Mechanisms of Spin-Dependent Heat Generation in Spin Valves

The extra heat generation in spin transport is usually interpreted in terms of the spin relaxation. Reformulating the heat generation rate, we find alternative current-force pairs without cross effects, which enable us to interpret the product of each pair as a distinct mechanism of heat generation. The results show that the spin-dependent part of the heat generation includes two terms. One is proportional to the square of the spin accumulation and arises from the spin relaxation. However, the other is proportional to the square of the spin-accumulation gradient and should be attributed to another mechanism, the spin diffusion. We illustrate the characteristics of the two mechanisms in a typical spin valve with a finite nonmagnetic spacer layer.

Mortality of Children with Mechanical Valve Prostheses at the CUOMO Cardio-Pediatric Center of University National Hospital of Fann (Dakar)

Introduction: Mechanical valve replacement in pediatric age is a dreaded but sometimes inevitable surgery. The purpose of this study was to determine the mortality of children with mechanical valve prostheses in the short, medium and long term. Patients and Methods: This was a retrospective and descriptive study conducted at the CUOMO cardio-pediatric center at Teaching National Hospital of Fann between January 1st, 2017 and December 31st, 2021. We included, children whose age is less than or equal to 16 years of age and who have benefited from a mechanical valve replacement and with a follow-up period of more than 6 months post-operative in the CUOMO cardio-pediatric center. Patients whose age at the time of surgery was over 16 years were excluded;patients who have benefited from bioprosthesis or valvular plastic surgery alone;as well as patients for whom a follow-up of more than 6 months was not found. Statistical analyses were carried out using the SPSS (Statistical Package for Social Science) software version 18 to calculate averages and percentages. Results: We included 85 patients. The average age was 12.84 ± 2.52 years. The male gender predominated with a sex ratio of 1.65. Dyspnea was found in 96.47% of children. Pure mitral regurgitation was the most common valve disease found in 67.06%. Rheumatic etiology was noted in 87.06% of cases. Mono valve replacement was performed in 84.71% of patients and double valve replacement in 15.3% of cases. Major mechanical complications were reported in 8 patients including 5 severe aortic mismatch cases. Hemorrhagic complications were observed in 4 patients requiring surgery. Hemodynamic complications were dominated by right ventricle dysfunction in 14 patients. Supraventricular rhythm disorders were present in 11 patients and one case of ventricular tachycardia. We found six cases of infectious endocarditis. Eight deaths were recorded with a mortality rate of 5.88%. Significant predictors of mortality were stage IV dyspnea of NYHA and preoperative overall heart failure. Conclusion: Our study showed good results in terms of short-, medium- and long-term mortality. Complications related to mechanical valve prostheses are not negligible, hence a rigorous lifetime monitoring after surgery.

Combined Low-dose Aspirin and Warfarin Anticoagulant Therapy of Postoperative Atrial Fibrillation Following Mechanical Heart Valve Replacement

The safety and efficacy of combined low dose aspirin and warfarin therapy in patients with atrial fibrillation after mechanical heart valve replacement were evaluated. A total of 1016 patients （620 females, mean age of 36.8-4-7.7 years） admitted for cardiac valve replacement and complicated with atrial fibrillation after surgery were randomly divided into study （warfarin plus 75-100 mg aspirin） or control （warfarin only） groups. International normalized ratio （INR） and prothrombin time were main- tained at 1.8-2.5 and 1.5-2.0 times the normal values, respectively. Thromboembolic events and major bleedings were registered during the follow-up period. Patients were followed up for 24±9 months. The average dose of warfarin in the study and control groups was 2.91±0.83 mg and 2.88±0.76 mg, respec- tively （P〉0.05）. The incidence of overall thromboembolic events in study group was lower than that in control group （2.16% vs. 4.35%, P=0.049）. No statistically significant differences were found in hem- orrhage events （3.53% vs. 3.95%, P=-0.722） or mortality （0.20% vs. 0.40%, P=0.559） between the two groups. Combined low dose aspirin and warfarin therapy in the patients with atrial fibrillation following mechanical heart valve replacement significantly decreased thromboembolic events as compared with warfarin therapy alone. This combined treatment was not associated with an increase in the risk of major bleeding or mortality.

