Vulnerability of paediatric myocardium to cardiac surgery

Predictive value of NT-proBNP and hs-TnT for outcomes after pediatric congenital cardiac surgery

BACKGROUND

The available evidence regarding the predictive value of troponins and natriuretic peptides for early postoperative outcomes in pediatrics is limited, controversial, and based on small sample sizes. The authors aimed to investigate the association of N-terminal pro B-type natriuretic peptide (NT-proBNP) and high-sensitivity troponin T (hs-TnT) with the in-hospital adverse outcomes after congenital cardiac surgeries.

METHODS

A secondary analysis based on a prospective study of pediatric congenital heart disease (CHD) patients was conducted to investigate the association of NT-proBNP and hs-TnT tested within 6 h postoperatively with in-hospital adverse events. A multivariate logistic regression analysis with a minimum P value approach was used to identify the optimal thresholds of NT-proBNP and hs-TnT for risk stratification.

RESULTS

NT-proBNP and hs-TnT are positively correlated with cardiopulmonary bypass time, mechanical ventilation duration, and pediatric intensive care unit stay. The predictive performance of NT-proBNP is excellent for adverse events in both patients younger than 1 year [area under the curve (AUC): 0.771, 0.693-0.850] and those older than 1 year (AUC: 0.839, 0.757-0.922). However, hs-TnT exhibited a satisfactory predictive value solely in patients aged over 1 year. (AUC: 0.784, 0.717-0.852). NT-proBNP levels of 2000-10 000 ng/l [odds ratio (OR): 3.79, 1.47-9.76] and exceeding 10 000 ng/l (OR: 12.21, 3.66-40.80) were associated with a higher risk of postoperative adverse events in patients younger than 1 year. Patients older than 1 year, with NT-proBNP higher than 500 ng/l (OR: 15.09, 6.05-37.66) or hs-TnT higher than 1200 ng/l (OR: 5.50, 1.47-20.59), had a higher incidence of postoperative adverse events.

CONCLUSIONS

NT-proBNP and hs-TnT tested within postoperative 6 h demonstrated significant predictive value for postoperative adverse events in CHD patients older than 1 year. However, among CHD patients younger than 1 year, only NT-proBNP exhibited commendable predictive performance for postoperative adverse events.

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.

Postoperative Serum Troponin Trends in Infants Undergoing Cardiac Surgery

Troponin-I (TN-I) levels are elevated following pediatric cardiac surgery with speculation that particular patterns may have prognostic significance. There is lack of procedure-specific data regarding postoperative TN-I levels in infants undergoing cardiac surgery. We hypothesized that TN-I elevation varies with type of surgery and persistent elevation predicts poor prognosis. We prospectively measured serial TN-I levels (preoperatively, 4, 8, 12, 24, and 48 hours postoperatively) in 90 infants (age < 1 year) undergoing cardiac surgery: off cardiopulmonary bypass (CPB) (n = 15), on CPB (n = 43), and on CPB with ventricular incision (CPB with ventricular incision; n = 32). All patients had undetectable baseline TN-I levels. The area under the curve of TN-I levels over the 48-hour period was significantly different among the surgical groups (P < 0.002), and highest in patients with CPB with ventricular incision. Generally, TN-I levels peaked by 4 hours after surgery and returned to near-normal levels within 48 hours. A persistent TN-I rise beyond 8 hours after surgery was a strong predictor of postoperative hypoperfusion injury (defined as a composite endpoint of end-organ injury resulting from inadequate perfusion, odds ratio 21.5; P = 0.001) and mortality (30% in those with persistently high TN-I, compared with 3.5% in the remaining patients; P < 0.001), independent of patient age, anatomy and/or complexity of surgery, and level of postoperative support. Our data provide benchmark values for TN-I levels following cardiac surgery in infants. Extent of TN-I elevation correlates with type of surgery. Persistent TN-I elevation beyond 8 hours after surgery is strongly associated with postoperative hypoperfusion injury and mortality.

Minimally invasive perventricular versus open surgical ventricular septal defect closure in infants and children: a randomised clinical trial

Background

Robust evidence is lacking regarding the clinical efficacy, safety and cardiopulmonary performance of perventricular closure. This study investigated the perioperative efficacy, safety and cardiorespiratory performance of perventricular closure of perimembranous ventricular septal defects (pmVSDs).

Methods

Operation-naïve infants and young children aged 5–60 months with isolated pmVSDs were randomised to receive either standard open surgical or minimally invasive perventricular closure via direct entry into the ventricle with a catheter from a subxiphoid incision. The primary outcomes included complete closure at discharge, major and minor adverse events and the changes in perioperative cardiorespiratory performance from baseline. Complete closure was mainly analysed in the modified intention-to-treat (mITT) population, with sensitivity analyses for the ITT, per-protocol (PP) and as-treated (AT) populations (non-inferiority margin −5.0%).

Results

We recruited 200 patients with pmVSDs for this study (mean age 24.38 months, range 7–58 months, 104 girls), of whom 100 were randomly allocated to one of the study groups. The non-inferiority of perventricular to surgical closure regarding complete closure at discharge was not shown in the ITT (absolute difference −0.010 (95% CI −0.078 to 0.058)) and mITT populations (−0.010 (95% CI −0.069 to 0.048)), but was shown in the PP (0.010 (95% CI −0.043 to 0.062)) and AT populations (0.048 (95% CI −0.009 to 0.106)). Perventricular closure reduced the rate of compromising cardiac haemodynamics, electrophysiological responses, cardiomyocyte viability, respiratory mechanics, ventilatory and gas exchange function and oxygenation and tissue perfusion compared with surgical closure (all between-group P<0.05).

Conclusions

For infants and young children with pmVSD, perventricular closure reduced the rate of postoperative cardiorespiratory compromise compared with surgical closure, but the non-inferiority regarding complete closure should be interpreted in the context of the specific population.

Trial registration number

NCT02794584 ;Results.

