Myocardial preservation in the neonate

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.

Deep hypothermic circulatory arrest or tepid regional cerebral perfusion: impact on haemodynamics and myocardial integrity in a randomized experimental trial

OBJECTIVES

Organ protective management during aortic arch surgery comprises deep hypothermic (18°C) circulatory arrest (DHCA), or moderate hypothermia (28°C/ 'tepid') with regional cerebral perfusion (TRCP). The aim of this experimental study was to evaluate the effect of distinct organ protective management on hemodynamic performance and myocardial integrity.

METHODS

Ten male piglets were randomized to group DHCA (n = 5) or TRCP (n = 5) group and operated on cardiopulmonary bypass (CPB) with 60 min of aortic cross-clamping. Blood gas analysis was performed throughout the experiment. Haemodynamic assessment was performed using a thermodilution technique before and after CPB. Myocardial biopsies were taken 2 h after CPB and evaluated using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick-end labelling assay and western blot analysis.

RESULTS

At reperfusion, levels of central venous saturation were significantly higher (P = 0.016) and levels of lactate significantly lower (P = 0.029) in the DHCA group. After CPB, thermodilution measurements revealed higher stroke volume and lower peripheral resistance in the TRCP group (P = 0.012 and 0.037). At the end of the experiment, no significant differences regarding laboratory and haemodynamic parameters were evident. All specimens showed enrichment of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick-end labelling-positive cells exclusively at the left ventricular subendocardium with no difference between groups and equal concentrations of cyclo-oxygenase-2.

CONCLUSIONS

TRCP is associated with decreased peripheral resistance and higher stroke volume immediately after CPB. However, this beneficial effect is contrasted by signs of lower body hypoperfusion, which is expressed by lower central venous saturations and higher lactate levels. Distinct strategies of organ protection did not seem to affect apoptotic/necrotic and inflammatory changes in the left ventricular myocardium.

Ischaemia/reperfusion in the posthypoxaemic re-oxygenated myocardium: haemodynamic study in the isolated perfused rat heart

In order to study the haemodynamics of reperfusion injury in the post hypoxaemic heart, we exposed buffer-perfused isolated rat hearts to either: (1) 20-minute low-flow ischaemia or (2) 20-minute hypoxaemia followed by re-oxygenation and further ischaemia/reperfusion. In group 2, the myocardial contractility recovered less (p <0.002) than in group 1. This model therefore represents with sufficient reliability the clinical situation where hypoxaemic hearts are re-oxgenated before ischaemia/reperfusion and receive more severe injury than hearts exposed to ischaemia/reperfusion only. To locate the major site of the injury, further data were obtained (1) with infusion of superoxide dismutase and catalase during hypoxaemia and in the first five minutes of re-oxygenation, and (2) by eliminating re-oxygenation. It appears that the major determinant of reperfusion injury in hypoxaemic hearts is to be looked for in the events underlying hypoxaemia or re-oxygenation, and is mediated by oxygen- derived free radicals.

Modified aortic cannulation for cardiopulmonary bypass in neonatal piglet model

Animal models are still essential for studying effects of cardiopulmonary bypass. We describe modifications in cannulation technique for a neonatal piglet model, which may also serve as an "everyday" technique in congenital cardiac surgery (age of animals <7 days; mean body weight 2.9 +/- 0.5 kg). Surgical approach through median sternotomy and cardiopulmonary bypass was established by cannulating right atrium and ascending aorta with a modified aortic root cannula. Left ventricular venting was performed placing a cannula into the apex and connecting this to the venous drainage line. The described technique has been applied in 19 cases, all but one were without technical problems.

Cardioplegia in pediatric cardiac surgery: do we believe in magic?

Cardioplegia has become the gold standard of myocardial protection for practically every type of heart surgery during which the ascending aorta must be clamped. Although there is little doubt about the efficacy of cardioplegia in the adult heart, there are few studies on the pediatric heart and their results are contradictory. The physiology of pediatric heart muscle differs considerably from that of the adult myocardium. The pediatric heart distinguishes itself from that of the adult most impressively in its greater tolerance for ischemia. This ischemia tolerance is enhanced by the use of hypothermia. Considering that hypothermia is a powerful tool to prolong ischemia tolerance and that most pediatric cardiac surgeons report similar results using different types of cardioplegia, some surgeons are tempted to suspect that the contribution of the cardioplegia composition to protecting the pediatric heart may be overestimated. This provocative statement is critically discussed in this article. We examine the protective potential of cardioplegia (in various compositions), or of hypothermia, or of both in pediatric cardiac surgery. We pay special attention to several key differences between the physiologies of the pediatric myocardium and the adult myocardium and attempt to relate them to the available surgical methods of myocardial protection. We conclude that the composition of cardioplegia indeed is an important component of successful operative management in pediatric heart surgery. We provide evidence that the benefit of cardioplegia over hypothermia alone is minor at low temperatures (below 15 degrees C), but becomes substantial when the temperature increases.

