Efficient parameterisation of non-collinear energy landscapes in itinerant magnets.

Magnetic exchange interactions determine the magnetic groundstate, as well as magnetic excitations of materials and are thus essential to the emerging and fast evolving fields of spintronics and magnonics. The magnetic force theorem has been used extensively for studying magnetic exchange interactions. However, short-ranged interactions in itinerant magnetic systems are poorly described by this method and numerous strategies have been developed over the years to overcome this deficiency. The present study supplies a fully self-consistent method for systematic investigations of exchange interactions beyond the standard Heisenberg model. In order to better describe finite deviations from the magnetic ground state, an extended Heisenberg model, including multi-spin interactions, is suggested. Using cross-validation analysis, we show that this extended Heisenberg model gives a superior description for non-collinear magnetic configurations. This parameterisation method allows us to describe many different itinerant magnetic systems and can be useful for high-throughput calculations.

Spinal cord protection in open- and endovascular thoracoabdominal aortic aneurysm repair: critical review of current concepts and future perspectives.

Unresolved for over half a century now since the beginning of aortic surgery spinal cord injury (SCI) remains the most devastating complication after extensive open and endovascular thoracoabdominal aortic aneurysm (TAA/A) repair. Over the past decade extensive research on spinal cord perfusion lead to a better understanding of previously unknown physiologic mechanisms involved in the suspension of the cord's arterial supply and the consecutive development of SCI underscoring the need for new concepts in treatment strategy and monitoring methods during and after TAA/A repair. Based on this knowledge, new treatment strategies in particular the staged-repair were developed. The first-in-man translation of this idea has just been published introducing the new concept: minimally invasive selective segmental artery coil-embolization. Another approach to overcome the most critical initial period after segmental artery occlusion due to stent graft deployment in the descending or thoracoabdominal aorta is temporary aneurysm sac perfusion, which also has recently been clinically trialed. Furthermore, the new non-invasive real-time monitoring method to record spinal cord viability by means of near-infrared spectroscopy of the paraspinal collateral network by means of near-infrared spectroscopy has also been suggested and successfully introduced in a pilot series to a clinical setting. This review addresses problems, unsolved questions and future perspectives regarding these three new concepts.

Effective diameter of the aortic annulus prior to transcatheter aortic valve implantation: influence of area-based versus perimeter-based calculation.

In computed tomography (CT) evaluation prior to transcatheter aortic valve implantation area- and perimeter-based calculation of the aortic annulus diameter, the so-called effective annulus diameter (ED), is the preferred parameter for decision making regarding prosthesis sizes. Currently, it is unclear how relevant the differences between the two methods of measurement are and how they are influenced by the cardiac cycle. The aim of this study was to compare area- and perimeter-based measurements in computed tomography derived aortic annulus sizing. A total of 60 patients who underwent evaluation for transcatheter aortic valve implantation were included in this study. All patients received pre-procedural ECG gated CT. The aortic annulus area and perimeter were measured and the derived ED compared using parametric statistics and Bland and Altman analysis. The mean patient age was 80.2 ± 4 years. Systolic aortic annulus area and perimeter were higher compared to diastolic results (mean difference area 12.8 ± 24 mm(2) and perimeter 0.72 ± 1 mm; p = 0.009-0.068). Both the area- and perimeter-based ED had a good agreement within two standard deviations for systolic and diastolic measurements. Effective diameter measurements derived from the area were significantly smaller compared to perimeter-based measurements (mean difference: systolic 0.72 ± 0.3 mm and diastolic 0.81 ± 0.4 mm; p < 0.001). While the area-based ED was significantly influenced by the cardiac cycle with a mean difference of 0.4 ± 0.6 mm (p = 0.009), no significant difference was found for the perimeter-based ED (mean difference: 0.2 ± 0.4; p = 0.07). For patients undergoing CT evaluation prior to transcatheter aortic valve implantation, the perimeter-based effective annulus diameter provides a reliable parameter for annulus sizing without significant affection by the cardiac cycle and therefore facilitates annulus measurements with a single heart phase. However, perimeter-based diameters of the annulus are significantly larger than area-based diameters.

