegrade or transapical approach via an arteriovenous wire loop that serves as a monorail, in order to advance and deploy a closure device. A few case reports1–3 have described a retrograde approach in patients with normal aortic valves, wherein the proximal disc of the device is deployed into the left atrium via an arterial wire. This approach saves operative time and fluoroscopy time, and lowers the risk of sequelae by avoiding a transseptal puncture and an arteriovenous loop.3 The retrograde approach is usually better in patients with medial defects or with defects that create a large gradient across the leak.4The concern is that advancing a guiding catheter across a mono- or bileaflet mechanical aortic valve can cause temporary valve malfunction and hemodynamic compromise. There have been a few published reports4,5 of cases wherein a small guiding catheter was advanced across a mechanical aortic valve to facilitate the making of an arteriovenous loop by advancing the wire through the left ventricle and across the defect into the left atrium. The wire is then snared into the venous system.Until this issue of the Texas Heart Institute Journal, there has, to our knowledge, been no mention in the literature of deploying a closure device through a mechanical aortic valve solely by the retrograde technique. The authors of the case series6 report 2 such instances, in which MPVLs were closed in a retrograde fashion. They first tested the hemodynamic effect of crossing the mechanical aortic valve by using a 6F catheter, and then proceeded with deployment. They gave themselves a 5-minute limit in each attempt and encountered no sequelae of great consequence. Despite their success, we worry that this approach of passing a catheter through a mechanical valve is dangerous. The authors appear to agree, because they limit each attempt to 5 minutes. The worst potential sequela is valve damage and leaflet immobility that result in “wide-open” aortic regurgitation and catastrophic hemodynamic consequences.In patients with MPVL and a mechanical aortic valve, we should still attempt an antegrade technique first, because it remains safer, with better support during deployment of the closure device. This case report shows the retrograde approach to be a feasible option only when the other approaches have failed in such patients, or are not viable. The retrograde approach should be the last resort in an otherwise-inoperable patient. Further studies are needed to validate the optimal timing and technique.

Mid- to long-term outcome comparison of the Medtronic Hancock II and bi-leaflet mechanical aortic valve replacement in patients younger than 60 years of age: a propensity-matched analysis.

This study aims to compare mid-long-term clinical outcomes between patients younger than 60 years of age undergoing bioprosthetic and mechanical aortic valve replacement. From January 2002 to December 2009, patients younger than 60 years of age who received Medtronic Hancock II porcine bioprostheses were selected and compared with those who received mechanical bi-leaflet valves in the aortic position. A stepwise logistic regression propensity score identified a subset of 112 evenly matched patient-pairs. Mid-long-term outcomes of survival, valve-related reoperations, thromboembolic events and bleeding events were assessed. The follow-up was only 95.1% complete. Fourteen measurable variables were statistically similar for the matched cohort. Postoperative in-hospital mortality was 3.6% (bioprosthetic valves) and 2.7% (mechanical valves) (P = 0.700). Survival at 5 and 10 years was 96.3 and 88.7% for patients receiving bioprosthetic valve replacement versus 96.3 and 87.9% for patients receiving mechanical valve replacement (P = 0.860), respectively. At 5 and 10 years after operations, freedom from valve-related reoperation was 97.2 and 94.8% for patients receiving mechanical valve replacement, and 96.3 and 90.2% for patients receiving bioprosthetic valve replacement (P = 0.296), respectively. There was no difference between freedom from thromboembolic events (P = 0.528) and bleeding events (P = 0.128) between the matched groups during the postoperative 10 years. In patients younger than 60 years of age undergoing aortic valve replacement, mid-long-term survival rate was similar for patients receiving bioprosthetic versus mechanical valve replacement. Bioprosthetic valves were associated with a trend for a lower risk of anticoagulation treatment and did not have significantly greater likelihood of a reoperation. These findings suggest that a bioprosthetic valve may be a reasonable choice for AVR in patients younger than 60 years of age.

