A Novel Biological Strategy for Myocardial Protection by Intracoronary Delivery of Mitochondria: Safety and Efficacy

Mitochondrial dysfunction is the determinant insult of ischemia-reperfusion injury. Autologous mitochondrial transplantation involves supplying one's healthy mitochondria to the ischemic region harboring damaged mitochondria. The authors used in vivo swine to show that mitochondrial transplantation in the heart by intracoronary delivery is safe, with specific distribution to the heart, and results in significant increase in coronary blood flow, which requires intact mitochondrial viability, adenosine triphosphate production, and, in part, the activation of vascular K_IR channels. Intracoronary mitochondrial delivery after temporary regional ischemia significantly improved myocardial function, perfusion, and infarct size. The authors concluded that intracoronary delivery of mitochondria is safe and efficacious therapy for myocardial ischemia-reperfusion injury.

Mitochondrial transplantation enhances murine lung viability and recovery after ischemia-reperfusion injury

The most common cause of acute lung injury is ischemia-reperfusion injury (IRI), during which mitochondrial damage occurs. We have previously demonstrated that mitochondrial transplantation is an efficacious therapy to replace or augment mitochondria damaged by IRI, allowing for enhanced muscle viability and function in cardiac tissue. Here, we investigate the efficacy of mitochondrial transplantation in a murine lung IRI model using male C57BL/6J mice. Transient ischemia was induced by applying a microvascular clamp on the left hilum for 2 h. Upon reperfusion mice received either vehicle or vehicle-containing mitochondria either by vascular delivery (Mito V) through the pulmonary artery or by aerosol delivery (Mito Neb) via the trachea (nebulization). Sham control mice underwent thoracotomy without hilar clamping and were ventilated for 2 h before returning to the cage. After 24 h recovery, lung mechanics were assessed and lungs were collected for analysis. Our results demonstrated that at 24 h of reperfusion, dynamic compliance and inspiratory capacity were significantly increased and resistance, tissue damping, elastance, and peak inspiratory pressure (Mito V only) were significantly decreased (P < 0.05) in Mito groups as compared with their respective vehicle groups. Neutrophil infiltration, interstitial edema, and apoptosis were significantly decreased (P < 0.05) in Mito groups as compared with vehicles. No significant differences in cytokines and chemokines between groups were shown. All lung mechanics results in Mito groups except peak inspiratory pressure in Mito Neb showed no significant differences (P > 0.05) as compared with Sham. These results conclude that mitochondrial transplantation by vascular delivery or nebulization improves lung mechanics and decreases lung tissue injury.

[Current surgical options and outcomes for newborns with hypoplastic left heart syndrome]

Since the first successful palliation was performed by Norwood et al. in 1983, there have been substantial changes in diagnosis, management, and outcomes of hypoplastic left heart syndrome, Survival for stage 1 palliation has increased to 90% in many centres, with patients potentially surviving into adulthood. However, the associated morbidity and mortality remain substantial. Although the principles of staged surgical palliation of hypoplastic left heart syndrome are well established, there is significant variability in surgical procedure and management between centres, and several controversial aspects remain unresolved. In this review, we summarize the current surgical and management options for newborns with hypoplastic left heart syndrome and their outcomes.

Preischemic autologous mitochondrial transplantation by intracoronary injection for myocardial protection

OBJECTIVE

To investigate preischemic intracoronary autologous mitochondrial transplantation (MT) as a therapeutic strategy for prophylactic myocardial protection in a porcine model of regional ischemia-reperfusion injury (IRI).

METHODS

The left coronary artery was cannulated in Yorkshire pigs (n = 26). Mitochondria (1 × 10⁹) or buffer (vehicle [Veh]) were delivered as a single bolus (MT_S) or serially (10 injections over 60 minutes; MT_SS). At 15 minutes after injection, the heart was subjected to temporary regional ischemia (RI) by snaring the left anterior descending artery. After 30 minutes of RI, the snare was released, and the heart was reperfused for 120 minutes.

