Contemporary Patterns of Care in Tetralogy of Fallot: Analysis of The Society of Thoracic Surgeons Data

BACKGROUND

Against the background of earlier studies, recent patterns in surgical management of tetralogy of Fallot (TOF) were assessed.

METHODS

A retrospective review of The Society of Thoracic Surgeons (STS) Congenital Database (2010-2020) was performed on patients aged <18 years with TOF or pulmonary stenosis and primary procedure TOF surgical repair or palliation. Procedural frequencies were examined by epoch. Demographics, clinical variables, and outcomes were compared between the initial palliation and primary repair groups. Among those operated on at 0 to 60 days of age, variation in palliation rates across hospitals was assessed.

RESULTS

The 12,157 operations included 11,307 repairs (93.0%) and 850 palliations (7.0%); 68.5% of all palliations were modified Blalock-Taussig-Thomas shunts. Of 1105 operations on neonates, 45.4% (502) were palliations. Among neonates, palliations declined from 49.0% (331 of 675) in epoch 1 (2010-2015) to 39.8% (171 of 430) in epoch 2 (2016-2020; P = .0026). Overall, the most prevalent repair technique (5196 of 11,307; 46.0%) was ventriculotomy with transanular patch, which was also used in 520 of 894 (58.2%) of repairs after previous cardiac operations. Patients undergoing initial palliation demonstrated more preoperative STS risk factors (50.1% vs 24.3% respectively; P < .0001) and more major morbidity and mortality than patients undergoing primary repair (21.2% vs 7.46%; P < .0001). In the 0- to 60-day age group, risk factor-adjusted palliation rates across centers varied considerably, with 32 of 99 centers performing significantly more or significantly fewer palliations than predicted on the basis of their case mix.

CONCLUSIONS

Surgical palliation rates have decreased across all age groups despite increasing prevalence of risk factors. Ventriculotomy with transanular patch remains the most prevalent repair type. The considerable center-level variation in rates of palliation was not completely explained by case mix.

Growth Differentiation Factor 15: A Novel Growth Biomarker for Children With Congenital Heart Disease

BACKGROUND

Failure to thrive (FTT), defined as weight or height less than the lowest 2.5 percentile for age, is prevalent in up to 66% of children with congenital heart disease (CHD). Risk stratification methods to identify those who would benefit from early intervention are currently lacking. We aimed to identify a novel growth biomarker to aid clinical decision-making in children with CHD.

METHODS

This is a cross-sectional study of patients 2 months to 10 years of age with any CHD undergoing cardiac surgery. Preoperative weight-for-age Z scores (WAZ) and height-for-age Z scores (HAZ) were calculated and assessed for association with preoperative plasma biomarkers: growth differentiation factor 15 (GDF-15), fibroblast growth factor 21, leptin, prealbumin, and C-reactive protein (CRP).

RESULTS

Of the 238 patients included, approximately 70% of patients had WAZ/HAZ < 0 and 34% had FTT. There was a moderate correlation between GDF-15 and WAZ/HAZ. When stratified by age, the correlation of GDF-15 to WAZ and HAZ was strongest in children under 2 years of age and persisted in the setting of inflammation (CRP > 0.5 mg/dL). Diagnoses commonly associated with congestive heart failure had high proportions of FTT and median GDF-15 levels. Prealbumin was not correlated with WAZ or HAZ.

CONCLUSIONS

GDF-15 represents an important growth biomarker in children with CHD, especially those under 2 years of age who have diagnoses commonly associated with CHF. Our data do not support prealbumin as a long-term growth biomarker.

Salvage of an epicardial lead in a pacemaker-dependent patient with Fontan palliation using an IS-1 extender

We present a case report of severed epicardial atrial lead salvage using an IS-1 lead extender. A 37-year-old male with single ventricle physiology, Fontan palliation, sinus node dysfunction, recurrent atrial tachycardias, and atrial fibrillation resulting in failing Fontan physiology presented with failure of the atrial pacing lead. The patient was initially paced with an epicardial system that had to be removed due to pocket infection, and the epicardial leads were cut and abandoned. Given his significant sinus node dysfunction he required atrial pacing to allow for rhythm control. The failing Fontan physiology of the patient precluded him from undergoing surgery for epicardial lead placement or a complex intravascular lead placement procedure (although anatomically feasible). We considered the option of salvaging the existing epicardial atrial leads to provide atrial pacing, allowing for rhythm control and improvement of his failing Fontan physiology as a bridge to a more permanent pacing solution. This case report is important because it demonstrates how a lead extender can be used to salvage a severed pacemaker lead. This may be useful for patients in whom implantation of new leads is not promptly feasible due to patient anatomy and/or clinical status.

