Age-dependent and hypoxia-related differences in myocardial protection during pediatric open heart surgery

Connecting Transcriptomics with Computational Modeling to Reveal Developmental Adaptations in the Human Pediatric Myocardium

Background

Nearly 1% or 1.3 million babies are born with congenital heart disease (CHD) globally each year - many of whom will require palliative or corrective heart surgery within the first few years of life. A detailed understanding of cardiac maturation can help to expand our knowledge on cardiac diseases that develop during gestation, identify age-appropriate cardiovascular drug therapies, and inform clinical care decisions related to surgical repair, myocardial preservation, or postoperative management. Yet, to date, our knowledge of the temporal changes that cardiomyocytes undergo during postnatal development is largely limited to animal models.

Methods

Right atrial tissue samples were collected from n=117 neonatal, infant, and pediatric patients undergoing correct surgery due to (acyanotic) CHD. Patients were stratified into five age groups: neonate (0-30 days), infant (31-364 days), toddler to preschool (1-5 years), school age (6-11 years), and adolescent to young adults (12-32 years). We measured age-dependent adaptations in cardiac gene expression, and used computational modeling to simulate action potential and calcium transients.

Results

Enrichment of differentially expressed genes (DEG) was explored, revealing age-dependent changes in several key biological processes (cell cycle, cell division, mitosis), cardiac ion channels, and calcium handling genes. Gene-associated changes in ionic currents exhibited both linear trends and sudden shifts across developmental stages, with changes in calcium handling ( I NCX ) and repolarization ( I K1 ) most strongly associated with an age-dependent decrease in the action potential plateau potential and increase in triangulation, respectively. We also note a shift in repolarization reserve, with lower I Kr expression in younger patients, a finding likely tied to the increased amplitude of I Ks triggered by elevated sympathetic activation in pediatric patients.

Conclusion

This study provides valuable insights into age-dependent changes in human cardiac gene expression and electrophysiology among patients with CHD, shedding light on molecular mechanisms underlying cardiac development and function across different developmental stages.

Bilateral remote ischemic conditioning in children: A two-center, double-blind, randomized controlled trial in young children undergoing cardiac surgery

Objective

The study objective was to determine whether adequately delivered bilateral remote ischemic preconditioning is cardioprotective in young children undergoing surgery for 2 common congenital heart defects with or without cyanosis.

Methods

We performed a prospective, double-blind, randomized controlled trial at 2 centers in the United Kingdom. Children aged 3 to 36 months undergoing tetralogy of Fallot repair or ventricular septal defect closure were randomized 1:1 to receive bilateral preconditioning or sham intervention. Participants were followed up until hospital discharge or 30 days. The primary outcome was area under the curve for high-sensitivity troponin-T in the first 24 hours after surgery, analyzed by intention-to-treat. Right atrial biopsies were obtained in selected participants.

Results

Between October 2016 and December 2020, 120 eligible children were randomized to receive bilateral preconditioning (n = 60) or sham intervention (n = 60). The primary outcome, area under the curve for high-sensitivity troponin-T, was higher in the preconditioning group (mean: 70.0 ± 50.9 μg/L/h, n = 56) than in controls (mean: 55.6 ± 30.1 μg/L/h, n = 58) (mean difference, 13.2 μg/L/h; 95% CI, 0.5-25.8; P = .04). Subgroup analyses did not show a differential treatment effect by oxygen saturations (pinteraction = .25), but there was evidence of a differential effect by underlying defect (pinteraction = .04). Secondary outcomes and myocardial metabolism, quantified in atrial biopsies, were not different between randomized groups.

Conclusions

Bilateral remote ischemic preconditioning does not attenuate myocardial injury in children undergoing surgical repair for congenital heart defects, and there was evidence of potential harm in unstented tetralogy of Fallot. The routine use of remote ischemic preconditioning cannot be recommended for myocardial protection during pediatric cardiac surgery.

Myocardial protection in paediatric cardiac surgery: building an evidence-based strategy

Cardioplegia is fundamental to the surgical repair of congenital heart defects by protecting the heart against ischaemia/reperfusion injury, characterised by low cardiac output and troponin release in the early postoperative period. The immature myocardium exhibits structural, physiological and metabolic differences from the adult heart, with a greater sensitivity to calcium overload-mediated injury during reperfusion. Del Nido cardioplegia was designed specifically to protect the immature heart, is widely used in North America and may provide better myocardial protection in children; however, it has not been commercially available in the UK, where most centres use St Thomas' blood cardioplegia. There are no phase 3 clinical trials in children to support one solution over another and this lack of evidence, combined with variations in practice, suggests the presence of clinical equipoise. The best cardioplegia solution for use in children, and the impact of age and other clinical factors remain unknown. In this Hunterian lecture, I propose an evidence-based strategy to improve myocardial protection during cardiac surgery in children through: (1) conducting multicentre clinical trials of established techniques; (2) improving our knowledge of ischaemia/reperfusion injury in the setting of cardioplegic arrest; (3) applying this to drive innovation, moving beyond current cardioplegia solutions; (4) empowering personalised medicine, through combining clinical and genomic data, including ethnic diversity; and (5) understanding the impact of cardioplegic arrest on the late outcomes that matter to patients and their families.

Adapting to a new environment: postnatal maturation of the human cardiomyocyte

The postnatal mammalian heart undergoes remarkable developmental changes, which are stimulated by the transition from the intrauterine to extrauterine environment. With birth, increased oxygen levels promote metabolic, structural and biophysical maturation of cardiomyocytes, resulting in mature muscle with increased efficiency, contractility and electrical conduction. In this Topical Review article, we highlight key studies that inform our current understanding of human cardiomyocyte maturation. Collectively, these studies suggest that human atrial and ventricular myocytes evolve quickly within the first year but might not reach a fully mature adult phenotype until nearly the first decade of life. However, it is important to note that fetal, neonatal and paediatric cardiac physiology studies are hindered by a number of limitations, including the scarcity of human tissue, small sample size and a heavy reliance on diseased tissue samples, often without age-matched healthy controls. Future developmental studies are warranted to expand our understanding of normal cardiac physiology/pathophysiology and inform age-appropriate treatment strategies for cardiac disease.

The effect of cardioplegic supplementation with sildenafil on cardiac energetics in a piglet model of cardiopulmonary bypass and cardioplegic arrest with warm or cold cardioplegia

Cardioplegic cardioprotection strategies used during paediatric open-heart surgery remain suboptimal. Sildenafil, a phosphodiesterase 5 (PDE-5) inhibitor, has been shown to be cardioprotective against ischemia/reperfusion injury in a variety of experimental models and this study therefore tested the efficacy of supplementation of cardioplegia with sildenafil in a piglet model of cardiopulmonary bypass and arrest, using both cold and warm cardioplegia protocols. Piglets were anaesthetized and placed on coronary pulmonary bypass (CPB), the aorta cross-clamped and the hearts arrested for 60 min with cardioplegia with or without sildenafil (10 nM). Twenty minutes after removal of cross clamp (reperfusion), attempts were made to wean the pigs from CPB. Termination was carried out after 60 min reperfusion. Throughout the protocol blood and left ventricular tissue samples were taken for analysis of selected metabolites (using HPLC) and troponin I. In both the cold and warm cardioplegia protocols there was evidence that sildenafil supplementation resulted in faster recovery of ATP levels, improved energy charge (a measure of metabolic flux) and altered release of hypoxanthine and inosine, two purine catabolites. There was no effect on troponin release within the studied short timeframe. In conclusion, sildenafil supplementation of cardioplegia resulted in improved cardiac energetics in a translational animal model of paediatric CPB surgery.

Early postnatal metabolic profile in neonates with critical CHDs

BACKGROUND

Cyanotic CHD is a life-threatening condition that presents with low oxygen saturation in the newborn period. Hypoxemia might cause alterations in the metabolic pathways. In the present study, we aimed to evaluate the early postnatal amino acid and carnitine/acylcarnitine profiles of newborn infants with cyanotic CHD.

METHODS

A single centre case-control study was conducted. Twenty-seven patients with cyanotic CHD and 54 healthy newborn controls were enrolled. As part of the neonatal screening programme, results of amino acid and carnitine/acylcarnitine were recorded and compared between groups.

RESULTS

Twenty-seven neonates with cyanotic CHD and 54 healthy newborns as controls were enrolled in the study. Cyanotic CHD neonates had higher levels of alanine, phenylalanine, leucine/isoleucine, citrulline, ornithine, C5, C5-OH; but lower levels of C3, C10, C12, C14, C14:1, C16, C16.1, C18, C5-DC, C6-DC, C16-OH, C16:1-OH when compared with the healthy controls.

CONCLUSION

This study showed that there are differences between patients with cyanotic CHD and healthy controls in terms of postnatal amino acid and carnitine/acylcarnitine profiles.

