Ventricle-pulmonary Artery Conduit Research Articles

Association between postoperative exposure to fine particulate matter and patency of the right ventricle–pulmonary artery conduit

BackgroundAmbient air pollution is a leading risk factor for cardiovascular diseases. No study has investigated the association between exposure to fine particulate matter <2.5 μm in aerodynamic diameter (PM2.5) and the prognosis of patients undergoing surgery for the right ventricle–pulmonary artery (RV-PA) conduit. MethodsFrom 2013 to 2020, patients with six complicated congenital heart defects who had undergone surgery for the RV–PA conduit were selected. Four conduit materials were used: bovine jugular vein graft (BJV), pulmonary homograft (PHG), aortic homograft (AHG), and handmade tri-leaflet expanded polytetrafluoroethylene (ePTFE) conduit. Telephone interviews were used to confirm the postoperative address of patients. The monthly average PM2.5 concentration was obtained from the ChinaHighPM2.5 dataset using the place of residence of patients. By comparing findings of echocardiography undertaken before patients' return to their residence and during re-examination, we defined an increase in the trans-conduit peak velocity of ≥1.5 m/s as the study endpoint. ResultsWe enrolled 232 patients. Compared with BJV conduits, homografts (AHGs and PHGs) (0.052 (95 % CI = 0.005–0.558), P = 0.015) and ePTFE conduits (0.009 (95 % CI = 0.002–0.054), P < 0.001) were protective factors. The cumulative monthly PM2.5 concentration (10 μg/m3) was a risk factor (1.014 (95 % CI = 1.001–1.026), P = 0.028). Winter experience was a risk factor (1.971 (95 % CI: 1.021–3.804), P = 0.043). In the subgroup analysis, Spearman correlation analysis indicated BJV conduits (r = 0.680, P < 0.001), PHGs (r = 0.559, P = 0.020), and AHGs (r = 0.745, P = 0.021) had medium-to-high positive correlations between the cumulative PM2.5 concentration and change in the conduit velocity. For ePTFE, the correlation was weak and not significant (r = 0.222, P = 0.073). ConclusionsPostoperative exposure to PM2.5 affects the patency of biologic prosthetic conduits (especially xenografts). The increase in the velocity of the ePTFE conduit is not associated with PM2.5 exposure, and is a suitable material for patients living in areas with high pollutant concentrations.

Cardiac Computed Tomographic Angiography Evaluation of Right Ventricle-Pulmonary Artery Conduits with Surgical Correlation.

Right ventricle-pulmonary artery (RV-PA) conduits are used in the treatment of certain congenital heart disease (CHD). RV-PA conduit complications might develop over time and require intervention. To evaluate how well cardiac computed tomographic angiography (CCTA) performs compared to transthoracic echocardiography (TTE) in evaluating RV-PA conduit complications by using surgical findings as the reference standard. A retrospective chart review of all patients over a 5-year period who underwent CCTA for RV-PA conduit evaluation was performed. Patient demographics and clinical data were recorded. Preoperative CCTA and TTE findings were compared to the operative findings for concordance or discordance. Forty-one patients were included, 51% females. The complications were conduit stenosis (28.68%), infection (7.17%) and aneurysm/pseudoaneurysm (6.15%). TTE and CCTA were consistently able to visualize focal conduit stenosis (96%). The greatest discrepancy between TTE and CCTA was in evaluating for aneurysm/pseudoaneurysm, where TTE detected only 2/6 (33%) compared to CCTA which detected 6/6 (100%) of the cases. However, TTE was slightly better at detecting conduit infection (3/7, 43%) compared to CCTA (2/7, 29%). Note that 5 out of 7 patients with endocarditis had bovine jugular graft. CCTA and TTE provide similar diagnostic accuracy evaluating certain types of RV-PA conduit complications. However, certain complications were only visualized on CCTA or TTE making both modalities complementary to each other during diagnostic evaluation.

Right Ventricular Outflow Tract Reconstruction in Truncus Arteriosus: A 30-Year Two-Center Comparison between Homografts and Bovine Jugular Vein.