HeartMate 3 in a ccTGA patient

A 49-year-old female with congenitally corrected (or levo-) transposition of the great arteries complicated by nonischemic cardiomyopathy presented for worsening heart failure despite guideline-directed medical therapy and was found to be in cardiogenic shock. She successfully underwent ventricular assist device placement with a HeartMate III to her systemic right ventricle as a bridge to transplantation.

Disorders of Adjustment, Mood, and Anxiety in Children and Adolescents Undergoing Heart Transplantation and the Association of Ventricular Assist Device Support

OBJECTIVE

To assess the prevalence of psychiatric disorders and associated therapies in children during their heart transplantation admission.

STUDY DESIGN

All pediatric heart transplant recipients (1999-2016) were included from a linked administrative and clinical registry database. Psychiatric disorders and associated therapies were identified using International Classification of Diseases or billing codes during the transplant admission. Data were analyzed using standard descriptive statistics. Multivariable logistic regression assessed factors independently associated with psychiatric disorders or therapies.

RESULTS

A total of 3073 pediatric heart transplant recipients were included. Psychiatric disorders were present in 434 (14.1%) patients during the heart transplant admission, with adjustment disorders being the most common. Antidepressant therapy was prescribed to 212 patients (6.9%) and selective serotonin reuptake inhibitors were most commonly used. Psychiatric diagnoses (8.4% vs 18.1%; P < .001) and the use of antidepressants (4.5% vs 8.9%; P < .001) increased over time (era 1, 1999-2009 vs era 2, 2010-2016). Psychiatric disorders were present in 39.8% of patients ≥8 years of age requiring ventricular assist device support at heart transplantation. The need for ventricular assist device support was independently associated with psychiatric diagnoses (aOR, 1.57; 95% CI, 1.18-2.1; P = .002) and antidepressant therapy (aOR, 2.11; 95% CI. 1.43-3.12; P < .001).

CONCLUSIONS

Psychiatric disorders are common in pediatric heart transplant recipients, especially among those bridged with ventricular assist device support. Psychiatric diagnoses and the use of antidepressants has increased over time, likely representing improved recognition of psychiatric comorbidities in this vulnerable population. Access to psychiatric services represents an important component of the multidisciplinary team caring for pediatric heart transplant recipients.

Left main coronary artery stent placement in a 7.0 kg infant with Williams Syndrome

We report the case of a 9-month-old male with Williams syndrome who underwent patch augmentation of supravalvar aortic stenosis and pulmonary artery stenosis, and required emergent drug-eluting left coronary artery stenting on post-operative day 1 for severe left ventricular dysfunction related to myocardial ischemia.

Extracorporeal membrane oxygenation use in the first 24 hours following pediatric heart transplantation: Incidence, risk factors, and outcomes

Primary graft dysfunction following HTx is associated with significant morbidity and mortality. This study aimed to assess the incidence of, risk factors for, and outcomes of children requiring ECMO within 24 hours of HTx. This study utilized a linked PHIS/SRTR database of pediatric HTx recipients (2002-2016). Post-HTx ECMO was identified using inpatient billing data. Logistic regression assessed risk factors for post-HTx ECMO. Kaplan-Meier analyses assessed in-hospital mortality and post-discharge survival. A total of 2820 patients were included with 224 (7.9%) requiring ECMO. Independent risk factors for post-HTx ECMO include age <1 year (aOR: 2.2, 95% CI: 1.3-3.7, P = 0.006) or 1-5 years (aOR: 2.1, 95% CI: 1.3-3.4, P = 0.002), and ECMO support at HTx (aOR: 27.4, 95% CI: 15.2-49.6, P < 0.001). Survival to discharge decreased with increasing duration of post-HTx ECMO support; 89% for 1-3 days, 79.1% for 4-6 days, 63.2% for 7-9 days, and 18.8% for ≥10 days. There was no difference in long-term survival for patients requiring post-HTx ECMO who survived to hospital discharge (P = 0.434). There are identifiable risk factors associated with the need for ECMO in the post-HTx period. Length of time on ECMO post-HTx is strongly associated with the risk of in-hospital mortality. Patients who require ECMO early post-HTx and survive to discharge have comparable outcomes to patients who did not require ECMO.