Anticoagulation early after mechanical heart valve replacement

Objective： To explore the changes of coagulation activity and the characters of anticoagulation early after mechanical heart valve replacement. Methods： All patients only took warfarin orally for anticoagulation. The predicted international normalized ratio （INR） was 1.5 to 2.0. Several coagulation markers were monitored early after valve replacement. Complications associated with anticoagulation were recorded and analyzed. The patients were divided into three groups based on the number and position of mechanical valve prothesis, including group M （mitral valve replacement）, group A （aortic valve replacement） and group D （mitral and aortic valve replacement）.Comparison was made between the three groups. Results： Three events of mild cerebral embolism and five events of mild bleeding occurred during the early postoperative period. One patient suffered from mild cerebral embolism on the 4th day after operation, accompanied by large volume of pericardial drainage. Two patients with bleeding had lower INRs than predicted range. However, INR in one patient with mild cerebral embolism was in the predicted range. There was no significant difference in thrombo time （TT）, activated partial thromboplastin time （APTT） and 1NR on the 3rd day after operation compared to those before operation; meanwhile, plasma fibrinogen （FIB） concentration was higher than that before operation （P〈0.05）. 1NR had no significant changes on the 2nd day after the beginning of anticoagulation compared to that before operation; however, 1NR was significantly elevated on the 4th day （P〈0.05）. Warfarin doses and INRs were similar among the three groups, but FIB concentrations in plasma were higher in groups M and D than in group A （P〈0.01）. Conclusion： Hypercoagulabale state exists early after mechanical heart valve replacement. When anticoagulation begins is determined by the change of coagulation markers, not by the volume of chest or pericardial drainage. INR can not accurately reflect the coagulation state sometimes, especially during the first 3 days after anticoagulation. The number and position of mechanical valve prothesis could affect coagulation state. Therefore, anticoagulation therapy should be regulated accordingly.

INFLUENCE OF MIMIC CARDIAC RATE ON HYDRODYNAMICS OF DIFFERENT MECHANICAL PROSTHETIC CARDIAC VALVES IN VITRO

Objective To assess the influence of mimic cardiac rate on hydrodynamics of different mechanical prosthetic cardiac valves. Methods US-made CarboMedics bileaflet valve, China-made Jiuling bileaflet valve and C-L tilting disc valve were tested via a pulsatile flow simulator in the aortic position. Testing conditions were set at mimic cardiac rates of 55 bpm, 75 bpm, 100 bpm with a constant mimic cardiac output of 4 L/min. The mean pressure differences (ΔP), leakage volumes (LEV) and closing volumes (CLV) across each valve, and effective orifice areas (EOA) were analyzed. Results Within physiological range, ΔP, LEV, and CLV decreased as mimic cardiac rate increased, with a large extent of variance. EOA increased along with an increase in mimic cardiac rate. It was a different response in terms of cardiac rate alteration for different types of mechanical prosthetic cardiac valves. Conclusion Mimic cardiac rate change affects hydrodynamics of mechanical prosthetic cardiac valves. Within physiological range, the hydrodynamic of prosthetic bileaflet valve is better than that of tilting disc valve.

Is it the time to reconsider the choice of valves for cardiac surgery： mechanical or bioprosthetic？

Valvular heart disease is a pathologic process involving one or more of the four valves(aortic,pulmonary,mitral and tricuspid)of the heart typified by stenosis or regurgitation and leading to patient symptoms.The most common causes are tissue degeneration,rheumatic fever and congenital heart diseases.Aortic valve replacement(AVR)using either mechanical or bioprosthetic(tissue)valves via open-heart surgical

Observations on Durability of a Pyrolytic Carbon Bileaflet Mechanical Heart Valve