RESULTS

Coronary blood flow (CBF) and myocardial function were increased temporarily during the pre-RI period. Following 30 minutes of RI, MT_S and MT_SS hearts had significantly increased CBF that persisted throughout reperfusion (Veh vs MT_S and MT_SS; P = .04). MT_S and MT_SS showed a significantly enhanced ejection fraction (Veh vs MT_S, P < .001; Veh vs MT_SS, P = .04) and developed pressure (Veh vs MT_S, P < .001; Veh vs MT_SS, P = .03). Regional function, assessed through segmental shortening (Veh vs MT_S, P = .03; Veh vs MT_SS, P < .001), fractional shortening (Veh vs MT_S, P < .001; Veh vs MT_SS, P = .04), and strain analysis (Veh vs MT_S, P = .002; Veh vs MT_SS, P = .003), was also significantly improved. Although there was no difference in the area at risk between treatment groups, infarct size was significantly reduced in both MT groups (Veh vs MT_S and MT_SS, P < .001).

CONCLUSIONS

Preischemic MT by single or serial intracoronary injections provides prophylactic myocardial protection from IRI, significantly decreasing infarct size and enhancing global and regional function.

An intraoperative test device for aortic valve repair

OBJECTIVE

Aortic valve repair is currently in transition from surgical improvisation to a reproducible operation and an option for many patients with aortic regurgitation. Our research efforts at improving reproducibility include development of methods for intraoperatively testing and visualizing the valve in its diastolic state.

METHODS

We developed a device that can be intraoperatively secured in the transected aorta allowing the aortic root to be pressurized and the closed valve to be inspected endoscopically. Our device includes a chamber that can be pressurized with crystalloid solution and ports for introduction of an endoscope and measuring gauges. We show use of the device in explanted porcine hearts to visualize the aortic valve and to measure leaflet coaptation height in normal valves and in valves that have undergone valve repair procedures.

RESULTS

The procedure of introducing and securing the device in the aorta, pressurizing the valve, and endoscopically visualizing the closed valve is done in less than 1 minute. The device easily and reversibly attaches to the aortic root and allows direct inspection of the aortic valve under conditions that mimic diastole. It enables the surgeon to intraoperatively study the valve immediately before repair to determine mechanisms of incompetence and immediately after the repair to assess competence. We also show its use in measuring valve leaflet coaptation height in the diastolic state.

CONCLUSIONS

This device enables more relevant prerepair valve assessment and also enables a test of postrepair valve competence under physiological pressures.

Mitochondrial transplantation prolongs cold ischemia time in murine heart transplantation

BACKGROUND

Cold ischemia time (CIT) causes ischemia‒reperfusion injury to the mitochondria and detrimentally effects myocardial function and tissue viability. Mitochondrial transplantation replaces damaged mitochondria and enhances myocardial function and tissue viability. Herein we investigated the efficacy of mitochondrial transplantation in enhancing graft function and viability after prolonged CIT.

METHODS

Heterotopic heart transplantation was performed in C57BL/6J mice. Upon heart harvesting from C57BL/6J donors, 0.5 ml of either mitochondria (1 × 10⁸ in respiration buffer; mitochondria group) or respiration buffer (vehicle group) was delivered antegrade to the coronary arteries via injection to the coronary ostium. The hearts were excised and preserved for 29 ± 0.3 hours in cold saline (4°C). The hearts were then heterotopically transplanted. A second injection of either mitochondria (1 × 10⁸) or respiration buffer (vehicle) was delivered antegrade to the coronary arteries 5 minutes after transplantation. Grafts were analyzed for 24 hours. Beating score, graft function, and tissue injury were measured.

RESULTS

Beating score, calculated ejection fraction, and shortening fraction were significantly enhanced (p < 0.05), whereas necrosis and neutrophil infiltration were significantly decreased (p < 0.05) in the mitochondria group as compared with the vehicle group at 24 hours of reperfusion. Transmission electron microscopy showed the presence of contraction bands in vehicle but not in mitochondria grafts.

CONCLUSIONS

Mitochondrial transplantation prolongs CIT to 29 hours in the murine heart transplantation model, significantly enhances graft function, and decreases graft tissue injury. Mitochondrial transplantation may provide a means to reduce graft failure and improve transplantation outcomes after prolonged CIT.

Technical performance scores are predictors of midterm mortality and reinterventions following congenital mitral valve repair

OBJECTIVES

The Technical Performance Score (TPS) has been shown to be predictive of postoperative mortality, morbidities and reinterventions following various cardiac procedures in children. We hypothesized that TPS is also a predictor of mitral valve repair outcomes.

