Short-term in vivo performance of the Cleveland clinic PediPump left ventricular assist device.

The PediPump was implanted in six healthy lambs (mean 25.6 ± 1.4 kg) between the left ventricular apex and the descending aorta to evaluate in vivo performance for up to 30 days. Anticoagulation was achieved by continuous heparin infusion. Three animals were euthanized prematurely, two because of respiratory dysfunction and one because of deteriorating pump performance resulting from thrombus formation inside the pump. Three lambs were electively sacrificed 30 days after implantation; all had stable hemodynamics and minimal hemolysis, as indicated by low plasma free hemoglobin (2.5 ± 3.1 mg/dL). Mean 30-day pump flow was 1.8 ± 0.1 L/min at a pump speed of 12 200 ± 400 rpm. Neither activated clotting time nor activated partial thromboplastin time followed the changes in heparin dose. At necropsy, depositions were observed at the front (n = 1) and rear rotor axial positioning stops (n = 4); improved polishing techniques on the stationary stop surfaces and the addition of a hard-carbon, thin-film coating on the rotating stop of the pumps used for the last two experiments addressed the deposition seen earlier. In conclusion, the PediPump showed excellent hydraulic performance and minimal hemolysis during support for up to 30 days. Depositions observed at the axial positioning stops in earlier experiments were addressed by design and material refinements. We continue to focus on developing effective anticoagulation management in the lamb model as well as on further evaluating and demonstrating pump biocompatibility.

The PediPump: a versatile, implantable pediatric ventricular assist device--update IV.

Cleveland Clinic's PediPump (Cleveland, OH, USA) is a ventricular assist device designed for the support of pediatric patients. The PediPump is a mixed-flow ventricular assist device with a magnetically suspended impeller measuring 10.5 mm in diameter by 64.5 mm in length. Progress and achievements for the PediPump program are considered according to the development project's three primary objectives: Basic engineering: along with size reductions, substantial design improvements have been incorporated in each design iteration including the motor, magnetic bearings, axial touch points, and heat transfer path; Anatomic modeling and device fitting studies: Techniques based on computed tomography and magnetic resonance imaging have been developed to create three-dimensional anatomic-modeling and device-fitting tools to facilitate device implantation and to assist in preoperative planning. For in vivo testing, to date, six acute (6-h duration) and nine chronic (30-day target duration) implantations have been performed in sheep; the implantation of the PediPump appears to be relatively easy with excellent hemodynamic performance and minimal hemolysis during support. Cleveland Clinic's PediPump program supported by the National Heart, Lung and Blood Institute's Pediatric Circulatory Support Program has led to the development of a pediatric ventricular assist device that has satisfactory performance in preclinical evaluation and appears to be ready to support a program of clinical testing.

Outcomes of children bridged to heart transplantation with ventricular assist devices: a multi-institutional study.

BACKGROUND: Current ventricular assist devices (VADs) in the United States are designed primarily for adult use. Data on VADs as a bridge to transplantation in children are limited. METHODS AND RESULTS: A multi-institutional, prospectively maintained database of outcomes in children after listing for heart transplantation (n=2375) was used to analyze outcomes of VAD patients (n=99, 4%) listed between January 1993 and December 2003. Median age at VAD implantation was 13.3 years (range, 2 days to 17.9 years); diagnoses were cardiomyopathy (78%) and congenital heart disease (22%). Mean duration of support was 57 days (range, 1 to 465 days). Seventy-three percent were supported with a long-term device, with 39% requiring biventricular support. Seventy-seven patients (77%) survived to transplantation, 5 patients were successfully weaned from support and recovered, and 17 patients (17%) died on support. In the recent era (2000 to 2003), successful bridge to transplantation with VAD was achieved in 86% of patients. Peak hazard for death while waiting was the first 2 weeks after VAD placement. Risk factors for death while awaiting a transplant included earlier era of implantation (P=0.05), female gender (P=0.02), and congenital disease diagnosis (P=0.05). There was no difference in 5-year survival after transplantation for patients on VAD at time of transplantation as compared with those not requiring VAD. CONCLUSIONS: VAD support in children successfully bridged 77% of patients to transplantation, with posttransplantation outcomes comparable to those not requiring VAD. These encouraging results emphasize the need to further understand patient selection and to delineate the impact of VAD technology for children.