This study aims to observe the durability of a pyrolytic carbon bileaflet mechanical valve prosthesis. The mechanical valves prosthesis was tested in vitro by the durability test instrument of valve prosthesis. Then in vivo, the durability of the implanted valves was observed with animal experiments and elinieal application. In the impact test for 5 min and durability test of 380 million eyeles in vitro, there was no the phenomenon of flyer, perforation and fracture observed, as well as no wear or pit found on the surface of valve leaflets. The valve leaflets could normally be turned on or off. The weight of the valve was（1.0031 ± 0.0004） g for 23 mm and（1.6003 ± 0.0002） g for 27 mm. The hydrodynamies test demonstrated that the valve prosthesis had still exeellent hemodynamic performance after the durability test. The animal autopsy showed that the valve leaflets could normally be turned on or off, and no wear was found. By follow-up of 62 patients implanted the valves, all patients had long-terms survival, no complication caused by valve was found. The age of the longest survival was more than 10 years. This study demonstrates that the new meehanieal valve prosthesis have excellent durable performance.

Early Postoperative Anticoagulation by Enoxaparin after Mechanical Aortic Valve Replacement

Background: The use of low molecular weight heparin for early anticoagulation after mechanical aortic valve replacement is still a matter of debate even more that the early postoperative phase is associated with maximum of thrombo-embolic and bleeding risks. The objective of this study is to verify the efficacy and the safety of low molecular weight heparin for the early anticoagulation after mechanical aortic valve replacement. Methods and Results: It is a prospective study conducted over 6 months and interested 40 consecutive patients (32 male and 8 female) with a mean age 53.83 ± 16.93 years (19-75 years) who underwent a mechanical aortic valve replacement and received enoxaparin as bridging therapy between continuous unfractionated heparin and fully effective vitamin K antagonist therapy. There was no in-hospital death and no in-hospital thromboembolic events. We report 2 major bleeding events (5%). Conclusion: The use of low molecular weight heparin should be an alternative to explore for early anticoagulation after valve heart surgery and the results of our study must be verified by large randomized studies before drawing any hasty conclusions.

Thrombus precursor protein for monitoring anticoagulation in patients with mechanical valve prosthesis

Objective: To evaluate the plasma concentration of thrombus precursor protein (TPP) in patients after mechanical heart valve replacement, and to explore whether it can be used as a marker for monitoring anticoagulation. Methods: Totally 60 patients who took warfarin after mitral valve replacement and 20 control patients with non-valvular heart diseases were subjected in this study. Their plasma TPP concentration and international normalized ratio (INR) were determined, and compared not only between the anticoagulant patients and the control patients, but also between the patients with atrial fibrillaiton (AF, n=37) and the patients with sinus rhythm (SR, n=23) after mechanical valve replacement. The relationship between plasma TPP concentration and INR in the 60 anticoagulant patients was analyzed with linear regression. Results: It was found that the anticoagulant therapy effectively decreased plasma TPP concentration and elevated INR. In the anticoagulant group, the patients with AF had higher plasma TPP concentration than the others with sinus rhythm (P<0.05), although there was no significant difference in INR level between these 2 groups of patients (P>0.05). No significant correlation was found between plasma TPP concentration and INR in the anticoagulant patients (P>0.05). INR did not accord with plasma TPP concentration in several patients. Conclusion: INR can’t reflect the coagulation status and guide the anticoagulation correctly sometimes; TPP may be a valuable assistant marker for monitoring anticoagulation in patients with mechanical heart valve prothesis; Patients with AF may require higher density of anticoagulation and TPP is strongly suggested to be monitored in these patients.

A COMPARATIVE STUDY OF THE OPENING AND CLOSING PROCESS OF TWO TYPES OF MECHANICAL HEART VALVES USING ALE FINITE ELEMENT METHOD

Using arbitrary Lagrangian-Eulerian(ALE)finite element method,this paper made a comparative study of the opening and closing behaviour of a downstream directional valve(DDM)and a St.Jude medical valve(SJM)through a two dimensional model of mechanical valve-blood interaction in which the valve is considered as a rigid body rotating around a fixed point,and the blood is simplified as viscous incompressible fluid It's concluded that:(1)Compared with SJM valve, DDM valve opens faster and closes the more gently.(2)The peak badk-flow-flow of DDM is smaller than that of SJM.The present investigation shows that being a better analogue of natural valve,DDM has a brighter potential on its durability than SJM.

