Henry L. Walters

Berlin Heart EXCOR Pediatric Ventricular Assist Device for Bridge to Heart Transplantation in US Children

Background— Recent data suggest that the Berlin Heart EXCOR Pediatric ventricular assist device is superior to extracorporeal membrane oxygenation for bridge to heart transplantation. Published data are limited to 1 in 4 children who received the device as part of the US clinical trial. We analyzed outcomes for all US children who received the EXCOR to characterize device outcomes in an unselected cohort and to identify risk factors for mortality to facilitate patient selection. Methods and Results— This multicenter, prospective cohort study involved all children implanted with the Berlin Heart EXCOR Pediatric ventricular assist device at 47 centers from May 2007 through December 2010. Multiphase nonproportional hazards modeling was used to identify risk factors for early (<2 months) and late mortality. Of 204 children supported with the EXCOR, the median duration of support was 40 days (range, 1–435 days). Survival at 12 months was 75%, including 64% who reached transplantation, 6% who recovered, and 5% who were alive on the device. Multivariable analysis identified lower weight, biventricular assist device support, and elevated bilirubin as risk factors for early mortality and bilirubin extremes and renal dysfunction as risk factors for late mortality. Neurological dysfunction occurred in 29% and was the leading cause of death. Conclusions— Use of the Berlin Heart EXCOR has risen dramatically over the past decade. The EXCOR has emerged as a new treatment standard in the United States for pediatric bridge to transplantation. Three-quarters of children survived to transplantation or recovery; an important fraction experienced neurological dysfunction. Smaller patient size, renal dysfunction, hepatic dysfunction, and biventricular assist device use were associated with mortality, whereas extracorporeal membrane oxygenation before implantation and congenital heart disease were not.

Pediatric cardiac surgical ECMO: Multivariate analysis of risk factors for hospital death

BACKGROUND Extracorporeal membrane oxygenation (ECMO) has emerged as an effective technique for the mechanical support of many pediatric postcardiotomy patients with medically refractory cardiac failure. METHODS We retrospectively reviewed the records of 73 pediatric patients with congenital heart disease who were placed on ECMO support between August 1984 and February 1994. The patients were divided into groups defined by the timing of ECMO cannulation relative to the time of operation. Group 1 patients (n = 7, 9.6%) were placed on ECMO preoperatively. Group 2 patients (n = 66, 90.4%) were a heterogeneous population placed on ECMO at any interval after cardiac repair. Subgroup 2A consisted of patients (n = 17, 25.8%) who could not be weaned from cardiopulmonary bypass and were converted directly to ECMO support immediately after repair. Subgroup 2B patients (n = 49, 74.2%) were cannulated postoperatively after an initial period of clinical stability. RESULTS Hospital survival for all study patients (42/73) and for group 2 patients (38/66) was 58%. Only 4 group 2A patients (23.5%) survived their hospitalization compared with 34 group 2B patients (69.4%) (p = 0.001). Multivariate analysis identified elevated right atrial pressure after ECMO decannulation (p = 0.049) and, possibly, membership in group 2A (p = 0.061) as independent risk factors for hospital death. CONCLUSIONS Extracorporeal membrane oxygenation is most effective in salvaging pediatric cardiac surgical patients who demonstrate medically refractory hemodynamic deterioration at some interval after being successfully weaned from cardiopulmonary bypass. The right atrial pressure after extracorporeal membrane oxygenation decannulation is an independent predictor of hospital death.

Congenital Heart Surgery Nomenclature and Database Project: double outlet right ventricle

Double outlet right ventricle (DORV) is a type of ventriculoarterial connection in which both great vessels arise entirely or predominantly from the right ventricle. Although the presence of aortic-mitral discontinuity and bilateral coni are important descriptors, they should not serve as absolute prerequisites for the diagnosis of DORV. The morphology of DORV is encompassed by a careful description of the ventricular septal defect (VSD) with its relationship to the semilunar valves, the great artery relationships to each other, the coronary artery anatomy, the presence or absence of pulmonary outflow tract obstruction (POTO) and aortic outflow tract obstruction (AOTO), the tricuspid-pulmonary annular distance, and the presence or absence of associated cardiac lesions. The preferred surgical treatment involves the connection of the left ventricle to the systemic circulation by an intraventricular tunnel repair connecting the VSD to the systemic semilunar valve. This ideal surgical therapy is not always possible due to the presence of confounding anatomical barriers. A multitude of alternative surgical procedures has been devised to accommodate these more complex situations. A framework for the development of the DORV module for a pediatric cardiac surgical database is proposed.