Center Variation in Hospital Costs for Pediatric Heart Transplantation: The Relationship Between Cost and Outcomes

There are limited published data addressing the costs associated with pediatric heart transplantation and no studies evaluating the variation in costs across centers. We aimed to describe center variation in pediatric heart transplant costs and assess the association of transplant hospitalization costs with patient outcomes. Using a linkage between the Pediatric Health Information System and Scientific Registry of Transplant Recipients databases, hospital costs were assessed for patients (< 18 years of age) undergoing heart transplantation (2007-2016). Severity-adjusted patient costs were calculated using generalized linear mixed-effects models with a random hospital intercept. Center variation in hospital cost was described after adjusting for the predicted risk of in-hospital mortality. Post-transplant survival was compared between low- and high-cost centers using Cox proportional hazard models. A total of 2156 patients were included from 24 centers. There was 3.7-fold variation in transplant hospitalization costs across centers, ranging from $329,477 to $1,226,507. Patients transplanted at high-cost centers have a higher predicted risk of in-hospital mortality (8.1% vs. 6.1%, p < 0.001). Both early (p = 0.008) and long-term (p = 0.003) post-transplant survival were better in patients transplanted at low-cost centers. Transplant at low-cost centers was associated with improved post-transplant survival, independent of patient-specific risk (adjusted hazard ratio 0.72; 95%CI 0.57-0.92, p = 0.008). There is wide variation in cost for pediatric heart transplant inpatient care among U.S. centers with low-cost centers demonstrating the best patient survival. Differences in patient populations likely contribute to these findings, but cannot account for all the variation seen. This suggests that variability in the delivery of care across centers may influence post-transplant survival.

Mechanical circulatory support costs in children bridged to heart transplantation - analysis of a linked database

BACKGROUND

Pediatric mechanical circulatory support (MCS) has evolved considerably over the past decade. Though marked improvements in waitlist survival have been realized, costs have not been reassessed. This project aimed to assess contemporary MCS costs in children bridged to heart transplant (HT).

METHODS

All pediatric HT recipients (2002-2016) were identified from a unique, linked PHIS/SRTR dataset. Costs were calculated from hospital charges, inflated to 2016 Dollars and adjusted for patient-specific characteristics using generalized linear mixed-effects models. Costs and length of stay (LOS) were compared across support strategies at the time of HT (no MCS, VAD, or ECMO) with select subgroup analyses.

RESULTS

A total of 2873 pediatric HT recipients were included; no MCS: 2268 (78.9%), VAD: 470 (16.4%), and ECMO: 135 (4.7%). Both VAD and ECMO were associated with greater total hospitalization costs compared to no MCS ($755,345 and $808,771 vs. $457,086; P < .001). Total costs and LOS were similar between VAD and ECMO groups; however, costs and LOS were greatest for VAD-supported patients in the pre-HT period and greatest for ECMO-supported patients post-HT. Post-HT costs and LOS were similar between patients who did not require MCS and those supported with a VAD ($324,887 and 18 days vs. $329,198 and 18 days respectively, p = NS). Outpatients with VAD support at HT demonstrated significantly lower total costs compared to those who were inpatient with continuous flow devices ($552,222 vs. $663,071, P = .003).

CONCLUSIONS

MCS as a bridge to HT in children is associated with greater total costs. While costs are similar between VAD and ECMO groups, the majority of costs associated with VAD support is incurred pre-HT while ECMO costs are incurred primarily post-HT. Discharging patients on VAD support awaiting HT may represent a strategy to reduce costs in this population.

Geographic Distance From Transplant Center Does Not Impact Pediatric Heart Transplant Outcomes

BACKGROUND

Many pediatric heart transplant recipients live a significant distance from their transplant center. This results in families either traveling long distances or relying on outside physicians to assume aspects of their care. Distance has been implicated to play a role in congenital heart disease outcomes, but its impact on heart transplantation has not been reported. The aim of this study was to assess the impact of distance on pediatric heart transplant outcomes.

METHODS

The Scientific Registry of Transplant Recipients database was queried for all pediatric heart transplant recipients from large US children's hospitals (1987-2014). Patients were stratified into 4 groups (<20, 20-50, 50-100, and >100 miles) based on distance. Survival curves were generated and compared using the log-rank test. Cox proportional hazards regression was performed to adjust for differences between groups.

RESULTS

A total of 4768 patients were included in the analysis, of which 1435 (30.1%) were <20 miles, 940 (19.7%) were 20 to 50 miles, 806 (16.9%) were 50 to 100 miles, and 1587 (33.3%) were >100 miles from their transplant center. There was no difference in posttransplant survival based on distance after adjusting for patient age, gender, ethnicity, blood type, diagnosis, listing status, and the need for pretransplant ventricular assist device, extracorporeal membrane oxygenation, or ventilator support.

CONCLUSION

There is no significant difference in graft survival after pediatric heart transplantation based on patient distance from their transplant center. Our data suggest the current strategy of transitioning some aspects of transplant care to local physicians or management from a distance does not increase posttransplant mortality risk.