Cardioplegia in Open Heart Surgery: Age Matters

INTRODUCTION

Cardioplegia is a pharmacological approach essential for the protection of the heart from ischemia-reperfusion (I-R) injury. Over the years, numerous cardioplegic solutions have been developed, with each cardioplegic approach having its advantages and disadvantages. Cardioplegic solutions can be divided into crystalloid and blood cardioplegic solutions, and an experienced surgeon chooses the type of solution based on the individual needs of patients in order to provide optimal heart protection. Importantly, the pediatric immature myocardium is structurally, physiologically, and metabolically different from the adult heart, and consequently its needs to achieve cardioplegic arrest strongly differ. Therefore, the present review aimed to provide a summary of the cardioplegic solutions available to pediatric patients with a special focus on emphasizing differences in heart injury after various cardioplegic solutions, the dosing strategies, and regimens.

MATERIAL AND METHODS

The PubMed database was searched using the terms cardioplegia, I-R, and pediatric population, and studies that investigated the influence of cardioplegic strategies on markers of cardiac muscle damage were further analyzed in this review.

CONCLUSIONS

A large body of evidence suggested more prominent benefits achieved with blood compared to those with crystalloid cardioplegia in pediatric myocardium preservation. However, standardized and uniform protocols have not been established so far, and an experienced surgeon chooses the type of cardioplegia solution based on the individual needs of patients, while the severity of myocardial damage strongly depends on the type and duration of the surgical procedure, overall patient condition, and presence of comorbidities, etc.

Comparative effects of different types of cardioplegia in cardiac surgery: A network meta-analysis

Objective

To compare the outcomes of four types of cardioplegia during cardiac surgery: del Nido (DN), blood cardioplegia (BC), histidine-tryptophan-ketoglutarate (HTK) and St. Thomas.

Methods

Randomized controlled trials (RCTs) and observational cohort studies from 2005 to 2021 were identified in PubMed, Embase, and Cochrane databases. Data were extracted for the primary endpoint of perioperative mortality as well as the following secondary endpoints: atrial fibrillation, renal failure, stroke, use of an intra-aortic balloon pump, re-exploration, intensive care unit stay and hospital stay. A network meta-analysis comparing all four types of cardioplegia was performed, as well as direct meta-analysis comparing pairs of cardioplegia types.

Results

Data were extracted from 18 RCTs and 49 observational cohort studies involving 18,191 adult patients (55 studies) and 1,634 children (12 studies). Among adult patients, risk of mortality was significantly higher for HTK (1.89, 95% CI 1.10, 3.52) and BC (RR 1.73, 95% CI 1.22, 2.79) than for DN. Risk of atrial fibrillation was significantly higher for BC (RR 1.41, 95% CI 1.09, 1.86) and DN (RR 1.51, 95% CI 1.15, 2.03) than for HTK. Among pediatric patients, no significant differences in endpoints were observed among the four types of cardioplegia.

Conclusions

This network meta-analysis suggests that among adult patients undergoing cardiac surgery, DN may be associated with lower perioperative mortality than HTK or BC, while risk of atrial fibrillation may be lower with HTK than with BC or DN.

Pathology-related changes in cardiac energy metabolites, inflammatory response and reperfusion injury following cardioplegic arrest in patients undergoing open-heart surgery

Introduction

Changes in cardiac metabolites in adult patients undergoing open-heart surgery using ischemic cardioplegic arrest have largely been reported for non-ventricular tissue or diseased left ventricular tissue, with few studies attempting to assess such changes in both ventricular chambers. It is also unknown whether such changes are altered in different pathologies or linked to the degree of reperfusion injury and inflammatory response. The aim of the present work was to address these issues by monitoring myocardial metabolites in both ventricles and to establish whether these changes are linked to reperfusion injury and inflammatory/stress response in patients undergoing surgery using cold blood cardioplegia for either coronary artery bypass graft (CABG, n = 25) or aortic valve replacement (AVR, n = 16).

Methods

Ventricular biopsies from both left (LV) and right (RV) ventricles were collected before ischemic cardioplegic arrest and 20 min after reperfusion. The biopsies were processed for measuring selected metabolites (adenine nucleotides, purines, and amino acids) using HPLC. Blood markers of cardiac injury (Troponin I, cTnI), inflammation (IL- 6, IL-8, Il-10, and TNFα, measured using Multiplex) and oxidative stress (Myeloperoxidase, MPO) were measured pre- and up to 72 hours post-operatively.

Results

The CABG group had a significantly shorter ischemic cardioplegic arrest time (38.6 ± 2.3 min) compared to AVR group (63.0 ± 4.9 min, p = 2 x 10-6). Cardiac injury (cTnI release) was similar for both CABG and AVR groups. The inflammatory markers IL-6 and Il-8 were significantly higher in CABG patients compared to AVR patients. Metabolic markers of cardiac ischemic stress were relatively and significantly more altered in the LV of CABG patients. Comparing diabetic and non-diabetic CABG patients shows that only the RV of diabetic patients sustained major ischemic stress during reperfusion and that diabetic patients had a significantly higher inflammatory response.

Discussion

CABG patients sustain relatively more ischemic stress, systemic inflammatory response and similar injury and oxidative stress compared to AVR patients despite having significantly shorter cross-clamp time. The higher inflammatory response in CABG patients appears to be at least partly driven by a higher incidence of diabetes amongst CABG patients. In addition to pathology, the use of cold blood cardioplegic arrest may underlie these differences.

Cardioprotection of Immature Heart by Simultaneous Activation of PKA and Epac: A Role for the Mitochondrial Permeability Transition Pore

Metabolic and ionic changes during ischaemia predispose the heart to the damaging effects of reperfusion. Such changes and the resulting injury differ between immature and adult hearts. Therefore, cardioprotective strategies for adults must be tested in immature hearts. We have recently shown that the simultaneous activation of protein kinase A (PKA) and exchange protein activated by cAMP (Epac) confers marked cardioprotection in adult hearts. The aim of this study is to investigate the efficacy of this intervention in immature hearts and determine whether the mitochondrial permeability transition pore (MPTP) is involved. Isolated perfused Langendorff hearts from both adult and immature rats were exposed to global ischaemia and reperfusion injury (I/R) following control perfusion or perfusion after an equilibration period with activators of PKA and/or Epac. Functional outcome and reperfusion injury were measured and in parallel, mitochondria were isolated following 5 min of reperfusion to determine whether cardioprotective interventions involved changes in MPTP opening behaviour. Perfusion for 5 min preceding ischaemia of injury-matched adult and immature hearts with 5 µM 8-Br (8-Br-cAMP-AM), an activator of both PKA and Epac, led to significant reduction in post-reperfusion CK release and infarct size. Perfusion with this agent also led to a reduction in MPTP opening propensity in both adult and immature hearts. These data show that immature hearts are innately more resistant to I/R injury than adults, and that this is due to a reduced tendency of MPTP opening following reperfusion. Furthermore, simultaneous stimulation of PKA and Epac causes cardioprotection, which is additive to the innate resistance.

A randomized controlled trial comparing controlled reoxygenation and standard cardiopulmonary bypass in paediatric cardiac surgery

OBJECTIVES

Controlled reoxygenation on starting cardiopulmonary bypass (CPB) rather than hyperoxic CPB may confer clinical advantages during surgery for congenital cyanotic heart disease.

METHODS

A single-centre, randomized controlled trial was carried out to compare the effectiveness of controlled reoxygenation (normoxia) versus hyperoxic CPB in children with congenital cyanotic heart disease undergoing open-heart surgery (Oxic-2). The co-primary clinical outcomes were duration of inotropic support, intubation time and postoperative intensive care unit (ICU) and hospital stay. Analysis of the primary outcomes included data from a previous trial (Oxic-1) conducted to the same protocol.

RESULTS

Ninety participants were recruited to Oxic-2 and 79 were recruited to the previous Oxic-1 trial. There were no significant differences between the groups for any of the co-primary outcomes: inotrope duration geometric mean ratio (normoxia/hyperoxic) 0.97, 95% confidence interval (CI) (0.69-1.37), P-value = 0.87; intubation time hazard ratio (HR) 1.03, 95% CI (0.74-1.42), P-value = 0.87; postoperative ICU stay HR 1.14 95% CI (0.77-1.67), P-value = 0.52, hospital stay HR 0.90, 95% CI (0.65-1.25), P-value = 0.53. Lower oxygen levels were successfully achieved during the operative period in the normoxic group. Serum creatinine levels were lower in the normoxic group at day 2, but not on days 1, 3-5. Childhood developmental outcomes were similar. In the year following surgery, 85 serious adverse events were reported (51 normoxic group and 34 hyperoxic group).

