Triiodothyronine supplementation and cytokines during cardiopulmonary bypass in infants and children

Triiodothyronine Supplementation in Infants Undergoing Cardiopulmonary Bypass: A Randomized Controlled Trial

Cardiopulmonary bypass (CPB) profoundly suppresses circulating thyroid hormone levels in infants. We performed a multicenter randomized placebo controlled trial to determine if triiodothyronine (T3) supplementation improves reduces time to extubation (TTE) in infants after CPB. Infants (n = 220) undergoing cardiac surgery with CPB and stratified into 2 age cohorts: ≤30 days and >30 days to <152 days were randomization to receive either intravenous triiodothyronine or placebo bolus followed by study drug infusion until extubated or at 48 hours, whichever preceded. T3 did not significantly alter the primary endpoint, TTE (hazard ratio for chance of extubation (1.08, 95% CI: 0.82-1.43, P = 0.575) in the entire randomized population with censoring at 21 days. T3 showed no significant effect on TTE (HR 0.82, 95% CI:0.55-1.23, P = 0.341) in the younger subgroup or in the older (HR 1.38, 95% CI:0.95-2.2, P = 0.095). T3 also did not significantly impact TTE during the first 48 hours while T3 levels were maintained (HR 1.371, 95% CI:0.942-1.95, P = 0.099) No significant differences occurred for arrhythmias or other sentinel adverse events in the entire cohort or in the subgroups. This trial showed no significant benefit on TTE in the entire cohort. T3 supplementation appears safe as it did not cause an increase in adverse events. The study implementation and analysis were complicated by marked variability in surgical risk, although risk categories were balanced between treatment groups.

Cardiac and Pulmonary Histopathology in Baboons Following Genetically-Engineered Pig Orthotopic Heart Transplantation

BACKGROUND Although improving, survival after pig orthotopic heart transplantation (OHTx) in baboons has been mixed and largely poor. The causes for the high incidence of early failure remain uncertain. MATERIAL AND METHODS We have carried out pig OHTx in 4 baboons. Two died or were euthanized within hours, and 2 survived for 3 and 8 months, respectively. There was evidence of a significant 'cytokine storm' in the immediate post-OHTx period with the elevations in IL-6 correlating closely with the final outcome. RESULTS All 4 baboons demonstrated features suggestive of respiratory dysfunction, including increased airway resistance, hypoxia, and tachypnea. Histopathological observations of pulmonary infiltration by neutrophils and, notably, eosinophils within vessels and in the perivascular and peribronchiolar space, with minimal cardiac pathology, suggested a role for early lung acute inflammation. In one, features suggestive of transfusion-related acute lung injury were present. The 2 longer-term survivors died of (i) a cardiac dysrhythmia with cellular infiltration around the conducting tissue (at 3 months), and (ii) mixed cellular and antibody-mediated rejection (at 8 months). CONCLUSIONS These initial findings indicate a potential role of acute lung injury early after OHTx. If this response can be prevented, increased survival may result, providing an opportunity to evaluate the factors affecting long-term survival.

A perspective on the potential detrimental role of inflammation in pig orthotopic heart xenotransplantation

There is a critical shortage of deceased human donor organs for transplantation. The need is perhaps most acute in neonates and infants with life-threatening congenital heart disease, in whom mechanical support devices are largely unsuccessful. If orthotopic (life-supporting) heart transplantation (OHTx) were consistently successful in the genetically engineered pig-to-nonhuman primate (NHP) model, a clinical trial of bridging with a pig heart in such patients might be justified. However, the results of pig OHTx in NHPs have been mixed and largely poor. We hypothesise that a factor is the detrimental effects of the inflammatory response that is known to develop (a) during any surgical procedure that requires cardiopulmonary bypass, and (b) immediately after an NHP recipient is exposed to a pig xenograft. We suggest that the combination of these two inflammatory responses has a direct detrimental effect on pig heart graft function, but also, and possibly of more importance, on recipient baboon pulmonary function, which further impacts survival of the pig heart graft. In addition, the inflammatory response almost certainly adversely impacts the immune response to the graft. If our hypothesis is correct, the potential steps that could be taken to reduce the inflammatory response or its effects (with varying degrees of efficacy) include (a) white blood cell filtration, (b) complement depletion or inactivation, (c) immunosuppressive therapy, (d) high-dose corticosteroid therapy, (e) cytokine/chemokine-targeted therapy, (f) ultrafiltration or CytoSorb hemoperfusion, (g) reduction in the levels of endogenous catecholamines, (h) triiodothyronine therapy and (i) genetic engineering of the organ-source pig. Prevention of the inflammatory response, or attenuation of its effects, by judicious anti-inflammatory therapy may contribute not only to early survival of the recipient of a genetically engineered pig OHTx, but also to improved long-term pig heart graft survival. This would open the possibility of initiating a clinical trial of genetically engineered pig OHTx as a bridge to allotransplantation.