Percutaneous Removal of Intravascular Pellet Following Penetrating Cardiac Trauma

There is controversy regarding the management of projectile embolization, a rare complication of penetrating trauma. We present the case of a 5-year-old, 20 kg male with retrograde venous projectile embolization following traumatic injury with a pellet gun. The projectile was successfully removed utilizing a novel, percutaneous approach.

A unique linkage of administrative and clinical registry databases to expand analytic possibilities in pediatric heart transplantation research

BACKGROUND

Large clinical, research, and administrative databases are increasingly utilized to facilitate pediatric heart transplant (HTx) research. Linking databases has proven to be a robust strategy across multiple disciplines to expand the possible analyses that can be performed while leveraging the strengths of each dataset. We describe a unique linkage of the Scientific Registry of Transplant Recipients (SRTR) database and the Pediatric Health Information System (PHIS) administrative database to provide a platform to assess resource utilization in pediatric HTx.

METHODS

All pediatric patients (1999-2016) who underwent HTx at a hospital enrolled in the PHIS database were identified. A linkage was performed between the SRTR and PHIS databases in a stepwise approach using indirect identifiers. To determine the feasibility of using these linked data to assess resource utilization, total and post-HTx hospital costs were assessed.

RESULTS

A total of 3188 unique transplants were identified as being present in both databases and amenable to linkage. Linkage of SRTR and PHIS data was successful in 3057 (95.9%) patients, of whom 2896 (90.8%) had complete cost data. Median total and post-HTx hospital costs were $518,906 (IQR $324,199-$889,738), and $334,490 (IQR $235,506-$498,803) respectively with significant differences based on patient demographics and clinical characteristics at HTx.

CONCLUSIONS

Linkage of the SRTR and PHIS databases is feasible and provides an invaluable tool to assess resource utilization. Our analysis provides contemporary cost data for pediatric HTx from the largest US sample reported to date. It also provides a platform for expanded analyses in the pediatric HTx population.

Neonatal Aortic Arch Reconstruction With Direct Splanchnic Perfusion Avoids Deep Hypothermia

BACKGROUND

Neonatal aortic arch reconstruction, typically performed with deep hypothermia and selective cerebral perfusion, leaves splanchnic organ protection dependent on hypothermia alone. A simplified method of direct in-field descending aortic perfusion during neonatal arch reconstruction permits the avoidance of deep hypothermia. We hypothesize that direct splanchnic perfusion at mild hypothermia provides improved or equivalent safety compared with deep hypothermia and may contribute to postoperative extracardiac organ recovery.

METHODS

Included were 138 biventricular patients aged younger than 90 days undergoing aortic arch reconstruction with cardiopulmonary bypass. Patients were grouped according to perfusion method A (selective cerebral perfusion with deep hyperthermia at 18° to 20°C) or method B (selective cerebral perfusion and splanchnic perfusion at 30° to 32°C). Patient characteristics and perioperative clinical and serologic data were analyzed. Significance was assigned for p of less than 0.05.

RESULTS

Of the 138 survivors, 63 underwent method A and 75 underwent method B. The median age at operation was 8.5 days (range, 6 to 15 days), and median weight was 3.2 kg (range, 2.8 to 3.73 kg), with no significant differences between groups. Cardiopulmonary bypass times were comparable between the two perfusion methods (p = 0.255) as were the ascending aortic cross-clamp times (p = 0.737). The postoperative glomerular filtration rate was significantly different between our groups (p = 0.028 to 0.044), with method B achieving a higher glomerular filtration rate. No significant differences were seen in ventilator time, postoperative length of stay, fractional increase of postoperative serum creatinine over preoperative serum creatinine, and postoperative lactate.

CONCLUSIONS

A simplified method of direct splanchnic perfusion during neonatal aortic arch reconstruction avoids the use of deep hypothermia and provides renal protection at least as effective as deep hypothermia.

Regional variation in the use of 1A status exceptions for pediatric heart transplant candidates: is this equitable?

The use of status exceptions (SE) was recently publicized as a strategy to reduce waitlist times for children awaiting heart transplant (HTx). The aim of this study was to assess SE use across UNOS regions and compare survival in patients listed using a SE to those listed by standard criteria. The OPTN database was queried for all pediatric patients listed for HTx (2000-2014). SE use was compared across UNOS regions. Survival curves were generated and compared using the log-rank test. 1A SE use is uncommon, being utilized in 108 of 4587 pediatric 1A listings (2.4%). There is significant variability in SE use across UNOS regions (0.7%-16.4% of 1A listings, P < .001). Waitlist survival is significantly higher in candidates listed using a 1A SE compared to those listed by standard criteria (P = .001) and is similar to 1B listings. Regional variation in 1A SE use has the potential to introduce bias into a system designed to be equitable. Waitlist survival in patients listed using a SE is similar to those listed status 1B, suggesting these patients may not require 1A status. Careful review of pediatric heart allocation policies is needed to optimize patient outcomes and ensure a fair and unbiased allocation system.

