Vincent K.H Tam

One hundred pulmonary valve replacements in children after relief of right ventricular outflow tract obstruction

BACKGROUND Surgical repair of obstructive lesions of the right ventricular outflow tract (RVOT) in children commonly creates pulmonary valve incompetence that may eventually require pulmonary valve replacement (PVR). We reviewed our experience with PVR late after RVOT reconstruction. METHODS We performed 100 PVRs in 93 children 1.1 months to 22.4 years (median 8) after RVOT reconstruction. Children with right ventricular to pulmonary artery conduits and primary PVRs were excluded. Age at PVR was 4.5 months to 27.9 years (median 9.5 years). Initial diagnosis was tetralogy of Fallot and variants, 62; critical pulmonary stenosis, 15; pulmonary atresia with intact ventricular septum, 7; and others, 9. Eleven patients had a redo PVR. A total of 62 PVRs were homografts; 38 were porcine valves. RESULTS There was one early death. On follow-up of 5 months to 12.4 years (mean 4.9 years) there were no late deaths although 1 child underwent cardiac transplantation. Actuarial freedom from redo PVR at 8 years was 100% for porcine valves but 70% for homograft valves (p = 0.17). For children younger than 3 years at PVR, freedom from reoperation was 76% at 1 year and 39% at 8 years compared with freedom from redo PVR at 8 years of 100% for children older than 3 years. On latest echocardiogram 97% of porcine valves had mild or no pulmonary regurgitation compared with 72% of homograft valves. CONCLUSIONS PVR after RVOT reconstruction can be performed with low risk. Porcine valves may be superior to homograft valves although this advantage may be due to older age at time of PVR.

Predicting and treating coagulopathies after cardiopulmonary bypass in children.

Coagulopathies in children after cardiopulmonary bypass (CPB) are complex.There are very limited data correlating coagulation tests with postoperative bleeding. We evaluated coagulation changes after CPB and after the administration of coagulation products to 75 children. Baseline coagulation tests were obtained and repeated after protamine administration, after transfusion of individual coagulation products, and on arrival in the intensive care unit (ICU). Regression analysis demonstrated no baseline coagulation test to predict postoperative chest tube drainage. Weight and duration of CPB were determined to be the only predictors of bleeding. Further analyses demonstrated that children <8 kg had more bleeding and required more coagulation products than children >8 kg. Postprotamine platelet count and fibrinogen level correlated independently with 24-h chest tube drainage in children <8 kg, whereas postprotamine platelet count and thrombelastographic values did so in patients weighing >8 kg. Platelet administration alone was found to restore effective hemostasis in many patients. With ongoing bleeding, cryoprecipitate improved coagulation parameters and limited blood loss. Fresh-frozen plasma administration after platelets worsened coagulation parameters and was associated with greater chest tube drainage and more coagulation product transfusions in the ICU. Objective data to guide post-CPB component therapy transfusion in children are suggested. Implications: Children <8 kg can be expected to have more severe coagulopathies, require more coagulation product transfusions, and bleed more after cardiopulmonary bypass. Correlations between coagulation tests and postoperative chest tube drainage are defined. Platelets and, if necessary, cryoprecipitate optimally restore hemostasis. Fresh-frozen plasma offers no benefits in correcting postcardiopulmonary bypass coagulopathies in children. (Anesth Analg 1997;85:1196-202)

In vitro flow experiments for determination of optimal geometry of total cavopulmonary connection for surgical repair of children with functional single ventricle

OBJECTIVES This study sought to evaluate the effect of offsetting cavopulmonary connections at varying pulmonary flow ratios to determine the optimal geometry of the connection. BACKGROUND Previous investigators have demonstrated energy conservation within the streamlined contours of the total cavopulmonary connection compared with that of the atriopulmonary connection. However, their surgical design of connecting the two cavae directly opposite each other may result in high energy losses. Others have introduced a unidirectional connection with some advantages but with concerns about the formation of arteriovenous malformation in the lung excluded from hepatic venous return. Thus, an optimal surgical design has not been determined. METHODS In the present models, the caval connections were offset through a range of 0.0 to 2.0 diameters by 0.5 superior cava diameter increments. Flow ratios were fixed for superior and inferior cavae and varied for right and left pulmonary arteries as 70:30, 60:40, 50:50, 40:60 and 30:70 to stimulate varying lung resistance. Pressure measurements and flow visualization were done at steady flows of 2, 4 and 6 liters/min to stimulate rest and exercise. RESULTS Our data show that the energy losses at the 0.0-diameter offset were double the losses of the 1.0 and 1.5 diameters, which had minimal energy losses. This result was attributable to chaotic patterns seen on flow visualization in the 0.0-diameters offset. Energy savings were more evident at the 50:50 right/left pulmonary artery ratio. Energy losses increased with increased total flow rates. CONCLUSIONS The results strongly suggest the incorporation of caval offsets in future total cavopulmonary connections.