Euthyroid sick syndrome in paediatric and adult patients requiring extracorporeal circulatory support and the role of thyroid hormone supplementation: a review

Non-thyroid disorders may modify thyroid hormone metabolism, resulting in an 'euthyroid sick syndrome'. Studies determining the association of cardiopulmonary bypass to thyroid function showed changes in line with this euthyroid sick syndrome. In some cases, cardiovascular dysfunction after cardiac surgery with cardiopulmonary bypass is comparable to that noticed in hypothyroidism associated with low cardiac output and elevated systemic vascular resistance. Numerous lines of research have proposed that triiodothyronine can behave acutely as a positive inotropic and vasodilator agent. The aim of this review is to present an update on the current literature about in what clinical situations the use of thyroid supplementation during the perioperative period of extracorporeal circulation in the adult and paediatric populations may impact outcome to any appreciable degree. The contribution of thyroid function in patients undergoing a ventricular assist device implantation is additionally reviewed and future study directions are proposed. This is a narrative review, where the search strategy consisted on retrieving the articles through an extensive literature search performed using electronic databases from January 1978 up to September 2019. All controlled trials randomly allocating to perioperative thyroid hormone administration in children and adults undergoing extracorporeal circulation for cardiac surgery were considered. Thyroid hormone supplementation may be recommended particularly in selected paediatric sub-populations. There is currently no firm evidence regarding the benefits of routine use of thyroid hormone administration in cardiac adult patients. Further studies are required to assess the beneficial effect of thyroid hormone on patients with end-stage heart failure supported by ventricular assist devices.

Cardioprotective effects of triiodothyronine supplementation against ischemia reperfusion injury by preserving calcium cycling proteins in isolated rat hearts

Hypothyroidism is associated with profound left ventricular dysfunction. Triiodothyronine (T₃) supplementation may improve cardiac function after ischemic reperfusion (I/R) injury. In the present study, the effect of T₃ on major calcium cycling proteins and high-energy phosphate content during I/R was evaluated. Isolated perfused rat hearts were divided into 5 groups: Sham Control (Sham, n=10), Control (n=8), T₃ 10 nM (T₃-10, n=10), T₃ 25 nM (T₃-25, n=10) and T₃ 50 nM (T₃-50, n=10). T₃ was administrated for 60 min before 30 min of ischemia and 120 min of reperfusion. The protein contents of Ca²⁺-release channels (RyR2), Ca²⁺-adenosine triphosphatase (SERCA2a), phospholamban (PLB), sarcolemmal Ca²⁺-adenosine triphosphatase (PMCA) and sodium-calcium exchanger (NCX), as well as the high-energy phosphate content in heart tissues were measured by western blot analysis. The results revealed that T₃ improved the contractile recovery (left ventricular developed pressure; +dP/dt, -dP/dt) after I/R. Western blotting assays demonstrated that I/R depressed the contents of RYR2, SERCA2a and phosphorylated RYR2 and PLB; there were no effects on the contents of PLB, PMCA and NCX. T₃ reversed I/R-induced degradation of RyR2 and SERCA2a, restored the phosphorylation of RyR2 and PLB, and preserved the high-energy phosphate contents of ATP and creatine phosphate. T₃ supplementation protected the heart against I/R injury via the preservation of Ca²⁺-cycling proteins and high-energy phosphate content.

Prevalence of Culture-Negative Fever in Infants With Down Syndrome Undergoing Cardiac Surgery

BACKGROUND

Children with Down syndrome (DS) often have congenital heart disease that requires surgical repair in the first year. Anecdotally, we have noted that patients with DS seem to have a higher rate of culture-negative postoperative fever. The objective was to evaluate the prevalence of postoperative fever and recovery among patients with DS undergoing cardiac surgery.

METHODS

We conducted a retrospective, case-control study of all patients at our institution less than one year of age with DS undergoing surgical repair of an atrioventricular septal defect or ventricular septal defect between 2010 and 2016. The control group was patients with no chromosomal anomalies who were age and surgery matched to the DS group. Temperatures were recorded for the first 72 hours postoperatively, with duration and degree of fever being assessed using the area under the curve.

RESULTS

Patients with DS (n = 34) had a significantly higher prevalence of fever than the control group (59% vs 24%, P = .003), longer ventilator time, and longer length of stay. Among the DS group, those who developed fever tended to be older at the time of surgery (146 ± 63 vs 103 ± 45 days, P = .04). The DS group with fever had similar cardiopulmonary bypass times, intensive care unit and total lengths of stay, ventilator days, and hospital costs compared to patients with DS without fever.

CONCLUSIONS

Patients with DS have a higher incidence of culture-negative fever within the first 72 hours. The presence of fever in these patients, however, does not affect their overall postoperative course.