Expanding the donor pool: regional variation in pediatric organ donation rates

There are limited published data on pediatric organ donation rates. The aim of this study was to describe the trends in pediatric organ donation over time and to assess the regional variation in pediatric deceased organ donation. OPTN data were utilized to assess the trends in pediatric organ donation over time. The number of deceased pediatric organ donors was indexed using regional mortality data obtained from the National Center for Health Statistics and compared across UNOS regions and two different eras. The number of pediatric deceased organ donors has declined in the recent era, largely driven by fewer adolescent donors. For all age groups, there is significant regional variation in organ donation rates, with identifiable high- and low-performing regions. Expansion of the donor pool may be possible by optimizing organ donation in regions demonstrating lower recruitment of pediatric donors. Using the region with the highest donation rate for each age group as the gold standard, we estimate a potential 24% increase in the number of donors if all regions performed comparably, equating to 215 new pediatric donors annually.

Laparoscopic Nissen fundoplication in infants with hypoplastic left heart syndrome

BACKGROUND/PURPOSE

Patients with hypoplastic left heart syndrome (HLHS) experience a higher risk for complications from gastroesophageal reflux, prompting frequent need for fundoplication. Patients between stage I and II palliation ("interstage") are at particularly high operative risk because of the parallel nature of their pulmonary and systemic blood flow. Laparoscopic approach for fundoplication is common for pediatric patients. However, its safety in interstage HLHS is relatively unknown. We examined the perioperative physiologic burden of a laparoscopic fundoplication in HLHS patients.

METHODS

All patients who underwent open or laparoscopic fundoplication during the interstage period at our institution since 2006 were reviewed. Perioperative physiologic data, echocardiographic findings, survival, and complications were collected from the anesthetic record and patient chart.

RESULTS

Nineteen patients with HLHS had laparoscopic fundoplication, 13 (68%) during the interstage period, compared to 64 performed by the open approach. Ten (77%) of 13 interstage patients had perioperative hemodynamic instability. Incidence of instability between open and laparoscopic groups was not different. One laparoscopic patient required ECMO support for shunt thrombosis.

CONCLUSIONS

Despite a high incidence of hemodynamic instability, overall outcomes are consistent with those reported in the literature for this high-risk patient population. Laparoscopic approach for fundoplication during the interstage period appears to be a relatively safe option for these patients.

Tissue plasminogen activator treatment of bilateral pulmonary emboli in a pediatric patient supported with a ventricular assist device

Bleeding and thrombosis are well-known potential complications of VAD support. We present a pediatric patient who developed massive bilateral pulmonary emboli while on BiVAD support that was successfully treated with intravenous tPA and bridged to heart transplant.

Cerebral ventriculomegaly after the bidirectional Glenn (BDG) shunt: a single-institution retrospective analysis

PURPOSE

The bidirectional Glenn (BDG) procedure involves the anastomosis of the superior vena cava (SVC) to the pulmonary artery, increasing central venous pressure (CVP). We hypothesize that this increase in CVP triggers an acute neurologic insult, leading to ventriculomegaly.

METHODS

In this retrospective analysis in a tertiary care children's hospital, we identified 167 patients who underwent the BDG procedure between August 2006 and July 2013. Within this initial cohort, 24 patients had head imaging (CT, MRI, or ultrasound) performed both before and after the BDG.

RESULTS

From head imaging available from these 24 patients, we measured the frontal-occipital horn ratio (FOR), a well-validated measure of lateral ventricle size. Using central venous catheter data, we assessed postoperative CVP at 12, 24, and 48 h. Paired t tests and linear regression were used to evaluate our cohort. Median age at surgery was 4.9 months. Paired analysis revealed that median FOR significantly increased between preoperative (median 0.38, IQR 0.37-0.41) and postoperative (median 0.42, IQR 0.40-0.45) head images (p = 0.005). Increasing change in FOR was associated with increased 12-h (R(2) = 0.369, p = 0.003) but not 24- or 48-h postoperative CVP.

CONCLUSIONS

To our knowledge, our study is the first to demonstrate ventriculomegaly developing after the BDG. Physiologically, increasing CVP after the BDG was associated with greater change in lateral ventricle size. This supports the contention that increasing CVP produced during the BDG may damage the developing brain. This study has informed a prospective evaluation of a link between the BDG procedure and neurologic outcomes.

Identifying predictors of hospital readmission following congenital heart surgery through analysis of a multiinstitutional administrative Database

BACKGROUND

Despite resource burdens associated with hospital readmission, there remains little multiinstitutional data available to identify children at risk for readmission following congenital heart surgery.