P-115: Case report of severe heart disease in a hypertensive and diabetic woman 17 years after chest radiation exposure for breast cancer

Objectifs Irradiation of the heart in patients with breast cancer increases the risk of the so-called “radiation-induced heart disease” (RIHD). Among risk factors of RIHD, overweight, hypertension and diabetes mellitus take a major place. To describe a clinical case of an obese hypertensive diabetes mellitus woman with breast cancer since the begining of her radiotherapy until heart failure on the basis of the report from the European Association of Cardiovascular Imaging consensus for evaluation of cardiovascular complications of radiotherapy in adults. Download : Download high-res image (75KB) Download : Download full-size image Abstract P-115 – Figure: Evaluation of Cardiovascular complications of Radiotherapy in a 67 yeats old woman. Methodes A 67 years old woman came to the emergency room with recent worsening of breathlessness. She has had uncontrolled hypertension since 27 years, diabetes mellitus since 17 years and obesity (31kg/m2). She had a complex past medical history. In 1997th she has had breast cancer followed by surgery and radiotherapy with a high cumulative dose of 50 Gy. At this time she was in complete remission. Ten years after, she developed coronary artery disease with subsequent coronary artery bypass surgery. Then she underwent mechanical aortic valve replacement related to mixed aortic valve disease followed by monochamber device for syncopal complete heart block. Few months later she developed heart failure despite upgrading her device to two chambers device. Physical examination: BP/HR: 120/70mmHg/70bpm under medical therapy. Shortness of breath (NYHA class III). Heart: Systolic murmur was audible over the mitral area and substitute sounds of her prosthetic aortic valve. The patient was taking ramipril 5mg daily, furosemide 80 mg daily, spironolactone 25mg daily, warfarin with an international normalized ratio (INR) between 3 and 4; rosuvastatin 20mg daily and beta blockers that was given previously had to be stopped for occurrence of heart failure. Echocardiography: leaflet calcifications on the mitral valve with a mixed lesion; good function of her bileaflet mechanical aortic valve. Depressed left systolic function and markedly elevated pulmonary artery pressure. Resultats After control of her risks factors and optimizing her medical therapy, patient felt much better after two weeks with decreasing of her pulmonary artery pressure. We follow her data closely. Conclusion This case suggests that patients with classical cardiovascular risk factors must be treated in a meticulous way in collaboration with oncologist and radiotherapist. Modifying risk factors as well as early detection and treatment of RIHD may improve the long-term cardiovascular outcome.

Reduced anticoagulation is safe in high-risk patients with the On-X mechanical aortic valve.

The goal of anticoagulation in patients with mechanical aortic valve replacement (AVR) is to maintain an optimal international normalized ratio (INR) that minimizes both the risk of bleeding and thromboembolic events. Here, we review the published data on anticoagulation with bileaflet mechanical prostheses, with a focus on the On-X valve (On-X Life Technologies, Austin, TX), which was designed to function with less anticoagulation or, in some cases, antiplatelet therapy only. Several long-term follow-up studies with the On-X valve demonstrate low rates of bleeding and thromboembolism with standard and low-dose anticoagulation. The Prospective Randomized On-X Anticoagulation Clinical Trial (PROACT) compared the safety of less aggressive anticoagulation (INR 1.5-2.0) with standard anticoagulation (INR 2.0-3.0) after implantation of On-X aortic prostheses for patients at high risk of thromboembolic events. The updated 5-year data confirm that low-dose warfarin is associated with lower major bleeding (1.6 vs. 3.9%/patient-year; P = 0.007) with no difference in thromboembolic events (0.11 vs. 0.52%/patient-year; P = 0.2). Nonrandomized studies and the PROACT data support the safety and efficacy of maintaining the On-X bileaflet mechanical aortic valve prosthesis at a lower target INR than current guideline recommendations for patients at high risk of thromboembolic events. These results offer the promise of a valve prosthesis with excellent durability combined with reduced anticoagulation-related complications.

Timing for pacing after acquired conduction disease in the setting of endocarditis.

A 53-year-old gentleman with a history of a mechanical aortic valve presented to the emergency department complaining of a sudden right-sided abdominal pain. He was found to have atrioventricular dissociation on his initial electrocardiogram and his blood cultures grew Streptococcus viridans. The suspicion for endocarditis with periaortic abscess was high so a transthoracic echocardiogram was performed and showed a mass in the left ventricular outflow tract. For better visualization, a transesophageal echocardiogram was recommended and revealed a bileaflet mechanical aortic valve with perivalvular abscess and valvular vegetation as well as severe eccentric paravalvular aortic regurgitation. After sterilization, the patient underwent a successful surgery. Postoperatively, he remained in complete heart block and a permanent pacemaker placement was performed after complete sterilization. He tolerated the procedure well and was discharged home in a stable condition. Perivalvular abscess is one of the most common cardiac complications of infective endocarditis and is associated with an increased risk of mortality. It is imperative to have appropriate treatment guidelines established. However, because of the relative nature of the disease process and the acuity at which intervention needs to be done, a true assessment of the duration of antibiotic therapy prior to surgical intervention, timing of pacemaker placement, and the type of pacemaker is controversial.