The National Heart, Lung, and Blood Institute Pediatric Circulatory Support Program.

Options for the circulatory support of pediatric patients under the age of 5 years are currently limited to short-term extracorporeal devices, the use of which is often complicated by infection, bleeding, and thromboembolism. Recognizing this void, the National Heart, Lung, and Blood Institute solicited proposals for the development of novel circulatory support systems for infants and children from 2 to 25 kg with congenital or acquired cardiovascular disease. Five contracts were awarded to develop a family of devices that includes (1) an implantable mixed-flow ventricular assist device designed specifically for patients up to 2 years of age, (2) another mixed-flow ventricular assist device that can be implanted intravascularly or extravascularly depending on patient size, (3) compact integrated pediatric cardiopulmonary assist systems, (4) apically implanted axial-flow ventricular assist devices, and (5) pulsatile-flow ventricular assist devices. The common objective for these devices is to reliably provide circulatory support for infants and children while minimizing risks related to infection, bleeding, and thromboembolism. The devices are expected to be ready for clinical studies at the conclusion of the awards in 2009.

Transhepatic Broviac catheter placement for long-term central venous access in critically ill children with complex congenital heart disease.

OBJECTIVE: Critically ill children with cardiac disease often require prolonged central venous access. Thrombosis of systemic veins or the need to preserve vessels for future cardiac procedures limits sites for placement of central venous catheters in these patients. This study evaluates the use of Broviac placement via the transhepatic approach for this patient population. DESIGN: A retrospective review. SETTING: A tertiary care center. PATIENTS: All children with complex congenital heart disease who underwent transhepatic Broviac placement between May 2000 and April 2004. INTERVENTIONS: Transhepatic Broviac placement. MEASUREMENTS AND MAIN RESULTS: Thirty-two children with a median age of 5 months (20 days-5.3 yrs) and a median weight of 4.2 kg (2.2-24.9 kg) underwent 40 transhepatic Broviac placements. There were three (8.8%) procedural-related complications. One patient suffered an intra-abdominal bleed requiring an urgent laparotomy and removal of the Broviac, one patient required transfusion because of a mild self-contained intra-abdominal bleed, and one patient developed temporary complete heart block. There was one catheter infection. Thrombus was noted by echocardiography on the tip of two Broviacs; however, no intracardiac vegetations or embolic events occurred. There was no mortality related to the procedure. Broviacs remained in place for a median of 36 days (1 day-6 months). Five Broviacs were dislodged inadvertently (two during cardiac massage and three resulting from patient manipulation). The remaining Broviacs were electively removed safely without coil embolization. At a median follow-up of 3.5 months (10 days-3 yrs), there have been no long-term complications related to the Broviacs. CONCLUSIONS: Transhepatic Broviac catheters can be used safely in critically ill children with cardiac disease and remain indwelling for adequate periods of time. This modality of prolonged vascular access should be considered for children whose veins are occluded or need to be preserved for future procedures.

Mechanical cardiac support in the young. Short-term support: ECMO.

Although based on technology developed several decades ago, extracorporeal membrane oxygenation (ECMO) retains great clinical relevance in the management of advanced pediatric cardiorespiratory disease. Largely because of its widespread use in pediatric patients with respiratory failure, familiarity with this technology has established ECMO as the most commonly used form of mechanical circulatory support in children. Clinical applications and technical aspects of ECMO support continue to evolve, ensuring the ongoing importance of this modality for pediatric circulatory support.

Pediatric mechanical circulatory support in the United States: past, present, and future.

Mechanical support of the failing myocardium has become standard therapy for adults who fail medical management. Historically, there have been fewer options for children with heart failure. Extracorporeal membrane oxygenation and centrifugal pump-based ventricular assist devices have been the most commonly used circulatory support modalities for pediatrics in the United States. During the last few years, substantial advances in pediatric circulatory support have been made, with greater availability of a number of devices suitable for pediatrics. For example, there has been increasing experience using the DeBakey VAD Child and the Berlin Heart VAD to provide circulatory support for children during this period. A number of innovative devices under development supported by the Pediatric Circulatory Support Program of the National Heart, Lung, and Blood Institute hold great promise for expanded options for pediatric mechanical circulatory support in the future.