The effect of stent graft oversizing on radial forces considering nitinol wire behavior and vessel characteristics.

Stent graft fixation in the vessel affects the success of endovascular aneurysm repair. Thereby the radial forces of the stent, which are dependent on several factors, play a significant role. In the presented work, a finite element sensitivity study was performed. The radial forces are 29% lower when using the hyperelastic approach for the vessel compared with linear elastic assumptions. Without the linear elastic modeled plaque, the difference increases to 35%. Modeling plaque with linear elastic material approach results in 8% higher forces than with a hyperelastic characteristic. The significant differences resulting from the investigated simplifications of the material lead to the conclusion that it is important to apply an anisotropic nonlinear approach for the vessel. The oversizing study shows that radial forces increase by 64% (0.54 N) when raising the oversize from 10 to 22%, and no further increase in force can be observed beyond these values (vessel diameter D=12 mm). Starting from an oversize of 24%, the radial force steadily decreases. The findings of the investigation show that besides the oversizing the material properties, the ring design and the vessel characteristics have an influence on radial forces.

Stent graft visualization and planning tool for endovascular surgery using finite element analysis.

PURPOSE: A new approach to optimize stent graft selection for endovascular aortic repair is the use of finite element analysis. Once the finite element model is created and solved, a software module is needed to view the simulation results in the clinical work environment. A new tool for interpretation of simulation results, named Medical Postprocessor, that enables comparison of different stent graft configurations and products was designed, implemented and tested. METHODS: Aortic endovascular stent graft ring forces and sealing states in the vessel landing zone of three different configurations were provided in a surgical planning software using the Medical Imaging Interaction Tool Kit (MITK) software system. For data interpretation, software modules for 2D and 3D presentations were implemented. Ten surgeons evaluated the software features of the Medical Postprocessor. These surgeons performed usability tests and answered questionnaires based on their experience with the system. RESULTS: The Medical Postprocessor visualization system enabled vascular surgeons to determine the configuration with the highest overall fixation force in 16+/-6 s, best proximal sealing in 56+/-24s and highest proximal fixation force in 38+/- s. The majority considered the multiformat data provided helpful and found the Medical Postprocessor to be an efficient decision support system for stent graft selection. The evaluation of the user interface results in an ISONORM-conform user interface (113.5 points). CONCLUSION: The Medical Postprocessor visualization software tool for analyzing stent graft properties was evaluated by vascular surgeons. The results show that the software can assist the interpretation of simulation results to optimize stent graft configuration and sizing.

Near-infrared spectroscopy monitoring of the collateral network prior to, during, and after thoracoabdominal aortic repair: a pilot study.

OBJECTIVE: The aim of this study was to evaluate the feasibility of non-invasive monitoring of the paraspinous collateral network (CN) oxygenation prior to, during, and after thoracoabdominal aortic repair in a clinical series. METHODS: Near-infrared spectroscopy optodes were positioned bilaterally-over the thoracic and lumbar paraspinous vasculature-to transcutaneously monitor muscle oxygenation of the CN in 20 patients (age: 66 ± 10 years; men = 11) between September 2010 and April 2012; 15 had open thoracoabdominal aortic repair (Crawford II and III), three had thoracic endovascular aortic repair (TEVAR; Crawford I), and two had a hybrid repair (Crawford II). CN oxygenation was continuously recorded until 48 hours postoperatively. RESULTS: Hospital mortality was 5% (n = 1), 15% suffered ischemic spinal cord injury (SCI). Mean thoracic CN oxygenation saturation was 75.5 ± 8% prior to anesthesia (=baseline) without significant variations throughout the procedure (during non-pulsatile cooling on cardiopulmonary bypass and with aortic cross-clamping; range = 70.6-79.5%). Lumbar CN oxygenation (LbS) dropped significantly after proximal aortic cross-clamping to a minimum after 11.7 ± 4 minutes (74 ± 13% of baseline), but fully recovered after restoration of pulsatile flow to 98.5% of baseline. During TEVAR, stent-graft deployment did not significantly affect LbS. Three patients developed relevant SCI (paraplegia n = 1/paraparesis n = 2). In these patients LbS reduction after aortic cross-clamping was significantly lower compared with patients who did not experience SCI (p = .041). CONCLUSIONS: Non-invasive monitoring of CN oxygenation prior to, during, and after thoracoabdominal aortic repair is feasible. Lumbar CN oxygenation levels directly respond to compromise of aortic blood circulation.

