Not all neonatal hearts are equally protected from ischemic damage during hypothermia

Two cases of "stone heart" with fatal outcome

The "stone heart" syndrome is a rare but often fatal complication of cardiac surgery associated with hypertrophy of the myocardium. The mechanisms behind the syndrome are not fully understood. In this case report, we describe two cases of stone heart in newborn girls. Both girls were born with congenital heart abnormalities including ventricular septum defects (VSD), hypertrophy of the myocardium and patent arterial duct (PDA), which was prenatally diagnosed. In each of the two cases, the stone heart became evident immediately after initiating cardiopulmonary bypass, and ended fatally.

Pediatric myocardial protection: a cardioplegic strategy is the "solution"

This article describes the experimental infrastructure and subsequent successful clinical application of a comprehensive cardioplegic strategy that limits intraoperative injury and improves postoperative outcomes in pediatric patients. The infant heart is at high risk of damage from poor protection as a result of preoperative hypertrophy, cyanosis, and ischemia. These factors may also make the immature (pediatric) heart more sensitive to cardioplegic arrest compared with the mature (adult) heart. The preoperative factors of cyanosis and pressure volume overload are discussed, followed by the infrastructure of the strategies of warm induction and reperfusion with substrate enhancements, multidose cardioplegia, and a "modified" integrated approach to allow ischemia only when visualization is needed in pediatric surgeries. The importance of using a blood cardioplegia solution, with reduced calcium, increased magnesium, and low perfusion pressure are also shown. A practical clinical framework based on these experimentally proven principles is then presented to allow the surgeon to apply these strategies clinically. The results of using these principles are depicted in a series of 567 patients, including 93 patients with hypoplastic left heart syndrome. Applications of these concepts should improve the safety of protection of the infant heart and reduce postoperative morbidity and mortality.

The role of leukodepletion in limiting ischemia/reperfusion damage in the heart, lung and lower extremity

This article describes the experimental infrastructure and subsequent clinical application of a comprehensive reperfusion strategy to limit the injury following ischemia, resulting in an improvement in post operative organ function. In particular, it examines the role of luekodepletion in minimizing damage and improving functional outcome in the heart, lung and lower extremity. During cardiothoracic procedures, various organs can be subjected to temporary ischemia, particularly the heart (cardioplegic arrest), lung (transplant), and lower extremity (femoral canulation, IABP). The background of ischemia/reperfusion injury is discussed as it applies to each of these 3 organs, as well as findings that ischemia followed by reperfusion results in a similar injury in each organ. Data are then presented to demonstrate that a comprehensive reperfusion strategy, utilizing a modified substrate-enriched blood reperfusate delivered at a low pressure can limit this injury, and that adding white blood cell filtration significantly improves the efficacy of this approach. These principles have now been used in a series of patients undergoing various surgical procedures with excellent results. Application of these concepts may significantly improve the outcome in patients undergoing procedures which subject these organs to temporary ischemia.

A long-term stable normothermic cardiopulmonary bypass model in neonatal swine

BACKGROUND

An appropriate animal model of cardiopulmonary bypass (CPB) is critical in order to study the morbidity and mortality in newborn children undergoing long-term cardiac surgery. Since this has been reported to be technically difficult, this paper describes a neonatal porcine CPB model (3 days old, n = 18) for up to 8 h to study long-term bypass.

METHODS

After anesthesia, neonates had arterial/venous monitoring lines inserted, they were heparinized (300 IU/kg), the aorta was cannulated for arterial retroperfusion, and a two-stage venous drainage catheter was placed in the right atrium. A Medtronic Minimax Plus oxygenator and the bypass circuit were primed with donor blood and CPB was instituted.

RESULTS

Line and mean arterial pressures were kept at 147.7 +/- 73 and 62.7 +/- 9 mm Hg, respectively. Myocardial (38.1 +/- 1.0 degrees C) and rectal temperatures (37.7 +/- 1.0 degrees C) were maintained. Heart rate was 184.8 +/- 34.5 bpm. Hematocrits were 29.6 +/- 6.0%, activated clotting time was sustained above 400 s throughout bypass, blood gas parameters were maintained in the normal range (pH, 7.39 +/- 0.1; PO(2), 123.1 +/- 65.2 mm Hg; PCO(2), 37.2 +/- 8.5 mm Hg; and HCO(3)(-), 21.5 +/- 3.6 mmol/L). CPB was terminated after 8 h and no visceral edema or other imbalances normally associated with swine on bypass were observed.

CONCLUSIONS

Results demonstrate a model of stable long-term bypass in neonatal swine which can be used to study issues critical to children requiring surgical correction and CPB at a young age. Overall effects of surgery and bypass on these younger patients have yet to be explored and therefore a stable long-term normothermic model of CPB would allow the study of numerous parameters associated with this complicated procedure.

Pediatric myocardial protection: an overview

This article describes the experimental infrastructure and subsequent successful clinical application of a comprehensive bypass and cardioplegic strategy that limits intraoperative injury and improves postoperative outcomes in pediatric patients. The infant heart is at high risk of damage from poor protection because of preoperative hypertrophy, cyanosis, and ischemia. The background factors of vulnerability to damage caused by cyanosis and ischemia are discussed, together with studies of the infrastructure of strategies to use normoxia versus hyperoxia as bypass starts, white blood cell filtration, warm induction and reperfusion with substrate enhancements, multidose blood cardioplegia, and an integrated approach to allow ischemia only when vision is needed in pediatric surgeries. Data on cardioplegic management, including reducing calcium, increasing magnesium, and reducing perfusion pressure are shown, as used during this technique. These principles were applied to a consecutive series of 567 patients at the Heart Institute for Children and University of Illinois hospital over a 2-year period. Included also were 72 patients with hypoplastic left heart over a 4-year period with this myocardial management strategy. Application of these concepts may improve the safety of protection in infant hearts.

