Pediatric myocardial protection

Microplegia in paediatric hearts

INTRODUCTION

A basic prerequisite for a good surgical outcome in heart surgery is optimal myocardial protection. However, cardioplegia strategies used in adult cardiac surgery are not directly transferable to infant hearts. Paediatric microplegia, analogous to Calafiore cardioplegia used in adult cardiac surgery, offers the advantage of safe myocardial protection without haemodilution. The use of concentration-dependent paediatric microplegia is new in clinical implementation.

MATERIAL AND METHODS

Paediatric microplegia has been in clinical use in our institution since late 2014. It is applied via an 1/8 inch tube of a S5-HLM roller pump (LivaNova, Italy). As cardioplegic additive, a mixture of potassium (K) 20 mL (2 mmol/mL potassium chloride 14.9% Braun) and magnesium (Mg) 10 mL (4 mmol/mL Mg-sulphate Verla® i. v. 50%) is fixed into a syringe-pump (B. Braun, Germany). This additive is mixed with arterial patient blood from the oxygenator in different flowdependent ratios to form an effective cardioplegia.

TECHNIQUE

After microplegia application of initially 25 mmol/L K with 11 mmol/L Mg for 2 min, a safe cardioplegic cardiac arrest is achieved, which after release of the coronary circulation, immediately returns to a spontaneous cardiac-rhythm. In the case of prolonged aortic clamping, microplegia is repeated every 20 min with a reduction of the application dose of K by 20% and Mg by 30% (20 mmol/L K; 8.5 mmol/L Mg) and a further reduction down to a maintenance dose (15 mmol/L K; 6 mmol/L Mg) after additional 20 min.

SUMMARY

The microplegia adapted to the needs of paediatric myocardium is convincing due to its simple technical implementation for the perfusionist while avoiding haemodilution. However, the required intraoperative interval of microplegia of approx. 20 min demands adapted intraoperative management from the surgeon.

A narrative review of modern approach and outcomes evaluation in congenital heart defects

OBJECTIVE

The purpose of this review is to highlight critical advances and innovative approaches to the most challenging clinical situations in congenital heart surgery, to establish a new perspective from which to evaluate current clinical practice patterns and contemporary United States program ranking systems.

BACKGROUND

The past decades have witnessed substantial advances in the treatment of congenital heart defects. New strategies are deeply rooted in calculated risk-taking innovations. Pioneer surgeons developed, improved and refined critical operative skills and techniques to optimize cardiovascular physiology, decrease operative mortality and improve clinical outcomes.

METHODS

Unfortunately, in the modern surgical era, supportive environments to allow surgeons to make similar gains and innovative contributions remain scarce. In the current practice, overall procedure volume is prioritized to safeguard quality metrics, including hospital survival and length of stay, surgical complications, and neurocognitive outcomes. As a result, exceptional surgical results have become translated and defined by public ranking systems such as the US News and World Report Best Children's Hospital National Ranking (USNWR) and the Congenital Heart Surgery Database of the Society for Thoracic Surgeons (CHSD-STS), primary based upon early post-operative mortality. This reality places surgeons in a vulnerable position where pressure to achieve a high clinical ranking contrasts with a surgeon definition of "acceptable" surgical risk. Currently, the most frequently used risk stratification tools do not factor in important differences in strategies, such as staged palliation versus complete repair, or bi-ventricular versus uni-ventricular physiology. This favors hospitals pursuing multistage surgical approaches, even if the result is worse long-term morbidity, mortality and increased resource utilization. This economy of ranking-based decision-making causes surgeons either avoid operating altogether or accept less advantageous multi-staged treatment strategies for patients with elevated expected mortality. Such an environment also might present much farther-reaching negative impacts on the growth and development of junior surgeons and trainees, as well as on the pursuit of new surgical innovations to aid future generations of patients.

CONCLUSIONS

Risk aversive surgical behavior is creating an environment not favorable for the children born with truly complex congenital heart defects.

KEYWORDS

Biventricular conversion; congenital heart surgery; multidisciplinary approach; risk-stratification; surgical outcomes.