ALE FINITE ELEMENT ANALYSIS OF THE OPENING AND CLOSING PROCESS OF THE ARTIFICIAL MECHANICAL VALVE

Employing arbitrary Lagrangian-Eulerian (ALE) finite element method, this poper studies the opening and closing process of a St. Jude medical valve through a two-dimensional model of the mechanical valve-blood interaction in which the valve is regarded as a rigid body rotating around a fixed point, and foe blood is simplified as viscous incompressible Newtonian fluid. The numerical analysis of the opening and closing behaviour of as St. Jude valve suggested that: 1. The whole opening and closing process of an artificial mechanical valve is consisted of four phases: (1) Opening phase; (2) Opening maintenance phase; (3) Closing phase; (4) Closing maintenance phase. 2. The St. Jude medical valve closes with prominent regurgitat which results in water-hammer effect. 3. During the opening and closing process of the St. Jude valve,high shear stresses occur in the middle region of the two leaflets and on the valve ring. The present model has made a breakthrough on the coupling computational analysis considering the interactive movement of the valve and blood.

The Effects of Lower Intensity Anticoagulation Therapy on Coagulation System in Patients With Mechanical Prosthetic Valves

Summary: To evaluate the effect of lower intensity anticoagulation therapy in patients with mechanical prosthetic valves, laboratory based hematological assays including prothrombin time (PT), activity of factor X, antithrombin Ⅲ (AT Ⅲ), D dimer, fibrinogen (Fg) and platel et al pha granular membrane protein (GMP 140) were performed in 65 patients who had been on warfarin treatment for over one month. The patients were assigned to 3 groups on the basis of their International Normalized Ratios (INR), ranging from 2.00 to 2.50; 2.51 to 3.00; 3.01 to 4.50, respectively. The results showed that the D dimer, Fg, GMP 140 levels were higher after mechanical valve replacement than those before operation, indicating the activation of coagulation and fibrinolysis system and the damage of platelets. Lower intensity anticoagulation therapy (INR 2 00 to 2.50) could effectively inhibit the activity of factor X and increase the level of AT Ⅲ. There were no appreciable differences among D dimer, Fg, GMP 140 and AT Ⅲ in the 3 anticoagulation intensity groups. These results suggest that in patients with new generation mechanical prosthetic valves, target anticoagulation level (INR 2 00 to 2.50) may result in good protection from thrombo embolism.

Role of thrombus precursor protein in assessment of anticoagulation in patients with atrial fibrillation after mechanical heart valve replacement

Objective: To explore the role of thrombus precursor protein (TpP) in assessment of anticoagulation and predict the risk of thromboembolism in the patients with atrial fibrillation (AF) after mechanical heart valve replacement. Methods: TpP plasma concentration and international normalization ratio (INR) were measured in 45 patients with atrial fibrillation and 45 patients with sinus rhythm both after mechanical heart valve replacement. Twenty patients with non valvular heart diseases were selected as the control. Furthermore, the patients with AF were divided into groups based on different TpP plasma concentration and TpP plasma concentration and INR were analyzed. Results: After mechanical heart valve replacement, those with AF had higher TpP plasma concentration than those with sinus rhythm. It was found that discordancy existed between INR and TpP plasma concentration in the patients with AF. There were 28 AF patients with TpP plasma concentration lower than 6 μg/ml and without bleeding, who might be at the optimal anticoagulant state. The 95% confidence of the mean INR value was 1.90-2.30 in these patients and TpP plasma concentration was between 2.84-5.74 μg/ml. Conclusion: Patients with AF might face higher risk of thromboembolism after mechanical valve replacement; INR between 1.90-2.30 and TpP plasma concentration between 2.84-6 μg/ml might be the optimal anticoagulant range for patients with AF after mechanical valve replacement.