Rationale for Implementation of Warm Cardiac Surgery in Pediatrics

Cardiac surgery was developed thanks to the introduction of hypothermia and cardiopulmonary bypass in the early 1950s. The deep hypothermia protective effect has been essential to circulatory arrest complex cases repair. During the early times of open-heart surgery, a major concern was to decrease mortality and to improve short-term outcomes. Both mortality and morbidity dramatically decreased over a few decades. As a consequence, the drawbacks of deep hypothermia, with or without circulatory arrest, became more and more apparent. The limitation of hypothermia was particularly evident for the brain and regional perfusion was introduced as a response to this problem. Despite a gain in popularity, the results of regional perfusion were not fully convincing. In the 1990s, warm surgery was introduced in adults and proved to be safe and reliable. This option eliminates the deleterious effect of ischemia-reperfusion injuries through a continuous, systemic coronary perfusion with warm oxygenated blood. Intermittent warm blood cardioplegia was introduced later, with impressive results. We were convinced by the easiness, safety, and efficiency of warm surgery and shifted to warm pediatric surgery in a two-step program. This article outlines the limitations of hypothermic protection and the basic reasons that led us to implement pediatric warm surgery. After tens of thousands of cases performed across several centers, this reproducible technique proved a valuable alternative to hypothermic surgery.

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.

Comparison of cardioprotective effects of volatile anesthetics in children undergoing ventricular septal defect closure

BACKGROUND

Volatile anesthetic agents may precondition the myocardium and protect against ischemia and infarction. Preconditioning by volatile anesthetic agents is well documented in adults but is underinvestigated in children. The present study compares the effect of preconditioning in children by three volatile anesthetic agents along with several other variables associated with cardioprotection.

METHOD

Eighty children scheduled for ventricular septal defect closure under cardioplegic arrest were assigned to preconditioning for five minutes after commencement of cardiopulmonary bypass (CPB) with one minimum alveolar concentration (MAC) of one of the following agents: isoflurane, sevoflurane, desflurane, or placebo (oxygen-air mixture). The plasma concentration of creatine kinase MB (CK-MB) was determined after initiation of CPB, and again 6 and 24 hours after admission to the intensive care unit (ICU) after surgery. Duration of inotropic support, mechanical ventilation, and length of ICU stay in all the groups were also recorded.

RESULTS

Preconditioning with isoflurane, sevoflurane, and desflurane was associated with significantly decreased postoperative release of CK-MB as compared to placebo group at 6 (group 1: 237.2 ± 189, group 2: 69.8 ± 15.8, group 3: 64.7 ± 37.8, and group 4: 70.4 ± 26.7) and 24 hours (group 1: 192.4 ± 158.2, group 2: 67.7 ± 25.0, group 3: 85.7 ± 66.8, and group 4: 50.4 ± 31.6) after admission to ICU. No significant differences were observed in the CK-MB levels among the three volatile anesthetic agents. Duration of inotropic support, mechanical ventilation, and length of ICU stay were greater in placebo group as compared to other groups without reaching statistical significance.

CONCLUSION

Volatile anesthetic appear to provide definite cardioprotection to pediatric myocardium. No conclusion can be drawn regarding the best preconditioning agent among isoflurane, sevoflurane, and desflurane.

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.

Cardioprotection from oxidative stress in the newborn heart by activation of PPARγ is mediated by catalase

Regulation of catalase (CAT) by peroxisome proliferator-activated receptor-γ (PPARγ) was investigated to determine if PPARγ activation provides cardioprotection from oxidative stress caused by hydrogen peroxide (H(2)O(2)) in an age-dependent manner. Left ventricular developed pressure (LVDP) was measured in Langendorff perfused newborn or adult rabbit hearts, exposed to 200μM H(2)O(2), with perfusion of rosiglitazone (RGZ) or pioglitazone (PGZ), PPARγ agonists. We found: (1) H(2)O(2) significantly decreased sarcomere shortening in newborn ventricular cells but not in adult cells. Lactate dehydrogenase (LDH) release occurred earlier in newborn than in adult heart, which may be due, in part, to the lower expression of CAT in newborn heart. (2) RGZ increased CAT mRNA and protein as well as activity in newborn but not in adult heart. GW9662 (PPARγ blocker) eliminated the increased CAT mRNA by RGZ. (3) In newborn heart, RGZ and PGZ treatment inhibited release of LDH in response to H(2)O(2) compared to H(2)O(2) alone. GW9662 decreased this inhibition. (4) LVDP was significantly higher in both RGZ+H(2)O(2) and PGZ+H(2)O(2) groups than in the H(2)O(2) group. Block of PPARγ abolished this effect. In contrast, there was no effect of RGZ in adult. (5) The cardioprotective effects of RGZ were abolished by inhibition of CAT. In conclusion, PPARγ activation is cardioprotective to H(2)O(2)-induced stress in the newborn heart by upregulation of catalase. These data suggest that PPARγ activation may be an effective therapy for the young cardiac patient.

Biomonitors of cardiac injury and performance: B-type natriuretic peptide and troponin as monitors of hemodynamics and oxygen transport balance

Serum biomarkers, such as B-type natriuretic peptide and troponin, are frequently measured in the cardiac intensive care unit. A review of the evidence supporting monitoring of these biomarkers is presented.

DESIGN

A search of MEDLINE, PubMed, and the Cochrane Database was conducted to find literature regarding the use of B-type natriuretic peptide and troponin in the cardiac intensive care setting. Adult and pediatric data were considered.

RESULTS AND CONCLUSION

Both B-type natriuretic peptide and troponin have demonstrated utility in the intensive care setting but there is no conclusive evidence at this time that either biomarker can be used to guide inpatient management of children with cardiac disease. Although B-type natriuretic peptide and troponin concentrations can alert clinicians to myocardial stress, injury, or hemodynamic alterations, the levels can also be elevated in a variety of clinical scenarios, including sepsis. Observational studies have demonstrated that perioperative measurement of these biomarkers can predict postoperative mortality and complications.