Tailoring magnetic interlayer coupling in La0.7Sr0.3MnO3/SrRuO3 superlattices.

The magnetic interlayer coupling in La0.7Sr0.3MnO3/SrRuO3 superlattices was investigated. High quality superlattices with ultrathin La0.7Sr0.3MnO3 and SrRuO3 layers were fabricated by pulsed laser deposition. The superlattices grew coherently with Mn/Ru intermixing restricted to about one interfacial monolayer. Strong antiferromagnetic interlayer coupling depended delicately on magnetocrystalline anisotropy and intermixing at interfaces. Ab initio calculations elucidated that the antiferromagnetic coupling is mediated by the Mn-O-Ru bond. The theoretical calculations allowed for a quantitative correlation between the total magnetic moment of the superlattice and the degree of Mn/Ru intermixing.

Telematics in medicine: a network infrastructure to optimize processes in cardiology and heart surgery.

OBJECTIVES: During the past 2 decades, cardiac surgery has developed into a high-tech field. Increasing numbers of urgent surgical procedures mean that the time interval from diagnosis to surgical treatment must become ever shorter. Optimizing inconvenient and slow processes such as postal correspondence by using internet services is therefore mandatory in current cardiosurgical practice, and this includes the electronic transfer of patient data and diagnostic imaging material [12]. This study focuses on the internet connection of several cardiac referral centers to a cardiosurgical institution. METHODS: Eleven cath lab centers were connected to a cardiosurgical center by internet. Auser program was especially developed to optimize connecting processes with the department. Data conversion was based on HL7 codes and angiograms were based on CD-ROM mediums and the DICOM standard. An online registration based on the HL7 communications standard was provided. RESULTS: All cath lab centers were successfully connected to the cardiosurgical institution. Angiography data were transmitted within 30 +/- 15minutes. The time interval from diagnosis to decision for surgery decreased from 36 +/- 13 hours to 1 +/- 0.5 hours (p = 0.01). Urgent or emergent surgery could be provided after 18 +/- 19 hours, compared to 56 +/- 35 hours before (p = 0.02). CONCLUSION: Special programs transmitting data via the internet significantly reduces the time interval from diagnosis to surgical treatment. Standardizing data transmitting processes from referral centers markedly optimizes cardiological and cardiosurgical treatments and could thereby improve survival rates and reduce costs.

The excor device - revival of an old system with excellent results.

OBJECTIVE: We report on our experience with the BerlinHeart Excor system in adults and paediatric patients who underwent placement of the mechanical support device under emergency conditions and demonstrate the exceptional advantages and the considerable versatility of the system. METHODS: Since 2003, 29 consecutive patients (25 adults and 4 infants) with ages ranging from 10 months to 54 years underwent implantation of an Excor system. Main underlying heart diseases in adults were acute myocardial infarction (n = 9), dilative cardiomyopathy (n = 6), acute myocarditis (n = 6), whereas most of the children suffered from dilative cardiomyopathy. Ten patients had undergone implantation of an extracorporeal membrane oxygenation system. RESULTS: In 26 cases, a left ventricular assist device (LVAD) was implanted, while 3 patients had biventricular support. The support interval of all patients surviving the perioperative period lasted from 30 to 412 days, mean period of support until heart transplantation or explantation was 184 +/- 117 days. Severe complications were rare. CONCLUSION: The Excor paracorporeal mechanical support system is an excellent and highly versatile device for the support of patients of all ages and different types of underlying heart disease in the mid-term and long-term. The implant procedure and the perioperative management are simple, and complication rates are low.