METHODS

A review of patients who underwent mitral valve repair from January 2000 to December 2013 was performed. Primary repair of complete atrioventricular defect was excluded. The scores were determined according to previously published criteria based on the need for reintervention and predischarge echocardiograms: Class 1 (no residua), Class 2 (minor residua) or Class 3 (pacemaker implantation, major residua or reintervention for major residua prior to discharge). Cox proportional hazard models and Kaplan-Meier estimator were used.

RESULTS

A total of 587 patients underwent mitral repair (median age 2.6 years). Median follow-up duration was 3 years. There were 125 (21.3%) post-discharge mitral reinterventions and freedom from reintervention was 85.2%, 78.2% and 69.4% at 1, 2 and 5 years, respectively. Both TPS Class 2 [hazard ratio (HR) 3.6, 95% confidence interval (CI) 1.4-10.0; P  = 0.02] and Class 3 (HR 8.7, 95% CI 3.0-25.1; P  < 0.001) were associated with post-discharge reinterventions. There were 31 late deaths/transplantations, and transplant-free survival at 1, 2 and 5 years was 97.8%, 95.3% and 93.2%. TPS 3 was associated with decreased post-discharge transplant-free survival (HR 5.5, 95% CI 1.2-25.0; P  = 0.03). Post-discharge mitral reintervention was not associated with increased mortality.

CONCLUSIONS

The TPS is a strong predictor of midterm mortality and post-discharge mitral reintervention in congenital patients who underwent mitral repair.

Alloreactivity and allorecognition of syngeneic and allogeneic mitochondria

Previously, we have demonstrated that the transplantation of autologous mitochondria is cardioprotective. No immune or autoimmune response was detectable following the single injection of autologous mitochondria. To expand the therapeutic potential and safety of mitochondrial transplantation, we now investigate the immune response to single and serial injections of syngeneic and allogeneic mitochondria delivered by intraperitoneal injection. Our results demonstrate that there is no direct or indirect, acute or chronic alloreactivity, allorecognition or damage-associated molecular pattern molecules (DAMPs) reaction to single or serial injections of either syngeneic or allogeneic mitochondria.

Soft robotic ventricular assist device with septal bracing for therapy of heart failure

Previous soft robotic ventricular assist devices have generally targeted biventricular heart failure and have not engaged the interventricular septum that plays a critical role in blood ejection from the ventricle. We propose implantable soft robotic devices to augment cardiac function in isolated left or right heart failure by applying rhythmic loading to either ventricle. Our devices anchor to the interventricular septum and apply forces to the free wall of the ventricle to cause approximation of the septum and free wall in systole and assist with recoil in diastole. Physiological sensing of the native hemodynamics enables organ-in-the-loop control of these robotic implants for fully autonomous augmentation of heart function. The devices are implanted on the beating heart under echocardiography guidance. We demonstrate the concept on both the right and the left ventricles through in vivo studies in a porcine model. Different heart failure models were used to demonstrate device function across a spectrum of hemodynamic conditions associated with right and left heart failure. These acute in vivo studies demonstrate recovery of blood flow and pressure from the baseline heart failure conditions. Significant reductions in diastolic ventricle pressure were also observed, demonstrating improved filling of the ventricles during diastole, which enables sustainable cardiac output.

Right ventricular outflow tract reintervention after primary tetralogy of Fallot repair in neonates and young infants

OBJECTIVE

To assess the outcomes following primary tetralogy of Fallot (TOF) repair in neonates and young infants with pulmonary stenosis (PS) and pulmonary atresia and compare differences in reintervention on the right ventricular outflow tract (RVOT) among those undergoing valve sparing repair (VSR), transannular RVOT patch (TAP), and right ventricle-to-pulmonary artery (RV-PA) conduit surgeries.

METHODS

Data were collected retrospectively in 101 patients who underwent TOF repair over a 10-year period between January 2005 and September 2015. The primary endpoint was reintervention on the RVOT, defined as a surgical procedure or cardiac catheterization-based RVOT reintervention.

RESULTS

Forty-three patients had TOF/PS, of whom 24 (56%) underwent TAP and 19 (44%) underwent VSR. Fifty-eight patients had TOF/PA, 14 (24%) underwent TAP and 44 (76%) underwent RV-PA conduit repair. Overall patient mortality was 2.9% (3 of 101). Thirty-three patients underwent surgical reintervention, and 52 underwent catheterization-based reintervention. Patients with TOF/PA who underwent RV-PA conduit repair had a higher surgical reintervention rate than those who underwent TAP (45% vs 21%). Patients with TOF/PSs undergoing VSR with a lower median birth weight (2.5 kg vs 3.7 kg) required more surgical reintervention.