RECOMMENDATION AND LEVEL OF EVIDENCE

(class IIb, level of evidence B): The use of B-type natriuretic peptide and/or troponin measurements in the evaluation of hemodynamics and postoperative outcome in pediatric cardiac patients may be beneficial.

Arterial Switch Operation: Troponin T Does Not Predict Ventilation Requirements

The aim of this study was to assess whether postoperative cardiac troponin T levels could predict ventilation requirements in infants undergoing the arterial switch operation. Cardiac troponin T was measured 6 hours after aortic cross clamping and prior to tracheal extubation in 20 consecutive patients; 10 had simple and 10 had complex (with ventricular septal defect) transposition of the great arteries. The mean plasma troponin T level prior to extubation did not differ significantly in patients who were re-intubated and those who were successfully extubated. The initial cardiac troponin T levels in the complex defect group was significantly higher than in the simple transposition group. There was no correlation between initial cardiac troponin T levels and the duration of mechanical ventilation. There was no difference in mean duration of ventilation between the 2 groups. It was concluded that the postoperative cardiac troponin T level is not a predictor of successful extubation or prolonged artificial ventilation in this subset.

Segmental Wall-Motion Abnormalities After an Arterial Switch Operation Indicate Ischemia

We prospectively studied 29 consecutive neonates undergoing an arterial switch operation to determine if segmental wall motion abnormalities (SWMA) represented myocardial ischemia. Intraoperative transesophageal echocardiogram was recorded at baseline and twice after cardiopulmonary bypass. Cardiac troponin I (cTnI) levels were measured before sternal incision and 3, 6, 12, 24, 48, and 72 h after removal of the aortic cross-clamp. Immediate postoperative Holter and 15-lead electrocardiograms (ECG) were evaluated for ischemia. Transthoracic echocardiograms were obtained before hospital discharge. At bypass termination, immediately after protamine administration, segmental wall motion was normal in nine neonates and abnormal in 20. SWMA were transient in five and present at the time of chest closure in 15 neonates. Neonates in whom SWMA were present at chest closure had more segments involved than those in whom SWMA were transient (P > 0.001). Neonates with SWMA at chest closure had higher cTnI levels postoperatively versus neonates with normal wall motion (P = 0.02). Postoperative ECG data were available in 26 neonates. There was ECG evidence of myocardial ischemia in two of eight neonates with normal wall motion, one of five with transient SWMA, and nine of 13 with SWMA at chest closure. CTnI levels at 12, 24, and 48 h and intraoperative SWMA were predictive of postoperative SWMA. We believe these data indicate that SWMA, which persist at the completion of an arterial switch operation, and which are present in multiple myocardial segments, correlate with myocardial ischemia. Further follow-up of these patients is needed to determine if increased intraoperative myocardial ischemia correlates with long-term outcomes.

Cardiac Troponin T Levels for Risk Stratification in Pediatric Open Heart Surgery

BACKGROUND

Cardiac troponin T has been found to be accurate predictor of complications and adverse clinical events after pediatric cardiac surgery. Contrary to adult cardiac surgery, the relationship of troponin T to patient survival after pediatric heart surgery has not been previously studied. The purpose of this study was to determine whether troponin T could predict death after pediatric open cardiac surgery.

METHODS

This was a retrospective cohort study in which data from 1001 consecutive children having cardiac surgery during a 5-year period were studied. Perioperative variables that could influence death at 30 postoperative days were evaluated.

RESULTS

Multivariate analysis, using a forward stepwise logistic regression, showed that troponin T measured on the first postoperative day was a strong independent predictor of death at 30 days. Level of troponin T greater than 5.9 microg/L on the first postoperative day predicted death (odds ratio, 10.7; 95% confidence interval: 5.2 to 22.1) as did admission lactate level greater than 5.2 mmol/L (odds ratio, 22.2; 95% confidence interval: 9.7 to 50.8) No other variable, including postoperative creatine kinase-MB mass concentration, age, diagnosis, surgical procedure, presence of cyanosis, chromosomal anomaly or ventriculotomy, duration of cardiopulmonary bypass, or aortic cross-clamp, had any independent effect on 30-day survival.

CONCLUSIONS

Cardiac troponin T level on the first postoperative day is a powerful independent risk marker of death in pediatric cardiac surgery.

Frequency of clinically unsuspected myocardial injury at a children's hospital

BACKGROUND

Ill children are at risk but rarely screened for myocardial injury. The frequency of such injury in ill children is unknown. Elevated levels of plasma cardiac troponin I (cTnI) can detect subclinical myocardial injury.

METHODS

We measured cTnI levels from 283 Children's Hospital, Boston patients (median age 2.10 years, range 0.13-22.4 years) seen in an outpatient or emergency clinic without clinically apparent cardiac disease. We took > or = 0.5 ng/mL as an indication of myocardial injury. We also measured plasma creatine kinase-MB, total creatine kinase, and myoglobin, and performed a chart review.

RESULTS

Fifteen (7.8%) of the 193 acutely ill children and 4 (4.4%) of the 90 well children had an elevated cTnI level (P = .44). Within the acutely ill group, the children with elevated cTnI were younger and had lower mean hemoglobin and hematocrit levels. Cardiac troponin I levels correlated with creatine kinase-MB (r = 0.22; P < .001) but not with creatine kinase or myoglobin. The 4 children with cTnI > 0.89 ng/mL, who also had plasma cardiac troponin T measured, showed cardiac troponin T elevations that were consistent with unstable angina levels in adults. Four children had high-level cTnI elevations (> 2 ng/mL) consistent with acute myocardial infarction levels in adults.

CONCLUSIONS

Elevated cTnI levels occur in children without clinically apparent cardiac disease and can be at adult unstable angina or acute myocardial infarction levels. Prospective studies to determine the clinical significance of these findings and their relationship to the development of cardiomyopathy are warranted.

