Hemodynamics of venous valve pairing and implications on helical flow.

BACKGROUND: It has been shown that venous valves have pairing arrangements with specific relative orientation and spacing that contribute to helical flows. The studies to date have not quantified the hemodynamic impact of helical flow formation. A computational model allows various valve orientations and spacings to be studied to better understand the hemodynamic effect of valve pairing. METHODS: Simulations were performed for paired valves at physiologically relevant spacing and orientations to study the flow features and hemodynamics associated with valve pairing configurations. The wall shear stress (WSS), residence time, and pressure drop were evaluated for the various valve pairing cases. RESULTS: It was found that the WSS on the lumen flow side (front) of the leaflet is several times higher than on the valve pocket side (back). With orthogonal paired valves, the WSS at the critical back side is increased. Helical flow was clearly observed only with orthogonal valve pairing. The residence time was reduced to less than half (0.47 vs 1.16 seconds) in the orthogonal valve case compared with the parallel valve cases. The farther spaced valves (6 cm) had the highest residence time. CONCLUSIONS: This simulation study shows that helical flow in the veins of lower extremities is strongly dependent on the relative orientation and spacing of the valves. For optimal orientation (∼90 degrees) and spacing (∼4 cm), strong helical flow is seen, which enhances WSS and reduces the flow resistance and residence time. These findings demonstrate a structure-function relation that optimizes flow patterns in normal physiology, which can be compromised in venous valve disease. The results of this study provide valuable insights that improve the current understanding of blood flow patterns around venous valves and the design of future multiple paired prosthetic valves.

Bacterial adherence to graft tissues in static and flow conditions.

BACKGROUND: Various conduits and stent-mounted valves are used as pulmonary valve graft tissues for right ventricular outflow tract reconstruction with good hemodynamic results. Valve replacement carries an increased risk of infective endocarditis (IE). Recent observations have increased awareness of the risk of IE after transcatheter implantation of a stent-mounted bovine jugular vein valve. This study focused on the susceptibility of graft tissue surfaces to bacterial adherence as a potential risk factor for subsequent IE. METHODS: Adhesion of Staphylococcus aureus, Staphylococcus epidermidis, and Streptococcus sanguinis to bovine pericardium (BP) patch, bovine jugular vein (BJV), and cryopreserved homograft (CH) tissues was quantified under static and shear stress conditions. Microscopic analysis and histology were performed to evaluate bacterial adhesion to matrix components. RESULTS: In general, similar bacteria numbers were recovered from CH and BJV tissue surfaces for all strains, especially in flow conditions. Static bacterial adhesion to the CH wall was lower for S sanguinis adhesion (P < .05 vs BP patch). Adhesion to the BJV wall, CH wall, and leaflet was decreased for S epidermidis in static conditions (P < .05 vs BP patch). Bacterial adhesion under shear stress indicated similar bacterial adhesion to all tissues, except for lower adhesion to the BJV wall after S sanguinis incubation. Microscopic analysis showed the importance of matrix component exposure for bacterial adherence to CH. CONCLUSIONS: Our data provide evidence that the surface composition of BJV and CH tissues themselves, bacterial surface proteins, and shear forces per se are not the prime determinants of bacterial adherence.

A Systematic Review of Infective Endocarditis in Patients With Bovine Jugular Vein Valves Compared With Other Valve Types.

OBJECTIVES: The aim of this study was to systematically evaluate the incidence of infective endocarditis (IE) in right ventricle-to-pulmonary artery conduits and valves, comparing bovine jugular vein (BJV) valves with all others. BACKGROUND: Recent evidence suggests that the incidence of IE is higher in patients with congenital heart disease who have undergone implantation of BJV valves in the pulmonary position compared with other valves. METHODS: Systematic searches of published research were conducted using electronic databases (MEDLINE, Embase, and CINAHL) and citations cross-referenced current to April 2016. Included studies met the following criteria: patients had undergone right ventricle-to-pulmonary artery conduit or percutaneous pulmonary valve implantation, and investigators reported on the type of conduit or valve implanted, method of intervention (surgery or catheter based), IE incidence, and follow-up time. RESULTS: Fifty studies (Levels of Evidence: 2 to 4) were identified involving 7,063 patients. The median cumulative incidence of IE was higher for BJV compared with other valves (5.4% vs. 1.2%; p < 0.0001) during a median follow-up period of 24.0 and 35.5 months, respectively (p = 0.03). For patients with BJV valves, the incidence of IE was not different between surgical and catheter-based valve implantation (p = 0.83). CONCLUSIONS: There was a higher incidence of endocarditis with BJV valves than other types of right ventricle-to-pulmonary artery conduits. There was no difference in the incidence of endocarditis between catheter-based bovine valves and surgically implanted bovine valves, suggesting that the substrate for future infection is related to the tissue rather than the method of implantation.