Harvest of the radial artery: technique of the skeletonization and pedicle preparation.

Nowadays, radial artery grafts play a significant role in coronary artery revascularization, however, harvesting techniques are not standardized. We developed various surgical techniques for radial artery harvesting considering the anatomic landmarks of the foramen, including conventional surgery (with scissors and clips) and procedures with ultrasonic scalpel and retrieving the radial artery graft in a pedicle or in a skeletonized manner.

Cardiothoracic surgery after heart and heart-lung transplantation.

OBJECTIVE: We sought to examine our management and the outcomes of cardiothoracic procedures after heart and heart lung transplantation. METHODS: We performed a retrospective review of cardiothoracic surgical procedures carried out between 1990 and 2004 in patients who had previously undergone heart or heart-lung transplantation at our institution. RESULTS: Twenty-one out of 340 patients (6.2 %) were identified. Cardiothoracic surgery was performed 44.4 +/- 33 months (range 1 - 115 months) after transplantation. Predominant types of surgery were coronary artery bypass grafting due to allograft vasculopathy (n = 5), aortic surgery due to acute dissection (n = 3), biventricular assist device implantation due to acute rejection (n = 1), tricuspid valve repair (n = 1), multiple cardiac surgical procedures including coronary artery bypass grafting, retransplantation, and tricuspid valve replacement (n = 2), explantation of a functionless heterotopic transplanted heart (n = 1). Lung surgery was performed in six patients due to pneumonia (n = 2), primary lung carcinoma (n = 3), lung torsion following heart-lung transplantation (n = 1). All patients underwent either lobectomy or segmental lung resection. Single lung retransplantation (n = 2) after prior heart-lung transplantation due to bronchiolitis obliterans was performed. In one patient a pneumonectomy (n = 1) due to severe chronic rejection of the contralateral lung was performed. Six subsequent deaths after cardiothoracic procedures were recorded after 1, 4, 78, 163, 205, and 730 days, respectively. Causes of death were advanced carcinoma (n = 1), multi-organ failure due to sepsis (n = 2), sudden heart death (n = 2), and advanced heart failure (n = 1). Fifteen out of 21 patients having undergone cardiothoracic procedures (71.4 %) survived the observation period of 56.6 +/- 34 months (range 1 - 114). CONCLUSIONS: Reasons for cardiothoracic procedures after prior heart or heart-lung transplantation were allograft vasculopathy, aortic dissections years after transplantation, chronic rejection, and either lung infections or malignancies. Surgical repair can be performed with an acceptable operative risk and good long-term survival rates.

Clinical situations demanding weaning from long-term ventricular assist devices.

OBJECTIVE: Ventricular assist devices are increasingly used to treat patients with acute or chronic end-stage heart failure. We report on circumstances, exemplified on four cases, where a surprisingly favorable clinical course of the patients ultimately demanded early explantation of the device, which was not anticipated prior to its implantation. METHODS: The four patients were provided with implantable (Micromed BeBakey trade mark, Incor trade mark ) and external pneumatically driven (Thoratec trade mark, Excor trade mark ) devices under emergency conditions and were listed for heart transplantation. RESULTS: All four patients had an unexpected recovery of myocardial pump function. After careful diagnostic evaluation, all device components were completely removed without extracorporeal circulation. No stepwise weaning protocol was employed. CONCLUSIONS: Weaning patients from ventricular assist devices after recovery of myocardial pump function can become necessary. Diagnostic evaluation and the implementation of a weaning protocol is still a matter of debate, while complete surgical removal of all device components without extracorporeal circulation is possible with a low risk.