Metabolic and functional response of neonatal pig hearts to the development of ischemic contracture: is recovery possible?

The potential for functional and metabolic recovery in neonatal hearts after the development of ischemic contracture remains controversial and undefined. This study documents post-ischemic recovery of metabolism and function in the in vivo neonatal heart after the development of onset and peak ischemic contracture. In piglets on cardiopulmonary bypass, hearts were reperfused after the development of either onset (TICo) or peak (TICp) ischemic contracture. Systolic (developed and systolic function, contractility) and diastolic (diastolic function, relaxation) performance was assessed throughout reperfusion. Biopsies were obtained at end-ischemia or end-reperfusion to assess metabolism. By end-ischemia, the metabolic profiles of both TICo and TICp hearts confirmed energy-store depletion and purine degradation that was quantitatively greater in TICp hearts. Hearts reperfused at TICo had consistent moderate impairment of developed function, contractility, diastolic function, and relaxation, whereas hearts reperfused at TICp had much more profound functional impairment. Diastolic function showed the worst functional recovery. In contrast, systolic function was not significantly altered in either study group and, thus, did not reflect the actual extent of injury. In addition, TICo hearts either did not further deplete or partially regenerated energy stores during reperfusion, whereas TICp hearts had further energy-store depletion and lactate accumulation. In summary, neonatal hearts reperfused after TICo maintained or partially restored energy stores and had significant but incomplete functional recovery. In contrast, further metabolic deterioration and profound functional impairment occurred with reperfusion after TICp, potentially indicating ongoing mitochondrial injury and compromised oxidative phosphorylation.

Development of cardiac sensitivity to oxygen deficiency: comparative and ontogenetic aspects

Hypoxic states of the cardiovascular system are undoubtedly associated with the most frequent diseases of modern times. They originate as a result of disproportion between the amount of oxygen supplied to the cardiac cell and the amount actually required by the cell. The degree of hypoxic injury depends not only on the intensity and duration of the hypoxic stimulus, but also on the level of cardiac tolerance to oxygen deprivation. This variable changes significantly during phylogenetic and ontogenetic development. The heart of an adult poikilotherm is significantly more resistant as compared with that of the homeotherms. Similarly, the immature homeothermic heart is more resistant than the adult, possibly as a consequence of its greater capability for anaerobic glycolysis. Tolerance of the adult myocardium to oxygen deprivation may be increased by pharmacological intervention, adaptation to chronic hypoxia, or preconditioning. Because the immature heart is significantly more dependent on transsarcolemmal calcium entry to support contraction, the pharmacological protection achieved with drugs that interfere with calcium handling is markedly altered. Developing hearts demonstrated a greater sensitivity to calcium channel antagonists; a dose that induces only a small negative inotropic effect in adult rats stops the neonatal heart completely. Adaptation to chronic hypoxia results in similarly enhanced cardiac resistance in animals exposed to hypoxia either immediately after birth or in adulthood. Moreover, decreasing tolerance to ischemia during early postnatal life is counteracted by the development of endogenous protection; preconditioning failed to improve ischemic tolerance just after birth, but it developed during the early postnatal period. Basic knowledge of the possible improvements of immature heart tolerance to oxygen deprivation may contribute to the design of therapeutic strategies for both pediatric cardiology and cardiac surgery.

Myocardial function is normal after rapid cooling of the in vivo neonatal heart

Rapid cooling (RC) on cardiopulmonary bypass (CPB) has been reported to be injurious to the neonatal myocardium when compared with slow cooling (SC). However, previous studies have been performed on isolated heart preparations using asanguineous perfusates and may not represent clinically valid conclusions. In this study, the effect of RC versus SC on post-CPB cardiac function in an in vivo neonatal heart model using a blood perfusate was investigated. Thirteen neonatal piglets underwent median sternotomy. Left ventricular ultrasonic dimension transducers were placed in the minor and major axis diameters, and an intraventricular micromanometer was placed. Baseline left ventricular pressure-dimension data were obtained during transient vena caval occlusion. Animals were then placed on CPB (blood prime; mean hematocrit, 25%) with the prime temperature at either 18 degrees C (RC) or 37 degrees C (SC) and perfusion cooled either quickly (RC) or gradually (SC) such that within 2 minutes of cooling the average myocardial temperature was 23.5 degrees C in the RC group versus 33.8 degrees C in the SC group (p = 0.0001). Animals were cooled to 20 degrees C, rewarmed to 37 degrees C, and then weaned from CPB. Left ventricular pressure-dimension data were obtained 30 minutes after CPB and compared with baseline. The slope (MW) and x-intercept (Vo) of the linear stroke work-end-diastolic volume relationship were used as load-insensitive indices of left ventricular function at baseline and after CPB. There was no statistically significant difference in baseline versus postbypass MW or Vo in the RC or SC groups.(ABSTRACT TRUNCATED AT 250 WORDS)