Experimental Observation on Antithrombotic Property of A New Bileaflet Mechanical Heart Valve in Sheep

Objective ： To observe the antithrombotic property of a new all-pyrolytic carbon bileaflet mechanical heart valve so as to provide evidence for clinical practice. Methods： 15 sheep underwent mitral valve replacement （MVR） with this new mechanical valve. Each animal was placed on cardiopulmonary bypass. All of the sheep were given in an anticoagulation protocol and followed for three months. Final studies were performed on all animals surviving for more than 12 weeks. Results ： 10 sheep died within 48 h after operation, 5 sheep survived. The long-term survivors were killed for autopsies,2 sheep were killed after 1 week, 1 after 12 weeks and 2 after two and half years. Pathological examination of 10 sheep which died early after operation revealed that there was neither evidence of thrombosis nor any failure of the mechanical valve. Autopsy studies in the 5 long-term survivors revealed that the sewing ring was covered by a thin layer of microthrombi consisted most of platelets and fibrin after 1 week. The sewing ring was covered by a tissue layer, with partial organized microthrombi and endothelialization after 12 weeks. Two and half years after operation, the complete endothelialization presented around the sewing ring without restriction of bileaflet motion. The tissue ingrowth tends to stop at the pyrolytic earbon-fabric interface on both surfaces of left atrium and ventricle. This study demonstrated that the new prosthetic heart valve had not promoted thrombosis and thrombembolism.

Low-intensity anticoagulation therapy in the pregnant women with mechanical heart valves:a report with 56 cases

Objective To evaluate the method of low-intensity anticoagulation therapy in the pregnant women who had received mechanical heart valve replacemant,and the effects of warfarin on the pregnant women and their fetus. Methods This retrospective study involved 56 pregnant women (61 pregnancies) who had received mechanical heart valve replacement. Their pregnant status,delivery, and anticoagulation therapy were observed

PARAMETERIZED-PROTOTYPE-BASED DYNAMIC OPTIMIZATION DESIGN FOR CAM PROFILE

Aiming at the problems in current cam profile optimization processes, such as simple dynamics models, limited geometric accuracy and low design automatization level, a new dynamic optimization mode is put forward. Based on the parameterization modeling technique of MSC. ADAMS platform, the different steps in current mode are reorganized, thus obtaining an upgraded mode called the ＂parameterized-prototype-based cam profile dynamic optimization mode＂. A parameterized prototype（PP） of valve mechanism is constructed in the course of dynamic optimization for cam profiles. Practically, by utilizing PP and considering the flexibility of the parts in valve mechanism, geometric accuracy and design automatization are improved.

基于时机理论的家庭护理对瓣膜置换患者康复及效果研究

目的探讨基于时机理论的家庭护理对机械瓣膜置换患者的康复及影响。方法根据统一的诊断、纳入及排除标准,选取102例患者,按随机数字表法分为对照组(52例)与试验组(50例)。对照组患者及家属接受心胸外科常规护理与随访;试验组在心胸外科常规护理的基础上接受家庭护理干预,分别于出院时、出院后3个月及6个月时对患者生活质量、华法林服用依从性及并发症发生率进行统计。结果出院后3个月和6个月时试验组患者生活质量、华法林服药依从性均优于对照组(p<0.001);研究结束时,试验组患者华法林相关并发症低于对照组,差异有统计学意义(p<0.05)。结论基于时机理论的家庭护理在机械瓣膜置换患者的康复中应用效果显著,可以有效提高患者华法林服药依从性及生活质量,降低华法林相关并发症的发生率。