Expandable Valve for Pediatric Application Constructed From Human Venous Valved Conduit Within a Stent.

PURPOSE: Options for pediatric valve replacement are limited by inability to adapt to child growth. An expandable valve design is presented in which human cryopreserved venous valved conduits are constructed within a bare-metal stent scaffold. We demonstrate functionality in vitro and acute competence in vivo. DESCRIPTION: A cryopreserved femoral venous valved conduit was compressed within a bare-metal stent scaffold and sutured at the proximal and distal ends. In vitro testing was performed at low and high pressure after sequential balloon expansion. Valve morphology was measured in the nondistended state. The construct was tested in 2 patients. EVALUATION: In vitro testing confirmed competence of the 14-mm femoral valve construct at 10-mm to 14-mm diameters. The median leaflet commissural height-to-diameter ratio was 2.2 (range, 1.6 to 4.1) for femoral. The construct was implanted in 2 patients at internal diameters of 6 mm and 8 mm. Echocardiograms demonstrated competence at short-term follow-up. In 1 patient, competence was demonstrated after balloon expansion. CONCLUSIONS: This study demonstrates the feasibility of this expandable valve design using an allograft venous valved conduit compressed within a stent.

Reconstruction of right ventricular outflow tract in neonates and infants using valved cryopreserved femoral vein homografts.

OBJECTIVES: Aortic or pulmonary homografts (A/PHs) are common biomaterials used for restoration of right ventricle to pulmonary artery continuity for repair of various congenital heart defects. The smaller sized homografts required for early primary repair in neonates and infants are prone to early failure and are in short supply. Due to these limitations, since 2008 it has been our preference to use valved segments of cryopreserved femoral vein homograft (cFVH) for right ventricle to pulmonary artery reconstruction. This study was undertaken to assess the performance of cFVH compared with A/PH in neonates and infants. METHODS: A retrospective review of all infants and neonates who underwent biventricular early primary repair with right ventricle to pulmonary artery reconstruction using homograft conduits at a single center was conducted. Patients who received cFVH constituted the study group, whereas all other patients received A/PH and formed the control group. Patients with pulmonary atresia, ventricular septal defect, and major aortopulmonary collaterals who had conduits placed to promote pulmonary artery growth or to unifocalized pulmonary vasculature were excluded from the study because they have different clinical indications for reoperation and reintervention. Demographic, anatomical, perioperative, and follow-up variables were compared between the groups using univariate and multivariable Cox regression analyses. Kaplan-Meier analysis and log-rank tests were used to identify intergroup differences in freedom from catheter intervention, reoperation, or overall freedom from reintervention (catheter and/or surgical). RESULTS: A total of 36 patients (20 cFVH and 16 A/PH) were included in the study. There were no intergroup differences in the demographic, anatomic, and perioperative variables, except for significantly shorter aortic crossclamp time in the cFVH group. Univariate analysis revealed a higher catheter reintervention rate as well as higher reoperation rate in the A/PH group. Multivariate Cox regression correcting for the intergroup differences in the length of follow-up revealed comparable freedom from catheter intervention, freedom from reoperation, or freedom from either intervention in the cFVH and the A/PH groups. CONCLUSIONS: Valved femoral vein homografts have comparable short- and intermediate-term performance to A/PHs for right ventricular outflow tract reconstruction and are an attractive alternative to other small conduits for use in neonates and infants.

Hemodynamic effects of implanting a unidirectional valve in the inferior vena cava of the Fontan circulation pathway: an in vitro investigation.