Serum Cardiac Troponin-I Elevation in Neonatal Cardiac Surgery is Lesion-Dependent

OBJECTIVE

Serum cardiac troponin-I (cTn-I) is a marker for myocardial injury in adults that undergoes developmental isoform change. To determine its utility as a myocardial injury marker in neonates, the authors examined the perioperative pattern of cTn-I elevation in neonates undergoing surgical repair for hypoplastic left-heart syndrome (HLHS) and transposition of great arteries (TGA).

DESIGN

A prospective cohort study.

SETTING

The study was performed in a tertiary teaching hospital that is a major referral center for congenital cardiac surgery.

PATIENTS

Forty-five neonates were enrolled, 17 with HLHS, 15 with TGA with intact septum (TGA + IVS), 8 with TGA with ventricular septal defect (TGA + VSD), and 5 neonates undergoing extracardiac surgery who did not require cardiopulmonary bypass (CPB).

INTERVENTIONS

None.

RESULTS

Preoperative cTn-I was elevated in all neonates undergoing cardiac surgery with CPB. Increases in postoperative cTn-I correlated with duration of aortic cross-clamp application and CPB. Peak elevation in serum cTn-I occurred between 6 and 24 hours postoperatively in all neonates after cardiac surgery. The perioperative pattern of cTn-I was different in TGA + VSD (peak cTn-I = 10.9 +/- 5.9 ng/mL) compared with HLHS (peak cTn-I = 4.62 +/- 3.4 ng/mL) and TGA + IVS (peak cTn-I = 4.46 +/- 3.5 ng/mL).

CONCLUSION

It was found that perioperative elevations in serum cTn-I in neonates with TGA and HLHS were influenced by duration of aortic cross-clamp application, CPB, and the presence of VSD.

Effect of dexamethasone on postoperative cardiac troponin T production in pediatric cardiac surgery

OBJECTIVE

Pediatric cardiac surgery is associated with a temporary rise in cardiac troponin T (cTnT) during the postoperative period. We examined whether dexamethasone given before cardiopulmonary bypass has myocardial protective effects as assessed by the postoperative production of cTnT.

DESIGN AND SETTING

Prospective randomized interventional study in the pediatric intensive care unit in a university hospital.

INTERVENTIONS

Patients were randomly allocated to act as controls or receive a single dose of dexamethasone (1 mg/kg) during induction of anesthesia.

MEASUREMENTS AND RESULTS

cTnT was measured four times postoperatively: immediately after admission to the pediatric intensive care unit (PICU) and 8, 15, and 24 h thereafter. The two groups had similar mean cTnT concentrations on PICU admission: those receiving dexamethasone 1.85 ng/ml (1.55-2.15) and those not receiving it 2 ng/ml (95% confidence interval 1.56-2.51). Concentrations of cTnT 8 h after admission to the PICU differed significantly after 8 h: 1.99 ng/ml (1.53-2.45) in those receiving dexamethasone and 3.08 ng/ml (2.46-3.69) in those not receiving it. After subgroup statistical analysis differences between the two groups remained significant only at 8 h, not those after 15 or 24 h.

CONCLUSIONS

The use of dexamethasone (1 mg/kg) before cardiopulmonary bypass is associated with a brief but significant reduction in postoperative cTnT production. The clinical significance of this effect is unclear.

Effect of three different anaesthetic agents on the postoperative production of cardiac troponin T in paediatric cardiac surgery

BACKGROUND

Paediatric cardiac surgery is associated with some degree of myocardial injury. Ischaemic preconditioning (IP) has been investigated widely in the adult population. Volatile agents have been shown to simulate IP providing extra protection to the myocardium during adult cardiopulmonary bypass (CPB) while propofol seems to act through different mechanisms. IP has not been investigated in the paediatric population to the same extent. Cardiac troponin T (cTnT) is a reliable marker of myocardial injury in neonates and children. We have investigated the relationship between three anaesthetic agents, midazolam, propofol, and sevoflurane, and postoperative production of cTnT.

METHODS

Ninety patients undergoing repair of congenital heart defect with CPB were investigated in a prospective randomized study. cTnT was measured four times during the first 24 h following admission to the paediatric intensive care unit. Other variables measured included arterial blood gases, lactate, fluid balance, use of inotropic drugs, PaO2/FiO2 ratio and ventilator hours.

RESULTS

cTnT was elevated in all three groups throughout the study period. The differences between the three groups were not statistically significant. Eight hours after admission to the intensive care unit cTnT concentrations tended to be higher in the midazolam group [mean (95% confidence intervals)]; 2.7 (1.9-3.5) ng ml(-1). Patients receiving a propofol-based anaesthesia had similar concentrations 2.6 (1.7-3.5) ng ml(-1) while those receiving sevoflurane tended to have a lower cTnT production 1.7 (1.3-2.2) ng ml(-1).

CONCLUSIONS

Midazolam, propofol, and sevoflurane appear to provide equal myocardial protection in paediatric cardiac surgery when using cTnT as a marker of myocardial damage.

Cardiac troponin I: evaluation of a biomarker for the diagnosis of heart disease in the dog

OBJECTIVES

To assess the value of measuring blood levels of the myocardial protein cardiac troponin I (cTnl) in the diagnosis of congenital and acquired heart disease in the dog and in the evaluation of the severity of heart failure.

METHODS

Serum samples obtained from healthy dogs (n = 26) and from dogs diagnosed with a variety of congenital and acquired heart conditions (n = 35) were assayed for cTnl concentration using an automated immunoassay method. Results were also analysed according to the degree of heart failure as assessed using the International Small Animal Cardiac Health Council's scheme.

RESULTS

Healthy dogs had very low or undetectable blood cTnl levels, as did dogs with congenital heart disease. However, cTnl levels were significantly elevated in dogs with acquired mitral valve disease, dilated cardiomyopathy and pericardial effusion. Blood cTnl levels also varied with severity of heart failure.

CLINICAL SIGNIFICANCE

Measurement of blood cTnl levels may be a useful aid in the diagnosis of dogs with suspected heart disease and in indicating the severity of heart failure.