CONCLUSIONS

Controlled reoxygenation (normoxic) CPB is safe but with no evidence of a clinical advantage over hyperoxic CPB.

CLINICAL TRIAL REGISTRATION NUMBER

Current Controlled Trials-ISRCTN81773762.

Chronic perinatal hypoxia delays cardiac maturation in a mouse model for cyanotic congenital heart disease

Compared with acyanotic congenital heart disease (CHD), cyanotic CHD has an increased risk of lifelong mortality and morbidity. These adverse outcomes may be attributed to delayed cardiomyocyte maturation, since the transition from a hypoxic fetal milieu to oxygen-rich postnatal environment is disrupted. We established a rodent model to replicate hypoxic myocardial conditions spanning perinatal development, and tested the hypothesis that chronic hypoxia impairs cardiac development. Pregnant mice were housed in hypoxia beginning at embryonic day 16. Pups stayed in hypoxia until postnatal day (P)8 when cardiac development is nearly complete. Global gene expression was quantified at P8 and at P30, after recovering in normoxia. Phenotypic testing included electrocardiogram, echocardiogram, and ex vivo electrophysiology study. Hypoxic P8 animals were 47% smaller than controls with preserved heart size. Gene expression was grossly altered by hypoxia at P8 (1,427 genes affected), but normalized after recovery (P30). Electrocardiograms revealed bradycardia and slowed conduction velocity in hypoxic animals at P8, with noticeable resolution after recovery (P30). Notable differences that persisted after recovery (P30) included a 65% prolongation in ventricular effective refractory period, sinus node dysfunction, 23% reduction in ejection fraction, and 16% reduction in fractional shortening in animals exposed to hypoxia. We investigated the impact of chronic hypoxia on the developing heart. Perinatal hypoxia was associated with changes in gene expression and cardiac function. Persistent changes to the electrophysiological substrate and contractile function warrant further investigation and may contribute to adverse outcomes observed in the cyanotic CHD population.NEW & NOTEWORTHY We utilized a new mouse model of chronic perinatal hypoxia to simulate the hypoxic myocardial conditions present in cyanotic congenital heart disease. Hypoxia caused numerous abnormalities in cardiomyocyte gene expression, the electrophysiologic substrate of the heart, and contractile function. Taken together, alterations observed in the neonatal period suggest delayed cardiac development immediately following hypoxia.

Intermittent antegrade warm-blood versus cold-blood cardioplegia in children undergoing open heart surgery: a protocol for a randomised controlled study (Thermic-3)

INTRODUCTION

Surgical repair of congenital heart defects often requires the use of cardiopulmonary bypass (CPB) and cardioplegic arrest. Cardioplegia is used during cardiac surgery requiring CPB to keep the heart still and to reduce myocardial damage as a result of ischaemia-reperfusion injury. Cold cardioplegia is the prevalent method of myocardial protection in paediatric patients; however, warm cardioplegia is used as part of usual care throughout the UK in adults. We aim to provide evidence to support the use of warm versus cold blood cardioplegia on clinical and biochemical outcomes during and after paediatric congenital heart surgery.

METHODS AND ANALYSIS

We are conducting a single-centre randomised controlled trial in paediatric patients undergoing operations requiring CPB and cardioplegic arrest at the Bristol Royal Hospital for Children. We will randomise participants in a 1:1 ratio to receive either 'cold-blood cardioplegia' or 'warm-blood cardioplegia'. The primary outcome will be the difference between groups with respect to Troponin T levels over the first 48 postoperative hours. Secondary outcomes will include measures of cardiac function; renal function; cerebral function; arrythmias during and postoperative hours; postoperative blood loss in the first 12 hours; vasoactive-inotrope score in the first 48 hours; intubation time; chest and wound infections; time from return from theatre until fit for discharge; length of postoperative hospital stay; all-cause mortality to 3 months postoperative; myocardial injury at the molecular and cellular level.

ETHICS AND DISSEMINATION

This trial has been approved by the London - Central Research Ethics Committee. Findings will be disseminated to the academic community through peer-reviewed publications and presentation at national and international meetings. Patients will be informed of the results through patient organisations and newsletters to participants.

TRIAL REGISTRATION NUMBER

ISRCTN13467772; Pre-results.

Bilateral Remote Ischaemic Conditioning in Children (BRICC) trial: protocol for a two-centre, double-blind, randomised controlled trial in young children undergoing cardiac surgery

INTRODUCTION

Myocardial protection against ischaemic-reperfusion injury is a key determinant of heart function and outcome following cardiac surgery in children. However, with current strategies, myocardial injury occurs routinely following aortic cross-clamping, as demonstrated by the ubiquitous rise in circulating troponin. Remote ischaemic preconditioning, the application of brief, non-lethal cycles of ischaemia and reperfusion to a distant organ or tissue, is a simple, low-risk and readily available technique which may improve myocardial protection. The Bilateral Remote Ischaemic Conditioning in Children (BRICC) trial will assess whether remote ischaemic preconditioning, applied to both lower limbs immediately prior to surgery, reduces myocardial injury in cyanotic and acyanotic young children.

METHODS AND ANALYSIS

The BRICC trial is a two-centre, double-blind, randomised controlled trial recruiting up to 120 young children (age 3 months to 3 years) undergoing primary repair of tetralogy of Fallot or surgical closure of an isolated ventricular septal defect. Participants will be randomised in a 1:1 ratio to either bilateral remote ischaemic preconditioning (3×5 min cycles) or sham immediately prior to surgery, with follow-up until discharge from hospital or 30 days, whichever is sooner. The primary outcome is reduction in area under the time-concentration curve for high-sensitivity (hs) troponin-T release in the first 24 hours after aortic cross-clamp release. Secondary outcome measures include peak hs-troponin-T, vasoactive inotrope score, arterial lactate and central venous oxygen saturations in the first 12 hours, and lengths of stay in the paediatric intensive care unit and the hospital.

ETHICS AND DISSEMINATION

The trial was approved by the West Midlands-Solihull National Health Service Research Ethics Committee (16/WM/0309) on 5 August 2016. Findings will be disseminated to the academic community through peer-reviewed publications and presentation at national and international meetings. Parents will be informed of the results through a newsletter in conjunction with a local charity.

TRIAL REGISTRATION NUMBER

ISRCTN12923441.

Normoxic management of cardiopulmonary bypass reduces myocardial oxidative stress in adult patients undergoing coronary artery bypass graft surgery

INTRODUCTION

We aimed to investigate whether normoxic cardiopulmonary bypass would limit myocardial oxidative stress in adults undergoing coronary artery bypass grafting.

METHODS

Patients scheduled to undergo elective isolated on-pump coronary artery bypass grafting were randomized to normoxia and hyperoxia groups. The normoxia group received 35% oxygen during anesthetic induction, 35% during hypothermic bypass, and 45% during rewarming. The hyperoxia group received 70%, 50%, and 70% oxygen, respectively. Coronary sinus blood samples were taken prior to initiation of cardiopulmonary bypass and after reperfusion for myocardial total oxidant and antioxidant status measurements. The primary endpoint was myocardial total oxidant status. Secondary endpoints were myocardial total antioxidant status and length of intensive care unit and hospital stay.

RESULTS

Forty-eight patients were included. Twenty-two received normoxic management. Mean ± standard deviation of age was 58 ± 9.07 years. Groups were balanced in terms of demographics, risk factors, and operative data. Myocardial total oxidant status was significantly lower in the normoxia group following reperfusion (p = 0.03). There was no statistically significant difference regarding myocardial total antioxidant status and length of intensive care unit and hospital stay (p = 0.08, p = 0.82, and p = 0.54, respectively).

CONCLUSIONS

Normoxic cardiopulmonary bypass is associated with reduced myocardial oxidative stress compared to hyperoxic cardiopulmonary bypass in adult coronary artery bypass patients.

MicroRNAs as potential biomarkers in congenital heart surgery

OBJECTIVE

Pediatric congenital heart surgery (CHS) involves intracardiac, valvular, and vascular repairs. Accurate tools to aid short-term outcome prediction in pediatric CHS are lacking. Clinical scores, such as the vasoactive-inotrope score and ventilation index, are used to define outcome in clinical studies. MicroRNA-1-3p (miR-1) is expressed by both cardiomyocytes and vascular cells and is regulated by hypoxia. In adult patients, miR-1 increases in the circulation after open-heart cardiac surgery, suggesting its potential as a clinical biomarker. Thus, we investigated whether perioperative circulating miR-1 measurements can help predict post-CHS short-term outcomes in pediatric patients.

METHODS

Plasma miR-1 was retrospectively measured in a cohort of 199 consecutive pediatric CHS patients (median age 1.2 years). Samples were taken before surgery and at the end of the operation. Plasma miR-1 concentration was measured by reverse transcription-quantitative polymerase chain reaction and expressed as miR-1 copies/μL and as relative expression to spiked-in exogenous cel-miR-39.