Homografts and bovine jugular vein are the most commonly used conduits for right ventricular outflow tract reconstruction at the time of primary repair of truncus arteriosus. We reviewed all truncus patients from 1990 to 2020 in two mid-volume centers. Inclusion criteria were primary repair, age under one year, and implantation of either homograft or bovine jugular vein. Kaplan-Meier analysis was used to estimate survival, freedom from reoperation on right ventricular outflow tract, and freedom from right ventricular outflow tract reoperation or catheter intervention. Seventy-three patients met the inclusion criteria, homografts were implanted in 31, and bovine jugular vein in 42. There was no difference in preoperative characteristics between the two groups. There were 25/73 (34%) early postoperative deaths and no late deaths. Follow-up for survivals was 17.5 (interquartile range 13.5) years for homograft group, and 11.5 (interquartile range 8.5) years for bovine jugular vein group (P=0.002). Freedom from reoperation on right ventricular outflow tract at one, five, and 10 years in the homograft group were 100%, 83%, and 53%; and in bovine jugular vein group, it was 100%, 85%, and 50% (P=0.79). There was no difference in freedom from reoperation or catheter intervention (P=0.32). Bovine jugular vein was equivalent to homografts up to 10 years in terms of survival and freedom from right ventricular outflow tract reoperation or catheter intervention. The choice of either valved conduit did not influence the durability of the right ventricle-pulmonary artery conduit in truncus arteriosus.

One-stage neonatal Yasui procedure: Presentation of our surgical experience and a new decision-making algorithm

ObjectivesThe aim of this study is to present our experience with three patients who underwent a neonatal Yasui procedure, and to show the new decision-making algorithm. MethodsThis is a series of three neonates operated on at our hospital between 2017 and 2022. ResultsAll the patients underwent a primary Yasui. The duration of cardiopulmonary bypass was 275, 249 and 391min, in patient 1, 2 and 3, respectively. After surgery, the Intensive Care Unit stay of patients 1, 2 and 3 was 29, 22 and 24 days, respectively. The patients were discharged in good condition. Subsequent complications during follow-up included the need for percutaneous intervention in patient 1 for the implantation of a stent in the right pulmonary branch (at 6 months postoperatively) and a stent in the right ventricle-pulmonary artery conduit (at 42 months). Patient 2 required right ventricle-pulmonary artery conduit replacement and repair of moderate-severe left ventricular outflow tract obstruction at 16 months postoperatively. Patient 3 needed a reoperation at 3 months postoperatively due to aortic arch stenosis at different levels and a residual ventricular septal defect. Currently, all patients are alive with adequate echocardiographic biventricular function. ConclusionsIn experienced centers, primary Yasui repair can be performed in the neonatal period with satisfactory results.

Surgical outcome of Yasui procedure for preserving biventricular function: single centre experience.

Yasui procedure is surgical repair intended to preserve biventricular function for patients with left ventricle outflow tract obstruction associated with aortic arch lesions and ventricular septal defect. Retrospective chart review analysis of all patients who had Yasui procedure (2008-2020) comparing midterm outcome of one versus two stage repair. Twenty patients (70% female) underwent Yasui procedure in our center. Eight patients (40%) had left ventricle outflow tract obstruction /interrupted aortic arch, 7 patients (35%) had left ventricle outflow tract obstruction /coarctation of aorta, 3 patients (15%) had double outlet ventricle and ventricular septal defect that were unattainable for tunneling to one of the semilunar valves without creating obstruction, and 2 patients (10%) had aortic atresia with hypoplastic aortic arch. All patients had associated ventricular septal defect. Fifteen patients (75%) had one-stage repair and 5 patients (25%) had two-stage repair. Means age and weight for one and two-stage repair were 1.3 ± 2 months, 13.4 ± 11.5 months and 3.3 ± 0.6 kg, 7.8 ± 3.4 kg, respectively. During follow up, 8 patients (40%) required re- intervention, mainly for right ventricle-pulmonary artery conduit either dilation or replacement. The average duration of follow up was 5 years with nil mortality. Yasui procedure is effective approach for children who have left ventricle outflow tract obstruction associated with aortic arch anomalies and ventricular septal defect. Survival rate with single or staged repair is comparably good. During the first 5 year of follow up, nearly 40% of operated patients required re-intervention.

Twin Root Replacement in Congenital Heart Disease: Expert Technique.