CONCLUSIONS

Neonatal TOF repair can be performed with low mortality but frequent RVOT reinterventions. Surgical reintervention is earlier and the rate is higher among patients with TOF/PA undergoing RV-PA conduit repair compared with those undergoing TAP. Although there were no overall differences in RVOT reintervention rate between patients with TOF/PS undergoing VSR and those undergoing TAP, a lower birth weight in the patients undergoing VSR is associated with a higher surgical reintervention rate.

Mitochondrial Transplantation in Myocardial Ischemia and Reperfusion Injury

Ischemic heart disease remains the leading cause of death worldwide. Mitochondria are the power plant of the cardiomyocyte, generating more than 95% of the cardiac ATP. Complex cellular responses to myocardial ischemia converge on mitochondrial malfunction which persists and increases after reperfusion, determining the extent of cellular viability and post-ischemic functional recovery. In a quest to ameliorate various points in pathways from mitochondrial damage to myocardial necrosis, exhaustive pharmacologic and genetic tools have targeted various mediators of ischemia and reperfusion injury and procedural techniques without applicable success. The new concept of replacing damaged mitochondria with healthy mitochondria at the onset of reperfusion by auto-transplantation is emerging not only as potential therapy of myocardial rescue, but as gateway to a deeper understanding of mitochondrial metabolism and function. In this chapter, we explore the mechanisms of mitochondrial dysfunction during ischemia and reperfusion, current developments in the methodology of mitochondrial transplantation, mechanisms of cardioprotection and their clinical implications.

Photo-oxidized bovine pericardium in congenital cardiac surgery: single-centre experience

Objectives

Dye-mediated photo-oxidation of pericardium is an alternative method to chemical treatment with glutaraldehyde for cross-linking collagen, providing biostability of the patch material while avoiding late calcification and cytotoxicity. There are few data available, on using photo-oxidation-treated pericardium, in congenital cardiac surgery. This study reports the outcomes using Photofix™ bovine pericardium in neonates, infants, children and young adults undergoing paediatric cardiac surgery.

Methods

A total of 490 patches in 383 consecutive operations (364 patients) were used in the surgical repair of congenital heart defects at our institution from October 2008 to October 2011. Recorded variables included demographic data, age at operation, primary cardiac diagnosis, associated complications and number, type and location of patches placed and patch-related reintervention.

Results

Median age at operation was 5.3 years, ranging from <1 month to 56 years. The overall survival rate at late follow-up was 92%, and no deaths were related to failure of the tissue substitute. Two patients (0.5%) underwent reintervention late due to patch material failure: one for residual shunt after Rastelli repair and one for aneurysmal dilatation of a right ventricular outflow tract patch. The patch material was explanted in 8 patients at a mean of 20 months (range, 1-72 months) following implantation. Histological examination revealed mild to moderate inflammation with variable calcification.

Conclusions

Photo-oxidized bovine pericardium demonstrated excellent performance when used as a patch material in cardiovascular repair in children. Its handling characteristics and biocompatibility are consistent with a wide range of applications.

An Intracardiac Soft Robotic Device for Augmentation of Blood Ejection from the Failing Right Ventricle

We introduce an implantable intracardiac soft robotic right ventricular ejection device (RVED) for dynamic approximation of the right ventricular (RV) free wall and the interventricular septum (IVS) in synchrony with the cardiac cycle to augment blood ejection in right heart failure (RHF). The RVED is designed for safe and effective intracardiac operation and consists of an anchoring system deployed across the IVS, an RV free wall anchor, and a pneumatic artificial muscle linear actuator that spans the RV chamber between the two anchors. Using a ventricular simulator and a custom controller, we characterized ventricular volume ejection, linear approximation against different loads and the effect of varying device actuation periods on volume ejection. The RVED was then tested in vivo in adult pigs (n = 5). First, we successfully deployed the device into the beating heart under 3D echocardiography guidance (n = 4). Next, we performed a feasibility study to evaluate the device's ability to augment RV ejection in an experimental model of RHF (n = 1). RVED actuation augmented RV ejection during RHF; while further chronic animal studies will provide details about the efficacy of this support device. These results demonstrate successful design and implementation of the RVED and its deployment into the beating heart. This soft robotic ejection device has potential to serve as a rapidly deployable system for mechanical circulatory assistance in RHF.