Numerical comparison of the closing dynamics of a new trileaflet and a bileaflet mechanical aortic heart valve

The closing velocity of the leaflets of mechanical heart valves is excessively rapid and can cause the cavitation phenomenon. Cavitation bubbles collapse and produce high pressure which then damages red blood cells and platelets. The closure mechanism of the trileaflet valve uses the vortices in the aortic sinus to help close the leaflets, which differs from that of the monoleaflet or bileaflet mechanical heart valves which mainly depends on the reverse flow. We used the commercial software program Fluent to run numerical simulations of the St. Jude Medical bileaflet valve and a new trileaflet mechanical heart valve. The results of these numerical simulations were validated with flow field experiments. The closing velocity of the trileaflet valve was clearly slower than that of the St. Jude Medical bileaflet valve, which would effectively reduce the occurrence of cavitation. The findings of this study are expected to advance the development of the trileaflet valve.

Low radiation dose non-contrast cardiac CT: is it of value in the evaluation of mechanical aortic valve

Prosthetic bileaflet mechanical valve function has been traditionally evaluated using echocardiography and fluoroscopy. Multidetector computed tomography (MDCT) is a novel technique for cardiac evaluation. To evaluate bileaflet mechanical aortic valves using a low-milliampere (mA), non-contrast MDCT protocol with a limited scan range. Forty patients with a bileaflet mechanical aortic valve were evaluated using a non-contrast, low-mA, ECG-gated 64 MDCT protocol with a limited scan range. MDCT findings of opening and closing valve angles were correlated to fluoroscopy and echocardiography. Also, the valve visibility was evaluated on MDCT and fluoroscopy according to a 3-point grading scale. The visualization score with the MDCT was significantly superior to the fluoroscopy (3 vs. 2.7). A strong correlation was noted between the opening (r = 0.82) and closing (r = 0.96) valve angles with MDCT and fluoroscopy without a statistically significant difference (P = 0.31 and 0.16, respectively). The mean effective radiation dose of the suggested protocol was 4 ± 0.5 mSv. Five valves were evaluated using transesophageal echocardiography because the valves were difficult to evaluate with transthoracic echocardiography, and all of these valves were evaluated optimally with MDCT. A high-pressure gradient was noted in nine valves, and the MDCT showed that seven of these valves inadequately opened, and two valves opened well, which resulted in patient valve mismatch. Incomplete valve closure was noted in five valves, and the echocardiography showed significant transvalvular regurgitation in all five valves. MDCT can provide a precise measurement of valve function and can potentially evaluate high-pressure gradients and transvalvular regurgitation.

In vitro assessment of prosthesis type and pressure recovery characteristics: Doppler echocardiography overestimation of bileaflet mechanical and bioprosthetic aortic valve gradients

Pressure recovery results in Doppler gradients greater than catheter gradients and is well established in association with bileaflet mechanical aortic valves. Because pressure recovery is influenced by orifice geometry, it might manifest differently with various valve prostheses. If true, then the reliability of Doppler echocardiography for the estimation of aortic valve gradients might be different with different prostheses. The purpose of the present study was to test, in an invitro setting, the degree to which pressure recovery results in Doppler overestimation of gradients for three commonly used aortic valve prostheses. Carpentier Edwards Perimount, Medtronic Mosaic, and St. Jude Medical bileaflet prostheses were tested under various flow conditions in a pulsatile mock flow loop with a normal aorta size. Mean pressure gradient was assessed with transducers 1 cm and 10 cm distal to the valve and with Doppler echocardiography. Pressure recovery was defined as the difference between the Doppler gradient and a 10-cm gradient. The percentage of the maximum pressure gradient composed of pressure recovery and the percentage of pressure recovery complete 1 cm distal to the valve were calculated. There was substantial pressure recovery for all valves in all flow states. Pressure recovery was responsible for 50% or more of the Doppler gradients for almost all conditions and was more than 70% complete within 1 cm for almost all conditions. Multivariate analysis found that flow and valve area (but not valve type) were predictors of pressure recovery; that flow was the major predictor of the percentage of Doppler gradient composed of pressure recovery (with minor contributions from the aorta size and prosthesis type); and that valve type and aorta size were the major predictors of the percentage of pressure recovery complete at 1 cm. In an invitro model with a normal aorta size, substantial pressure recovery occurred with all three aortic valve prostheses. Although statistically significant differences were found between valve types in the percentage of pressure recovery and percentage of pressure recovery complete at 1 cm, the differences were small and clinically unimportant. Clinically, among patients with an ascending aorta diameter less than 3.0 cm, Doppler echocardiography likely substantially overestimates aortic valve mean gradient, regardless of prosthesis type.