In adult congenital heart disease, there are situations that require both the aortic and pulmonary roots to be replaced at the time of a reoperation. This commonly involves the replacement of a previously implanted right ventricle-pulmonary artery conduit in a patient with late aortic root dilation and/or neo-aortic valve dysfunction following the Ross procedure. Similar scenarios are encountered in patients having undergone previous repair of conotruncal anomalies such as truncus arteriosus and tetralogy of Fallot with pulmonary atresia. We describe our standardized technique for twin root replacement.

Characteristics of Interstage Death After Discharge from Stage I Palliation.

Interstage mortality (IM) remains high for patients with single-ventricle congenital heart disease (SVCHD) in the period between Stage 1 Palliation (S1P) and Glenn operation. We sought to characterize IM. This was a descriptive analysis of 2184 patients with SVCHD discharged home after S1P from 60 National Pediatric Cardiology Quality Improvement Collaborative sites between 2008 and 2015. Patients underwent S1P with right ventricle-pulmonary artery conduit (RVPAC), modified Blalock-Taussig-Thomas shunt (BTT), or Hybrid; transplants were excluded. IM occurred in 153 (7%) patients (median gestational age 38weeks, 54% male, 77% white), at 88 (IQR 60,136) days of life, and 39 (IQR 17,84) days after hospital discharge; 13 (8.6%) occurred ≤ 30days after S1P. The mortality rate for RVPAC was lower (5.2%; 59/1138) than BTT (9.1%; 65/712) and Hybrid (20.1%; 27/134). More than half of deaths occurred at home (20%) or in the emergency department (33%). The remainder occurred while inpatient at center of S1P (cardiac intensive care unit 36%, inpatient ward 5%) or at a different center (5%). Fussiness and breathing problems were most often cited as harbingers of death; distance to surgical center was the biggest barrier cited to seeking care. Cause of death was unknown in 44% of cases overall; in the subset of patients who underwent post-mortem autopsy, the cause of death remained unknown in 30% of patients, with the most common diagnosis being low cardiac output. Most IM occurred in the outpatient setting, with non-specific preceding symptoms and unknown cause of death. These data indicate the need for research to identify occult causes of death, including arrhythmia.

Approaches to Pulmonary Atresia With Major Aortopulmonary Collateral Arteries

Pulmonary atresia with major aortopulmonary collateral arteries (MAPCAs) is one of the most challenging surgical conditions to manage-not only because of the technical complexity of the surgery but also in terms of defining the anatomy of the pulmonary vasculature, the timing of surgery, and decision making on staged vs complete repair. The importance of early definition of pulmonary blood supply is paramount, establishing which areas of the lung are supplied by MAPCAs alone and which have dual supply with the native system (noting that 20% of patients have absent intrapericardial native vessels). Early unifocalization (3-6 months) is ideal, with closure of the ventricular septal defect (VSD) performed if 15 or more out of 20 lung segments can be recruited. Leaving the ventricular septal defect open with a limiting right ventricle-pulmonary artery conduit can be a useful interim or even definitive circulation in patients with borderline vasculature. Rehabilitation of small native vessels with central shunts can be very effective, but best outcomes are achieved by a combination of unifocalization of MAPCAs together with the native vessels (if present). A variety of reconstructive techniques are necessary to be able to effect these complex repairs with careful choice of materials. Ideally, surgery can be completed through sternotomy alone, but separate thoracotomies may be necessary to control and access some MAPCAs.

Early diagnosis of right ventricle–pulmonary artery conduit endocarditis by PET/CT

Early diagnosis of right ventricle–pulmonary artery conduit endocarditis by PET/CT

Patient Selection Process for the Harmony Transcatheter Pulmonary Valve Early Feasibility Study

This early feasibility study was designed to obtain in vivo data to confirm assumptions on device loading conditions of the Medtronic Harmony transcatheter pulmonary valve (TPV). Secondary objectives included procedural feasibility, safety, and valve performance. The Harmony TPV was developed for nonsurgical pulmonary valve replacement in non-right ventricle-pulmonary artery conduit patients. The Native Outflow Tract TPV Research Clinical Study was the first study approved under the Food and Drug Administration Early Feasibility Study guidance. Enrollment required that patient anatomy be precisely matched to the single-size Harmony TPV implant, necessitating a rigorous selection process. The study was nonrandomized, prospective, and performed at 3 sites. All patients met standard indications for surgical pulmonary valve replacement. The goal of the screening committee was to match the candidate anatomy to predetermined engineering criteria thought to be predictive of secure Harmony TPV implantation for the single-size device under study. A majority of the screening committee was required to recommend a patient as eligible for implant. A total of 270 patients underwent prescreening cardiac magnetic resonance imaging, 66 were enrolled and received a computed tomography scan (24%), 21 met criteria for implant and were catheterized (8%), and 20 underwent implant. Nineteen of 20 met criteria for implant success. In conclusion, the Medtronic Harmony TPV represents an emerging therapeutic option for patients with complex postoperative right ventricular outflow tract failure. The initial clinical evaluation of this technology was unique, and the highly variable anatomy of this population required careful screening to ensure acceptable device fit.