Coronary Sinus Ostial Atresia With Persistent Left Superior Vena Cava

BACKGROUND Atresia of the coronary sinus orifice with a persistent left superior vena cava is an intrinsically benign cardiac anomaly with important surgical implications. METHODS THe medical records of 5 patients with atresia of the coronary sinus orifice with a persistent left superior vena cava were reviewed retrospectively, and a computer search of the world literature describing this cardiac malformation was undertaken. RESULTS The 5 patients ranged in age from 9 months to 5 years. In 2, the diagnosis was made preoperatively by angiocardiography, and in 3, the abnormality was found incidentally at the time of cardiotomy for repair of associated congenital heart disease. Four of the 5 patients underwent repair of associated cardiac lesions. During operation, care was taken to avoid disruption of left superior vena cava flow to prevent coronary venous obstruction. All patients survived and are doing well at follow-up. CONCLUSIONS Atresia of the coronary sinus orifice with persistent left superior vena cava is, in itself, a benign anomaly without physiologic consequence. However, the recognition of this lesion during repair of associated cardiac lesions is of vital importance to the cardiac surgeon. Interruption of this sole route of coronary venous drainage can potentially lead to myocardial ischemia and necrosis.

Chronic performance of steroid-eluting epicardial leads in a growing pediatric population: a 10-year comparison.

Patient size and congenital heart defects complicate pacemaker therapy in children favoring an initial epicardial approach. Steroid‐eluting (SE) epicardial (EPI) leads maintain stable, low pacing thresholds in the short‐term when compared to the nonsteroid (NSE) epicardial (EPI) leads. The purpose of this study was to evaluate chronic, 10‐year performance of SE leads in growing children compared with NSE EPI leads implanted during the same time interval. From 1990 to 2000, 35 patients (age 1 month to 18 year, median 3 years), 28 with and 7 without congenital heart disease (CHD) received 51 SE leads: 27 ventricular and 24 atrial. NSE leads were implanted in 27 patients (age 1–28 years, median 8 years), 24 with and 3 without CHD: 27 ventricular and 1 atrial. Pacing lead threshold, impedance, and energy were measured at implant and during a 10‐year follow‐up. Unpaired t‐test showed that impedance remained stable for all leads with lower mean values for the SE (376 ± 55 vs 443 ± 109 Ω) (P = NS) . The mean energy requirement for SE leads at 10 years (1.2 ± 0.9 μJ) was significantly lower than for NSE (4.4 ± 5.5 μJ) (P < 0.05) . At 2.5‐V output, chronic thresholds for SE leads did not significantly differ from implant values for atrial (0.08 vs 0.09 ms) or ventricular (0.08 vs 0.08 ms) sites. There were no differences in SE lead performances among patients with or without CHD. Fracture or dislodgement occurred in two SE (4%) and four NSE (14%) leads. SE outperform NSE EPI leads and show stable, chronic low thresholds over time in all growing children. (PACE 2003; 26[Pt. I]:1467–1471)

Improving the mechanical properties of chitosan-based heart valve scaffolds using chitosan fibers

Chitosan is being widely studied for tissue engineering applications due to its biocompatibility and biodegradability. However, its use in load-bearing applications is limited due to low mechanical properties. In this study, we investigated the effectiveness of a chitosan fiber reinforcement approach to enhancing the mechanical properties of chitosan scaffolds. Chitosan fibers were fabricated using a solution extrusion and neutralization method and incorporated into porous chitosan scaffolds. The effects of fiber/scaffold mass ratio, fiber mechanical properties and fiber length on scaffold mechanical properties were studied. The results showed that incorporating fibers improved scaffold strength and stiffness in proportion to the fiber/scaffold mass ratio. A fiber-reinforced, heart valve scaffold achieved leaflet tensile strength values of 220±17 kPa, comparable to the radial values of human pulmonary valve leaflets. Additionally, the effects of 2 mm fibers were found to be up to threefold greater than 10 mm fibers at identical mass ratios. Heparin crosslinking of fibers produced a reduction in fiber strength, and thus failed to produce additional improvements to fiber-reinforced scaffold properties. Despite this reduction in fiber strength, heparin-modified fibers still improved the mechanical properties of reinforced scaffolds, but to a lesser extent than unmodified fibers. The results demonstrate that chitosan fiber reinforcement can be used to achieve porous chitosan scaffold strength approaching that of tissue, and that fiber length and mechanical properties are important parameters in defining the degree of mechanical improvement.