RESULTS

Baseline plasma miR-1 did not vary across different diagnoses, increased during surgery (204-fold median relative increase, P < .001), and was associated with aortic crossclamp duration postoperatively (P < .001). Importantly, miR-1 levels at the end of the operation positively correlated with intensive care stay (P < .001), early severe cardiovascular events (P = .01), and with high vasoactive-inotrope score (P = .001) and ventilation index (P < .001), suggesting that miR-1 could accelerate the identification of patients with cardiopulmonary bypass-related ischemic complications, requiring more intensive support.

CONCLUSIONS

Our study suggests miR-1 as a novel potential circulating biomarker to predict early postoperative outcome and inform clinical management in pediatric heart surgery.

Myocardial protection in the arterial switch operation: Custodiol versus cold blood cardioplegia

OBJECTIVES

The optimal myocardial protective solution in the neonatal arterial switch operation remains controversial. The aim of this study was to demonstrate that Bretschneider's histidine-tryptophan-ketoglutarate crystalloid solution (Custodiol) offers protection at least similar to that of cold blood cardioplegia.

METHODS

Patients who underwent the neonatal arterial switch operation with Custodiol between January 2016 and December 2018 (n = 23) were compared with an historical cohort from August 2010 to December 2015 in which cold blood cardioplegia was used (n = 41). A linear mixed-effect model for repeated measures was performed to test the recovery of myocardial function based on inotropic and vasoactive inotropic scores, cardiac enzyme release and left ventricular ejection fraction.

RESULTS

Patients in the cold blood cardioplegia group had higher inotropic scores in the first 24 h (0 h, P = 0.001 and 24 h, P = 0.006) and higher vasoactive inotropic scores in the first 72 h (0 h, 24 h and 48 h, P < 0.001; 72 h, P = 0.012). Cardiac troponin-I concentrations were higher in the cold blood cardioplegia group at postoperative hours 1-72 (1 h, 6 h, 12 h and 24 h, P < 0.001; 48 h, P = 0.001 and 72 h, P = 0.003). Creatinine-kinase-MB concentrations were higher in the cold blood cardioplegia group at postoperative hours 1-24 (1 h, 6 h and 12 h, P < 0.001; 24 h, P = 0.042). The left ventricular ejection fraction was higher in the Custodiol group just after the operation (P = 0.005), at 24 h (P = 0.001) and on the first day without inotropic support (P = 0.011).

CONCLUSIONS

Neonatal myocardium protected with Custodiol during the arterial switch operation presented optimal ventricular function recovery with less inotropic support and less myocardial damage compared with cold blood cardioplegia.

Single-Shot Cold Histidine-Tryptophan-Ketoglutarate Cardioplegia for Long Aortic Cross-Clamping Durations in Neonates

OBJECTIVE

More than 30% of European pediatric cardiac surgery centers use single-dose cold histidine-tryptophan-ketoglutarate cardioplegia (Custodiol; Dr Franz Köhler Chemie GmbH, Bensheim, Germany). In neonates with transposition of the great arteries, arterial switch surgery (ASO) implies aortic division, and it is unknown whether repeated ostial cannulation causes intimal insult and affects long-term results, and therefore, single-dose Custodiol is appealing. The present study investigated the association among myocardial no-flow duration, postoperative troponins, and postoperative outcomes in neonates undergoing ASO with Custodiol cardioplegia.

DESIGN

Retrospective analysis of the association among myocardial no-flow duration, postoperative troponin release (concentration magnitude × measurement duration within 48 h), and outcomes using stratification according to coronary anatomy and attending surgeon.

SETTING

Single-institutional, tertiary pediatric cardiac surgery unit of a university hospital.

PARTICIPANTS

The study comprised 101 neonates undergoing ASO.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The mean age of patients was 6.1 ± 5.4 days, the cardiopulmonary bypass duration was 108.7 ± 54.1 minutes, the temperature during cross-clamping was 31.1°C ± 1.7°C, the duration of mechanical ventilation was 4 (3-6) days, the length of intensive care unit stay was 7 (5-8) days, delayed sternal closure occurred in 32 (31.7%) patients, and no patients died. The myocardial no-flow duration averaged 62.3 ± 14.6 minutes and was linked with both troponin release (p = 0.04) and low cardiac output syndrome, as assessed by the requirement for delayed sternal closure (p = 0.03), regardless of cardiopulmonary bypass duration and temperature. Eighty-two percent of the patients with myocardial no-flow duration >74 minutes necessitated delayed sternal closure.

CONCLUSIONS

Single-dose Custodiol may be inadequate for prolonged cross-clamping durations without myocardial perfusion in neonates.

Cardioplegia in paediatric cardiac surgery: a systematic review of randomized controlled trials

OBJECTIVES

Cardioplegia is the primary method for myocardial protection during cardiac surgery. We conducted a systematic review of randomized controlled trials of cardioplegia in children to evaluate the current evidence base.

METHODS

We searched MEDLINE, CENTRAL and LILACS and manually screened retrieved references and systematic reviews to identify all randomized controlled trials comparing cardioplegia solutions or additives in children undergoing cardiac surgery published in any language; secondary publications and those reporting inseparable adult data were excluded. Two or more reviewers independently screened studies for eligibility and extracted data; the Cochrane Risk of Bias tool was used to assess for potential biases.

RESULTS

We identified 26 trials randomizing 1596 children undergoing surgery; all were single-centre, Phase II trials, recruiting few patients (median 48, interquartile range 30-99). The most frequent comparison was blood versus crystalloid in 10 (38.5%) trials, and the most common end points were biomarkers of myocardial injury (17, 65.4%), inotrope requirements (15, 57.7%) and length of stay in the intensive care unit (11, 42.3%). However, the heterogeneity of patients, interventions and reported outcome measures prohibited meta-analysis. Overall risk of bias was high in 3 (11.5%) trials, unclear in 23 (88.5%) and low in none.

CONCLUSIONS

The current literature on cardioplegia in children contains no late phase trials. The small size, inconsistent use of end points and low quality of reported trials provide a limited evidence base to inform practice. A core outcome set of clinically important, standardized, validated end points for assessing myocardial protection in children should be developed to facilitate the conduct of high-quality, multicentre trials.

PROSPERO registration

CRD42017080205.

Comparative Analysis of Myocardial Protection with HTK Solution and Hypothermic Hyperkalemic Blood Solution in the Correction of Acyanogenic Congenital Cardiopathies - A Randomized Study

OBJECTIVE

The goal of the present study was to compare the myocardial protection obtained with histidine-tryptophan-ketoglutarate (HTK) cardioplegic solution (Custodiol®) and with intermittent hypothermic blood solution.

METHODS

Two homogenous groups of 25 children with acyanotic congenital heart disease who underwent total correction with mean aortic clamping time of 60 minutes were evaluated in this randomized study. Troponin and creatine kinase-MB curves, vasoactive-inotropic score, and left ventricular function were obtained by echocardiogram in each group. The values were correlated and presented through graphs and tables after adequate statistical treatment.

RESULTS

It was observed that values of all the studied variables varied over time, but there was no difference between the groups.

CONCLUSION

We conclude that in patients with acyanotic congenital cardiopathies submitted to total surgical correction, mean aortic clamping time around one hour, and cardiopulmonary bypass with moderate hypothermia, the HTK crystalloid cardioplegic solution offers the same myocardial protection as the cold-blood hyperkalemic cardioplegic solution analyzed, according to the variables considered in our study model.

The Pediatric Cell Atlas: Defining the Growth Phase of Human Development at Single-Cell Resolution

Single-cell gene expression analyses of mammalian tissues have uncovered profound stage-specific molecular regulatory phenomena that have changed the understanding of unique cell types and signaling pathways critical for lineage determination, morphogenesis, and growth. We discuss here the case for a Pediatric Cell Atlas as part of the Human Cell Atlas consortium to provide single-cell profiles and spatial characterization of gene expression across human tissues and organs. Such data will complement adult and developmentally focused HCA projects to provide a rich cytogenomic framework for understanding not only pediatric health and disease but also environmental and genetic impacts across the human lifespan.