The Fontan surgical procedure used for treating patients with single ventricle congenital heart disorders results in a total cavopulmonary connection (TCPC) of the vena cavae to the pulmonary arteries (PAs). Sluggish TCPC flow and elevated hepatic venous pressures are commonly observed in this altered physiology, which in turn can lead to long-term complications including liver congestion and cirrhosis. The hypothesis of this study is that placement of a unidirectional valve within the inferior vena cava (IVC) will improve hemodynamics of the Fontan circulation by preventing retrograde flow and lowering hepatic venous pressure. An in vitro experimental setup consisting of an idealized TCPC model with flexible walls was used for investigation, and a bovine venous valve was inserted in the IVC below the TCPC. Pressure fluctuations were introduced in the flow through the model to simulate venous pulsatility. Hemodynamics of baseline and valve-implanted conditions were compared across total caval flows ranging from 1.0 to 2.5 l/min with varying caval flow distributions. The results indicated that valve closure occurred for 15-20% of the total cycle, with consequent reduction in the upstream hepatic venous pressure by 5 to 10 mmHg. Energy loss (EL) through the TCPC was lowered with valve implantation to 20-50% of baseline, occurring across all flow conditions considered with mean caval and PA pressures greater than 10 mmHg. The results of this in vitro modeling suggest that IVC valve placement has the potential to improve hemodynamics in the Fontan circulation by decreasing hepatic venous hypertension and EL.

Longevity and outcomes of axillary valve transplantation for severe lower extremity chronic venous insufficiency.

BACKGROUND: To assess the efficacy of axillary vein transplantation in the treatment of severe chronic venous insufficiency (CVI). METHODS: Among 139 complex venous reconstructions performed between 1991 and 2007 for CVI, 18 patients underwent upper extremity to lower extremity venous valve transplantation. An upper extremity valve was transplanted to the popliteal vein in 13 cases, to the common femoral vein in six cases, and to the saphenofemoral junction in two cases for a total of 21 procedures. All patients had follow-up with duplex scanning to assess valve competency and clinical visits to assess clinical improvement. Mean follow-up period was 37 months. RESULTS: Mean patient age was 44 years, and 57% were men. Clinically, 57% of the limbs were Clincal (C) class C5-C6. The mean preoperative venous disability score was 2.95. Most of the patients (66%) had post-thrombotic valvular dysfunction. At the time of valve transplantation, there was no proximal venous obstruction documented. A successful operation was defined as a competent valve at the end of the procedure and was achieved in 20 of 21 (95%) patients. Eight patients had at least one postoperative complication, primarily bleeding. The mean postoperative venous disability score was 2.65 and this increased to 2.75 (p = not significant as compared with baseline) at the last postoperative visit. Median time to return of symptoms was 12 months, and median reflux-free survival period was 15 months. CONCLUSION: Despite initial technical and symptomatic success with venous valve transplantation, there is a poor long-term valve competency rate and symptomatic control. These data suggest that a better understanding and therapy for severe CVI associated with valvular incompetence needs to be found.

Bovine jugular vein valved conduit: up to 10 years follow-up.

OBJECTIVE: The present study evaluated the mortality and conduit failure in bovine jugular vein (BJV) conduits. METHODS: Between October 1999 and February 2009, 193 patients (mean age, 6.7 ± 5.8 years; range, 5 days to 18 years; mean weight, 23.9 ± 21.0 kg; range, 2.4-105.4 kg) had been discharged after BJV implantation. The reason for BJV implantation was right ventricular outflow tract reconstruction in 117 conduit replacement in 44, and the Ross procedure in 32. The diameter of the BJV was 12 mm in 18 patients (9.3%), 14 mm in 16 (8.3%), 16 mm in 42 (21.7%), 18 mm in 37 (19.2%), 20 mm in 15 (7.8%), and 22 mm in 65 (33.7%). RESULTS: At a mean ± SD follow-up of 4.6 ± 2.3 y/patient (range, 8 months to 10 years), 5 late deaths (2.6%) had occurred, all unrelated to conduit failure. Conduit-related problems required an interventional procedure as the first treatment in 10 patients (5.2%) within a mean interval of 2.5 ± 1.4 years (range, 8 months to 5.3 years) or surgical revision in 5 patients (2.6%) after 2.1 ± 1.9 years (range, 19 days to 4.1 years). Late deaths occurred in 5.9% (2/34) of patients with a BJV size of 12 to 14 mm versus 1.9% (3/159) in patients with a size of 16 to 22 mm (P = NS). An interventional procedure or surgical revision was required in 29.4% (10/34) of patients with a BJV size of 12 to 14 mm versus 3.1% (5/159) in patients with a size of 16 to 22 mm (P < .0005). CONCLUSIONS: After 10 years of experience with the BJV, this conduit has remained a reliable alternative to pulmonary homografts with respect to survival and freedom from conduit failure. However, the incidence was greater and the presentation of conduit failure was earlier in patients with a smaller size BJV conduit (12-14 mm).