Vascular Endothelial Growth Factor Prevents Endothelial-to-Mesenchymal Transition in Hypertrophy

BACKGROUND

In hypertrophy, progressive loss of function caused by impaired diastolic compliance correlates with advancing cardiac fibrosis. Endothelial cells contribute to this process through endothelial-to-mesenchymal transition (EndMT) resulting from inductive signals such as transforming growth factor (TGF-β). Vascular endothelial growth factor (VEGF) has proven effective in preserving systolic function and delaying the onset of failure. In this study, we hypothesize that VEGF inhibits EndMT and prevents cardiac fibrosis, thereby preserving diastolic function.

METHODS

The descending aorta was banded in newborn rabbits. At 4 and 6 weeks, hypertrophied animals were treated with intrapericardial VEGF protein and compared with controls (n = 7 per group). Weekly transthoracic echocardiography measured peak systolic stress. At 7 weeks, diastolic stiffness was determined through pressure-volume curves, fibrosis by Masson trichrome stain and hydroxyproline assay, EndMT by immunohistochemistry, and activation of TGF-β and SMAD2/3 by quantitative real-time polymerase chain reaction.

RESULTS

Peak systolic stress was preserved during the entire observation period, and diastolic compliance was maintained in treated animals (hypertrophied: 20 ± 1 vs treated: 11 ± 3 and controls: 12 ± 2; p < 0.05). Collagen was significantly higher in the hypertrophied group by Masson trichrome (hypertrophied: 3.1 ± 0.9 vs treated: 1.8 ± 0.6) and by hydroxyproline assay (hypertrophied: 2.8 ± 0.6 vs treated: 1.4 ± 0.4; p < 0.05). Fluorescent immunostaining showed active EndMT in the hypertrophied group but significantly less in treated hearts, which was directly associated with a significant increase in TGF-β/SMAD-2 messenger RNA expression.

CONCLUSIONS

EndMT contributes to cardiac fibrosis in hypertrophied hearts. VEGF treatment inhibits EndMT and prevents the deposition of collagen that leads to myocardial stiffness through TGF-β/SMAD-dependent activation. This presents a therapeutic opportunity to prevent diastolic failure and preserve cardiac function in pressure-loaded hearts.

Boston Children׳s Hospital Cardiovascular Program

The Cardiovascular program at Boston Children's Hospital has been characterized as a "great institution" by the editors. This designation is the result of a commitment to innovation interdisciplinary collaboration, rigorous review of results and continuous self-improvement, training the next generation, and an ability to "get the right people on the bus".

WITHDRAWN: Surgically induced myocardial ischemia: How best to mitigate the injury

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The human thymus perivascular space is a functional niche for viral-specific plasma cells

The human thymus is susceptible to viral infections that can severely alter thymopoiesis and compromise the mechanisms of acquired tolerance to self-antigens. In humans, plasma cells residing primarily in the bone marrow confer long-lasting protection to common viruses by secreting antigen-specific antibodies. Since the thymus also houses B cells, we examined the phenotypic complexity of these thymic resident cells and their possible protective role against viral infections. Using tissue specimens collected from subjects ranging in age from 5 days to 71 years, we found that starting during the first year of life, CD138⁺ plasma cells (PC) begin accumulating in the thymic perivascular space (PVS) where they constitutively produce IgG without the need for additional stimulation. These, thymic PC secrete almost exclusively IgG1 and IgG3, the two main complement-fixing effector IgG subclasses. Moreover, using antigen-specific ELISpot assays, we demonstrated that thymic PC include a high frequency of cells reactive to common viral proteins. Our study reveals an unrecognized role of the PVS as a functional niche for viral-specific PCs. The PVS is located between the thymic epithelial areas and the circulation. PCs located in this compartment may therefore provide internal protection against pathogen infections and preserve the integrity and function of the organ.

Myocardial rescue with autologous mitochondrial transplantation in a porcine model of ischemia/reperfusion

OBJECTIVE

To demonstrate the clinical efficacy of autologous mitochondrial transplantation in preparation for translation to human application using an in vivo swine model.