METHODS AND RESULTS

Children undergoing congenital heart surgery and discharged home between January of 2011 and December 2012 were identified within the Pediatric Health Information System database, a multiinstitutional collection of clinical and administrative data. Patient discharges were assigned to derivation and validation cohorts for the purposes of predictive model design, with 17 871 discharges meeting inclusion criteria. Readmission within 30 days was noted following 956 (11%) of discharges within the derivation cohort (n = 9104), with a median time to readmission of 9 days (interquartile range [IQR] 5-18 days). Readmissions resulted in a rehospitalization length of stay of 4 days (IQR 2-8 days) and were associated with an intensive care unit (ICU) admission in 36% of cases. Independent perioperative predictors of readmission included Risk Adjustment in Congenital Heart Surgery score of 6 (odds ratio [OR] 2.6, 95% confidence interval [CI] 1.8-3.7, P < .001) and ICU length of stay of at least 7 days (OR 1.9 95% CI 1.6-2.2, P < .001). Demographic predictors included Hispanic ethnicity (OR 1.2, 95% CI 1.1-1.4, P = .014) and government payor status (OR 1.2, 95% CI 1.1-1.4, P = .007). Predictive model performance was modest among validation cohort (c statistic 0.68, 95% CI 0.66-0.69, P < .001).

CONCLUSIONS

Readmissions following congenital heart surgery are common and associated with significant resource consumption. While we describe independent predictors that may identify patients at risk for readmission prior to hospital discharge, there likely remains other unreported factors that may contribute to readmission following congenital heart surgery.

Endothelial progenitor cells as a sole source for ex vivo seeding of tissue-engineered heart valves

PURPOSES

We investigated whether circulating endothelial progenitor cells (EPCs) can be used as a cell source for the creation of a tissue-engineered heart valve (TEHV).

METHODS

Trileaflet valved conduits were fabricated using nonwoven polyglycolic acid/poly-4-hydroxybutyrate polymer. Ovine peripheral blood EPCs were dynamically seeded onto a valved conduit and incubated for 7, 14, and 21 days.

RESULTS

Before seeding, EPCs were shown to express CD31(+), eNOS(+), and VE-Cadherin(+) but not alpha-smooth muscle actin. Histological analysis demonstrated relatively homogenous cellular ingrowth throughout the valved conduit. TEHV constructs revealed the presence of endothelial cell (EC) markers and alpha-smooth muscle actin(+) cells comparable with native valves. Protein levels were comparable with native valves and exceeded those in unseeded controls. EPC-TEHV demonstrated a temporal pattern of matrix metalloproteinases-2/9 expression and tissue inhibitors of metalloproteinase activities comparable to that of native valves. Mechanical properties of EPC-TEHV demonstrated significantly greater stiffness than that of the unseeded scaffolds and native valves.

CONCLUSIONS

Circulating EPC appears to have the potential to provide both interstitial and endothelial functions and could potentially serve as a single-cell source for construction of autologous heart valves.

Healing and remodeling of bioengineered pulmonary artery patches implanted in sheep

PURPOSE

We hypothesized that cell-seeded patches implanted into sheep pulmonary artery would undergo progressive and complete healing into a viable structure well integrated with the arterial wall.

METHODS

Autologous ovine blood-derived endothelial progenitor cells (EPCs) and bone marrow-derived mesenchymal stem cells (MSCs) were isolated and cultured in vitro. MSCs and EPCs were seeded onto poly-4-hydroxybutyrate (P4HB)-coated polyglycolic acid (PGA) nonwoven biodegradable mesh scaffolds (10x20 mm) and cultured for 5 days in a laminar fluid flow system. Seeded patches were implanted into the wall of sheep pulmonary artery for 1-2 weeks (n=4) or 4-6 weeks (n=3). Preimplant and postexplant specimens were analyzed by histology and immunohistochemistry.

RESULTS

Unimplanted constructs contained alpha-smooth muscle actin (SMA)-positive cells and early extracellular matrix formation (primarily glycosaminoglycans). One week after implantation, seeded patches had surface thrombus formation and macrophage infiltration. Seeded patches implanted for 2 weeks showed granulation tissue, early pannus formation, macrophages, foreign body giant cells around disintegrating polymer, and early angiogenesis (microvessel formation). After 4 weeks in vivo, seeded patches contained glycosaminoglycans, collagen, and coverage of the luminal surface by host artery-derived pannus containing alpha-SMA-positive cells and laminated elastin; polymer scaffold degradation was almost complete with replacement by fibrous tissue containing viable cells.