Nomenclature and databases - The past, the present, and the future: A primer for the congenital heart surgeon

This review discusses the historical aspects, current state of the art, and potential future advances in the areas of nomenclature and databases for congenital heart disease. Five areas will be reviewed: (1) common language = nomenclature, (2) mechanism of data collection (database or registry) with an established uniform core data set, (3) mechanism of evaluating case complexity, (4) mechanism to ensure and verify data completeness and accuracy, and (5) collaboration between medical subspecialties.During the 1990s, both the Society of Thoracic Surgeons (STS) and the European Association for Cardiothoracic Surgery (EACTS) created congenital heart surgery outcomes databases. Beginning in 1998, the EACTS and STS collaborated in the work of the International Congenital Heart Surgery Nomenclature and Database Project. By 2000, a common congenital heart surgery nomenclature, along with a common core minimal data set, were adopted by the EACTS and the STS and published in the Annals of Thoracic Surgery. In 2000, the International Nomenclature Committee for Pediatric and Congenital Heart Disease was established; this committee eventually evolved into the International Society for Nomenclature of Paediatric and Congenital Heart Disease (ISNPCHD). The working component of ISNPCHD is the International Working Group for Mapping and Coding of Nomenclatures for Paediatric and Congenital Heart Disease, also known as the Nomenclature Working Group (NWG). By 2005, the NWG cross-mapped the EACTS–STS nomenclature with the European Paediatric Cardiac Code of the Association for European Paediatric Cardiology and created the International Paediatric and Congenital Cardiac Code (IPCCC) (http://www.IPCCC.NET).This common nomenclature (IPCCC), and the common minimum database data set created by the International Congenital Heart Surgery Nomenclature and Database Project, are now utilized by both EACTS and STS; since 1998, this nomenclature and database have been used by both the STS and EACTS to analyze outcomes of more than 75,000 patients. Two major multi-institutional efforts have attempted to measure case complexity; the Risk Adjustment in Congenital Heart Surgery-1 and the Aristotle Complexity Score. Efforts to unify these two scoring systems are in their early stages but are encouraging. Collaborative efforts involving the EACTS and STS are under way to develop mechanisms to verify data completeness and accuracy. Further collaborative efforts are also ongoing between pediatric and congenital heart surgeons and other subspecialties, including pediatric cardiac anesthesiologists (via the Congenital Cardiac Anesthesia Society), pediatric cardiac intensivists (via the Pediatric Cardiac Intensive Care Society), and pediatric cardiologists (via the Joint Council on Congenital Heart Disease). Clearly, methods of congenital heart disease outcomes analysis continue to evolve, with continued advances in five areas: nomenclature, database, complexity adjustment, data verification, and subspecialty collaboration.

Aortic root dilation after the Ross procedure.

This study evaluated changes in neoaortic root geometry in patients who underwent the Ross procedure. Serial postoperative echocardiographic measurements of the neoaortic root indexed to the square root of body surface area (centimeters divided by meters) were obtained from 30 patients (age range 3.1 to 31.4 years) and compared with paired preoperative and immediate postoperative values. Normal aortic root diameter Z scores were derived from root dimensions obtained from 217 healthy controls. Compared with preoperative values, an immediate stretch of the neoaortic versus pulmonary root (annulus and sinuses of valsalva) was observed at a mean follow-up period of 1 week. Additional aortic annular dilation from baseline prehospital discharge values was observed at 2 to 12 months (baseline vs follow-up annulus Z score: 1.4 vs 2.6, p <0.01, n = 16) and at 16 to 33 months follow-up (0.8 vs 2.0, p <0.05, n = 12). In a similar fashion, there was additional enlargement of the aortic sinus from its stretched state at hospital discharge at 2 to 12 months (baseline vs follow-up sinus Z score: 2.0 vs 3.3, p <0.01, n = 17) and at 16 to 33 months (1.7 vs 3.0, p <0.01, n = 13). There were no differences in root size between 2 to 12 and 16 to 33 months after surgery. There was a decrease in left ventricular size with no alteration in blood pressure or degree of aortic valve regurgitation. Thus, aortic root dilation occurs up to the first year after the Ross procedure but does not appear to progress beyond this time.