METHODS

A left mini-thoracotomy was performed on Yorkshire pigs. The pectoralis major was dissected, and skeletal muscle tissue was removed and used for the isolation of autologous mitochondria. The heart was subjected to regional ischemia (RI) by temporarily snaring the circumflex artery. After 24 minutes of RI, hearts received 8 × 0.1 mL injections of vehicle (vehicle-only group; n = 6) or vehicle containing mitochondria (mitochondria group; n = 6) into the area at risk (AAR), and the snare was released. The thoracotomy was closed, and the pigs were allowed to recover for 4 weeks.

RESULTS

Levels of creatine kinase-MB isoenzyme and cardiac troponin I were significantly increased (P = .006) in the vehicle-only group compared with the mitochondria group. Immune, inflammatory, and cytokine activation markers showed no significant difference between groups. There was no significant between-group difference in the AAR (P = .48), but infarct size was significantly greater in the vehicle group (P = .004). Echocardiography showed no significant differences in global function. Histochemistry and transmission electron microscopy revealed damaged heart tissue in the vehicle group that was not apparent in the mitochondria group. T2-weighted magnetic resonance imaging and histology demonstrated that the injected mitochondria were present for 4 weeks.

CONCLUSIONS

Autologous mitochondrial transplantation provides a novel technique to significantly enhance myocardial cell viability following ischemia and reperfusion in the clinically relevant swine model.

Development of a Vascularized Heterotopic Neonatal Rat Heart Transplantation Model

BACKGROUND/PURPOSE

Rodent adult-to-adult heterotopic heart transplantation is a well-established animal model, and the detailed surgical technique with several modifications has been previously described. In immature donor organ transplantation, however, the surgical technique needs to be revised given the smaller size and fragility of the donor graft. Here, we report our surgical technique for heterotopic abdominal (AHTx) and femoral (FHTx) neonatal rat heart transplantation based on an experience of over 300 cases.

METHODS

Heterotopic heart transplantation was conducted in syngeneic Lewis rats. Neonatal rats (postnatal day 2-4) served as donors. AHTx was performed by utilizing the conventional adult-to-adult transplant method with specific modifications for optimal aortotomy and venous anastomosis. In the FHTx, the donor heart was vascularized by connecting the donor's aorta and pulmonary artery to the recipient's right femoral artery and vein, respectively, in an end-to-end manner. A specifically fashioned butterfly-shaped rubber sheet was used to align the target vessels properly. The transplanted graft was visually assessed for its viability and was accepted as a technical success when the viability met specific criteria. Successfully transplanted grafts were subject to further postoperative evaluation. Forty cases (AHTx and FHTx; n = 20 each) were compared regarding perioperative parameters and outcomes.

RESULTS

Both models were technically feasible (success rate: AHTx 75% vs. FHTx 70%) by refining the conventional heterotopic transplant technique. Injury to the fragile donor aorta and congestion of the graft due to suboptimal venous connection were predominant causes of failure, leading to refractory bleeding and poor graft viability. Although the FHTx required significantly longer operation time and graft ischemic time, the in situ graft viabilities were comparable. The FHTx provided better postoperative monitoring as it enabled daily graft palpation and better echocardiographic visualization.

CONCLUSIONS

We describe detailed surgical techniques for AHTx and FHTx while addressing neonatal donor-specific issues. Following our recommendations potentially reduces the learning curve to achieve reliable and reproducible results with these challenging animal models.

Cellular and Molecular Mechanisms of Low Cardiac Output Syndrome after Pediatric Cardiac Surgery

Several cellular and molecular mechanisms have been implicated in the development of myocardial dysfunction and low cardiac output in pediatric patients undergoing heart surgery. Ischemia- reperfusion injury with alterations in calcium homeostasis as well as mitochondrial function has been strongly related to myocyte damage and heart failure in this population. In this article, we will review the main mechanisms of postoperative cardiac dysfunction at cellular and molecular levels and the subsequent protective strategies. In addition, we will describe cellular features of the neonatal or immature myocardium and will suggest possible protective management strategies. This article addresses the first of eight topics comprising the special issue entitled "Pharmacologic strategies with afterload reduction in low cardiac output syndrome after pediatric cardiac surgery".

Surgical reconstruction of semilunar valves in the growing child: Should we mimic the venous valve? A simulation study

OBJECTIVES

Neither heart valve repair methods nor current prostheses can accommodate patient growth. Normal aortic and pulmonary valves have 3 leaflets, and the goal of valve repair and replacement is typically to restore normal 3-leaflet morphology. However, mammalian venous valves have bileaflet morphology and open and close effectively over a wide range of vessel sizes. We propose that they might serve as a model for pediatric heart valve reconstruction and replacement valve design. We explore this concept using computer simulation.