Developmental differences in myocyte contractile response after cardioplegic arrest

Although developmental differences in left ventricular function after cardioplegic arrest and rewarming have been postulated, whether differences exist at the level of the myocyte remains unexplored. This project tested the hypothesis that there is a differential effect of hypothermic hyperkalemic cardioplegic arrest with subsequent rewarming on contractile function of immature compared with adult ventricular myocytes. Myocytes were isolated from the left ventricular free wall of five immature and five adult rabbits and incubated for 2 hours in hyperkalemic modified Ringer's solution at 4 degrees C (cardioplegia) or for 2 hours in cell culture medium at 37 degrees C (normothermia). Myocytes were resuspended ("rewarmed") in 37 degrees C cell culture medium after the incubation protocol. Normothermic baseline contractile performance was lower in immature, compared with adult, myocytes. Specifically, myocyte shortening velocity was 62 +/- 4 microm/sec in immature and 112 +/-6 microm/sec in adult myocytes (p < 0.01). After cardioplegia and rewarming, immature myocyte contractile function was unchanged, whereas adult myocyte contractile function was significantly diminished. For example, myocyte shortening velocity was 65 +/- 4 microm/sec in immature and 58 +/- 3 microm/sec in adult myocytes (p < 0.01 versus normothermic). Myocyte surface area, which reflects myocyte volume, was increased after cardioplegia and rewarming in adults (3582 +/- 55 versus 3316 +/- 46 microm2, p < 0.01), but remained unchanged in immature myocytes (2212 +/- 27 versus 2285 +/- 28 microm2, P = not significant). These unique findings demonstrate a preservation of myocyte contractile function and volume regulation in immature myocytes after cardioplegic arrest and rewarming. Thus this study directly demonstrates that developmental differences exist in myocyte responses to hypothermic hyperkalemic cardioplegic arrest with subsequent rewarming.

Depression of cardiac function after deep hypothermic circulatory arrest in deeply anesthetized neonatal lambs

Cardiac dysfunction is common after neonatal cardiac operations. Previous in vivo studies in neonatal animal models however, have failed to demonstrate decreased left ventricular function after ischemia and reperfusion. Cardiac dysfunction may have been masked in these studies by increased endogenous catecholamine levels associated with the use of light halothane anesthesia. Currently, neonatal cardiac operations are often performed with deep opiate anesthesia, which suppresses catecholamine surges and may affect functional recovery. We therefore examined the recovery of left ventricular function after ischemia and reperfusion in neonatal lambs anesthetized with high-dose fentanyl citrate (450 micrograms/kg administered intravenously). Seven intact neonatal lambs with open-chest preparation were instrumented with left atrial and left ventricular pressure transducers, left ventricular dimension crystals, and a flow transducer. The lambs were cooled (< 18 degrees C) on cardiopulmonary bypass (22 +/- 6 minutes), exposed to deep hypothermic circulatory arrest (46 +/- 1 minutes), and rewarmed on cardiopulmonary bypass (30 +/- 10 minutes). Catecholamine levels and indexes of left ventricular function were determined before (baseline) and 30, 60, 120, 180, and 240 minutes after termination of cardiopulmonary bypass. Levels of epinephrine, norepinephrine, and dopamine were unchanged from baseline values. Left ventricular contractility (slope of end-systolic pressure-volume relationship) was depressed from baseline value (31.7 +/- 9.3 mm Hg/ml) at 30 minutes (15.7 +/- 6.4 mm Hg/ml) and 240 minutes (22.7 +/- 6.4 mm Hg/ml) but unchanged between 60 and 180 minutes. Left ventricular relaxation (time constant of isovolumic relaxation) was prolonged from baseline value (19.0 +/- 3.0 msec) at 30 minutes (31.4 +/- 10.0 msec) and 240 minutes (22.1 +/- 2.8 msec) but unchanged between 60 and 180 minutes. Afterload (left ventricular end-systolic meridional wall stress) was decreased at 30, 60, and 240 minutes. Indexes of global cardiac function (cardiac output, stroke volume), preload (end-diastolic volume), and left ventricular compliance (elastic constant of end-diastolic pressure-volume relationship) were unchanged from baseline values. In deeply anesthetized neonatal lambs exposed to ischemia and reperfusion, left ventricular contractility, relaxation, and afterload are markedly but transiently depressed early after reperfusion and mildly depressed late after reperfusion.