Improved contractility with tepid modified full blood cardioplegia compared with cold crystalloid cardioplegia in a piglet model

OBJECTIVES

Experience regarding warm blood cardioplegia according to Calafiore results from its broad use in adult patients. In this experimental study, tepid (28°C) modified full blood cardioplegia (MBC) was adopted for paediatric use and compared with cold crystalloid cardioplegia (CCC).

METHODS

Twenty male piglets (mean weight: 11.1 ± 1.0 kg) were operated on cardiopulmonary bypass (CPB) in moderate hypothermia (28°C) and randomized to MBC (n = 8) or CCC (n = 12) for 60 min aortic cross-clamping. Blood levels of myocardial proteins [N-terminal pro-brain natriuretic peptide (NT-pro-BNP), myoglobin, creatine kinase type MB and troponin-I] were investigated at the beginning of the experiment and after CPB. Haemodynamic measurements included thermodilution and conductance-catheter technique inserted through the left ventricle-apex. Pressure-volume loop analysis was performed with dobutamine-stress test and inflow occlusion, enabling preload independent evaluation of myocardial performance. Changes of measured data post-CPB were calculated in relation to baseline-levels (%).

RESULTS

Baseline and operative data in both groups were similar. During the experiment, cardiac markers showed no significant variations between groups. Pressure-volume loop analysis during stress test revealed a significantly higher preload independent contractility (slope of end-systolic pressure-volume relation: Ees) with MBC compared with CCC (MBC: 123 ± 35% [confidence interval (CI95): 93-153] vs CCC: 78 ± 34% [CI95: 54-102]; P = 0.042), whereas cardiac output was not significantly different between groups {MBC: 122 ± 16% [95% confidence interval (CI95): 109-135] vs CCC: 105 ± 17% [CI95: 93-116]; P = 0.069}.

CONCLUSION

This randomized animal study proves feasibility and safety of MBC for paediatric use. Haemodynamic evaluation and cardiac markers did not show inferiority to standard CCC. Moreover, MBC seems to be associated with superior contractility post bypass, which encourages us to use MBC in paediatric patients in the near future.

The effect of tepid amino acid-enriched induction cardioplegia on the outcome of infants undergoing cardiac surgery

Background:

Despite promising experimental results, no information has been published on the clinical effects of amino acid-enriched induction cardioplegic solution on outcome in children undergoing cardiac surgery.

Methods:

This is a retrospective study of 185 consecutive patients younger than 12 months with one of the following defects undergoing open heart surgery: atrioventricular septal defect, transposition of the great arteries, tetralogy of Fallot or ventricular septal defect. Patients were divided into two groups according to the following myocardial protection approaches: tepid substrate-enriched induction cardioplegia followed by cold blood cardioplegia (n=113) or only cold blood induction cardioplegia (n=72). Patient allocation was determined by the anesthesiologist in charge of cardiopulmonary bypass (CPB). The primary outcome measure was postoperative myocardial injury assessed by troponin T level and inotrope score.

Results:

Demographic data were similar for both groups. Cardioplegic induction had no overall effect for inotrope score (16.3 ± 9.2 vs.17.9 ± 10.0, p=0.276) or lactate release (1.8 ± 1.3 vs. 1.6 ± 0.8, p=0.110) on arrival to the paediatric intensive care unit. On the first postoperative day, there were no significant differences between the cardioplegia groups for inotrope score (13.7 ± 8.7 vs.14.3 ± 9.1, p=0.657), troponin T (2.4 ± 1.6 vs. 2.8 ± 2.7 μg/L, p=0.267), lactate (1.5 ± 2.0 vs. 1.5 ± 0.8, p=0.972), or any of the other clinical outcome measures.

Conclusions:

Compared to cold cardioplegia alone, the administration of tepid induction cardioplegia had no effect on the clinical outcome of infants who underwent cardiac surgery.

The crystalloid cardioplegia: advantages with a word of caution

Technical success and absence of iatrogenic injury from inadequate myocardial protection are the foremost targets of every cardiac surgical procedure. The current trends of pediatric cardiac surgery are aimed to achieve definitive repair of complex cardiac defects at birth as to avoid the risks related with palliative surgery and to reduce the long term impact of the untreated defect on the cardiac function. Thus, even newborn patients are exposed to a prolonged time of myocardial ischemia. The aim of this paper is to describe the impact of crystalloid HKT Custodiol cardioplegia infusion on myocardial protection in the early and late outcome of newborn patients who underwent arterial switch operation (ASO) for transposition of the great arteries (TGA).