P41 A national cohort study of the incidence of infective endocarditis in paediatric congenital heart disease

Background NICE guidelines on antibiotic prophylaxis against infective endocarditis (IE) were published in 2008 resulting in a change in practice. There are recommendations for ongoing audit to monitor the incidence of IE, particularly in the high risk congenital heart disease (CHD) population. Methods This is a retrospective review of cases of infective endocarditis in paediatric patients with CHD in Scotland. Patients were identified from the cardiac unit database. The current 30-month period was compared to two previous audits that covered the period immediately before and after the guideline release. Results The period prior to the guidelines only identified 2 cases but this is most likely due to under-reporting. The period following the guidelines identified 8 cases of IE compared with 15 cases in the current study period. All patients had a history of cardiac surgery, median age was 5 years, median weight 19 kg and 4/15(26.7%) had DiGeorge syndrome. Only 1/15(6.7%) had a dental procedure and another 4/15(26.7%) had a cardiac surgical procedure within 3-months of diagnosis. Therefore the majority (10/15(66.7%)) had no invasive procedure within 3-months of diagnosis. Of note, in 9/15(60%) the site of infection was a right ventricle-pulmonary artery conduit. 7/9 (77.8%) were a Contegra conduit. Summary Ongoing surveillance of IE is vitally important and our study has revealed an increase in the incidence in our population. The majority of the cases were spontaneous infections. Further analysis will be required to determine if this is an ongoing trend and the causes are likely multifactorial.

Successful use of recombinant activated factor VII (eptacog alfa, Novoseven®) in a refractory bleeding during pediatric cardiac surgery: a case report.

A 2-year-and-7-month-old boy underwent an emergent reconstruction surgery of the right ventricle-pulmonary artery (RV-PA) conduit. Although he was successfully weaned from cardiopulmonary bypass (CPB) after reconstruction of the RV-PA conduit, the bleeding continued despite the massive transfusion of red blood cell (RBC), fresh frozen plasma (FFP), and platelets. Because of persistent bleeding and abnormal coagulation laboratory results, we administered the recombinant activated factor VII (rFVIIa), which was not approved for use in the treatment of post-CPB coagulopathy. After administration of rFVIIa, his coagulation data dramatically improved, the bleeding decreased, and the operation was able to be finished.

Percutaneous pulmonary valve placement.

Patients with congenital heart disease and pulmonary valve disease need multiple procedures over their lifetimes to replace their pulmonary valves. Chronic pulmonary stenosis, regurgitation, or both have untoward effects on ventricular function and on the clinical status of these patients. To date, all right ventricle-pulmonary artery conduits have had relatively short lifespans. Percutaneous pulmonary valve implantation, although relatively new, will probably reduce the number of operative procedures that these patients will have to undergo over a lifetime. Refinement and further development of this procedure holds promise for the extension of this technology to other patient populations.

Percutaneous pulmonary valve implantation.