Successful long-term bridge to transplant in a 5-year-old boy with the EXCOR left ventricular assist device.

We report on a 5-year-old boy who presented with postcardiotomy failure after aortic valve replacement and had to undergo implantation of a Berlin Heart-Excor system since treatment with ECMO did not improve myocardial pump function. After a stormy postoperative course with delayed sternal closure after 9 days, the young boy finally recovered and could be fully mobilized. Until successful heart transplantation after a support interval of 77 days, he experienced no device-related infectious or thromboembolic complications.

First experience with rapamycin-based immunosuppression to improve kidney function after heart transplantation.

UNLABELLED: This study was designed to gain initial experience with rapamycin in thoracic organ transplant recipients with severely compromised kidney function, i.e. to see whether and how kidney function will improve with a rapamycin-based immunosuppressive protocol. METHODS: Twelve heart transplant patients were included into the study (serum creatinine > 2.5 mg/dL), with an average time after transplantation of more than 4 years. The calcineurin inhibitor (cyclosporine A = 9, tacrolimus = 3) was reduced by 50 %, and rapamycin added to reach a target level of 8 - 12 ng/dL. Azathioprine was halted, corticosteroid treatment remained unchanged. RESULTS: After implementing the rapamycin-based immunosuppression kidney function improved in all patients within one week. Serum creatinine dropped from 3.1 +/- 0.6 mg/dL to 2.7 +/- 0.5 mg/dL ( p = 0.0004), creatinine clearance increased from 30.4 +/- 11 mL/min to 40.8 +/- 10.5 mL/min ( p = 0.003). This improvement continued until 3 months after the conversion ( p = 0.032). Thereafter, no statistically significant changes were noted up to 6 months posttransplant ( p = 0.41). Serum cyclosporine levels dropped from 180 +/- 40 ng/mL to 132 +/- 46 ng/mL on average ( p = 0.002). Side-effects occurred in 4 patients and were all related to a rapamycin level exceeding 12 ng/mL. CONCLUSIONS: We conclude that transplant patients with impaired kidney function will have an immediate benefit from partially replacing calcineurin inhibitors by rapamycin.

Evaluation of two oxygen analyzers by computerized data acquisition and processing.

Monitoring of inspired oxygen concentration during anesthesia with nitrous oxide is becoming accepted as essential. This type of monitoring demands accurate monitors that respond rapidly. We evaluated two such devices for their response patterns to rapid changes in oxygen concentration, a galvanic or "fuel cell" unit and a polarographic device. Data were stored after analog-to-digital conversion. The response patterns to stepwise changes in nitrous oxide and oxygen mixtures were recorded at flow rates ranging from 2 to 10 L/min. Both units responded accurately to all changes in the absolute oxygen concentration; the polarographic unit was, on average, twice as fast. Responsiveness to nitrous oxide was low (less than 0.4% at 100% nitrous oxide), and the stability of the signals was good. The 90% response time (T90) was consistent for any stepwise increase or decrease in oxygen concentration between 0, 21, 33, 50, and 100%. After a step change from 0 to 100% oxygen at a gas flow rate of 10 L/min, the T90 was 5.8 seconds in the polarographic device and 11.4 seconds in the galvanic device (p less than 0.01). After a decrease from 100 to 0% oxygen, the T90 was 0.6 second longer in both monitors. Comparing flow rates of 2 L/min with 10 L/min, the T90 was delayed by 1.1 and 2.3 seconds for an increase, and by 1.4 and 2.9 seconds for a decrease in oxygen concentration. Experimental data suggest that both sensors respond adequately during routine clinical use. The faster response of the polarographic device is probably of limited clinical relevance, but it may aid in calibration.