Functional Polymorphisms of the Type 1 and Type 2 Iodothyronine Deiodinase Genes in Autoimmune Thyroid Diseases

Graves' disease (GD) and Hashimoto's disease (HD) are major autoimmune thyroid diseases (AITDs), and their pathological conditions vary among patients. Type 1 iodothyronine deiodinase (D1) and type 2 iodothyronine deiodinase (D2) convert from thyroxine (T4) to triiodothyronine (T3). However, few findings have been described concerning the association between polymorphisms in D1 and D2 genes and AITD. Therefore, we genotyped D1 rs11206244, D2 rs225014, and rs12885300 polymorphisms in 134 GD patients, including 54 patients with intractable GD and 44 patients with GD in remission and 132 HD patients, including 57 patients with severe HD, 45 patients with mild HD, and 84 healthy controls using PCR-RFLP. In the D2 rs225014 polymorphism, the TT genotype, which was correlated with higher D2 activity, was less frequent in AITD, especially in HD, than in control subjects (P = 0.0032 and 0.0002, respectively). Moreover, they were also less frequent in HD than in GD (P = 0.0199). The TT genotype and T allele were less frequent in severe HD and mild HD than in control subjects (P = 0.0003, 0.0006, 0.0432, and 0.0427, respectively). In conclusion, the low frequency of the TT genotype D2 rs225014 polymorphism was associated with the development of AITD and severity of HD.

Thyroid Hormone in the Pediatric Intensive Care Unit

Thyroid hormones are key factors necessary for normal growth and development in children. They have tight control of metabolic rate and, as a result, frequently become altered in their synthesis and/or release during times of stress or critical illness. Disturbances in thyroid hormone homeostasis have been well described in several pathologic states, including sepsis/septic shock, renal failure, trauma, severe malnutrition, and following cardiopulmonary bypass. Specifically, a decrease in serum triiodothyronine (T₃) and a concomitant increase in reverse triiodothyronine (rT₃) levels are the most common changes observed. It is further noteworthy that serum thyroxine (T₄), rT₃, and T₃ levels change in relation to severity of nonthyroidal illness. Many past investigators have speculated that these alterations are a teleological adaptation to severe illness and the increased metabolic demands that critical illness bears. However, this paradigm has been challenged through multiple avenues and has lost support over the past few years. Instead the "inflammatory hypothesis" has emerged implicating a cytokine surge as the mediator of thyroid hormone disruption. Overall, the demonstrated association between low thyroid hormone levels and poor clinical outcomes, the beneficial effects of thyroid hormone supplementation in multiple critically ill subpopulations, and the well-established safety profile of T₃ therapy make thyroid hormone supplementation in the pediatric ICU worth consideration.

Neonatal Extracorporeal Membrane Oxygenation: Update on Management Strategies and Long-Term Outcomes

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) can be deployed to support patients with severe cardiorespiratory failure unresponsive to conventional medical interventions. Neonatal trials have demonstrated that ECMO is an effective treatment of severe respiratory failure, with acceptable cognitive and functional outcomes. Technological advances in ECMO have resulted in improved safety and accessibility, contributing to decreased morbidity and improved survival of increasingly complex patients requiring ECMO support.

PURPOSE

This review aims to describe the innovations in ECMO technology and management in the neonatal population in the last decade. The long-term outcomes of neonatal patients requiring ECMO support will be discussed.

SEARCH STRATEGY

Relevant clinical trials from MEDLINE and the Cochrane Library were identified. The following key words were used: ECMO, infant, neonate, and outcomes.

FINDINGS

Challenges still remain in supporting the premature and/or low-birth-weight infant with severe respiratory failure, as well as infants with congenital diaphragmatic hernia. Neonatal ECMO survivors can present with neurodevelopmental and respiratory problems, which become more prominent with time.

IMPLICATIONS FOR PRACTICE

While newer technologies have led to fewer neonates with respiratory failure progressing to ECMO, it remains an important tool to in those who have failed conventional therapies. Given the presence of neurodevelopmental problems in neonatal ECMO survivors, multidisciplinary follow-up targeting motor performance, exercise capacity, behavior, and subtle learning deficits is warranted.

IMPLICATIONS FOR RESEARCH

With the overall decreasing use of neonatal ECMO, ECMO centers must find ways to maintain their expertise in the light of lower patient volumes amidst complex patient physiology.