Development of patient-specific three-dimensional pediatric cardiac models.

The availability of algorithms to create three-dimensional (3D) models from medical images has made it possible to render and build patient-specific reconstructions of individual body parts. In the present study, this technology was used to create 3D models of pediatric hearts for use in medical device development. Digital models were created using CT datasets of pediatric hearts and commercially available 3D image processing software. Using this software, stacked CT data were viewed, and pixels representing the heart and rib cage were selected and rendered as 3D models. Stereolithography and 3D printing technology were used to create rigid and flexible physical heart models (biomodels) from the digital models. Twelve on-screen models of the thorax and cardiac structures were created from cardiac CT scans obtained from 11 patients with and without congenital heart disease (median age, 3 years; range, 2 days to 13 years). Rigid and flexible physical heart models were generated from the digital models to provide tactile and visual information. 3D models of pediatric cardiac and chest anatomy provide enhanced understanding and tactile representation of complex anatomy. Precise representation of the spatial relationships between anatomic structures is particularly useful during the development and placement of medical devices.

The PediPump: development status of a new pediatric ventricular assist device: update II.

The PediPump is a new ventricular assist device with a hydraulic output range designed for children from newborn infants to adolescents. The design is based on a mixed-flow rotary pump; the rotating assembly consists of a front impeller, front and rear radial magnetic bearings, and a central motor magnet. Two different implantable pumps were designed initially: an intravascular pump measuring 7 x 75 mm and an extravascular pump measuring 14 x 85 mm. Current prototypes are substantially smaller: The current intravascular version measures 4.5 x 55 mm, whereas the current extravascular version measures 11 x 70 mm. Both devices provide pressure and flows capable of supporting adults, far exceeding the initially defined physiologic requirements for children weighing 2 to 25 kg. This basic pump design may be used in acute or chronic clinical settings to provide right ventricular, left ventricular, or biventricular support. There are three objectives for the PediPump development program: 1) determination of basic engineering requirements for hardware and control logic including design analysis for system sizing, evaluation of control concepts, and bench testing of prototypes; 2) performance of preclinical anatomic fitting studies using CT-based 3D modeling; and 3) animal studies to provide characterization and reliability testing of the device.

Long-term outcome of surgically treated patients with corrected transposition of the great arteries.

OBJECTIVES: The purpose of the study was to examine long-term outcome after traditional surgical treatment of corrected transposition of the great arteries to provide a basis for comparison with new procedures, such as the double-switch or Senning-Rastelli procedures. METHODS: Patient- and procedure-related variables in 123 patients with corrected transposition and 2 functional ventricles operated on between 1963 and 1996 were analyzed. Patients with intracardiac procedures underwent either a traditional 2-ventricle repair or a Fontan procedure. RESULTS: The 1-, 5-, 10-, and 15-year survivals after the operation were 84%, 75%, 68%, and 61%, respectively. Patients requiring tricuspid valve replacement (27 patients) at any time during follow-up had a significantly worse outcome ( P < .001; hazard ratio, 4.4), whereas the best outcome was seen in patients undergoing the Fontan procedure (17 patients, 0 deaths). Right ventricular end-diastolic pressure of greater than 17 mm Hg before the operation ( P < .0001), complete heart block after the operation ( P = .001), subvalvular pulmonary stenosis ( P = .013), Ebstein malformation of the tricuspid valve ( P = .025), and preoperative systemic (right) ventricular dysfunction ( P = .041) were identified as risk factors for death at any time by means of univariate analysis. Ebstein malformation of the tricuspid valve ( P = .036; hazard ratio, 1.5) was identified as a risk factor for death by multivariate analysis. CONCLUSIONS: The long-term outcome of patients with corrected transposition after a classic surgical approach is unsatisfactory. The poorest outcome was seen in patients who required tricuspid valve replacement either at their initial operation or later during follow-up. Alternative surgical approaches, such as the double-switch, Senning-Rastelli, or Fontan procedures, are likely to have better long-term results, especially in the highest risk groups.

Management of the failing systemic right ventricle.