Basal metabolic state of hearts of patients with congenital heart disease: the effects of cyanosis, age, and pathology

BACKGROUND

Experimental models have established numerous myocardial metabolic changes with chronic hypoxia and maturation. We conducted this study to specifically look at the effects of cyanosis, age, and pathology upon the basal metabolic state of the immature human heart.

METHODS

One hundred and eighty-one pediatric patients (37 cyanotic, 144 acyanotic) undergoing open heart surgery were recruited. A myocardial biopsy was collected before ischemia and analyzed for adenine nucleotides, purines, and lactate. The effect of cyanosis was estimated by an analysis of age-matched pairs of children with either ventricular septal defects or tetralogy of Fallot, and by multiple regression modeling. The effects of age and pathology were estimated in acyanotic children also by multiple regression modeling (adjustments were made for baseline differences).

RESULTS

The only effect of cyanosis was for lactate where the paired t test, and unadjusted and adjusted regression analyses were all consistent (ranging from 1.33 to 1.48 times higher in cyanotic than acyanotic children). The concentrations of adenosine triphosphate (ATP), adenosine diphosphate (ADP), and adenosine monophosphate (AMP) declined with age, whereas the ATP/ADP ratio increased; these associations remained significant even in the adjusted regression analysis. None of the effects of acyanotic pathology were highly significant (p < 0.01), implying that few important metabolic differences were attributable to pathology.

CONCLUSIONS

Cyanosis and age are important factors that determine the basal metabolic state of the pediatric heart. Cyanotic patients have higher myocardial lactate concentrations, whereas young age is associated with lower ATP/ADP ratios and higher adenine nucleotide levels.

Evaluation of heart fatty acid–binding protein as a rapid indicator for assessment of myocardial damage in pediatric cardiac surgery

OBJECTIVES

Perioperative myocardial damage is a major determinant of postoperative cardiac dysfunction for congenital heart disease. Heart fatty acid-binding protein is reported to be a rapid marker of perioperative myocardial damage that peaks earlier than creatine kinase isoenzyme MB or cardiac troponin T in adults. The objective of this study was to assess the suitability of using serum concentrations of heart fatty acid-binding protein for evaluation of perioperative myocardial damage in pediatric cardiac surgery.

METHODS

After institutional review board approval and informed consent, 100 children undergoing open procedures for congenital heart disease were prospectively enrolled in the study. Mean age at operation was 4.9 +/- 0.4 years. Serum concentrations of heart fatty acid-binding protein, creatine kinase isoenzyme MB, and cardiac troponin T were measured serially before operation and at 0, 1, 2, 3, and 6 hours after aortic declamping. Relationships between serum peak level of heart fatty acid-binding protein and intraoperative and postoperative clinical variables were evaluated.

RESULTS

Serum heart fatty acid-binding protein reached its peak level at 1 hour after declamping in 95 patients (95%), which was significantly earlier (P <.01) than serum creatine kinase isoenzyme MB or cardiac troponin T. In addition, serum heart fatty acid-binding protein level immediately after declamping correlated strongly with serum peak heart fatty acid-binding protein level (r = 0.91, P <.01). The serum peak level of heart fatty acid-binding protein correlated with those of creatine kinase isoenzyme MB (r = 0.77, P <.01) and cardiac troponin T (r = 0.80, P <.01). In the forward stepwise multiple regression analysis, age (P <.0001), aortic crossclamp time (P <.0001), the presence of a ventriculotomy (P <.001), and the lowest hematocrit level during cardiopulmonary bypass (P <.05) were significant intraoperative variables that influenced the release of heart fatty acid-binding protein. There were significant relationships between serum peak heart fatty acid-binding protein level and postoperative inotropic support, duration of intubation, and intensive care unit stay (P <.01 for each).

CONCLUSIONS

Heart fatty acid-binding protein is a rapid marker for assessment of myocardial damage and clinical outcome in pediatric cardiac surgery. In particular, serum heart fatty acid-binding protein level immediately after aortic declamping may be a potentially useful prognostic indicator of myocardial damage as well as clinical outcome in pediatric cardiac surgery.

Critical care in cardiovascular medicine

The field of cardiac intensive care is rapidly evolving with nearly simultaneous advances in surgical techniques and adjunctive therapies, respiratory care, intensive care technology and monitoring, pharmacologic research and development, and computing and electronics. The focus of care has now shifted toward reducing morbidity and improving "quality of life" while the survival of infants and children with congenital heart defects, including those with univentricular hearts has dramatically improved during the last three decades. Despite these advances, there remains a predictable fall in cardiac output after cardiopulmonary bypass. This article focuses on early identification and aggressive treatment of the low cardiac output syndrome peculiar to these patients. The authors also briefly review the recent advances in the treatment of pulmonary hypertension, mechanical support, and neurologic surveillance after cardiac surgery.

Effect of two different bypass techniques on the serum troponin-T levels in newborns and children: does pH-Stat provide better protection?

BACKGROUND

Cardiac troponin-T is a sensitive marker of myocardial damage. In a prospective study, the effect of 2 different pH strategies during cardiopulmonary bypass on ischemic myocardial injury and clinical outcome was measured in a pediatric population.

METHODS AND RESULTS

One hundred one patients (31 neonates 13.2+/-8.3 days and 70 children 34.5+/-44.1 months of age) undergoing open-heart surgery were selected to either alpha-stat (n=51) or pH-stat (n=50) acid-based management protocol. Serum troponin-T levels were measured before and 30 minutes after bypass and then 4 and 24 hours postoperatively. Surgical procedure, bypass details, inotropic support requirement, and postoperative recovery were recorded. Baseline troponin-T level was higher in neonates than in children (0.18+/-0.22 versus 0.04+/-0.05 microg/L, P=0.02). Also, a higher baseline level was found in patients with pulmonary hypertension (0.13+/-0.21 versus 0.04+/-0.05 microg/L, P=0.04). Cyanotic children showed a higher peak troponin-T level (3.76+/-3.11 versus 1.67+/-1.33 microg/L, P=0.04). Peak troponin levels showed a correlation with the length of circulatory arrest and aortic cross-clamp time. Postoperative levels remained high at 24 hours in patients requiring inotropic support. Peak troponin-T levels were significantly lower in the pH-stat group in patients with pulmonary hypertension (P=0.03) and in cases where circulatory arrest (P=0.01) or inotropic support (P=0.01) was necessary during operation than in those with alpha-stat technique. Postoperative ventilation time and length of intensive care unit stay were also significantly longer with alpha-stat than with pH-stat technique (P=0.005 and P=0.006, respectively).