Myocardial protection and clinical outcomes in Tetralogy of Fallot patients undergoing intracardiac repair: a randomized study of two cardioplegic techniques

Background:

Myocardial protection in Tetralogy of Fallot patients undergoing intracardiac repair is suboptimal due to hypertrophied right ventricle. Hypertrophied myocardium is more susceptible to poor myocardial preservation because of inadequate capillary density as compared to the myocytes. There is a capillary to myocyte ratio mismatch. But del Nido Cardioplegia owing to its less viscosity is able to get more evenly distributed under hypothermic cardiopulmonary bypass as opposed to blood Cardioplegia. We hypothesized that the del Nido Cardioplegia technique, would be beneficial in myocardial protection because of its composition and method of delivery, leading into better early and late clinical outcomes in patients undergoing Tetralogy of Fallot repair as compared to blood cardioplegia reconstituted using St Thomas Cardioplegia solution. The objective of the study was to identify a better technique of myocardial preservation in Tetralogy of Fallot patient.

Methods:

In total, 56 Tetralogy of Fallot patients undergoing intracardiac repair under mild hypothermic cardiopulmonary bypass were randomly allocated to receive antegrade Cardioplegia with either standard blood Cardioplegia (Group I) or del Nido Cardioplegia (Group II). Preoperative as well as postoperative data including echocardiographic parameters for right ventricle functions, creatine kinase MB level, inotropic requirement, mechanical ventilation duration, intensive care unit stay and hospital mortality were evaluated.

Results:

Inotropic score in the first 24 hours postoperatively was significantly lower in Group II compared to Group I (13.4 ± 7.2 vs. 21.2 ± 9.6, p = 0.003). Creatine kinase MB level (ng/mL) was comparable between the groups. Echocardiographic parameters for right ventricle functions were also comparable between the groups during early as well as after 3 to 6 months postoperatively.

Conclusion:

Del Nido Cardioplegia is equally efficacious in providing myocardial protection during intracardiac repair under mild hypothermic cardiopulmonary bypass in Tetralogy of Fallot patients as compared to blood Cardioplegia solution with the added benefit of reducing inotropic requirement in first 24 hours postoperative period.

Cardioplegia practice in paediatric cardiac surgery: a UK & Ireland survey

Introduction:

Many techniques are available for cardioplegic arrest in children, but there is a lack of late phase clinical trials to guide practice. We surveyed paediatric cardiac surgeons and perfusionists to establish current practice and willingness to change within a clinical trial.

Methods:

An online survey was sent to all consultant paediatric cardiac surgeons and chief perfusionists in paediatric centres in the UK and Ireland. Information was sought on cardioplegia type, composition, temperature, topical cooling, dosing for induction and maintenance, interval between doses, whether practice changed with patient age or complexity and whether respondents would be willing and able to use different cardioplegia solutions within a randomised trial.

Results:

Responses were obtained from 32 (78.0%) surgeons and 12 (100%) perfusionists. Twenty-seven (84.4%) surgeons use blood cardioplegia in infants, with St. Thomas’ Harefield preparation the most popular (19, 59.4%), used routinely in eight (66.7%) centres. Twenty-two (68.8%) administer at 4-6°C, 18 (56.3%) use topical cooling, 18 (56.3%) give 30 ml/kg induction and 15 ml/kg maintenance, with 23 (71.9%) re-dosing every 20-25 minutes. Thirty (93.8%) surgeons were open to randomising patients in a trial, with del Nido (29, 90.6%) the most popular.

Conclusions:

This survey demonstrates heterogeneity in cardioplegia practice. Whilst most surgeons use blood cardioplegia, there is variation in type, temperature, topical cooling, dosing and intervals. Combined with a lack of evidence from late phase trials, our findings support the presence of clinical equipoise. Surgeons are willing to change practice, suggesting that a pragmatic, multi-centre, randomised, controlled trial of cardioplegia in children is feasible.

Remote ischemic preconditioning triggers changes in autonomic nervous system activity: implications for cardioprotection

Cardioprotective efficacy of remote ischemic preconditioning (RIPC) remains controversial. Experimental studies investigating RIPC have largely monitored cardiovascular changes during index ischemia and reperfusion with little work investigating changes during RIPC application. This work aims to identify cardiovascular changes associated with autonomic nervous system (ANS) activity during RIPC and prior to index ischemia. RIPC was induced in anesthetized male C57/Bl6 mice by four cycles of 5 min of hindlimb ischemia using inflated cuff (200 mmHg) followed by 5 min reperfusion. Electrocardiography (ECG) and microcirculatory blood flow in both hindlimbs were recorded throughout RIPC protocol. Heart rate variability (HRV) analysis was performed using ECG data. Hearts extracted at the end of RIPC protocol were used either for measurement of myocardial metabolites using high‐performance liquid chromatography or for Langendorff perfusion to monitor function and injury during 30 min index ischemia and 2 h reperfusion. Isolated‐perfused hearts from RIPC animals had significantly less infarct size after index ischemia and reperfusion (34 ± 5% vs. 59 ± 7%; mean ± SE P < 0.05). RIPC protocol was associated with increased heart rate measured both in ex vivo and in vivo. Frequency ratio of HRV spectra was altered in RIPC compared to control. RIPC was associated with a standard hyperemic response in the cuffed‐limb but there was a sustained reduction in blood flow in the uncuffed contralateral limb. RIPC hearts (prior to index ischemia) had significantly lower phosphorylation potential and energy charge compared to the control group. In conclusion, RIPC is associated with changes in ANS activity (heart rate, blood flow, HRV) and mild myocardial ischemic stress that would contribute to cardioprotection.

Consecutive Isoproterenol and Adenosine Treatment Confers Marked Protection against Reperfusion Injury in Adult but Not in Immature Heart: A Role for Glycogen

Consecutive treatment of adult rat heart with isoproterenol and adenosine (Iso/Aden), known to consecutively activate PKA/PKC signaling, is cardioprotective against ischemia and reperfusion (I/R). Whether this is cardioprotective in an immature heart is unknown. Langendorff-perfused hearts from adult and immature (60 and 14 days old) male Wistar rats were exposed to 30 min ischemia and 120 min reperfusion, with or without prior perfusion with 5 nM Iso for 3 min followed by 30 μM Aden for 5 min. Changes in hemodynamics (developed pressure and coronary flow) and cardiac injury (Lactate Dehydrogenase (LDH) release and infarct size) were measured. Additional hearts were used to measure glycogen content. Iso induced a similar inotropic response in both age groups. Treatment with Iso/Aden resulted in a significant reduction in time to the onset of ischemic contracture in both age groups whilst time to peak contracture was significantly shorter only in immature hearts. Upon reperfusion, the intervention reduced cardiac injury and functional impairment in adults with no protection of immature heart. Immature hearts have significantly less glycogen content compared to adult. This work shows that Iso/Aden perfusion confers protection in an adult heart but not in an immature heart. It is likely that metabolic differences including glycogen content contribute to this difference.

Changes in contractile protein expression are linked to ventricular stiffness in infants with pulmonary hypertension or right ventricular hypertrophy due to congenital heart disease

Background

The right ventricle (RV) is not designed to sustain high pressure leading to failure. There are no current medications to help RV contraction, so further information is required on adaption of the RV to such hypertension.

Methods

The Right Ventricle in Children (RVENCH) study assessed infants with congenital heart disease undergoing cardiac surgery with hypertensive RV. Clinical and echocardiographic data were recorded, and samples of RV were taken from matched infants, analysed for proteomics and compared between pathologies and with clinical and echocardiographic outcome data.

Results

Those with tetralogy of Fallot (TOF) were significantly more cyanosed than those with ventricular septal defect (median oxygen saturation 83% vs 98%, P=0.0038), had significantly stiffer RV (tricuspid E wave/A wave ratio 1.95 vs 0.84, P=0.009) and had most had restrictive physiology. Gene ontology in TOF, with enrichment analysis, demonstrated significant increase in proteins of contractile mechanisms and those of calmodulin, actin binding and others associated with contractility than inventricular septal defect. Structural proteins were also found to be higher in association with sarcomeric function: Z-disc, M-Band and thin-filament proteins. Remaining proteins associated with actin binding, calcium signalling and myocyte cytoskeletal development. Phosphopeptide enrichment led to higher levels of calcium signalling proteins in TOF.

Conclusion

This is the first demonstration that those with an RV, which is stiff and hypertensive in TOF, have a range of altered proteins, often in calcium signalling pathways. Information about these alterations might guide treatment options both in terms of individualised therapy or inotropic support for the Right ventricle when hypertensive due to pulmoanry hypertension or congenital heart disease.

