The DeBakey VAD Child ventricular assist device (MicroMed Technology, Inc., Houston, TX) is available in the United States through a Food and Drug Administration Humanitarian Device Exemption program for children 5–16 years old with a body surface area of more than 0.7 m2.1 This device is based on axial flow technology originally introduced in the adult version of the DeBakey VAD2 and has been shown to provide long-term circulatory support. The shortage of donor hearts, especially those suitable for pediatric transplantation, has increased the need for mechanical support as a bridge to transplantation. Here, we report the second successful DeBakey VAD Child implantation and the first successful use of this device as bridge to transplantation for a pediatric patient.
A 14-year-old boy with repaired transposition of the great arteries and ventricular septal defect presented in atrial flutter with severe mitral and tricuspid regurgitation and heart failure. He had undergone pulmonary artery banding as a neonate. At 4 months of age, he had the arterial switch operation with closure of the ventricular septal defect and pacemaker placement for complete atrioventricular block. At age 12 years, severe mitral valve regurgitation developed and he underwent mitral valvuloplasty, repair of pulmonary artery stenosis, and placement of a transvenous dual-chamber pacing system.
At age 14 years, atrial flutter with a rapid ventricular rate and severe heart failure developed. He had experienced a weight loss of 4 kg over 2 months. The echocardiogram on admission showed marked left ventricular dysfunction and hypokinesis. The pacemaker was reprogrammed to provide a slower ventricular response. Overdrive pacing was unsuccessful. Cardioversion restored sinus rhythm but there was no improvement in ventricular function, despite atrioventricular optimization. He required continuous inotropic support with dobutamine and milrinone for persistent hypotension, poor ventricular function, and mitral/tricuspid valve regurgitation. Blood lactic acid levels increased. Worsening cardiac function required extracorporeal membrane oxygenation (ECMO) support via right carotid artery and right internal jugular vein and left femoral vein.
Heart catheterization, with ECMO temporarily suspended, showed a right ventricular systolic pressure of 63 mm Hg, main pulmonary artery pressure of 52/20 mm Hg, and a pulmonary capillary wedge pressure of 20 mm Hg. Systemic arterial pressure was 106/84 mm Hg. The measured cardiac index was 1.6 l·min−1·m−2. Right pulmonary artery stenosis was shown by angiography. After 2 days of ECMO support, the boy was implanted with the DeBakey VAD Child device with the aid of cardiopulmonary bypass via a median sternotomy. The mitral and tricuspid valves were repaired and the transvenous pacing system was removed and replaced with an epicardial system.
For the first 2 days after implantation, the child required aggressive management of bleeding, including transfusion of 1 unit of fresh frozen plasma, five platelet phoresis, and 8 units of packed red blood cells. Nonetheless, VAD support provided good hemodynamic stability. The overall average daily morning VAD flow was 3.3 ± 0.9 l/min with an averages for pump speed of 8,600 ± 500 rpm, power of 7.5 ± 0.8 W, and current of 0.56 ± 0.08 A. Re-exploration of the mediastinum for bleeding was necessary three times for bleeding in the first 11 postoperative days, including re-exploration for cardiac tamponade on the sixth day of support that occurred when the temporary pacing leads were removed. He was extubated 5 days after implantation, oral feedings were resumed, and soon he was ambulating with assistance.
Severe nausea and vomiting developed 19 days after implantation. Superior mesenteric artery (SMA) syndrome was diagnosed by upper gastrointestinal scan. Total parenteral nutrition was given, followed by gradual transpyloric feeding.
After initial stabilization, the child received systemic heparin anticoagulation. Heparin was interrupted only briefly to manage episodes of hemorrhage and tamponade. Acetylsalicylate was begun on the fourth day of support and Coumadin on the sixth day. Coumadin anticoagulation was difficult to maintain (Figure 1) and was complicated by poor intestinal absorption because of SMA syndrome. As a supplement, clopidogrel was used intermittently.
Plasma free hemoglobin and bilirubin increased 36 days after implantation and the patient became increasingly anemic, requiring transfusion of multiple units of packed red blood cells (Figure 2). After further afterload reduction, plasma free hemoglobin levels decreased and fewer red blood cell transfusions were needed.