CONCLUSIONS

Cardiac troponin-T sensitively reflects myocardial damage in children. Our results suggest that pH-stat acid-based management protocol may provide better protection against ischemic myocardial damage than alpha-stat technique.

Pathology-related troponin I release and clinical outcome after pediatric open heart surgery

BACKGROUND

Perioperative myocardial injury is determined by the ischemic duration, pathology, and preoperative myocardial status. Our aim was to evaluate pathology-related differences in troponin I (TnI) release, a sensitive and specific marker of myocardial injury, and its relation to clinical outcome after pediatric open heart surgery.

METHODS

Troponin I was measured serially postoperatively in 133 children undergoing repair of atrial (ASD, n = 41) and ventricular septal defects (VSD, n = 46), and tetralogy of Fallot (TOF, n = 46). The length of the right ventricular outflow tract (RVOT) incision in the latter was classified as either minimum(n = 33) or extended(n = 13).

RESULTS

Postoperative TnI levels were lesion specific and did not correlate with clinical outcome for ASDs. Peak TnI correlated with inotropic duration for VSD (r = 0.69, p < 0.0001) and TOF (r = 0.51, p = 0.0004). Significant correlations were also observed for the durations of ventilation (r = 0.64 and 0.36, respectively) and ICU stay (r = 0.60 and 0.55). Younger age (<1 year old) in children with VSDs and an extended incision into the RVOT in TOF were associated with greater TnI release and worse clinical outcome.

CONCLUSIONS

Postoperative TnI release is pathology related and reflects myocardial damage from both ischemia-reperfusion injury and direct myocardial trauma.

Dexamethasone reduces postoperative troponin levels in children undergoing cardiopulmonary bypass

OBJECTIVE

We previously demonstrated that dexamethasone treatment before cardiopulmonary bypass in children reduces the postoperative systemic inflammatory response. The purpose of this study was to test the hypothesis that dexamethasone administration before cardiopulmonary bypass in children correlates with a lesser degree of myocardial injury as measured by a decrease in cardiac troponin I release.

DESIGN

A prospective, randomized, double-blind study.

SETTING

The cardiac surgery operating room and intensive care unit of a pediatric referral hospital.

SUBJECTS

Twenty-eight patients who underwent open-heart surgery for congenital heart defects.

INTERVENTIONS

Patients received either placebo (group I, n = 13) or dexamethasone, 1 mg/kg iv (group II, n = 15), 1 hr before initiation of cardiopulmonary bypass. Plasma cardiac troponin I samples were obtained at three time points: immediately before study agent (sample 1), 10 mins after protamine sulfate administration after cardiopulmonary bypass (sample 2), and 24 hrs postoperatively (sample 3).

MEASUREMENTS AND MAIN RESULTS

Mean cardiac troponin I levels (+/-sd) were significantly lower at sample time 3 in group II (dexamethasone; 33.4 +/- 20.0 ng/mL) vs. group I (control; 86.9 +/- 81.1) (p =.04).

CONCLUSION

Dexamethasone administration before cardiopulmonary bypass in children resulted in a significant decrease in cardiac troponin I levels at 24 hrs postoperatively. We postulate that this may represent a decrease in myocardial injury, and, thus, a possible cardioprotective effect produced by dexamethasone.

Myocardial injury in children following resuscitation after cardiac arrest

BACKGROUND

Myocardial dysfunction occurs immediately after successful cardiac resuscitation. Our purpose was to determine whether measurement of cardiac troponin I in children with acute out-of-hospital cardiac arrest predicts the severity of myocardial injury.

METHODS AND RESULTS

This prospective, observational study was performed in the Pediatric Intensive Care Unit (PICU) on 24 patients following arrest, ranging in age from 8 months to 17 years. Troponin measurements were obtained on admission, and at 12, 24, and 48 h. Transthoracic echocardiograms were performed within 24 h after admission. Survival to hospital discharge was 29% (7/24). The mean age was 5.9+/-4.6 years for survivors and 4.2+/-5.3 years for non-survivors. The median (range) duration of cardiac arrest times for survivors was 6 min (3 to 63 min) versus 34 min (4 to 70 min) for nonsurvivors (P=0.02). Survivors received 1.3+/-2.2 doses of epinephrine (adrenaline) compared with 2.9+/-1.6 doses for non-survivors (P=0.02). Only one patient had ventricular fibrillation and defibrillation was unsuccessful. The ejection fraction for survivors averaged 73.2+/-11.2%, but for nonsurvivors only 55.4+/-19.8% (P=0.04). Ejection fraction correlated inversely with troponin at 12 h (r=-0.54, P=0.01) and at 24 h (r=-0.59, P=0.02). Circumferential fiber shortening for survivors was 37.5+/-7.8 and 25.5+/-10.7% for nonsurvivors (P=0.02). It also correlated inversely with troponin (r=-0.46, P=0.03 for survivors and r=-0.65, P=0.01, for nonsurvivors).

CONCLUSION

After cardiac arrest and resuscitation in pediatric patients, the severity of myocardial dysfunction was reflected in troponin I levels.

Cardiac troponin T and myocardial injury during routine cardiac catheterisation in children

BACKGROUND

This study aims to investigate whether intracardiac catheterization produces myocardial damage on pediatric heart.