STEROID-ELUTING EPICARDIAL PACING ELECTRODES : SIX YEAR EXPERIENCE OF PACING THRESHOLDS IN A GROWING PEDIATRIC POPULATION

Indications for pacemaker implantation in the pediatric population often include sinus or atrioventricular node dysfunction following surgery for congenital heart defects. However, patient size, cardiac defects, and vascular and valvular concerns may limit transvenous lead utilization. Since the epicardial surface of these patients often exhibits variable degrees of fibrosis from scar tissue formation or pericardial adhesions, chronic low output (2.5/1.6 V, 0.3 ms) epicardial pacing from implant is not currently recommended in children due to frequent threshold changes and electrode exit block. As a result, pacing in children is often viewed as a less efficient system than in adults. The addition of steroid combined with newer low threshold electrode designs however stabilizes the electrode‐tissue interface and eliminates postimplant changes seen with standard smooth surface electrodes potentially permitting efficient chronic pacemaker application to all patient ages. The stability of chronic low output epicardial pacing with steroid‐eluting electrodes was prospectively studied in 22 patients (ages 2 days‐18.5 years, median 3.5 years) for up to 6 years. Chronic pulse width thresholds were compared according to implant site and association of prior cardiac surgery. A total of 26 pacing leads were implanted. The acute implant mean pulse width threshold (2.5 V) for all the electrodes studied was 0.10 ms ± 0.05 ms. Stable low thresholds were maintained for up to 6 years without significant variation from implant. Mean ventricular pulse width thresholds (0.12 ms ± 0.05 ms) were significantly higher (P < 0.001) than atrial thresholds (0.06 ms ± 0.03 ms) at implant and throughout the study period. The thresholds in the patients following cardiac surgery were comparable to those without previous cardiac surgery (P = NS). Stable low thresholds may be chronically maintatined for up to 6 years for epicardial steroid‐eluting electrodes irrespective of pacing site or associated cardiac surgery.

Chitosan fibers with improved biological and mechanical properties for tissue engineering applications

The low mechanical properties of hydrogel materials such as chitosan hinder their broad utility for tissue engineering applications. Previous research efforts improved the mechanical properties of chitosan fiber through chemical and physical modifications; however, unfavorable toxicity effects on cells were reported. In this paper, we report the preparation of chitosan fibers with improved mechanical and biocompatibility properties. The structure-property relationships of extruded chitosan fibers were explored by varying acetic acid (AA) concentration, ammonia concentration, annealing temperature and degree of heparin crosslinking. Results showed that optimizing AA concentration to 2vol% improved fiber strength and stiffness by 2-fold. Extruding chitosan solution into 25wt% of ammonia solution reduced fiber diameters and improved fiber strength by 2-fold and stiffness by 3-fold, due to an increase in crystallinity as confirmed by XRD. Fiber annealing further reduced fiber diameter and improved fiber strength and stiffness as temperature increased. Chitosan fibers crosslinked with heparin had increased diameter but lower strength and stiffness properties and higher breaking strain values. When individual parameters were combined, further improvement in fiber mechanical properties was achieved. All mechanically improved fibers and heparin crosslinked fibers promoted valvular interstitial cells (VIC) attachment and growth over 10 day cultures. Our results demonstrate the ability to substantially improve the mechanical properties of chitosan fibers without adversely affecting their biological properties. The investigated treatments offer numerous advantages over previous physical/chemical modifications and thus are expected to expand the utility of chitosan fibers with tunable mechanical properties in various tissue engineering applications.