METHODS

We use a finite element method to simulate the ability of a reconstructed cardiac semilunar valve to close competently in a growing vessel, comparing a 3-leaflet design with a 2-leaflet design that mimics a venous valve. Three venous valve designs were simulated to begin to explore the parameter space.

RESULTS

Simulations show that for an initial vessel diameter of 12 mm, the venous valve design remains competent as the vessel grows to 20 mm (67%), whereas the normal semilunar design remains competent only to 13 mm (8%). Simulations also suggested that systolic function, estimated as effective orifice area, was not detrimentally affected by the venous valve design, with all 3 venous valve designs exhibiting greater effective orifice area than the semilunar valve design at a given level of vessel growth.

CONCLUSIONS

Morphologic features of the venous valve design make it well suited for competent closure over a wide range of vessel sizes, suggesting its use as a model for semilunar valve reconstruction in the growing child.

Neonatal Mitral Valve Repair in Biventricular Repair, Single Ventricle Palliation, and Secondary Left Ventricular Recruitment: Indications, Techniques, and Mid-Term Outcomes

Objectives

Although mitral valve repair is rarely required in neonates, this population is considered to be at high risk for adverse outcomes. The aim of this study was to review the indications for surgery, mechanisms, repair techniques, and mid-term outcomes of neonatal mitral valve repair.

Methods

The demographic, procedural, and outcome data were obtained for all neonates who underwent mitral valve repair from 2005 to 2012. The primary endpoints included mortality, transplantation, and mitral valve reoperation.

Results

Twenty patients were included during the study period. Median age at operation was 11 days (range: 3–25). Eleven patients (55%) presented with mitral stenosis, three had regurgitation (15%), and six had mixed mitral disease (30%). Nineteen of 20 patients had mild or less regurgitation on immediate postoperative imaging. During a median follow-up of 5 months (1 month–4.8 years), six patients died at a median of 33 months (7–41 months) from repair and one patient required orthotopic heart transplantation. Six patients required mitral valve reoperation, five for mitral valve re-repair, and one for mitral valve replacement. Freedom from death, transplantation, or mitral valve replacement was 84.2 ± 8.4% at 1 month, 71.3 ± 11% at 6 months, 64.1 ± 12% at 1 year, and 51.3 ± 15% at 2 years and was worse for patients presenting with mitral regurgitation compared to stenosis or mixed mitral valve disease.

Conclusion

Although mitral valve repair can be performed with acceptable immediate postoperative result, this procedure carries a high burden of late death and mitral valve reoperations.

Mechanical stress is associated with right ventricular response to pulmonary valve replacement in patients with repaired tetralogy of Fallot

OBJECTIVE

Patients with repaired tetralogy of Fallot account for a substantial proportion of cases with late-onset right ventricular failure. The current surgical approach, which includes pulmonary valve replacement/insertion, has yielded mixed results. Therefore, it may be clinically useful to identify parameters that can be used to predict right ventricular function response to pulmonary valve replacement.

METHODS

Cardiac magnetic resonance data before and 6 months after pulmonary valve replacement were obtained from 16 patients with repaired tetralogy of Fallot (8 male, 8 female; median age, 42.75 years). Right ventricular ejection fraction change from pre- to postpulmonary valve replacement was used as the outcome. The patients were divided into group 1 (n = 8, better outcome) and group 2 (n = 8, worst outcome). Cardiac magnetic resonance-based patient-specific computational right ventricular/left ventricular models were constructed, and right ventricular mechanical stress and strain, wall thickness, curvature, and volumes were obtained for analysis.

RESULTS

Our results indicated that right ventricular wall stress was the best single predictor for postpulmonary valve replacement outcome with an area under the receiver operating characteristic curve of 0.819. Mean values of stress, strain, wall thickness, and longitudinal curvature differed significantly between the 2 groups with right ventricular wall stress showing the largest difference. Mean right ventricular stress in group 2 was 103% higher than in group 1.

CONCLUSIONS

Computational modeling and right ventricular stress may be used as tools to identify right ventricular function response to pulmonary valve replacement. Large-scale clinical studies are needed to validate these preliminary findings.