Long-Standing Cyanosis in Congenital Heart Disease Does not Cause Diffuse Myocardial Fibrosis

The assumption of the presence of diffuse myocardial fibrosis in long-standing cyanotic congenital heart disease (CHD) inspired us to noninvasively determine the myocardial extracellular volume (ECV) using contrast CMR. T1 maps were measured pre and 10 min after the injection of 0.15 mmol/kg of gadolinium in 25 subjects. Seven patients with long-standing cyanotic CHD and no previous cardiac surgery (aged 16-53 years and oxygen saturations of 69-90%), nine normal subjects (aged 14-49 years), and nine patients with previously cyanotic CHD, who had been corrected by open heart surgery (aged 2 months-58 years, mean 9 years). Late gadolinium enhancement was performed to exclude scar areas. The T1 values were measured in the interventricular septum and in the left lateral or inferior ventricular wall, such that same areas were assessed in every patient in the pre- and post-contrast T1 scan. ECV was calculated according to ΔR1myocardium/ΔR1blood * (1 - hematocrit). Cyanotic patients had significantly lower ECV percentage than the previous cyanotic patients (septum: 22 ± 2.7% vs 35 ± 4.6%, p = 0.002; LV wall: 22 ± 2.2% vs 30 ± 3.7%, p = 0.01, respectively). No significant differences were found between cyanotic patients and normal controls (septum: 22 ± 2.7% vs 24 ± 1.4%, p = 0.44; LV wall: 22 ± 2.2% vs 24 ± 2%, p = 0.57, respectively). Long-standing cyanosis in CHD without cardiac surgery does not cause diffuse myocardial fibrosis or expansion of the myocardial ECV.

Blood Versus Crystalloid Cardioplegia in Pediatric Cardiac Surgery: A Systematic Review and Meta-analysis

The benefit of blood cardioplegia (BCP) compared to crystalloid cardioplegia (CCP) is still debatable. Our aim was to systematically review and synthesize all available evidence on the use of BCP and CCP to assess if any modality provides superior outcomes in pediatric cardiac surgery. A systematic literature search of the PubMed and Cochrane databases was performed with respect to the PRISMA statement (end-of-search date: January 30th, 2017). We extracted data on study design, demographics, cardioplegia regimens, and perioperative outcomes as well as relevant biochemical markers, namely cardiac troponin I (cTnI), lactate, and ATP levels at baseline, after reperfusion and postoperatively at 1, 4, 12, and 24 h as applicable. Data were appropriately pooled using random and mixed effects models. Our systematic review includes 56 studies reporting on a total of 7711 pediatric patients. A meta-analysis of the 10 eligible studies directly comparing BCP (n = 416) to CCP (n = 281) was also performed. There was no significant difference between the two groups with regard to cTnI and Lac at any measured time point, ATP levels after reperfusion, length of intensive care unit stay (WMD: -0.08, 95% CI -1.52 to 1.36), length of hospital stay (WMD: 0.13, 95% CI -0.85 to 1.12), and 30-day mortality (OR 1.11, 95% CI 0.43-2.88). Only cTnI levels at 4 h postoperatively were significantly lower with BCP (WMD: -1.62, 95% CI -2.07 to -1.18). Based on the available data, neither cardioplegia modality seems to be superior in terms of clinical outcomes, ischemia severity, and overall functional recovery.

Lysophosphatidic Acid Pretreatment Attenuates Myocardial Ischemia/Reperfusion Injury in the Immature Hearts of Rats

The cardioprotection of the immature heart during cardiac surgery remains controversial due to the differences between the adult heart and the newborn heart. Lysophosphatidic acid (LPA) is a small bioactive molecule with diverse functions including cell proliferation and survival via its receptor: LPA₁–LPA₆. We previously reported that the expressions of LPA₁ and LPA₃ in rat hearts were much higher in immature hearts and then declined rapidly with age. In this study, we aimed to investigate whether LPA signaling plays a potential protective role in immature hearts which had experienced ischemia/reperfusion (I/R) injury. The results showed that in Langendorff-perfused immature rat hearts (2 weeks), compared to I/R group, LPA pretreatment significantly enhanced the cardiac function, attenuated myocardial infarct size and CK-MB release, decreased myocardial apoptosis and increased the expression of pro-survival signaling molecules. All these effects could be abolished by Ki16425, an antagonist to LPA₁ and LPA₃. Similarly, LPA pretreatment protected H9C2 from hypoxia-reoxygenation (H/R) induced apoptosis and necrosis in vitro. The mechanisms underlying the anti-apoptosis effects were related to activation of the phosphatidylinositol 3-kinase (PI3K)/protein kinas B (AKT) signaling pathways as well as phosphorylation of the downstream effector of AKT, glycogen synthase kinase 3 beta (GSK3β), through LPA₁ and/or LPA₃. What's more, we found that LPA preconditioning increased glucose uptake of H9C2 subjected to H/R by the activation of AMP-Activated Protein Kinase (AMPK) but not the translocation of GLUT4. In conclusion, our study indicates that LPA is a potent survival factor for immature hearts against I/R injuries and has the potential therapeutic function as a cardioplegia additive for infantile cardiac surgery.

Propofol Is Cardioprotective in a Clinically Relevant Model of Normothermic Blood Cardioplegic Arrest and Cardiopulmonary Bypass

The general anesthetic propofol has been shown to be cardioprotective. However, its benefits when used in cardioplegia during cardiac surgery have not been demonstrated. In this study, we investigated the effects of propofol on metabolic stress, cardiac function, and injury in a clinically relevant model of normothermic cardioplegic arrest and cardiopulmonary bypass. Twenty anesthetized pigs, randomized to propofol treatment ( n = 8) and control ( n =12) groups, were surgically prepared for cardiopulmonary bypass (CPB) and cardioplegic arrest. Doses of warm blood cardioplegia were delivered at 15-min intervals during a 60-min aortic cross-clamped period. Propofol was continuously infused for the duration of CPB and was therefore present in blood cardioplegia. Myocardial biopsies were collected before, at the end of cardioplegic arrest, and 20 mins after the release of the aortic cross-clamp. Hemodynamic parameters were monitored and blood samples collected for cardiac troponin I measurements. Propofol infusion during CPB and before ischemia did not alter cardiac function or myocardial metabolism. Propofol treatment attenuated the changes in myocardial tissue levels of adenine nucleotides, lactate, and amino acids during ischemia and reduced cardiac troponin I release on reperfusion. Propofol treatment reduced measurable hemodynamic dysfunction after cardioplegic arrest when compared to untreated controls. In conclusion, propofol protects the heart from ischemia-reperfusion injury in a clinically relevant experimental model. Propofol may therefore be a useful adjunct to cardioplegic solutions as well as being an appropriate anesthetic for cardiac surgery.

Myocardial cytochrome oxidase activity increases with age and hypoxemia in patients with congenital heart disease

BACKGROUND

Myocardial tolerance to ischemia is influenced by age and preoperative cyanosis through unknown mechanisms and significantly affects postoperative outcomes. Cytochrome c oxidase (CcOx), the terminal enzyme of the mitochondrial electron transport chain, may play a role in the susceptibility to ischemic-reperfusion (IR) injury. Our study aimed at investigating changes in human myocardial CcOx activity based on age and preoperative oxygen saturation to understand its role in transition from neonatal to mature myocardium and hypoxic conditions.

METHODS

The right atrial appendage from patients undergoing first time surgical repair/palliation of congenital heart defects was analyzed for steady state CcOx activity by oxidation of ferrocytochrome c via spectrophotometry and steady state CcOx subunit I protein content by protein immunoblotting. Student's t-test compared CcOx activity and protein levels between patients with preoperative hypoxia and normoxia. Multiple linear regression analysis was used to assess the effects of age and preoperative arterial oxygen saturations (SaO₂) on CcOx protein activity and protein content.

RESULTS

Thirty-two patients with a median (interquartile range) age of 83 days (8-174) and preoperative oxygen saturation 98% (85-100%) were enrolled. Independent of age, preoperative SaO₂ ⩽90% was associated with significantly greater CcOx steady state activity (p=0.004). Additionally, older age itself was associated with increased CcOx steady state activity (p=0.022); the combination of preoperative SaO₂ and age account for 33% of the variation in CcOx steady state activity (R²=0.332). There was no increase in the CcOx subunit I protein content with either age or preoperative hypoxia.

CONCLUSIONS

In patients with congenital heart disease, an increase in CcOx steady state activity is seen with increasing age. Hypoxia leads to upregulation of CcOx steady state activity without an increase in the amount of enzyme protein itself. Higher CcOx activity in older and cyanotic patients may indicate CcOx-dependent reactive oxygen species as the mechanism for IR injury.

Tolerance to ischemia reperfusion injury in a congenital heart disease model

BACKGROUND

Open heart surgery-associated ischemia/reperfusion (I/R) injury affects postoperative outcome, and a leading cause of this is lipid peroxidation. Congenital heart disease (CHD) patients, however, are less sensitive to I/R injury. Although little is known about the underlying molecular mechanisms, CHD-associated hypoxia alters the polyunsaturated fatty acid (PUFA) composition of membranes, which are the preferential targets for reactive oxygen species (ROS) generated during I/R. Here, using an animal model, we investigated the molecular mechanisms underlying I/R tolerance in CHD.