METHODS

Five blood samples were collected (basal, immediate post procedure, at 4, 12 and 24 h after the procedure) for troponin T and creatine kinase MB (CKMB) from 48 consecutive patients (age: 5.34+/-6.03 years). The effect of age, duration of procedure, pulmonary hypertension, cyanosis, and medication taken for congestive heart failure on the levels of troponin T and CKMB were sought.

RESULTS

The increase in CKMB (basal CKMB: 3.93+/-3.70 ng/ml; peak CKMB: 8.68+/-10.89 ng/ml; P<0.0001) and troponin levels (basal troponin: 0.002+/-0.003 ng/ml; peak troponin: 0.11+/-0.23 ng/ml; P<0.0001) over time was significant in the study group. Additionally younger patients (</=1 year), patients with pulmonary hypertension (mean pulmonary artery pressure >25 mmHg), longer procedure time (>30 min), and patients taking anti-congestive heart failure therapy had significantly higher levels of CKMB and troponin (P>0.05).

CONCLUSION

All patients undergoing cardiac catheterization are under risk of myocardial injury, and younger patients with pulmonary hypertension and especially with compensated cardiac failure have increased risk of myocardial damage, and need to be handled carefully.

Cardiac troponin I is increased after interventional closure of atrial septal defects

This study was designed to assess possible myocardial injury caused by interventional closure of atrial septal defects (ASDs) compared to diagnostic catheterization by measuring cardiac troponin I (cTn-I). Forty patients were enrolled; in 33 ASDs were successfully closed, while in 7 a diagnostic balloon sizing of the defect was performed only. Total cTn-I increased significantly from 0.1 to 1.9 microg/l at the end of the intervention and 2.23 at 4 hr and decreased to 1.35 at 15 hr. No significant increase could be detected in patients with diagnostic balloon sizing only or of CK/CK-MB levels either. Following interventional closure of ASDs with Amplatzer septum/PFO occluders, increased cTn-I levels for several hours indicate some transient, reversible myocardial membrane instability due to the device. Discrimination of ventricular myocardial infarction might be possible by estimating less sensitive CK and CK-MB levels only.

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

BACKGROUND

Current cardioplegic protection techniques used in pediatric cardiac surgery do not take into consideration age and cyanotic differences. The aim of the present work was to address this question by monitoring clinical outcome, myocardial metabolism, and reperfusion injury in pediatric patients protected by cold-crystalloid cardioplegia.

METHODS AND RESULTS

Fifty-eight patients (31 children and 27 infants) with or without hypoxic stress (cyanosis) undergoing open heart surgery with cold-crystalloid cardioplegia were included in the study. Clinical outcome measures assessed included inotropic and ventilatory support, intensive care, and hospital stay. Ischemia-induced changes in metabolism (adenine nucleotides, purines, lactate, and amino acids) were determined in ventricular biopsies collected at the beginning and end of ischemic time (cross-clamp time). Reperfusion injury was assessed by measuring postoperative serial release of troponin I. Evidence was observed of ischemic stress during cardioplegic arrest in children and infants as shown by significant changes in cellular metabolites. Compared with infants, children had significantly less reperfusion injury and better clinical outcome, and these factors were related to duration of ischemic time. Cyanosis did not influence outcome in infants, but cyanotic children showed worse reperfusion injury and clinical outcome than acyanotic children.

CONCLUSIONS

Extent of myocardial protection with cold-crystalloid cardioplegia in pediatric open heart surgery is dependent on age and degree of cyanosis.

Acute right ventricular restrictive physiology after repair of tetralogy of Fallot: association with myocardial injury and oxidative stress

BACKGROUND

Acute right ventricular (RV) restrictive physiology after tetralogy of Fallot repair results in low cardiac output and a prolonged stay in the intensive care unit (ICU). However, its mechanism remains uncertain.

METHODS AND RESULTS

In the first 24 hours after tetralogy of Fallot repair (n=11 patients), serial prospective measurements were performed of cardiac troponin T, indexes of NO production (NO(2)(-) and NO(3)(-) combined as NOx), and iron metabolism and antioxidants. RV diastolic function was assessed by transthoracic Doppler echocardiography. Patients who had a long stay in the ICU were characterized by restrictive RV physiology (nonrestrictive group [n=7]: 3.0+/-0.6 days [mean+/-SD]; restrictive group [n=4]: 10.7+/-3.1 days). Troponin T peak concentration and the area under its concentration-time curve (AUC) were higher in the restrictive RV group (peak: restrictive group 17. 0+/-2.8 microg/L, nonrestrictive group 10.4+/-4.6 microg/L, P<0.03; AUC: restrictive group 268.8+/-73.6 microg. h(-1). L(-1), nonrestrictive group 136.2+/-48.3 microg. h(-1). L(-1), P<0.03). Plasma NOx/creatinine concentrations were higher in the restrictive group than the nonrestrictive group at 2 hours after bypass (restrictive group 1.3+/-0.4, nonrestrictive group 0.8+/-0.2; P=0. 04) but were similar by 24 hours. Iron loading peaked 2 to 10 hours after bypass and was more severe in the restrictive group (peak transferrin saturation: restrictive group 83.9+/-13.0%, nonrestrictive group 58.3+/-16.2%, P=0.05; minimum total iron-binding capacity: restrictive group 0.59+/-0.21%, nonrestrictive group 0.76+/-0.06%, P=0.04; minimum iron-binding antioxidant activity to oxyorganic radicals: restrictive group 9. 5+/-22.4%, nonrestrictive group 50.6+/-11.4%, P=0.01).

CONCLUSIONS

After tetralogy of Fallot repair, acute restrictive RV physiology is associated with greater intraoperative myocardial injury and postoperative oxidative stress with severe iron loading of transferrin.

Comparison of troponin-I and troponin-T after pediatric cardiovascular operation

BACKGROUND

Although the diagnostic value of troponin-T in childhood is documented, little is known about the significance of troponin-I. It was the aim of this study to compare the diagnostic value of troponin-I and troponin-T in children and newborns to assess the perioperative potential myocardial damage.