Valve replacement in pediatric patients： a single center experience

Background Reconstructive surgery is the primary goal in pediatric patients with valve disease.However,in cases with irreparable valve lesions,valve replacement is the only option.This study aimed to retrospectively analyze the clinical experience of heart valve prosthesis replacement in children.Methods Between January 1990 and July 2009,35 pediatric patients （16 boys,19 girls） underwent mechanical valve replacement in Shandong University Qilu Hospital.The ages ranged from 2.5 to 14 years （mean,（8.8±3.8） years） and body weight varied from 11 to 37 kg （mean,（22.1±5.2） kg）.Mechanical valve replacement was performed because of congenital heart disease in 23 patients,rheumatic disease in ten patients and infective endocarditis in two patients.St.Jude bileaflet mechanical valves were implanted in all the 35 patients including mitral valve replacement （MVR） in 18,aortic valve replacement （AVR） in 12,tricuspid valve replacement （TVR） in two,AVR and MVR in two and MVR and TVR in one.The size of the prostheses ranged between 19 and 27 mm.All patients received long-term anticoagulation treatment with sodium warfarin,aiming to maintain an international normalized ratio between 1.5 to 2.0.Follow-up was performed in all the patients with a total follow-up of 119.4 patient-years.Results The operative mortality was 8.57% （3/35）.One patient,who underwent cardiac debridement and AVR,died 2 hours after being admitted to the intensive care unit because of severe low cardiac output syndrome and ventricular fibrillation.Two patients died of cardiogenic shock and renal failure during initial hospitalization after the operation.One patient who received replacement of a tricuspid valve developed complete heart block requiring temporary pacing and recovered sinus rhythm 4 days later.Thirty-two patients survived and their cardiac function was in New York Heart Association （NYHA） class Ⅰ to class Ⅱ when discharged.Late events included hemorrhage and endocarditis.Two patients required reoperation.No late deaths occurred during the follow-up.Conclusions Mechanical valve replacement remains an acceptable treatment option in children when the valve reparation is impossible or unsuccessful.The operative mortality and incidence of any valve-related events such as endocarditis,reoperation,thromboembolism or anticoagulation-related bleeding are acceptable.

A NUMERICAL ANALYSIS OF THE BLOOD FLOW AROUND THE BILEAFLET MECHANICAL HEART VALVES WITH DIFFERENT ROTATIONAL IMPLANTATION ANGLES

The effects of implantation angles of Bileaflet Mechanical Heart Valves （BMHVs） on the blood flow and the leaflet motion are investigated in this paper. The physiological blood flow interacting with the moving leaflets of a BMHV is simulated with a strongly coupled implicit Fluid-Structure Interaction （FSI） method based on the Arbitrary-Lagrangian-Eulerian （ALE） approach and the dynamic mesh method （remeshing） in Fluent. BMHVs are widely used to be implanted to replace the diseased heart valves, but the patients would suffer from some complications such as hemolysis, platelet activation, tissue overgrowth and device failure. These complications are closely related to both the flow characteristics near the valves and the leaflet dynamics. The current numerical model is validated against a previous experimental study. The numerical results show that as the rotation angle of BMHV is increased the degree of asymmetry of the blood flow and the leaflet motion is increased, which may lead to an unbalanced force acting on the BMHVs. This study shows the applicability of the FSI model for the interaction between the blood flow and the leaflet motion in BMHVs.

An Experimental Study on the Flexibility of Prevention against Thrombosis Following Mechanical Valve Replacement by tPA Gene Transduction

Objectives Use a gene suture immersed recombinant tissue-type plasminogen activator （r-tPA）expression plasmid to transduce myocardia to prevent the thrombosis after mechanical tricuspid valve replacement in pigs. Methods A r-tPA gene plasmid was constructed and conjugated to a novel cationic phosphonolipid and a r-tPA gene suture was made. Eighteen pigs were selected and divided into two groups at randomization. There were 9 pigs in the experimental group and 9 in the control group, all the 18 pigs＇ tricuspids were replaced with mechanical valves. The gene threads were sutured into the right ventricular walls near mechanical valves and an ultrasound was used on the surfaces of the right ventricular walls for the gene transfer in the experimental group. Coagulative function, D-dimer level of the blood and the thrombosis on the surfaces of the valves were observed. Results r-tPA gene plasmid was successfully constructed and r-tPA protein was expressed in the ventricular cells around the gene sutures. D-dimer reached its peak level （ 1.67 ±0. 79） μg · mL^-1 in 1 week after operation in two groups, but it decreased to preoperation level thereafter in control group and kept on the high level and reincreased to a new high level （ 1.89 ± 0.79 ） μg · mL^-1 until the end of the experiment in experimental group. The thromboses around the valves were found in all the control group （100%） but only 1 （ 11.11% ） case in experimental group. There were no changes in prothrombin time pre and post operation in two groups. Conclusions Using gene suture immersed r-tPA expression plasmid to transduce myocardia might be a best substitution for life long anti-coagulation therapy for the patients, who underwent operation.