Conditions in which the right ventricle serves as the systemic pumping chamber are frequently complicated by the development of right ventricular failure and tricuspid valve regurgitation. The right ventricle is the systemic ventricle in conditions of ventriculoarterial discordance with atrioventricular concordance (transposition of the great arteries) or with atrioventricular discordance (congenitally corrected transposition of the great arteries). Concerns regarding actual or potential systemic right ventricular failure in these cases may lead to surgical evaluation and treatment designed to reestablish the left ventricle as the systemic pump. In cases where the left ventricle has prolonged exposure to low pressures in the pulmonary circulation, the left ventricle must be "retrained" to assume a systemic pressure load. Anatomic repair, with or without a preparatory period of left ventricular retraining, is a consideration for three clinically relevant scenarios: (1) patients with transposition of the great arteries after an atrial level switch (Senning or Mustard procedure), (2) patients with congenitally corrected transposition who are unoperated or who have undergone physiologic ("classic") repair, and (3) unoperated patients with transposition who present after the neonatal period.

Pediatric mechanical circulatory support.

Extracorporeal membrane oxygenation (ECMO) is based on technology that has been used clinically for decades. Largely because of its widespread use in pediatric patients with respiratory failure, familiarity with this technology has established ECMO as the most commonly used form of circulatory support for children. However, clinical applications and technical aspects of ECMO support continue to evolve, ensuring the ongoing importance of this modality for pediatric circulatory support. Although traditionally lagging behind development for adult applications, the use of ventricular assist devices (VADs) is expanding in pediatrics. Of particular interest, a number of new VADs designed specifically for children are becoming available, while early development of some innovative devices for pediatric circulatory support is currently underway.

The pedipump: development status of a new pediatric ventricular assist device.

The PediPump is a new rotary dynamic ventricular assist device designed specifically for pediatric applications. Although it is capable of providing support for adults, the small size of the PediPump makes it suitable for newborn circulatory support while retaining excellent hemodynamics. Current and future development plans include: (1) determination of the basic engineering requirements for hardware and control logic, including design analysis for system sizing, evaluation of control concepts and bench testing of prototypes; (2) performance of preclinical anatomical fitting studies using computed tomography-based three-dimensional modeling; and, (3) evaluation with animal studies to provide characterization and reliability testing of the device.

Comparison of extracardiac Fontan techniques: pedicled pericardial tunnel versus conduit reconstruction.

OBJECTIVE: This study was designed to determine whether either of 2 alternative methods of extracardiac Fontan reconstruction provides superior results. METHODS: We reviewed 58 consecutive Fontan procedures performed between 1995 and 2001 with a pedicled pericardial tunnel (group P, n = 21) or an extracardiac conduit of polytetrafluoroethylene or allograft aorta (group C, n = 37). Operations were performed with cardiopulmonary bypass at 32 degrees C; an aortic crossclamp was applied in only 6 patients. All group P patients and 33 (89%) group C patients received fenestrations. RESULTS: The groups were similar in terms of age, weight, anatomy, and preoperative hemodynamics. There were 3 hospital deaths (5%; 70% confidence limit, 2%-30%), all in group C. Median durations of mechanical ventilation (group P, 1 day; group C, 1 day), intensive care unit stay (group P, 3 days; group C, 3 days), chest tube drainage (group P, 8 days; group C, 7 days), and hospitalization (group P, 10 days; group C, 9 days) were not significantly different. There were no late deaths. All patients received warfarin sodium, and there were no late strokes. Before the Fontan procedure, 1 patient in group P and 3 patients in group C required pacemaker implants. Of the 51 surviving patients in sinus rhythm before the Fontan procedure, only 1 patient in group C subsequently required a pacemaker. CONCLUSIONS: Extracardiac Fontan procedures with either a pericardial baffle or conduit are associated with low operative mortality and low risks of arrhythmia and late thromboembolic complication.

Comparison of autograft and allograft aortic valve replacement in children.

