Simulating the Gradually Deteriorating Performance of an RTG

Degra (now in version 3) is a computer program that simulates the performance of a radioisotope thermoelectric generator (RTG) over its lifetime. Degra is provided with a graphical user interface that is used to edit input parameters that describe the initial state of the RTG and the time-varying loads and environment to which it will be exposed. Performance is computed by modeling the flows of heat from the radioactive source and through the thermocouples, also allowing for losses, to determine the temperature drop across the thermocouples. This temperature drop is used to determine the open-circuit voltage, electrical resistance, and thermal conductance of the thermocouples. Output power can then be computed by relating the open-circuit voltage and the electrical resistance of the thermocouples to a specified time-varying load voltage. Degra accounts for the gradual deterioration of performance attributable primarily to decay of the radioactive source and secondarily to gradual deterioration of the thermoelectric material. To provide guidance to an RTG designer, given a minimum of input, Degra computes the dimensions, masses, and thermal conductances of important internal structures as well as the overall external dimensions and total mass

What price support? Ventricular assist device induced systemic response

Use of ventricular support systems has been associated with myriad systemic complications. Engendered by the blood-biomaterial interface of a unique host/device relationship, these complications include diverse humoral dyscrasias that frequently culminate in episodes of bleeding, hemolysis and thrombogenicity, heightened susceptibility to inflammation and infection, and transient immunal compromise. Recent endeavor in biocompatibility research has served to illustrate the critical role played by cellular, humoral, and neurohormonal components in regulating cytokine expression and has provided insight into the complexities involved in such biomechanical juxtapositions. The following is intended as a review of current literature attempting to address the many aspects of this host/device interaction and their consequences for the supported patient

Axial flow induces distinct gene expression profiles in LVAD recipients

Introduction: Implantation of a left ventricular assist device (LVAD) has been shown to reverse cardiac remodeling through a distinct pattern of gene expression. We sought to determine if the differences in flow rendered by an axial flow pump would produce a distinct transcriptome when compared with a pulsatile device. Methods: RNA was isolated from paired myocardial tissues taken from the left ventricular apex of LVAD recipients at the time of device insertion and again at transplantation. Three of the patients who were studied underwent implantation of an axial flow pump (Micromed DeBakey VAD) while three patients received a pulsatile device (Heartmate). Double-stranded cDNA was synthesized from total RNA and hybridized to the Affymetrix Human U133 Plus 2.0 Array chip. Normalization and expression value summarization were performed using robust multi-chip average. The local pooled error method was used to determine differential expression. Results: A total of 2332 genes were found to undergo statistically significant change following LVAD support with an axial flow pump. Of these, 62 genes were found to be significantly changed in the pulsatile device group while 2270 genes were found to be expressed in the axial flow group alone. Conclusions: These findings suggest that differences in pulsatility during LVAD support induce distinct changes in gene expression. Additional studies are needed to correlate these results with alterations in function

End-Stage Heart Failure with Multiple Intracardiac Thrombi: A Rescue Strategy

The use of ventricular assist devices as a bridge to transplantation has become a widely used option for patients with end-stage heart failure. In contrast to total artificial hearts, ventricular assist devices support the failing heart by bypassing one or both ventricles. In certain cases (myocardial tumors, graft failure, transplant rejection, endocarditis, intracardiac thrombus formation), however, it may be advantageous to excise the heart and replace it with an artificial device. Total artificial hearts are intracorporeal devices designed for this purpose. Unfortunately, some patients are too small or are, for other reasons, ineligible for a total artificial heart. We describe the case of a 55-year-old woman who had ischemic cardiomyopathy and thrombus formation in all 4 cardiac chambers. To reduce the risk of thromboembolic events, we elected to replace her heart completely with 2 extracorporeal ventricular assist devices. The heart was excised via a median sternotomy approach, and the outflow cannulae (from device to patient) were connected to both atrial remnants. The 2 inflow cannulae (from patient to device) were anastomosed end-to-end to the aorta and the pulmonary artery, respectively. After attaining a flow of more than 5 L, the 2 extracorporeal assist devices effectively and efficiently performed the work of the native heart. Thus re-established, organ perfusion was improved by this mechanically driven circulation, as signified by an initial decrease in creatinine and blood urea nitrogen levels. The patient, however, did not recover from postoperative neurological dysfunction and died of respiratory insufficiency and multiple-organ failure on the 26th postoperative day