Physical stress testing of bovine jugular veins using magnetic resonance imaging, echocardiography and electrical velocimetry.

Bovine jugular veins (BJVs) (Contegra) are valve-bearing pulmonary artery substitutes. Their valves have higher profiles than human pulmonary valves; this might result in less optimal performance. Therefore, we investigated the impact of stress and undersizing on conduit performance with ergometry, echocardiography and magnetic resonance imaging (MRI). Between April 2007 and June 2008, 20 BJV recipients (age 7.9-19.6 years) underwent spiroergometry and subsequent echocardiography; after due rest, ergometry was repeated and followed by MRI during recovery. A year later, exams were repeated. Data was evaluated as follows: comparison of stress related maximal individual valve performance changes (magnetic resonance: exercise induced average stroke volume changes by 61+/-49%; mean insufficiency increased by 2% in patients with <1% rest insufficiency and by 8% after rest insufficiency of >10%; the average rest gradient of 24+/-11 mmHg rose to 40+/-20 mmHg), and stratification of pooled observations by regurgitation fraction, insufficiency grades and z-values (insufficiency rose with increasing heart rate and decreasing stroke volume; undersizing increased gradients during recovery by 7+/-0.7 mmHg/z-value). Contegras high-profile valves tolerate stress without performance drop. Stress induced changes of insufficiency and gradient were clinically not significant, but sufficient to distort examination results; therefore, constant examination conditions are indispensable for a correct follow-up.

[Comparison between canine decellularized venous valve stent combined with endothelial progenitor cells and native venous valve on venous valve closure mechanism in normal physiological conditions].

OBJECTIVE: To compare canine decellularized venous valve stent combining endothelial progenitor cells (EPC) with native venous valve in terms of venous valve closure mechanism in normal physiological conditions. METHODS: Thirty-six male hybrid dogs weighing 15-18 kg were used. The left femoral vein with valve from 12 dogs was harvested to prepare decellularized valved venous stent combined with EPC. The rest 24 dogs were randomly divided into the experimental group and the control group (n=12 per group). In the experimental group, EPC obtained from the bone marrow through in vitro amplification were cultured, the cells at passage 3 (5 x 10(6) cells/mL) were seeded on the stent, and the general and HE staining observations were performed before and after the seeding of the cells. In the experimental group, allogenic decellularized valved venous stent combined with EPC was transplanted to the left femoral vein region, while in the control group, the autogenous vein venous valve was implanted in situ. Color Doppler Ultrasound exam was performed 4 weeks after transplantation to compare the direction and velocity of blood flow in the distal and proximal end of the valve, and the changes of vein diameter in the valve sinus before and after the closure of venous valve when the dogs changed from supine position to reverse trendelenburg position. RESULTS: General and HE staining observations before and after cell seeding: the decellularized valved venous stent maintained its fiber and collagen structure, and the EPC were planted on the decellularized stent successfully through bioreactor. During the period from the reverse trendelenburg position to the starting point for the closure of the valve, the reverse flow of blood occurred in the experimental group with the velocity of (1.4 +/- 0.3) cm/s; while in the control group, there was no reverse flow of blood, but the peak flow rate was decreased from (21.3 +/- 2.1) cm/s to (18.2 +/- 3.3) cm/s. In the control group, the active period of valve, the starting point for the closure of the valve, and the time between the beginning of closure and the complete closure was (918 +/- 46), (712 +/- 48), and (154 +/- 29) ms, respectively; while in the experimental group, it was (989 +/- 53), (785 +/- 43), and (223 +/- 29) ms, respectively. There was significant difference between two groups (P < 0.05). After the complete closure of valve, no reverse flow of blood occurred in two groups. The vein diameter in the valve sinus of the experimental and the control group after the valve closure was increased by 116.8% +/- 2.0% and 118.5% +/- 2.2%, respectively, when compared with the value before valve closure (P > 0.05). CONCLUSION: Canine decellularized venous valve stent combined with EPC is remarkably different from natural venous valve in terms of the valve closure mechanism in physiological condition. The former relies on the reverse flow of blood and the latter is related to the decreased velocity of blood flow and the increased pressure of vein in the venous sinus segment.