The Pharmacokinetics of Milrinone in Pediatric Patients after Cardiac Surgery

BACKGROUND Milrinone has been shown to increase cardiac output in children after cardiac surgery, but pharmacokinetic analysis has not been used to identify effective dose regimens. The purpose of this study was to characterize the pharmacokinetics of milrinone in infants and children and to apply the results to the issue of dosing. METHODS Twenty children were studied after they underwent repair of congenital cardiac defects. Control hemodynamic measurement was made after the children were separated from cardiopulmonary bypass, and each patient was given a loading dose of 50 microg/kg progressively in 5 min. Hemodynamic measurements were recorded again at the end of the loading dose and when a blood sample was taken to determine milrinone plasma concentrations. Further blood samples were taken during the next 16 h for milrinone plasma concentration analysis. The pharmacokinetics of milrinone were analyzed using the population pharmacokinetic program NONMEM. RESULTS The loading dose of milrinone resulted in a mean decrease in mean blood pressure of 12% and a mean increase in cardiac index of 18% at a mean peak plasma concentration of 235 ng/ml. The pharmacokinetics of milrinone were best described by a three-compartment model. In the optimal model, all volumes and distribution clearances were proportional to weight, and weight-normalized elimination clearance was proportional to age; ie., Cl1 = 2.5 x weight x (1 + 0.058 x age) where Cl1 is expressed as ml/min, and the units of weight and age are kg and months, respectively. CONCLUSIONS A loading dose of 50 microg/kg effectively increases cardiac index in children after cardiac surgery. Simulations indicate that the peak plasma concentration can be maintained by following the loading dose of 50 microg/kg with an infusion of approximately 3 microg x kg(-1) x min(-1) for 30 min and then a maintenance infusion, which may require adjustment for age.

Deletion of Chromosome 22q11.2 and Outcome in Patients With Pulmonary Atresia and Ventricular Septal Defect

BACKGROUND The 22q11.2 deletion (del22q) is present in many patients with conotruncal abnormalities including pulmonary atresia with ventricular septal defect (PA/VSD). We sought to determine the impact of the del22q on outcome in subjects with PA/VSD. METHODS We reviewed the experience for all patients with PA/VSD who were born between January 1993 and April 2002 and presented to our institution. Patients with conotruncal defects were routinely evaluated for genetic disorders including del22q. Fluorescence in situ hybridization was used to test for del22q. RESULTS There were 67 subjects with PA/VSD who presented during that time period; testing for del22q was performed in 58 of 67 (87%) and these 58 patients comprised the study population. The 22q11.2 deletion was present in 20 of 58 (34%) patients tested. Major aortopulmonary collaterals were defined by angiography and were present in 27 (47%). These collaterals were significantly more common among subjects with del22q (13 of 20, 65%; p = 0.04). The median cross sectional area of the pulmonary arteries, the Nakata index, was significantly less for patients with del22q (41 versus 142 mm(2)/m(2); p = 0.006). There were 3 subjects, all of whom had del22q, who did not undergo surgery owing to markedly hypoplastic pulmonary arteries. Of the remaining 55 patients, 53 had arteriopulmonary shunt with or without unifocalization as the initial procedure and 35 patients have undergone complete repair. There were 8 operative deaths and 1 nonoperative death. The 5-year survival was 36% for patients with del22q versus 90% for patients without del22q. The 22q11.2 deletion was a significant risk factor for death, even after adjusting for the presence of major aortopulmonary collaterals (p = 0.004). There was no significant difference between the two groups with respect to the incidence of serious viral, bacterial, or fungal infections in the perioperative period. CONCLUSIONS Patients with del22q and PA/VSD are at increased risk for death owing to a variety of factors including less favorable pulmonary artery anatomy. A better understanding of del22q, pulmonary artery anatomy, and outcome is required.

Hematologic and Economic Impact of Aprotinin in Reoperative Pediatric Cardiac Operations

BACKGROUND Aprotinin consistently reduces blood loss and transfusion requirements in adults during and after cardiac surgical procedures, but its effectiveness in children is debated. We evaluated the hemostatic and economic effects of aprotinin in children undergoing reoperative cardiac procedures with cardiopulmonary bypass. METHODS Control, low-dose aprotinin, and high-dose aprotinin groups were established with 15 children per group. Platelet counts, fibrinogen levels, and thromboelastographic values at baseline and after protamine sulfate administration, number of blood product transfusions, and 6-hour and 24-hour chest tube drainage were used to evaluate the effects of aprotinin on postbypass coagulopathies. Time needed for skin closure after protamine administration and lengths of stay in the intensive care unit and the hospital were recorded prospectively to determine the economic impact of aprotinin. RESULTS Coagulation tests performed after protamine administration rarely demonstrated fibrinolysis but did show significant decreases in platelet and fibrinogen levels and function. The thromboelastographic variables indicated a preservation of platelet function by aprotinin. Decreased blood product transfusions, shortened skin closure times, and shortened durations of intensive care unit and hospital stays were found in the aprotinin groups, most significantly in the high-dose group with a subsequent average reduction of nearly

Modified Fontan without use of cardiopulmonary bypass

3,000 in patient charges. CONCLUSIONS In children undergoing reoperative cardiac surgical procedures, aprotinin is effective in attenuating postbypass coagulopathies, decreasing blood product exposure, improving clinical outcome, and reducing patient charges.