Organ-specific regulation of pro-inflammatory molecules in heart, lung, and kidney following brain death

Nonspecific inflammatory events following brain death may increase the intensity of the immunological host response. The present study investigated the course of pro-inflammatory molecules in heart, lung, kidney, and plasma after brain death induction. Brain death was induced in five pigs by inflation of an intracranial Foley catheter and five pigs were sham-operated as controls. Each experiment was terminated 6 h after brain death/sham operation and the organs were harvested. We measured the mRNA and protein levels for TNF-α, IL-1β, and IL-6 in heart, lung, kidney, and plasma. Additionally, the mRNA expression for IL-6R, ICAM-1, MCP-1, and TGF-β was determined in each organ. After 6 h, the plasma cytokine levels were higher in the brain-dead animals than in the sham-operated. In heart, lung, and kidney there was an increase in IL-6 and IL-1β following brain death, while TNF-α was up-regulated in lung only ( P < 0.05). MCP-1 and TGF-β were significantly higher in heart and lung and IL-6R increased in heart after brain death ( P < 0.05). Brain death was associated with non-uniform cytokine expression patterns in the investigated organs. These expression patterns may cause variable pro-inflammatory priming resulting in different degrees of damage and explain the organ-specific variation in outcomes after transplantations

Degree of cardiac fibrosis and hypertrophy at time of implantation predicts myocardial improvement during left ventricular assist device support

Background: There have been increasing reports of cardiac improvement in heart failure patients supported by left ventricular assist devices (LVADs i.e.), including a number of patients who have tolerated removal of the device without the benefit of cardiac transplant. In the current study, we retrospectively investigated echocardiographic and histologic changes in patients supported by LVADs ( n = 18). The goal of our study was to determine if the degree of cardiac fibrosis and myocyte size in pre-implant biopsies could predict myocardial improvement as assessed by improvements in ejection fraction (EF) during LVAD support. Methods: We determined total collagen content in myocardial biopsy specimens by a semi-quantitative analysis of positive Picro-Sirius Red-stained areas and myocyte size measurements by computerized edge detection software. Results: During LVAD support, 9 of the 18 patients (Group A) were distinguished by significant improvement in ejection fraction (pre <20% vs unloaded 34 ± 5%). In addition, Group A patients had significantly less fibrosis and smaller myocytes than their Group B counterparts, whose EF did not improve. There was an inverse correlation between pre-implant biopsy collagen levels and myocyte size with increases in EF during LVAD unloading. Conclusions: We found that the patients who demonstrated the greatest improvements in EF during support had less fibrosis and smaller myocytes at the time of device implantation. We propose that tissue profiling a patient’s pre-implant biopsy for fibrosis and myocyte size may allow stratification in Stage IV heart failure and may predict myocardial improvement during LVAD support

LVAD coordinator effects on outcomes in patients undergoing LVAD implantation: The Methodist DeBakey Heart Center experience Betreuung von patienten an linksventrikulären unterstü tzungssystemen mittels koordinator: Erfahrungen des Methodist DeBakey Heart Centers