Aging reduces postischemic recovery of coronary endothelial function

The aging process is known to be associated with profound changes in the heart. To determine whether resistance of coronary endothelial and vascular smooth muscle function to ischemia may be related to age, four groups of rats (n = 6 in each group) of different ages (1, 5, 15, and 26 months) were subjected to cardioplegic arrest for 4 hours at 4 degrees C. The postischemic basal release of nitric oxide by endothelium, as assessed by the percentage loss of coronary flow in response to 0.5 mmol/L L-monomethylarginine, an inhibitor of nitric oxide synthase, was as follows: (mean +/- standard error of the mean): 87.1% +/- 1.7%, 81.2% +/- 2.3%, 79.6% +/- 1.9%, and 74.9% +/- 2.4% in groups 1, 2, 3, and 4, respectively. Stimulated release of nitric oxide, as assessed by percentage increase of coronary flow to 10(-5) mmol/L 5-hydroxytryptamine, an endothelium-dependent vasodilator, was as follows (mean +/- standard error of the mean): 88.3% +/- 1.5%, 83.4% +/- 2.4%, 71.1% +/- 2.7%, and 63.1% +/- 3.3% in groups 1, 2, 3, and 4, respectively. Significant differences were found between each group (p < 0.05) for both basal and stimulated release of nitric oxide. Vascular smooth muscle function, as assessed by the percentage increase in coronary flow in response to glyceryl trinitrate, an endothelium-independent vasodilator, was (mean +/- standard error of the mean): 96.7% +/- 2.1%, 92.3% +/- 5.2%, 92.9% +/- 5.0%, and 98.1% +/- 2.4% in groups 1, 2, 3, and 4 respectively. No significant difference was found between groups (p = not significant). In a protocol mimicking conditions for transplantation, the postischemic recovery of the basal and stimulated release of nitric oxide, but not vascular smooth muscle function, diminished with age.

Age-related changes in the efficacy of crystalloid cardioplegia

Recent work has shown that multi-dose St. Thomas' Hospital cardioplegia solution (STHC) may not provide reliable protection of the neonatal myocardium. We have used an isolated working heart model to study the age-related development of this observation. Sets of eight hearts from 2-, 4-, 6-, and 8-week-old rabbits were subjected to 90 min of ischemia at 10 degrees C. STHC was infused at 30-min intervals in a dose of 10 ml/kg. There were no differences in the preservation of ATP stores during ischemia among the groups. The percentage recovery of preischemic mean aortic pressure, left atrial pressure, and heart rate were not different among groups, but the percentage recovery of aortic flow (AF) (expressed as means +/- standard error of the mean) was significantly lower in the 2- and 4-week hearts (44.1 +/- 8.2 and 66.2 +/- 7.7%) than in the 6- and 8-week hearts (93.0 +/- 6.4 and 97.6 +/- 4.7%). We have confirmed that the use of multi-dose STHC impairs recovery of ventricular function in the neonatal rabbit heart. This effect, however, diminishes rapidly as the immature animal develops and is not present by 6 weeks of age. Additional experimentation is necessary to identify those aspects of the developing myocardium that account for these observations.

Purines, lactate and phosphate release from child and adult heart during cardioplegic arrest

The release of lactate, phosphate and purine catabolites from the heart in adult and children undergoing cardiac surgery was recorded. The compounds were determined in the coronary effluent collected during subsequent infusions of cardioplegic solution into the coronary root. As compared to the infusion just after onset of ischemia, both in adults and children manifold increase of the release was observed during subsequent infusions. The rates of release of lactate, phosphate and purines (adenosine + inosine + hypoxanthine) were 1.5 to 2.5 times higher in children than in adult hearts during the second cardioplegic infusion and 3 to 7 times higher during the third cardioplegic infusion in spite of a more frequent infusion of cardioplegic solution in children. A much greater increase of the release of lactate, phosphate and purines provides evidence for more severe metabolic injury during cardioplegic arrest to the heart in children than in adults.