CONCLUSIONS

This study shows that cell-seeded patches implanted in sheep pulmonary artery remodel to layered and viable tissue well integrated into the native arterial wall. The key remodeling processes included (1) intimal overgrowth at the luminal surface (pannus formation; neointima) and (2) granulation tissue formation and fibrosis with foreign body reaction.

Endothelial progenitor and mesenchymal stem cell-derived cells persist in tissue-engineered patch in vivo: application of green and red fluorescent protein-expressing retroviral vector

An unresolved question regarding tissue-engineered (TE) cardiac valves and vessels is the fate of the transplanted cells in vivo. We have developed a strategy to track the anatomic location of seeded cells within TE constructs and neighboring tissues using a retroviral vector system encoding green and red fluorescent proteins (GFPs and RFPs, respectively) in ovine circulating endothelial progenitor cells (EPCs) and bone marrow-derived mesenchymal stem cells (BMSCs). We demonstrate that stable transduction ex vivo with high-titer Moloney murine leukemia virus-based retroviral vector yields transduction efficiency of greater than 97% GFP(+) EPC- and RFP(+) mesenchymal stem cell (MSC)-derived cells. Cellular phenotype and transgene expression were also maintained through 25 subsequent passages. Using a retroviral vector system to distinguish our pre-seeded cells from tissue-resident progenitor cells and circulating endothelial and marrow-derived precursors, we simultaneously co-seeded 2 x 10(6) GFP(+) EPCs and 2 x 10(5) RFP(+) MSCs onto the TE patches. In a series of ovine pulmonary artery patch augmentation studies, transplanted GFP(+) EPC- and RFP(+) MSC-derived cells persisted within the TE patch 7 to 14 days after implantation, as identified using immunofluorescence. Analysis showed 81% luminal coverage of the TE patches before implantation with transduced cells, increasing to 96% at day 7 and decreasing to 67% at day 14 post-implantation. This suggests a temporal association between retroviral expression of progenitor cells and mediating effects of these cells on the physiological remodeling and maturation of the TE constructs. To our knowledge, this is the first cardiovascular tissue-engineering in vivo study using a double-labeling method to demonstrate a direct evidence of the source, persistence, and incorporation into a TE vascular patch of co-cultured and simultaneously pre-seeded adult progenitor cells.

Aprotinin improves cerebral protection: Evidence from a survival porcine model

OBJECTIVE

Aprotinin is a serine protease inhibitor used during cardiac surgery to reduce blood loss and preserve platelet function. It has also been shown to reduce leukocyte activation during and after cardiopulmonary bypass. The goal of the study was to test the hypothesis that aprotinin could reduce cerebral injury after low-flow cardiopulmonary bypass and deep hypothermic circulatory arrest.

METHODS

Sixteen piglets (mean weight, 13.6 +/- 1.3 kg) were randomly assigned to receive aprotinin or placebo (8 animals per group) before a 120-minute period of deep hypothermic circulatory arrest (15 degrees C) or 25 mL x kg(-1) x min(-1) low-flow cardiopulmonary bypass (25 degrees C or 34 degrees C). Piglets had a cranial window placed over the parietal cerebral cortex for direct examination of the microcirculation by means of intravital microscopy. Rhodamine-stained leukocytes were observed in postcapillary venules, with analysis for adhesion and rolling. Plasma was labeled with fluorescein isothiocyanate-dextran for assessment of functional capillary density. Neurologic and histologic scores were used as the primary outcome measures.

RESULTS

During rewarming, the mean number of both rolling and adherent leukocytes was significantly lower after aprotinin administration (P < .05). At 5 and 15 minutes of rewarming, functional capillary density recovered faster with aprotinin treatment (P < .05). Functional outcome (neurologic deficit score) on postoperative day 1 was significantly improved in aprotinin-treated piglets (P < .05).

CONCLUSIONS

Aprotinin reduces inflammation and improves neurologic outcome after a prolonged period of deep hypothermic circulatory arrest or low-flow cardiopulmonary bypass.

Transforming Growth Factor-β1 Modulates Extracellular Matrix Production, Proliferation, and Apoptosis of Endothelial Progenitor Cells in Tissue-Engineering Scaffolds

Background— Valvular endothelial cells and circulating endothelial progenitor cells (EPCs) can undergo apparent phenotypic change from endothelial to mesenchymal cell type. Here we investigated whether EPCs can promote extracellular matrix formation in tissue engineering scaffolds in response to transforming growth factor (TGF)-β1.