Linksventrikuläre mechanische Supportsysteme, left ventricular assist devices oder kurz LVAD, erlauben, Patientien mit terminalen Herzversagen bis zur Transplantation zu unterstützen. Dies hat positiven Einfluss zum einen auf die Überlebensrate als auch auf mögliche peri-operative Komplikationen. Wir berichten über unsere Erfahrungen mit einem LVAD-Koordinator, insbesondere hinsichtlich Patientengenesung und Inzidenz an Komplikationen.In der Zeit vom Juni 2000 und Januar 2002 erhielten 28 Patienten mit terminaler therapierefrakterer Herzinsuffizienz ein linksventrikuläres Assist Device, 14 Patienten in der Zeit vor Einsatz eines LVAD-Koordinators und weitere 14 Patienten unter der Betreuung eines LVAD-Koordinators. Die untersuchten Kriterien waren dabei Auftreten von Infektionen, lebensbedrohlichen Thromboembolien, Blutungsereignissen und Kostenaufwand, definiert als reine Krankenhauskosten ohne Personal- und Materialkosten.In der Prä-Koordinator-Gruppe wurden 2 Patienten mit Ihrem LVAD nach Hause entlassen, 7 Patienten (50%) entwickelten eine therapiepflichtige Infektion, 5 Patienten (35%) hatten lebensbedrohliche thrombembolische Komplikationen. 6 Patienten aus dieser Gruppe wurden transplantiert und 8 Patienten verstarben an dem Unterstützungssystem, woraus sich eine Überlebensrate von 42% errechnet. In der von einem LVAD-Koordinator betreuten Patientengruppe wurden 7 Patienten mit ihrem LVAD nach Hause entlassen, 4 Patienten entwickelten Infektionen und 1 Patient cerebrale Thrombembolien mit irreversiblen neurologischen Schäden. 10 Patienten wurden transplantiert, 3 Patienten verstarben am Assist Device und 1 Patient war bei Studienende noch am Assist Device. Die Überlebensrate in dieser Gruppe war 78%.Der Einsatz eines LVAD-Koordinators für die Betreuung von an linksventrikulären Assist Devices befindlichen Patienten trug in unserem Patienten-Kollektiv zu einer höheren Überlebensrate, niedrigeren Komplikationsrate und auch niedrigeren Krankenhauskosten bei.Use of left ventricular assist devices (LVAD) for support of endstage heart failure patients as a bridge to cardiac transplantation creates opportunities both for improved patient survival rate and for lower peri-operative complications. We investigated the effect on patient outcomes and incidence of complication of assigning an LVAD coordinator for heightened clinical monitoring and patient management in this population.Between June 2000 and January 2002, 28 patients with terminal heart failure underwent LVAD implantation, 14 patients prior to LVAD-coordinator employment and 14 patients under supervision of the LVAD coordinator. Patients’ records were retrospectively analyzed for incidence of infection, life-threatening thromboembolic and bleeding events, and hospital charges.In the pre-coordinator group, two patients were discharged home while on LVAD support. Seven patients (50%) developed infections requiring antibiotic treatment; five patients (35%) had severe life-threatening thromboembolic events. Six patients were transplanted and eight patients died while on LVAD support, giving an overall survival of 42% in this group. In the post-coordinator group, seven patients were discharged home while on LVAD support. Four patients developed infections, one patient had a severe life-threatening thromboembolic event. Ten patients were successfully transplanted, one patient is currently supported on the device, and 3 patients died, for an overall survival of 78% in this group.The use of a fulltime professional coordinator has had a beneficial impact on patient outcomes. Patient survival was improved, device-related complications were reduced and eligible patients could be discharged safely from the hospital

Placement of a left ventricular assist device in a patient with dextrocardia

Dextrocardia most commonly presents in the setting of situs inversus, but it may occur as an isolated anomaly with normal position of the abdominal organs. Herein we present a 54-year-old man with ischemic cardiomyopathy and dextrocardia with normal position of the abdominal organs who presented with an exacerbation of congestive heart failure requiring inotropic support as well as mechanical ventilation. An implantable, wearable left ventricular assist device was placed in this patient to allow for ambulation and eventual discharge home. The patient survived 4 months before he developed pneumonia and expired