In vivo flow dynamics of the total cavopulmonary connection from three-dimensional multislice magnetic resonance imaging ☆

BACKGROUND Direct cavopulmonary connection using an extracardiac conduit has a number of theoretical advantages in the staged management of children with single ventricular congenital heart defects. With appropriate planning, completion Fontan using an extracardiac connection may be accomplished without the use of cardiopulmonary bypass. METHODS From January 1995 to October 1997, 32 consecutive patients underwent completion Fontan using an extracardiac cavopulmonary connection. Twenty-one of these patients had completion Fontan without the use of cardiopulmonary bypass (No CPB group). Their postoperative outcome was retrospectively compared with a second group of 11 patients who underwent completion Fontan with an extracardiac conduit with the use of cardiopulmonary bypass. RESULTS There was no operative or hospital mortality in either group. Early postoperative hemodynamics appear to be significantly improved in the No CPB group. Transfusion of cryoprecipitate and platelets was significantly less in the group without the use of cardiopulmonary bypass (p = 0.026, p < 0.001, respectively). Review of the most recent 12 patients also demonstrated a substantially shorter extubation time and intensive care unit stay. The length of hospital stay was significantly shorter (p = 0.036). CONCLUSIONS Completion Fontan without the use of cardiopulmonary bypass results in improved immediate postoperative hemodynamics, and decreased use of blood and blood products. The most recent group appears to demonstrate a more rapid recovery time and shorter hospital stay (p = 0.036).

Current results with pediatric heart transplantation

BACKGROUND The total cavopulmonary connection (TCPC) design continues to be refined on the basis of flow analysis at the connection site. These refinements are of importance for myocardial energy conservation in the univentricular supported circulation. In vivo magnetic resonance phase contrast imaging provides semiquantitative flow visualization information. The purpose of this study was to understand the in vivo TCPC flow characteristics obtained by magnetic resonance phase contrast imaging and compare the results with our previous in vitro TCPC flow experiments in an effort to further refine TCPC surgical design. METHODS Twelve patients with TCPC underwent sedated three-dimensional, multislice magnetic resonance phase contrast imaging. Seven patients had intraatrial lateral tunnel TCPC and 5 had extracardiac TCPC. RESULTS In all patients in both groups a disordered flow pattern was observed in the inferior caval portion of the TCPC. Flow at the TCPC site appeared to be determined by connection geometry, being streamlined at the superior vena cava-pulmonary junction when the superior vena cava was offset and flared toward the left pulmonary artery. Without caval offset, intense swirling and dominance of superior vena caval flow was observed. In TCPC with bilateral superior vena cavae, the flow patterns observed included secondary vortices, a central stagnation point, and influx of the superior vena cava flow into the inferior caval conduit. A comparative analysis of in vivo flow and our previous in vitro flow data from glass model prototypes of TCPC demonstrated significant similarities in flow disturbances. Three-dimensional magnetic resonance phase contrast imaging in multiple coronal planes enabled a comprehensive semiquantitative flow analysis. The data are presented in traditional instantaneous images and in animated format for interactive display of the flow dynamics. CONCLUSIONS Flow in the inferior caval portion of the TCPC is disordered, and the TCPC geometry determines flow characteristics.

De Vega tricuspid annuloplasty for tricuspid regurgitation in children

BACKGROUND Cardiac transplantation is an accepted treatment for children with end-stage heart failure or complex or inoperable congenital defects. METHODS Since 1988, 95 transplants have been performed in 89 children aged 4 days to 18 years (median 6.9 years, 42 patients 0-5 years). Fifty-eight (61%) had congenital or acquired heart disease, 31 (33%) had idiopathic cardiomyopathy, and 6 (6%) were retransplants. Fifty-seven of the patients had prior cardiac surgery with a range of one to eight procedures (mean 3.4 procedures/patient). At the time of transplantation, 53 (56%) were United Network for Organ Sharing (UNOS) status I, including 23 children on mechanical ventilation and 4 with mechanical circulatory support. RESULTS Thirty-day survival in this group was 96%. Posttransplant results showed a median time of ventilation of 1 day (mean 3.0+/-5.7 days), median duration of inotropic support of 2 days (mean 2.7+/-2.3 days), median intensive care unit (ICU) stay of 4 days (mean 6.9+/-9.6 days), and median hospitalization of 9 days (mean 14.3+/-13.9 days). Follow-up from 1 month to 10.3 years (mean 3.1 years) has demonstrated a 1-year actuarial survival of 79% and a 5-year actuarial survival of 69%. Rejection, both acute and chronic, accounted for the vast majority of deaths. CONCLUSIONS Pediatric heart transplantation can be accomplished with excellent early survival despite multiple prior cardiac operations and relative severity of illness. Parameters such as postoperative ventilation, inotropic support, ICU stay, and hospitalization can be kept at reasonable levels with acceptable long-term results, although rejection remains a serious problem.