METHODS

Forty-eight children, mean, 51+/-54 months (mean value +/-1 standard deviation) (range, 1 day to 204 months) undergoing cardiac operation were prospectively enrolled in the present study. Troponin-I, troponin-T, creatine kinase (CK), and the MB isoenzyme were measured before operation and postoperatively within 2 days.

RESULTS

Postoperative values of troponin-I for children undergoing extracardiac operation were in the normal range. In children with interventions through the right atrium (n = 10) the mean value increase to 6.5+/-6.1 microg/L (range, 1.8 to 24.3 microg/L) and even to a mean of 29.9+/-21.1 microg/L (range, 7.5 to 90 microg/L) (p<0.01) in children with atrial and additional ventricular surgical approach (n = 23). Troponin-I was of equal specificity and sensitivity compared to troponin-T, excepted in patients with postoperative renal failure in whom troponin-T raised to false pathological results.

CONCLUSIONS

For detection of perioperative myocardial damage troponin-I shows a higher specificity than CK-MB activity and CK-MB mass. The diagnostic value of troponin-I is similar to troponin-T, but compared with troponin-T, it has the advantage of not being influenced by renal failure.

Patterns and potential value of cardiac troponin I elevations after pediatric cardiac operations

BACKGROUND

Perioperative myocardial injury is a major determinant of postoperative cardiac dysfunction for congenital heart disease, but its assessment during this period is difficult. The objective of this study was to determine the suitability of using postoperative serum concentrations of cardiac troponin I (cTnI) for this purpose.

METHODS

Cardiac troponin I levels were measured serially in the serum of patients undergoing uncomplicated repairs of atrial septal defect (n = 23), ventricular septal defect (n = 16) or tetralogy of Fallot (n = 16). The concentrations were correlated with intraoperative parameters (cardiopulmonary bypass time, aortic cross-clamp time, and cardiac bypass temperature), and postoperative parameters (magnitude of inotropic support, duration of intubation, and postoperative intensive care and hospital stay).

RESULTS

Postoperative absolute cTnI levels were lesion specific, with a pattern of increase and decrease similar for each lesion. For the total cohort, significant correlations between postoperative cTnI levels at all times (r = 0.43 to 0.83, p < 0.05) until 72 hours were noted for all parameters, except for cardiac bypass temperature. When evaluated as individual procedure groups, no significant relationships were noted in the atrial septal defect group, whereas postoperative cTnI levels were more strongly correlated with all intraoperative and postoperative parameters in the ventricular septal defect group than in the tetralogy of Fallot group.

CONCLUSIONS

This study suggests that cTnI values immediately after operation reflect the extent of myocardial damage from both incisional injury and intraoperative factors. Cardiac tropinin I levels in the first hours after operation for congenital heart disease are a potentially useful prognostic indicator for difficulty of recovery.

Predictive value of cardiac troponin T in pediatric patients at risk for myocardial injury

BACKGROUND

Biochemical markers have not been routinely used in children at risk for myocardial damage. Yet, because of somatic growth and the duration of survival, a low level of myocardial damage may ultimately be of more consequence in children than in adults.

METHODS AND RESULTS

We investigated the utility of cardiac troponin T (cTnT) blood levels (CARDIAC T ELISA Troponin T, Boehringer Mannheim Corp) in 51 consecutively sampled patients from 1 day to 34 years of age (median=5.7 years) undergoing cardiovascular (n=19) or noncardiovascular (n=17) surgery or who received doxorubicin for acute lymphoblastic leukemia (ALL) (n=15). Minimum detectable cTnT elevations were 0.03 ng/mL. cTnT was measurable in children of all ages with myocyte damage. In patients who underwent cardiovascular surgery, a correlation was noted between a score of increasing surgical severity and the mean level of postoperative cTnT (r=.79, P<.0001). Postoperative cTnT levels were elevated in children who completed cardiovascular surgery with an open chest compared with those with a closed chest (P=.0083). In addition, cTnT levels before cardiovascular surgery predicted postoperative survival (P=.007). cTnT elevations were observed after initial doxorubicin therapy for ALL. The magnitude of elevation predicted left ventricular dilatation (r=.80 when variables were treated as continuous, P=.003) and wall thinning (r=.61, P=.044) 9 months later.

CONCLUSIONS

Elevations of blood cTnT in children relate to the severity of myocardial damage and predict subsequent subclinical and clinical cardiac morbidity and mortality.

Effects of age and ischemic times on biochemical evidence of myocardial injury after pediatric cardiac operations

INTRODUCTION

The vulnerability of pediatric myocardium to ischemia is poorly documented in the clinical setting.

METHODS

Serial measurements of serum concentrations of myoglobin, the MB isoenzyme of creatine kinase, and cardiac troponins T and I and their respective areas under the curve were obtained, with particular reference to age and ischemic time, in 80 children undergoing cardiac operations. Sixteen (the control group) did not require cardiopulmonary bypass and 64 did.

RESULTS

In the control group there were increases (p < 0.01) in myoglobin and creatine kinase MB isoenzyme but no increase in cardiac troponin T or I; by contrast, the group treated with cardiopulmonary bypass had significant increases in all four markers but with differing temporal patterns. Younger age (especially < 12 months) was a highly significant explanatory variable only for the release of cardiac troponins T and I, and ischemic time was a significant explanatory variable for the release of creatine kinase MB isoenzyme, cardiac troponins T and I, but not myoglobin. In comparison with previous studies in adults, creatine kinase MB and cardiac troponin T concentrations were three times greater in children than in adults.

CONCLUSIONS

This study supports the specificity of cardiac troponins T and I as markers of myocardial injury after pediatric cardiac operations and defines the importance of age and ischemic time in determining their release. In comparison with previous data in adults, our results raise the possibility that the pediatric heart may be more vulnerable to the effects of ischemia and reperfusion. Cardiac troponins will permit comparison of new myocardial protective strategies or other potentially therapeutic myocardial interventions.