Effectiveness of dabigatran etexilate for thromboprophylaxis of mechanical heart valves

Warfarin reduces risk of stroke in patients with mechanical heart valves but increases risk of hemorrhage and is difficult to use. Dabigatran etexilate, a new oral direct thrombin inhibitor, is safe and effective in reducing risk of stroke among patients with atrial fibrillation. No data exist in the setting of mechanical heart valves. We tested the hypothesis that dabigatran etexilate is as effective as heparin for thromboprophylaxis of mechanical valves in a porcine heterotopic aortic valve model. Thirty swine underwent implantation of modified bileaflet mechanical valved conduit bypassing the ligated, native descending thoracic aorta. Animals randomly received no anticoagulation (n=10), enoxaparin 2mg/kg subcutaneously twice daily (n=10), or dabigatran etexilate 20 mg/kg orally twice daily. Primary end point was amount of valve thrombus at 30 days. Secondary end points included quantitative measurement of platelet deposition on valve prosthesis, thromboelastography, and hemorrhagic and embolic events. At 30 days, we observed 638 ± 895 mg thrombus in no anticoagulation group, 121 ± 128 mg in enoxaparin group, and 19 ± 31 mg in dabigatran etexilate group (P = .01 enoxaparin vs dabigatran etexilate). Fewer platelets were deposited on valves in dabigatran etexilate group (2.7×10(8)) than in enoxaparin group (1.8×10(9), P=.03). No major or occult hemorrhagic or embolic events were observed. By thromboelastographic analysis, dabigatran etexilate produced less prolongation of K value (P=.01) and less decreases in angle (P=.01) and maximum amplitude (P=.001) than enoxaparin. Dabigatran etexilate is as effective as enoxaparin for short-term thromboprophylaxis of mechanical valves. It prevents valve thrombus and platelet deposition at 30 days without increased adverse events. These promising results serve as a foundation for prospective clinical trials with dabigatran etexilate as an alternative to warfarin in patients with bileaflet mechanical aortic valves.

LOWERing the INtensity of oral anticoaGulant Therapy in patients with bileaflet mechanical aortic valve replacement: Results from the “LOWERING-IT” Trial

Moderate anticoagulation after mechanical heart valve replacement has been proposed to reduce the risk of bleeding related to lifelong anticoagulation. However, the efficacy of such reduced antithrombotic regimens is still unknown. The present prospective open-label, single-center, randomized controlled trial aimed to evaluate the safety and feasibility of reduced oral anticoagulation after isolated mechanical aortic valve replacement. Low-risk patients undergoing bileaflet mechanical aortic valve replacement were randomized to a low International normalized ratio (INR) target (1.5-2.5; LOW-INR group) or to the standard currently recommended INR (2.0-3.0; CONVENTIONAL-INR group) through daily coumarine oral therapy. No aspirin was added. Median follow-up was 5.6 years. The primary outcome was assessment of noninferiority of the low over the standard anticoagulation regimen on thromboembolic events. Secondary end point was the superiority of the reduced INR target strategy on bleeding events. We analyzed 396 patients (197 in the LOW-INR group and 199 in the CONVENTIONAL-INR group). The mean of INR was 1.94 +/- 0.21 and 2.61 +/- 0.25 in the LOW-INR and CONVENTIONAL-INR groups, respectively (P < .001). One versus three thromboembolic events occurred in the LOW-INR and CONVENTIONAL-INR, respectively, meeting the noninferiority criterion (P = .62). Total hemorrhagic events occurred in 6 patients in the LOW-INR group and in 16 patients in the CONVENTIONAL-INR group (P = .04). LOWERING-IT trial established that the proposed LOW-INR target is safe and feasible in low-risk patients after bileaflet aortic mechanical valve replacement. It results in similar thrombotic events and in a significant reduction of bleeding occurrence when compared to the conventional anticoagulation regimen.