[first paragraph of article] Percutaneous pulmonary valve implantation (PPVI) is one of the most exciting recent developments in the treatment of structural heart disease and has evolved as an attractive alternative to surgery in patients with dysfunctional right ventricle-pulmonary artery conduits. Although surgical pulmonary valve replacement is associated with low morbidity and mortality rates, there are many instances when operative risks are high or surgery is prohibitive. Patients requiring RVOT reconstruction require multiple sternotomies and cardiac surgical procedures throughout their lives due to the limited lifespan of such conduits (10 years). Patient management strategies have, therefore, been based on delaying surgical intervention for as long as possible, in order to minimize the number of surgical procedures. However, this approach carries the risk of delaying surgery beyond a point of irreversible right ventricular (RV) dysfunction. A balance between the deleterious effects of RVOT dysfunction and the need to minimize the total number of lifetime surgeries for a given patient is a clinically challenging task prompting the need to develop minimally invasive valve therapies. Since the introduction of PPVI in 2000, the learning curve with this technology lead to significant improvements in both valve design and procedural approach, with several clinical trials demonstrating the safety and efficacy in restoring valvular competence with excellent short to medium term outcomes; transforming this technique from its early pioneering nature into routine clinical care at specialized centers. Evolving data from these studies have shown beneficial effects of PPVI in right ventricular volume reduction, left ventricular filling properties, exercise capacity and electrical remodeling. This review discusses the evolution, indications, and technical aspects of PPVI using the Melody and Edwards SAPIEN transcatheter heart valve as non-surgical treatment options for dysfunctional RVOT/pulmonary trunk.

One size does not fit all: the influence of age at surgery on outcomes following Norwood operation.

BackgroundGiven our large catchment area that often results in later presentation age, we sought to understand our institutional outcomes for the Norwood operation in the context of published data. Specifically, we studied whether operative and late death post-Norwood are dependent on age at operation.MethodsRetrospective review of 105 consecutive infants undergoing Norwood (2004–2011) at our institution. Patients were divided into those undergoing Norwood ≤ 7 days of age (N = 43; 41%) and those undergoing Norwood > 7 days of age (N = 63; 59%). Operative mortality (≥30 days), interstage mortality (between Norwood and superior bidirectional Glenn), STS-mortality (operative death + in-hospital death), and late mortality, occurring any time following hospital discharge were compared among groups. Multivariable factors for mortality at each time-point were compared using logistic regression models.ResultsUnderlying diagnosis was HLHS in 67 (64%) with the remainder (N = 38; 36%) being other single ventricle variants. Median age at surgery was 8 days (range 1–63 days) and mean weight at surgery was 3.2 ± 0.6 kg. Pulmonary blood flow was provided by a right ventricle-pulmonary artery conduit in 94% (N = 99). Overall operative survival was 92%, with 73% (N = 66) undergoing bidirectional Glenn. Median age was higher for operative survivors compared to non-survivors (12 days vs. 5 days; P = 0.036), with operative mortality higher for infants ≤7 days at Norwood compared to infants >7 days at Norwood (14% vs. 3%; P = 0.04). After censoring for in-hospital death, age ≤ 7 days was also associated with increased risk for late death (26% vs. 5%; P = 0.005).ConclusionsIn contrast to other institutional series, infants at our center undergoing Norwood operation at an earlier age have worse outcomes. Adoption of published practice patterns could lead to different local outcomes because of intangible center-specific effects, underscoring the principle that results from one institution may not be generalizable to others. Targeted center-specific internal review, if possible, should precede externally recommended changes in practice.

Establishment of right ventricle-pulmonary artery continuity as the first-stage palliation in older infants with pulmonary atresia with ventricular septal defect may be preferable to use of an arterial shunt

Right ventricle-pulmonary artery (RV-PA) conduit and systemic-to-pulmonary artery (S-PA) shunt in younger infants for the first-stage palliation with pulmonary atresia with ventricular septal defect (PAVSD) obtained good results. However, the pulmonary arteries (PA) grow slow in older infants undergoing an S-PA shunt. We compared the clinical outcomes of the two procedures in older infants with PAVSD. A total of 48 patients with PAVSD underwent the first-stage palliative procedure between January 2010 and July 2012. Patients were divided into the RV-PA group and the S-PA group based on whether they had an RV-PA conduit (n = 24) or an S-PA shunt (n = 24). The early and late outcomes were compared between groups. There was no significant difference in in-hospital mortality, mechanical ventilation time, paediatric intensive care unit stay and hospital stay between groups (all P > 0.05). The RV-PA conduits were associated with better PA growth compared with the S-PA shunts (P < 0.001). The RV-PA group had a higher rate of second-stage biventricular surgery compared with the S-PA group (P = 0.03). The early outcomes among different conduits of the RV-PA conduit were not different (all P > 0.05). A positive correlation was found between the size of conduits and body weight (R(2) = 0.684, P < 0.001). In older infants with PAVSD who underwent the first-stage palliative procedure, early outcomes showed no difference between the RV-PA conduit group and the S-PA shunt group. The RV-PA conduits were associated with better growth of the PA and higher rates of second-stage biventricular repair. Autologous pericardium is a good choice for RV-PA conduits, and there is a correlation between body weight and size of conduit.