High levels of fatty acids increase contractile function of neonatal rabbit hearts during reperfusion following ischemia

In the neonatal heart the transition from using carbohydrates to using fatty acids has not fully matured and oxidative metabolism/ATP generation may be limiting contractile function after ischemia. This study tested the hypothesis that increasing fatty acid availability increases recovery of left ventricular (LV) work by increasing palmitate oxidation, tricarboxylic acid (TCA) cycle activity, and ATP generation. Isolated working hearts from 7-day-old rabbits were perfused with Krebs solution containing low (0.4 mM) or high (2.4 mM) palmitate and 5.5 mM glucose. Hearts were subjected to 35-min global ischemia before 40-min reperfusion, and rates of glycolysis, glucose oxidation, and palmitate oxidation were assessed. LV work was similar before ischemia but was greater during reperfusion in hearts perfused with 2.4 mM palmitate compared with hearts perfused with 0.4 mM palmitate [6.98 ± 0.14 ( n = 15) vs. 3.01 ± 0.23 ( n = 16) mJ·beat−1·g dry wt−1; P < 0.05]. This was accompanied by increased LV energy expenditure during reperfusion [35.98 ± 0.16 ( n = 8) vs. 19.92 ± 0.18 ( n = 6) mJ·beat−1·g dry wt−1; P < 0.05]. During reperfusion the rates of palmitate oxidation [237.5 ± 28.10 ( n = 7) vs. 86.0 ± 9.7 ( n = 6) nmol·g dry wt−1·min−1; P < 0.05], total TCA cycle activity [2.65 ± 0.39 ( n = 7) vs. 1.36 ± 0.14 ( n = 6) μmol acetyl-CoA·g dry wt−1·min−1; P < 0.05], and ATP generation attributable to palmitate oxidation [26.6 ± 3.1 ( n = 7) vs. 12.6 ± 1.7 ( n = 6) μmol·g dry wt−1·min−1; P < 0.05] were greater in hearts perfused with 2.4 mM palmitate. These data indicate that the neonatal heart has decreased energy reserve, and, in contrast to the mature heart, increasing availability of fatty acid substrate increases energy production and improves recovery of function after ischemia.

Impact of normothermic perfusion and protein supplementation on human endothelial cell function during organ preservation

BACKGROUND

Hypothermia-induced changes in endothelial cell (EC) morphology and function after organ storage may influence the initial outcome and development of transplant-associated coronary artery disease.

METHODS

Human saphenous vein ECs were incubated with saline (NaCl), University of Wisconsin (UW), and histidine-tryptophan-ketoglutarate (HTK) solution, with and without protein additives, at 4 degrees C and 37 degrees C. After 6 hours, ECs were recultivated for 24 and 48 hours with culture medium (reperfusion). Mitochondrial activity, adenosine triphosphate concentration, cell count, and inflammatory responses were analyzed.

RESULTS

Cold preservation did not affect the mitochondrial activity of ECs and allowed a complete regeneration of the metabolic turnover after reperfusion. However, under normothermic conditions the metabolism of the cells was influenced by time and type of preservation solution. While both the mitochondrial activity and cell count did not change after treatment with NaCl and culture medium, the metabolic turnover of cells treated with HTK and UW solution significantly increased (twofold) and decreased (twofold, p < 0.05), respectively, after reperfusion. The endothelial reactivity remained unchanged after treatment with NaCl and HTK. The addition of serum proteins significantly improved mitochondrial activity of cells treated with warm NaCl and HTK (p < 0.05). The UW-treated cells burned out through a significant up-regulation of the ATP concentration resulting in a complete metabolic regression after reperfusion and induction of apoptosis.

CONCLUSIONS

Normothermic preservation in UW prevented regeneration of ECs, while treatment with HKT solution did not irreversibly affect mitochondrial activity of ECs and allowed complete regeneration of metabolism and function. Serum proteins improved the preservation effect of HTK and NaCl.