Comparison of fluoroscopic and imageless registration in surgical navigation of the acetabular component.

OBJECTIVE: This study compared the repeatability and reproducibility of acetabular component positioning using imageless and fluoroscopic-referenced navigation methods. METHODS: A single cadaveric pelvis had a modular acetabular component securely fixed. Cup position was evaluated using imageless and fluoroscopic registration techniques. These were compared to measurements of a coordinate measuring machine (CMM) and a validated CT scan protocol. RESULTS: The CMM-determined anatomical acetabular inclination measurement was 46.02 degrees (SD = 1.07), while the CMM-determined anatomical anteversion (pubic symphysis) was 15.79 degrees (SD = 0.41). Computed tomography revealed inclination of 42.2 degrees (SD = 0.65); anteversion with pubic tubercle referencing of 12.1 degrees (SD = 0.14); and anteversion with pubic symphysis referencing of 14.3 degrees (SD = 0.89). Evaluation of repeatability (one surgeon; n = 8) with the imageless system (pubic tubercle) revealed inclination of 41.8 degrees (SD = 0.46) and anteversion of 11.2 degrees (SD = 0.8). For the fluoroscopic system (pubic symphysis), inclination was 42.8 degrees (SD = 1.6) and anteversion was 17.6 degrees (SD = 3.1). Evaluation of reproducibility (three surgeons; n = 24) with the imageless system revealed inclination of 41.8 degrees (SD = 0.82) and anteversion of 15.2 degrees (SD = 1.06). For the fluoroscopic system, inclination was 48.5 degrees (SD = 0.9) and anteversion was 17.8 degrees (SD = 2.5). Imageless referencing of cup inclination and anteversion were found to be process capable using the Six Sigma Cp and Cpk capability indices. Fluoroscopic referencing was process capable for cup inclination but not for cup anteversion (Cp - 1.1; Cpk - 1.0). An F-test revealed significantly greater variance with fluoroscopic referenced anteversion (p < 0.002). CONCLUSIONS: Imageless referencing was process capable for computer navigation of cup placement in the ex-vivo setting. Fluoroscopic referencing for pelvic landmarks is problematic as locating points from radiographic images is difficult, especially for cup anteversion.     

Ex vivo resuscitation of adult pig hearts

One possible way to expand the human heart donor pool is to include non-heart-beating human donors. To begin validating this approach, we developed an ex vivo cardiac perfusion circuit to support large mammalian hearts in Langendorff mode and beating-ejecting mode and to assess and improve their ischemic tolerance. In vivo hemodynamic data and heparinized blood (4.0 +/- 0.5 L) were collected from 6 anesthetized pigs. Hearts were isolated and connected to a recirculating perfusion circuit primed with autologous buffered blood (pH, 7.40). After retrograde aortic perfusion in Langendorff mode, the left atrium was gravity-filled at 10-20 mmHg, and the left ventricle began to eject against a compliance chamber in series with a systemic reservoir set to a hydraulic afterload of 100-120 mmHg. Left ventricular function was restored and maintained in all 6 hearts for 30 min. Cardiac output, myocardial oxygen consumption, stroke work, aortic pressure, left atrial pressure, and heart rate were measured. The mean myocardial oxygen consumption was 4.8 +/- 2.7 mL/min/100 g (95.8% of in vivo value); and mean stroke work, 5.3 +/- 1.1 g x m/100 g (58.95% of in vivo value). One resuscitated heart was exposed to 30 min of normothermic ischemic arrest, then flushed with Celsior and re-resuscitated. The ex vivo perfusion method described herein restored left ventricular ejection function and allowed assessment of ischemic tolerance in large mammalian hearts, potentially a 1st step toward including non-heart-beating human donors in the human donor pool.     