Bex-Nikaidoh concept for repair of d-transposition of the great arteries with ventricular septal defect and pulmonary stenosis or pulmonary atresia

Methods Between 2008 and 2013 seven patients underwent modified Bex-Nikaidoh at median (M) age of 7.5 months (CI 25-75% [4.2; 26.4]). The conal septum was divided in 4 (CI 25-75% [44.4; 68.9]) patients including 1 patient with the surgical creation of outflow tract of the left ventricle due to pulmonary atresia. Modified technique of aortic root translocation included replantation of coronary arteries and placement into the ortotopic position of “oversized” pulmonary ventricle–pulmonary artery conduit. The evaluation of conduit performance was based on transthoracic and transesophageal echocardiogram and computed tomography.

Cardiovascular MR Imaging after Surgical Correction of Tetralogy of Fallot: Approach Based on Understanding of Surgical Procedures

Tetralogy of Fallot (TOF) is one of the most common congenital heart diseases for which patients are referred for postoperative magnetic resonance (MR) imaging evaluation. The most common surgical procedures for TOF repair include infundibulectomy, transannular pulmonary artery patch repair, and right ventricle-pulmonary artery conduit placement. In the past few decades, surgery has proved successful, but most patients require repeat imaging throughout their lives. MR imaging is now frequently used for morphologic and functional evaluation after TOF repair. The most common late postoperative sequelae and residual lesions include right ventricular outflow tract aneurysm and dyskinesis, conduit failure, pulmonary regurgitation, tricuspid regurgitation, right ventricular failure, residual main and branch pulmonary artery stenosis, branch pulmonary artery aneurysm, left pulmonary artery kinking, and residual or recurrent ventricular septal defect. The imaging approach for the evaluation of patients with repaired TOF should be guided by the surgical procedure used and the complications that are expected. Knowledge of the most common postoperative problems and their cardiovascular MR imaging appearances is essential for good radiology practice in this clinical setting.

Complex TAPVC-Experience with Six Patients

Total anomalous pulmonary venous connection becomes a totally different subset when associated with complex congenital anomalies. The combination of two separate life-threatening congenital heart defects complicates the management of these patients. Six patients with total anomalous pulmonary venous connection associated with complex congenital heart disease were studied. There were 2 girls and 4 boys. Three of them were less than 5 kg in weight, and the other 3 were more than 5 kg in weight. Four patients had severe pulmonary arterial hypertension and 2 patients had pulmonary stenosis. Three patients had supracardiac type with a right vertical vein, one had drainage to the right atrium superior vena cava junction, one patient had supra cardiac type but split flow to both the superior vena cava and one patient had cardiac type. Three patients had double outlet right ventricle. Three patients had atrioventricular canal defect and 2 patients had preoperative pulmonary vein obstruction. All patients underwent rerouting of pulmonary veins. Concomitant procedures included intraventricular tunnel repair of ventricular septal defect and infundibular resection in double outlet right ventricle. Atrioventricular canal repair was done for Rastelli type A atrioventricular canal. Superior vena caval plasty, atrioventricular canal repair and pulmonary artery banding were done in unbalanced atrioventricular septal defect and large double outlet right ventricle. Intracardiac repair through transatrial approach was done for tetralogy of Fallot. Right ventricle-pulmonary artery conduit was done for truncus arteriosus. Single ventricle repair was done for corrected transposition of great arteries. There were 2 hospital deaths.

Left Coronary Artery Occlusion After Percutaneous Pulmonary Valve Implantation

Percutaneous pulmonary valve implantation (PPVI) is an attractive option for patients with pulmonary valve insufficiency or stenotic right ventricular outflow tracts. We present the case of a 26-year-old patient in which PPVI was used to treat d-transposition of the great arteries, uncommon coronary artery anatomy, and conduit stenosis that resulted from multiple operations on the right outflow. Days after discharge to home, she experienced acute chest discomfort correlating with ischemia noted on an electrocardiogram and elevated troponin levels. Coronary angiography confirmed mechanical compression of the left anterior descending coronary artery. The valve was removed in an emergency operation and replaced with a biological conduit.