OBJECTIVE: This study was undertaken to compare the clinical and hemodynamic results following aortic valve replacement with a pulmonary valve autograft (Ross procedure) or an allograft valve in children. METHODS: The records of 107 pediatric aortic valve replacements from 1994 through 2001 were reviewed, including 78 autografts and 25 allografts. Four mechanical aortic valve replacements performed during this period were excluded from analysis. RESULTS: There were 3 perioperative deaths and 1 late death. Reoperations were required in 5 autograft recipients (with autograft preservation in 4) and in 3 allograft recipients (all requiring valve re-replacement). Seven-year survival (96% in both groups) and reoperation-free survival (88% in the autograft group; 73% in the allograft group, P =.5) were not significantly different. Serial echocardiographic studies showed that in the autograft group, left ventricular outflow tract maximal velocity (2.0-1.8 m/s, P =.02) and left ventricular thickness (10.1-8.4 mm, P <.0001) fell significantly. In the allograft group, maximal velocity (2.3-3.0 m/s, P =.03) increased significantly and left ventricular thickness (9.5-9.0 mm, P =.2) showed minimal change. Analysis according to preoperative physiology (aortic stenosis versus insufficiency), congenital cardiac anatomy, number or type of previous operations, age of patient, and use of balloon valvotomy did not predict outcomes. CONCLUSIONS: Aortic valve replacement with either the autograft or allograft provides excellent clinical results in children during an intermediate duration of observation. The Ross procedure achieves a superior hemodynamic result, which may be clinically important with longer follow-up.

Staged repair of tetralogy of Fallot with pulmonary atresia and major aortopulmonary collateral arteries.

OBJECTIVE: To assess the results of a staged surgical approach for tetralogy of Fallot with pulmonary atresia, hypoplastic or absent pulmonary arteries, and major aortopulmonary collateral arteries. METHODS: We retrospectively reviewed a consecutive series of these patients from a single institution. RESULTS: From July 1993 to April 2001, 46 consecutive patients with tetralogy of Fallot, pulmonary atresia, and major aortopulmonary collateral arteries were treated with staged surgical repair. The operative sequence usually began with a central aortopulmonary shunt followed by unifocalization of aortopulmonary collateral arteries depending on the source and distribution of pulmonary blood flow. Twenty-eight patients (61%) subsequently underwent complete repair with ventricular septal defect closure and right ventricle to pulmonary artery connection. Those patients who underwent complete repair had a median of 3 total operations (range 1-6). The ratio of the mean pulmonary artery pressure to the mean systemic blood pressure at the time of complete repair was 0.36 (range 0.19-0.58). Two of the 28 repaired patients (7.1%) required subsequent fenestration of the ventricular septal defect closure due to later development of supersystemic right ventricular pressure and right ventricular failure. Eighteen patients (39%) have undergone 1 or more staging operations and are considered good candidates for eventual complete repair. There were no hospital deaths. There was 1 late death (2.2%; 95% CI 0.4-11.3%) in a patient born prematurely who developed severe bronchopulmonary dysplasia precluding complete repair. CONCLUSIONS: For tetralogy of Fallot with pulmonary atresia and major aortopulmonary collateral arteries, a staged surgical approach yields low overall mortality and acceptable hemodynamics after complete repair.

Mechanical circulatory support for infants and children with cardiac disease.

Mechanical circulatory support is assuming an expanding role in the practice of congenital cardiac surgery. Extracorporeal membrane oxygenation and centrifugal ventricular assist devices are still the mainstay of mechanical circulatory support for children; however, newly developed pulsatile, paracorporeal ventricular assist devices designed for pediatric applications are achieving increased utilization. In addition, several new, continuous flow devices that are under development as fully implantable systems for adults, ultimately may be useful for pediatric patients.

Pulmonary arteriovenous malformations after cavopulmonary anastomosis.

Pulmonary arteriovenous malformations (PAVMs) are a cause of progressive cyanosis after cavopulmonary anastomosis in children with single ventricle physiology who are on the pathway leading to a Fontan procedure. Investigations into possible mechanisms for the etiology of PAVMs are ongoing and suggest that the liver might play a key regulatory role in the development of these lesions.

Anatomic correction for corrected transposition after pulmonary unifocalization.

A Senning plus Rastelli operation was performed in a patient who had a rare combination of congenitally corrected transposition of the great arteries (S,L,L) with dextrocardia, major aortopulmonary collaterals, and diminutive central pulmonary arteries with arborization defects. The patient required four preparatory operations including bilateral unifocalizations of the aortopulmonary artery collaterals. Pulmonary artery to systemic pressure ratio after the double switch operation was 0.6. The patient demonstrates good biventricular function on echocardiogram at 3 months after the operation.