METHODS

In order to reproduce I/R injury in vitro, we used a working heart perfusion model, isolated from juvenile control and CHD model rats (CHD rats), and examined the recovery of cardiac function during a period of I/R. PUFA composition of the plasma membrane was determined on gas chromatography/mass spectrometry. Oxidative stress-related cellular responses were investigated on immunoblotting, using antibodies against nuclear factor erythroid 2-related factor (Nrf-2), hemeoxygenase-1 (HO-1), and 4-hydroxy-2-hexanal (4-HHE)-modified protein.

RESULTS

Ischemia/reperfusion-induced cardiac dysfunction was markedly suppressed in CHD rats, compared with the control rats. n-3/n-6 PUFA ratio was significantly increased in both the pre- and post-I/R phase in CHD rats, but not in the controls. Four-HHE-modified protein, Nrf-2, and HO-1 were significantly increased in CHD rats as well, compared with the controls.

CONCLUSIONS

Following open heart surgery in CHD patients, the increased n-3/n-6 PUFA ratio may lead to the upregulation of cellular antioxidative system components through the oxidation product, 4-HHE, resulting in an increased tolerance to I/R injury.

Evidence for a significant myocardial contribution to total metabolic burden during hypothermic cardiopulmonary bypass: a study of continuously measured oxygen consumption and arterial lactate levels in pigs

Objective: We assessed the causes of imbalance of oxygen transport by continuously measuring oxygen consumption (VO2) during hypothermic cardiopulmonary bypass (CPB) in pigs.

Methods: Six pigs (17.2±1.6 kg) underwent hypothermic (328C) CPB for 180 min with 120 min of aortic crossclamping (ACC). An AMIS 2000 mass spectrometer was adapted for the on-line measurement of VO2. Arterial lactate was measured at the beginning of CPB, the end of hypothermia, before and 10 min after ACC release, 20 min later, and at the end of CPB.

Results: Arterial lactate increased from 1.8±0.7 to 5.1±1.8 mmol/L during CPB. Hypothermia reduced VO2by 0.63±0.29 ml/min/kg per 8C, but lactate increased to 4.2±1.5 mmol/L ( p <0.05). The most rapid rise of VO2and lactate occurred during the first 10 min after ACC removal, accounting for 26% and 68%, respectively, of the total rise during rewarming.

Conclusions: Inadequate tissue oxygenation persists throughout hypothermic CPB. The rise in systemic VO2 and lactate immediately after ACC release may reflect inadequate oxygen transport within the myocardium during ischemia and manifest on reperfusion. This simple technique may be used to provide important information regarding the dynamic balance of systemic and myocardial oxygen transport during ischemia - reperfusion.

Comparison of high glucose concentration blood and crystalloid cardioplegia in paediatric cardiac surgery: a randomized clinical trial

OBJECTIVES

This study investigates the effects of high glucose content on patients undergoing cold crystalloid versus cold blood cardioplegia in terms of early clinical results, functional myocardial recovery and ischaemia-reperfusion injury in patients undergoing repair of acyanotic cardiac lesions.

METHODS

Patients were randomly assigned to receive either crystalloid (n = 31) or blood cardioplegia (n = 31). Early clinical results were assessed. Changes in left ventricular fractional shortening, arterial blood lactate levels, central venous saturation, cardiac Troponin I release and blood glucose concentration were measured during the first 24 h after ischaemia.

RESULTS

There was no significant difference in clinical outcomes and postoperative complication rates between groups. The postoperative changes in left ventricular function, lactate levels, central venous saturation and Troponin I were not significantly different between groups. The use of crystalloid cardioplegia was associated with significant increases in serum glucose compared with blood cardioplegia.

CONCLUSIONS

A high glucose content blood cardioplegia does not show any advantage compared with crystalloid cardioplegia in terms of clinical outcomes, functional recovery and the degree of ischaemic injury in infants and children undergoing repair of acyanotic heart lesions. High glucose concentration of the cardioplegic solution might potentiate ischaemia-reperfusion injury and diminish the beneficial effects of blood cardioplegia.

Investigating the effect of remote ischaemic preconditioning on biomarkers of stress and injury-related signalling in patients having isolated coronary artery bypass grafting or aortic valve replacement using cardiopulmonary bypass: study protocol for a randomized controlled trial

Background

Ischaemia-reperfusion injury occurs during heart surgery that uses cardiopulmonary bypass (CPB) and cardioplegic arrest. It is hypothesised that remote ischaemic preconditioning (RIPC) protects the heart against such injury. Despite the numerous studies investigating the protective effects of RIPC, there is still uncertainty about the interpretation of the findings as well as conflicting results between studies. The objective of this trial is to investigate the cardioprotective effect of RIPC in patients having coronary artery bypass grafting (CABG) or aortic valve replacement surgery. This will be achieved by estimating the effect of the intervention in the two groups of pathologies and by investigating the signalling mechanisms that may underpin the cardioprotective effect.

Methods/Design

A two-centre randomised controlled trial will be used to investigate the effects of RIPC in two pathologies: patients having isolated CABG and those having aortic valve replacement surgery (AVR) with CPB. Participants will be randomised to RIPC or control (sham RIPC), stratified by surgical stratum. The intervention will be delivered by a research nurse. Data will be collected by a research nurse blinded to the intervention. The patient and the theatre staff are also blinded to the allocation. Markers of myocardial injury and inflammation will be measured in myocardial biopsies and in blood samples at different times.

Discussion

This trial is designed to investigate whether RIPC will reduce myocardial injury and inflammation following heart surgery and whether there is a difference in effect between participants having CABG or AVR. This trial is a unique opportunity to study the mechanisms associated with RIPC using human myocardial tissue and blood, and to relate these to the extent of myocardial injury/protection.

Trial registration

Current Controlled Trials ISRCTN33084113 (25 March 2013).

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-015-0696-z) contains supplementary material, which is available to authorized users.

Cellular redox status determines sensitivity to BNIP3-mediated cell death in cardiac myocytes

The atypical BH3-only protein Bcl-2/adenovirus E1B 19-kDa interacting protein 3 (BNIP3) is an important regulator of hypoxia-mediated cell death. Interestingly, the susceptibility to BNIP3-mediated cell death differs between cells. In this study we examined whether there are mechanistic differences in BNIP3-mediated cell death between neonatal and adult cardiac myocytes. We discovered that BNIP3 is a potent inducer of cell death in neonatal myocytes, whereas adult myocytes are remarkably resistant to BNIP3. When exploring the potential underlying basis for the resistance, we discovered that adult myocytes express significantly higher levels of the mitochondrial antioxidant manganese superoxide dismutase (MnSOD) than neonatal myocytes. Overexpression of MnSOD confers resistance to BNIP3-mediated cell death in neonatal myocytes. In contrast, the presence of a pharmacological MnSOD inhibitor, 2-methoxyestradiol, results in increased sensitivity to BNIP3-mediated cell death in adult myocytes. Cotreatment with the mitochondria-targeted antioxidant MitoTEMPO or the MnSOD mimetic manganese (III) tetrakis (4-benzoic acid) porphyrin chloride abrogates the increased cell death by 2-methoxyestradiol. Moreover, increased oxidative stress also restores the ability of BNIP3 to induce cell death in adult myocytes. Taken together, these data indicate that redox status determines cell susceptibility to BNIP3-mediated cell death. These findings are clinically relevant, given that pediatric hearts are known to be more vulnerable than the adult heart to ischemic injury. Our studies provide important insight into why pediatric hearts are more sensitive to ischemic injury and may help in the clinical management of childhood heart disease.

Normothermia for pediatric and congenital heart surgery: an expanded horizon

Cardiopulmonary bypass (CPB) in pediatric cardiac surgery is generally performed with hypothermia, flow reduction and hemodilution. From October 2013 to December 2014, 55 patients, median age 6 years (range 2 months to 52 years), median weight 18.5 kg (range 3.2-57 kg), underwent surgery with normothermic high flow CPB in a new unit. There were no early or late deaths. Fifty patients (90.9%) were extubated within 3 h, 3 (5.5%) within 24 h, and 2 (3.6%) within 48 h. Twenty-four patients (43.6%) did not require inotropic support, 31 (56.4%) received dopamine or dobutamine: 21 ≤5 mcg/kg/min, 8 5-10 mcg/kg/min, and 2 >10 mcg/kg/min. Two patients (6.5%) required noradrenaline 0.05-0.1 mcg/kg/min. On arrival to ICU and after 3 and 6 h and 8:00 a.m. the next morning, mean lactate levels were 1.9 ± 09, 2.0 ± 1.2, 1.6 ± 0.8, and 1.4 ± 0.7 mmol/L (0.6-5.2 mmol/L), respectively. From arrival to ICU to 8:00 a.m. the next morning mean urine output was 3.8 ± 1.5 mL/kg/h (0.7-7.6 mL/kg/h), and mean chest drainage was 0.6 ± 0.5 mL/kg/h (0.1-2.3 mL/kg/h). Mean ICU and hospital stay were 2.7 ± 1.4 days (2-8 days) and 7.2 ± 2.2 days (4-15 days), respectively. In conclusion, normothermic high flow CPB allows pediatric and congenital heart surgery with favorable outcomes even in a new unit. The immediate post-operative period is characterized by low requirement for inotropic and respiratory support, low lactate production, adequate urine output, minimal drainage from the chest drains, short ICU, and hospital stay.