Experience and intermediate-term results using the Contegra heterograft for right ventricular outflow reconstruction in adults.

OBJECTIVES: The Contegra bioprosthesis (valved heterologous bovine jugular vein) is used for reconstruction of the right ventricular outflow tract (RVOT) in congenital heart malformations and pulmonary valve replacement in different settings. Compared to pulmonary homografts, the Contegra conduit is readily available 'on the shelf'. So far, its use was mainly described in children. The aim of this study is to evaluate the feasibility and the outcome of Contegra graft implantation in the adult. METHODS: Between November 1999 and December 2007, a total of 32 Contegra grafts were implanted in 31 patients (24 men and 7 women), with a mean age of 35.7+/-10.5 years (range 18-54 years). All operations have been completed through median sternotomy with cardiopulmonary bypass. Indications included: Ross procedure for aortic valve disease (n=22); re-operation of corrected Fallot-tetralogy (n=5); isolated pulmonary valve disease (n=2); re-operation of double outlet right ventricle (DORV) (n=1); pulmonary stenosis in congenital dilated cardiomyopathy (DCM) (n=1). Conduit sizes included 22 mm (n=31), 20 mm (n=1). RESULTS: There was no hospital mortality and no valved conduit related early morbidity. In the median follow-up of 38 months (range 1-99 months) of 28 patients there was one late death, not conduit related (total mortality 3.6%). Re-operation for symptomatic graft stenosis was realised in two patients, 7 and 16 months after primo-implantation, corresponding to graft related late morbidity of 7.1%. CONCLUSIONS: In this small review of 32 operations using the Contegra graft for RVOT reconstruction in adult cardiac surgery for different indications, we observed good postoperative mid-term results concerning conduit function. Mean transpulmonary pressure gradients remain low (13.3+/-6.6 mmHg postoperative, 14.5+/-7.9 mmHg at follow-up). The use of the Contegra graft seems to be a good alternative to the homograft with low operative mortality and morbidity. Long-term outcome data are not available and further investigations must be performed to evaluate results.

Autogenous venous valve construction.

AIM: The aim of this study was to assess the results of a new type of antireflux operation on the deep venous system in patients with venous ulceration not responding to treatment of the superficial system and compression. METHODS: In the period comprised between 1991-2002, the authors treated 56 patients with venous ulceration by Fegan's technique, that consists in compression sclerotherapy combined with antireflux operation of the deep veins. All patients selected had pathological reflux in the deep venous system and their ulcers did not respond to superficial and perforating vein therapy, and elastic compression. RESULTS: Using this technique of complex antireflux treatment, it was possible to heal 53 (95.4%) of the 56 ulcers with average time of complete ulcer epitelisation within 39+/-12 days. The recurrence rate, within the 5 year follow-up was 18% (10 patients), but 7 of the recurrent ulcers responded to compression sclerotherapy and healed within 3 months. CONCLUSIONS: In situ made valvuloplasty has several advantages: the valve is constructed from autogenous vein wall; all luminal valve surfaces have native venous endothelium; intraluminal foreign material is not introduced; the likelihood of thrombosis is reduced; the valve is size-matched to the host vein and this technique provides a competent bicuspid valve.