Method and Results— Characterized ovine peripheral blood EPCs were seeded onto poly (glycolic acid)/poly (4-hydroxybutyrate) scaffolds for 5 days. After seeding at 2×10 6 cells/cm 2 , scaffolds were incubated for 5 days in a roller bottle, with or without the addition of TGF-β1. After seeding at 15×10 6 cells/cm 2 , scaffolds were incubated for 10 days in a roller bottle with or without the addition of TGF-β1 for the first 5 days. Using immunofluorescence and Western blotting, we demonstrated that EPCs initially exhibit an endothelial phenotype (ie, CD31 + , von Willebrand factor + , and α–smooth muscle actin (SMA) − ) and can undergo a phenotypic change toward mesenchymal transformation (ie, CD31 + and α-SMA + ) in response to TGF-β1. Scanning electron microscopy and histology revealed enhanced tissue formation in EPC-TGF-β1 scaffolds. In both the 10- and 15-day experiments, EPC-TGF-β1 scaffolds exhibited a trend of increased DNA content compared with unstimulated EPC scaffolds. TGF-β1–mediated endothelial to mesenchymal transformation correlated with enhanced expression of laminin and fibronectin within scaffolds evidenced by Western blotting. Strong expression of tropoelastin was observed in response to TGF-β1 equal to that in the unstimulated EPC. In the 15-day experiments, TGF-β1–stimulated scaffolds revealed dramatically enhanced collagen production (types I and III) and incorporated more 5-bromodeoxyuridine and TUNEL staining compared with unstimulated controls.

Conclusions— Stimulation of EPC-seeded tissue engineering scaffolds with TGF-β1 in vitro resulted in a more organized cellular architecture with glycoprotein, collagen, and elastin synthesis, and thus noninvasively isolated EPCs coupled with the pleiotropic actions of TGF-β1 could offer new strategies to guide tissue formation in engineered cardiac valves.

Cerebral Endothelial Nitric Oxide Synthase Expression is Reduced After Very Low Flow Bypass

BACKGROUND

In previous studies we have shown that delayed capillary reperfusion after low flow bypass predicts neurologic injury. In this acute study, we hypothesized that low flow reduces endothelial nitric oxide synthase (eNOS) expression, which may lead to more profound inflammatory response and delayed capillary perfusion.

METHODS

Twelve piglets (13.2 +/- 0.7 kg) had a cranial window placed over the parietal cerebral cortex for direct examination of the microcirculation using intravital fluorescence microscopy. Animals were cooled to 15 degrees C or 34 degrees C on cardiopulmonary bypass (pH stat, hematocrit 30%, pump flow 100 mL/kg/minute) followed by 2 hours of low flow (50 mL/kg/minute) or very low flow (10 mL/kg/minute). Rhodamine staining was used to observe adherent and rolling leukocytes in postcapillary venules. The eNOS protein expression was determined by Western immunoblotting.

RESULTS

High temperature and low flow rate correlated with significantly reduced eNOS expression (p < 0.01). Univariate comparisons based on Student t tests indicated that eNOS protein levels were lower at 34 degrees C than at 15 degrees C (0.7 +/- 0.6 vs 1.7 +/- 0.5, p < 0.01) and at 10 mL/kg per minute compared with 50 mL/kg per minute (0.8 +/- 0.7 vs 1.6 +/- 0.5, p = 0.03). Moreover, two-way analysis of variance revealed that temperature (F = 21.6, p < 0.001) and flow rate (F = 13.8, p = 0.005) were independent multivariate predictors of eNOS expression. During low flow bypass, eNOS was inversely correlated with numbers of adherent (p = 0.002) and rolling (p = 0.006) leukocytes, following an exponential decay curve closely.

CONCLUSIONS

eNOS expression is reduced after very low flow bypass, particularly at a higher bypass temperature. This is associated with delayed capillary reperfusion. Reduced eNOS is also associated with increased white cell activation which may lead to greater neurologic injury.

Application of tissue-engineering principles toward the development of a semilunar heart valve substitute

Heart valve disease is a significant medical problem worldwide. Current treatment for heart valve disease is heart valve replacement. State of the art replacement heart valves are less than ideal and are associated with significant complications. Using the basic principles of tissue engineering, promising alternatives to current replacement heart valves are being developed. Significant progress has been made in the development of a tissue-engineered semilunar heart valve substitute. Advancements include the development of different potential cell sources and cell-seeding techniques; advancements in matrix and scaffold development and in polymer chemistry fabrication; and the development of a variety of bioreactors, which are biomimetic devices used to modulate the development of tissue-engineered neotissue in vitro through the application of biochemical and biomechanical stimuli. This review addresses the need for a tissue-engineered alternative to the current heart valve replacement options. The basics of heart valve structure and function, heart valve disease, and currently available heart valve replacements are discussed. The last 10 years of investigation into a tissue-engineered heart valve as well as current developments are reviewed. Finally, the early clinical applications of cardiovascular tissue engineering are presented.