On the 54th day of VAD support, power and current levels suddenly increased. Pump thrombosis was suspected and an infusion of tissue plasminogen activator was given; previous power and current levels were restored (Figure 1). Two days after initiating the tissue plasminogen activator infusion, cardiac tamponade twice again developed within 8 hours. Tamponade was diagnosed by noting increasing filling pressures despite no change in pump flows. The pericardium was drained via a transxiphoid incision.
Before VAD implantation, panel reactive antibody (PRA) was 3%; soon afterward, it was 100%. Both Class I and Class II antibodies were elevated to 98–100% by both complement-dependent cytotoxicity assay and flow cytometry. On the 56th day after implantation, the child underwent orthotopic cardiac transplantation. Plasmapheresis was performed during cardiopulmonary bypass and afterward. Although there was an initial period of graft dysfunction, there was no evidence of rejection 5 months after transplantation (endocardial biopsy grade 1A and PRA Class I = 20% and Class II = 17% at 5½ months).
There are several kinds of circulatory support for children, such as ECMO, intraaortic balloon pump, and right and left ventricular assist devices.3 Smaller paracorporeal devices using axial continuous flow technology have allowed development of smaller VAD devices such as the DeBakey VAD Child4,5 and the Berlin Heart INCOR (Berlin Heart AG, Berlin, Germany). MicroMed, Inc. produced the DeBakey VAD Child device for the pediatric population based on the design used for the adult model. It has the same size axial flow pump, but the angle of the metal inflow cannula is more acute to allow closer approximation of the device to the curvature of a smaller heart.
Goldstein6 reported 150 patients with DeBakey VAD implants and only a 12% incidence of significant hemolysis and an 11.3% incidence of pump thrombus. We suspect that our patient may have had periods of insufficient anticoagulation because of poor intestinal absorption of Coumadin with SMA syndrome that developed after VAD implantation. SMA syndrome has been reported7 for patients with characteristics similar to ours, including tall thin body build, adolescence, severe weight loss due to catabolic states, and prolonged bed rest. Preimplantation heart failure resulted in negative nitrogen balance and significant weight loss, increasing the risk for SMA syndrome after implantation.
The more recently released Type 2X DeBakey VAD Child has been redesigned on the outflow side to increase the gap of exposed axle between the impeller and the diffuser (MicroMed Technology, Inc: Redesign of the Type 2X DeBakey VAD® Child Pump. Personal communication, May 2005). The angle of the blades of the diffuser on the outflow side of the pump was altered as well. As a result, turbulence within the diffuser has been reduced and there is better washing of the rear hub. The new design, while not anticipated to directly reduce hemolysis, may lessen clot formation within the pump.
The high PRA titers may have resulted from extensive transfusion for hemolysis and bleeding. A prospective cross match was not possible. Risks for chronic rejection are increased after cardiac transplantation for recipients with a high PRA.8 Nonetheless, our patient successfully underwent cardiac transplantation and had no evidence of rejection either clinically or on endomyocardial biopsy at 5 months posttransplant.
The DeBakey VAD Child had been used previously as reported by Morales et al.9 in a 6-year-old child with an idiopathic cardiomyopathy. Although the child initially improved clinically, neurologic deterioration of unclear etiology developed after the first week. A left frontoparietal stroke was found on computed tomography, but likely predated the VAD placement. On the 13th day after VAD insertion, what was thought to be a consumptive coagulopathy developed. She had persistent bleeding of the pleural side of the right chest wall due to abrasion by the flow probe and gastrointestinal bleeding manifested by massive hematochezia. Anticoagulation was discontinued for a short period to control life-threatening bleeding. However, clot formed in the left atrium at the site of a prior Biomedicus cannulation and extended into the inflow cannula of the pump, minimizing pump output despite resumed anticoagulation with heparin. The child died with medical management, as she was not a candidate for aggressive hemolytic therapy or replacement of the device.
Our patient is the first successful cardiac transplantation after using the DeBakey VAD Child as a bridge to transplantation. VAD devices for pediatric patients are rapidly evolving technologies that have recently become life-saving options as bridges to transplant for terminal heart failure in children. Further refinement of anticoagulation management will need to evolve simultaneously with pediatric VAD technologies, because bleeding and clot formation within the VAD remain as major risks.
1.United States Food and Drug Administration: Humanitarian Use Devices: May 2005 [FDA Web site].
Available at: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfHDE/HDEInformation.cfm
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