Triiodothyronine activates lactate oxidation without impairing fatty acid oxidation and improves weaning from extracorporeal membrane oxygenation

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) provides a rescue for children with severe cardiac failure. It has previously been shown that triiodothyronine (T3) improves cardiac function by modulating pyruvate oxidation during weaning. This study focused on fatty acid (FA) metabolism modulated by T3 for weaning from ECMO after cardiac injury. METHODS AND RESULTS: Nineteen immature piglets (9.1-15.3 kg) were separated into 3 groups with ECMO (6.5 h) and wean: normal circulation (Group-C); transient coronary occlusion (10 min) for ischemia-reperfusion (IR) followed by ECMO (Group-IR); and IR with T3 supplementation (Group-IR-T3). 13-Carbon ((13)C)-labeled lactate, medium-chain and long-chain FAs, was infused as oxidative substrates. Substrate fractional contribution (FC) to the citric acid cycle was analyzed by(13)C-nuclear magnetic resonance. ECMO depressed circulating T3 levels to 40% of the baseline at 4 h and were restored in Group-IR-T3. Group-IR decreased cardiac power, which was not fully restorable and 2 pigs were lost because of weaning failure. Group-IR also depressed FC-lactate, while the excellent contractile function and energy efficiency in Group-IR-T3 occurred along with a marked FC-lactate increase and [adenosine triphosphate]/[adenosine diphosphate] without either decreasing FC-FAs or elevating myocardial oxygen consumption over Group-C or -IR.

CONCLUSIONS

T3 releases inhibition of lactate oxidation following IR injury without impairing FA oxidation. These findings indicate that T3 depression during ECMO is maladaptive, and that restoring levels improves metabolic flux and enhances contractile function during weaning.

Triiodothyronine facilitates weaning from extracorporeal membrane oxygenation by improved mitochondrial substrate utilization

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) provides a bridge to recovery after myocardial injury in infants and children, yet morbidity and mortality remain high. Weaning from the circuit requires adequate cardiac contractile function, which can be impaired by metabolic disturbances induced either by ischemia-reperfusion and/or by ECMO. We tested the hypothesis that although ECMO partially ameliorates metabolic abnormalities induced by ischemia-reperfusion, these abnormalities persist or recur with weaning. We also determined if thyroid hormone supplementation (triiodothyronine) during ECMO improves oxidative metabolism and cardiac function.

METHODS AND RESULTS

Neonatal piglets underwent transient coronary ischemia to induce cardiac injury then were separated into 4 groups based on loading status. Piglets without coronary ischemia served as controls. We infused into the left coronary artery [2-(13)C]pyruvate and [(13)C6, (15)N]l-leucine to evaluate oxidative metabolism by gas chromatography-mass spectroscopy and nuclear magnetic resonance methods. ECMO improved survival, increased oxidative substrate contribution through pyruvate dehydrogenase, reduced succinate and fumarate accumulation, and ameliorated ATP depletion induced by ischemia. The functional and metabolic benefit of ECMO was lost with weaning, yet triiodothyronine supplementation during ECMO restored function, increased relative pyruvate dehydrogenase flux, reduced succinate and fumarate, and preserved ATP stores.

CONCLUSIONS

Although ECMO provides metabolic rest by decreasing energy demand, metabolic impairments persist, and are exacerbated with weaning. Treating ECMO-induced thyroid depression with triiodothyronine improves substrate flux, myocardial oxidative capacity and cardiac contractile function. This translational model suggests that metabolic targeting can improve weaning.

Myocardial oxidative metabolism and protein synthesis during mechanical circulatory support by extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) provides essential mechanical circulatory support necessary for survival in infants and children with acute cardiac decompensation. However, ECMO also causes metabolic disturbances, which contribute to total body wasting and protein loss. Cardiac stunning can also occur, which prevents ECMO weaning, and contributes to high mortality. The heart may specifically undergo metabolic impairments, which influence functional recovery. We tested the hypothesis that ECMO alters oxidative metabolism and protein synthesis. We focused on the amino acid leucine and integration with myocardial protein synthesis. We used a translational immature swine model in which we assessed in heart 1) the fractional contribution of leucine (FcLeucine) and pyruvate to mitochondrial acetyl-CoA formation by nuclear magnetic resonance and 2) global protein fractional synthesis (FSR) by gas chromatography-mass spectrometry. Immature mixed breed Yorkshire male piglets (n = 22) were divided into four groups based on loading status (8 h of normal circulation or ECMO) and intracoronary infusion [(13)C(6),(15)N]-L-leucine (3.7 mM) alone or with [2-(13)C]-pyruvate (7.4 mM). ECMO decreased pulse pressure and correspondingly lowered myocardial oxygen consumption (∼40%, n = 5), indicating decreased overall mitochondrial oxidative metabolism. However, FcLeucine was maintained and myocardial protein FSR was marginally increased. Pyruvate addition decreased tissue leucine enrichment, FcLeucine, and Fc for endogenous substrates as well as protein FSR. The heart under ECMO shows reduced oxidative metabolism of substrates, including amino acids, while maintaining 1) metabolic flexibility indicated by ability to respond to pyruvate and 2) a normal or increased capacity for global protein synthesis.