Effect of aortic root infusion of sufentanil on ischemia-reperfusion injury in patients undergoing mitral valve replacement

OBJECTIVE

This study investigated the effects of aortic root infusion of sufentanil on myocardial ischemia/reperfusion injury in patients undergoing elective mitral valve replacement (MVR) with cardiopulmonary bypass (CPB).

DESIGN

A prospective, randomized, clinical study.

SETTING

A university-affiliated teaching hospital.

PARTICIPANTS

Fifty-three adult patients undergoing elective MVR with CPB.

INTERVENTIONS

Bolus infusions of sufentanil (0.2 μg/kg, n = 24) or normal saline (n = 29) were administered through the aortic root cardioplegia perfusion catheter 5 minutes before aortic unclamping.

MEASUREMENTS AND MAIN RESULTS

Plasma concentrations of CK-MB and cTnI and variables including heart rate, mean arterial pressure, central venous pressure, cardiac output, stroke volume, duration of mechanical ventilation, length of ICU stay, length of hospital stay, and 24-hour postoperative inotropic scores were recorded. Plasma concentrations of CK-MB and cTnI were significantly lower 4 and 8 hours after aortic unclamping in the sufentanil postconditioning group compared to control (p<0.05). Inotropic drug use, duration of mechanical ventilation, and length of ICU and hospital stays were reduced significantly in the sufentanil postconditioning group compared to control (p< 0.05).

CONCLUSIONS

The present study demonstrated that sufentanil can attenuate myocardial ischemia-reperfusion injury in patients undergoing elective MVR with CPB.

Normoxic and hyperoxic cardiopulmonary bypass in congenital heart disease

Cyanotic congenital heart disease comprises a diverse spectrum of anatomical pathologies. Common to all, however, is chronic hypoxia before these lesions are operated upon when cardiopulmonary bypass is initiated. A range of functional and structural adaptations take place in the chronically hypoxic heart, which, whilst protective in the hypoxic state, are deleterious when the availability of oxygen to the myocardium is suddenly improved. Conventional cardiopulmonary bypass delivers hyperoxic perfusion to the myocardium and is associated with cardiac injury and systemic stress, whilst a normoxic perfusate protects against these insults.

Metabolic derangement and cardiac injury early after reperfusion following intermittent cross-clamp fibrillation in patients undergoing coronary artery bypass graft surgery using conventional or miniaturized cardiopulmonary bypass

Myocardial ischemic stress and early reperfusion injury in patients undergoing coronary artery bypass grafting (CABG) operated on using intermittent cross-clamp fibrillation (ICCF) are not presently known. The role of mini-cardiopulmonary bypass (mCPB) versus conventional CPB (cCPB) during ICCF has not been investigated. These issues have been addressed as secondary objective of randomised controlled trial (ISRCTN30610605) comparing cCPB and mCPB. Twenty-six patients undergoing primary elective CABG using ICCF were randomised to either cCPB or mCPB. Paired left ventricular biopsies collected from 21 patients at the beginning and at the end of CPB were used to measure intracellular substrates (ATP and related compounds). Cardiac troponin T (cTnT) and CK-MB levels were measured in plasma collected from all patients preoperatively and after 1, 30, 60, 120, and 300 min after institution of CPB. ICCF was associated with significant ischemic stress as seen by fall in energy-rich phosphates early after reperfusion. There was also a fall in nicotinamide adenine dinucleotide (NAD(+)) indicating cardiomyocyte death which was confirmed by early release of cTnT and CK-MB during CPB. Ischemic stress and early myocardial injury were similar for cCPB and mCPB. However, the overall cardiac injury was significantly lower in the mCPB group as measured by cTnT (mean ± SEM: 96 ± 14 vs. 59 ± 8 µg/l, p = 0.02), but not with CK-MB. ICCF is associated with significant metabolic derangement and early myocardial injury. This early outcome was not affected by the CPB technique. However, the overall cardiac injury was lower for mCPB only when measured using cTnT.

Myocardial injury in critically ill children: a case control study

Objectives. The aim of this study was to investigate the occurrence of myocardial injury in critically ill children through assessment of cardiac troponin T levels and whether levels are associated with disease severity and myocardial dysfunction measured by echocardiography. Methods. Over a 6-month period, this case control study included 50 patients admitted to Pediatric Intensive Care Unit of Zagazig University Children's Hospital. Twenty-five healthy children were included as a control group. Demographic and clinical data including the pediatric index of mortality II score were recorded. Echocardiographic examination was done and level of cardiac troponin T was measured using Elecsys Troponin T STAT Immunoassay. Results. Cardiac troponin T levels were significantly higher in critically ill in comparison to healthy children (median 22 (18–28) pg/mL versus 10 (10-10) pg/mL, P < 0.05). Cardiac troponin T levels correlated positively with duration of ventilation as well as with disease severity and correlated negatively with left ventricular fractional shortening. Moreover, cardiac troponin T levels were significantly higher in nonsurvivors when compared to survivors (median 34.5 (27.5–41.5) pg/mL versus 20 (18–24) pg/mL, P < 0.05). Conclusion. In critically ill children, cardiac troponin T levels were elevated and were associated with duration of ventilation and disease severity.

Cardiac troponin I after cardiopulmonary bypass in infants in comparison with older children

OBJECTIVE

At the present time, there is a trend towards performing open heart surgery at a younger age. Myocardium of infants has been thought to be more vulnerable to cardiopulmonary bypass in comparison with adults. For this study, we evaluated the degree of myocardial injury by measurement of cardiac troponin levels in infants in comparison with older children for similar surgeries.

METHODS

Serum was collected before bypass, after bypass, and daily after surgery and serum cardiac troponin I level (micrograms per litre). The demographic data, cardiac diagnoses, types of surgery performed, and peri-operative parameters were collected.

RESULTS

Of the 21 children enrolled consecutively, five were infants. Among the 21 patients, four patients had post-operative peak troponin values greater than 100 (three were infants) and all four patients survived and had normal left ventricular systolic function upon discharge echocardiogram. The five infants had peak troponin levels of 222.3, 202, 129, 26.7, and 82.3. The post-operative peak troponin levels were significantly higher in infants (mean 132.5 with a standard deviation of 81.6) than in the older children (mean 40.3 with a standard deviation of 33.4), although there was no significant difference in bypass time, bypass temperature, cross-clamp time, or the length of stay in the intensive care unit between the two age groups.

CONCLUSIONS

Higher troponin release is seen in infants in comparison with older children after bypass for similar surgeries. A troponin level greater than 100 after bypass does not necessarily predict death or a severe cardiovascular event in the very young.

Heat shock protein 27 is increased in cyanotic tetralogy of Fallot myocardium and is associated with improved cardiac output and contraction

Tetralogy of Fallot (TOF) is a congenital heart condition in which the right ventricle is exposed to cyanosis and pressure overload. Patients have an increased risk of right ventricle dysfunction following corrective surgery. Whether the cyanotic myocardium is less tolerant of injury compared to non-cyanotic is unclear. Heat shock proteins (HSPs) protect against cellular stresses. The aim of this study was to examine HSP 27 expression in the right ventricle resected from TOF patients and determine its relationship with right ventricle function and clinical outcome. Ten cyanotic and ten non-cyanotic patients were studied. Western blotting was used to quantify HSP 27 in resected myocardium at (1) baseline (first 15 min of aortic cross clamp and closest representation of pre-operative status) and (2) after 15 min during ischemia until surgery was complete. The cyanotic group had significantly increased haematocrit, lower O2 saturation, thicker interventricular septal wall thickness and released more troponin-I on post-operative day 1 (p < 0.05). HSP 27 expression was significantly increased in the < 15 min cyanotic compared to the < 15 min non-cyanotic group (p = 0.03). In the cyanotic group, baseline HSP 27 expression also significantly correlated with oxygen extraction ratio (p = 0.028), post-operative basal septal velocity (p = 0.036) and mixed venous oxygen saturation (p = 0.02), markers of improved cardiac output/contraction. Increased HSP 27 expression and associated improved right ventricle function and systemic perfusion supports a cardio-protective effect of HSP 27 in cyanotic TOF.