Vascular thrombosis during support with continuous flow ventricular assist devices: correlation with computerized flow simulations

Continuous flow pumps are increasingly used to treat severe heart failure. These pumps alter flow physiology by lowering pulsatility in the arterial circulation. In patients with peripheral stenosis, continuous flow pumps may lead to thrombosis of peripheral vessels, possibly predisposing to vascular thrombosis in areas of non-flow-limiting stenosis. The authors performed a computerized flow modeling simulation to analyze the effects of altered hemodynamics in a stenotic area. Drawing on previous clinical experience, we modeled a stenotic area in the common carotid artery. Computerized flow modeling revealed blood stagnation zones with low shear stress and velocity adjacent to the stenotic area during nonpulsatile flow. Such stagnation was not present during pulsatile flow. These results indicate a mechanism by which altered physiologic flow may accelerate occlusion of arterial conduits in patients with preexisting stenosis. This finding may be important for patients with continuous flow devices who have peripheral vascular disease; therefore, further study is warranted.     

Clinical Experience with the TandemHeart Percutaneous Ventricular Assist Device as a Bridge to Cardiac Transplantation

Cardiac support with a ventricular assist device is among the few treatments for heart-failure patients who have profound cardiogenic shock unresponsive to vasopressors and intra-aortic balloon pumps. The TandemHeart® percutaneous ventricular assist device can provide temporary support until another device can be placed or a donor heart becomes available.We examined the TandemHeart''s effect on cardiac index, central venous pressure, mixed venous oxygen saturation, creatinine, mean arterial pressure, urine output, and 30-day mortality rate in 5 heart-failure patients (2 with nonischemic and 3 with ischemic cardiomyopathy; mean preoperative left ventricular ejection fraction, 0.17 ± 0.056). Two patients were undergoing cardiopulmonary resuscitation when the device was inserted. The average duration of TandemHeart support was 7.6 ± 3.2 days; all patients were successfully bridged to transplantation.The TandemHeart improved the cardiac index (1.9 ± 0.3 vs 3.5 ± 0.8 L/[min·m²], P= 0.01), mean arterial pressure (69 ± 12.5 vs 91 ± 4.3 mmHg, P=0.009), mixed venous oxygen saturation (45.4 ± 14.3 vs 71.4 ± 7.5, P=0.009), and urine output (1,861 ± 988 vs 4,314 ± 1,346 mL/hr, P=0.01). The device decreased central venous pressure (21.2 ± 7.4 vs 12.8 ± 5.9 mmHg, P=0.02) and pressor requirements (2.4 ± 1.1 vs 1.0 ± 0.7 agents, P=0.02). Average long-term follow-up after heart transplantation was 8.4 ± 9.9 months, with no deaths.We conclude that the TandemHeart can provide hemodynamic support for patients with profound, refractory cardiogenic shock. Furthermore, the device can bridge patients to cardiac transplantation and can be placed percutaneously, without invasive surgery.Key words: Assisted circulation/instrumentation/methods, blood vessel prosthesis implantation, cardiac output, cardiomyopathies/complications/mortality/therapy, equipment design, heart-assist devices, heart failure/complications/therapy, hemodynamics, preoperative care, shock, cardiogenic/mortality/physiopathology/therapy, treatment outcomeDespite improvements in the medical treatment of heart failure and the well-established usefulness of the intra-aortic balloon pump (IABP),^1–3 the mortality rate of patients with cardiomyopathy and cardiogenic shock remains considerable.⁴ Treatment options for this high-risk group include ventricular assist devices (VADs), but these are associated with substantial morbidity, especially in acute circumstances. In addition, the invasive procedure necessary to implant VADs requires cardiopulmonary bypass (CPB), which significantly increases the risk of morbidity and death.A newly available option for these patients is the TandemHeart® percutaneous VAD (pVAD) (CardiacAssist, Inc.; Pittsburgh, Pa)—an extracorporeal, axial-flow pump connected to a catheter that crosses the atrial septum and aspirates blood from the left atrium. The blood is then returned to the body through an outflow cannula that is inserted into the femoral artery. This pump can be placed quickly in the cardiac catheterization laboratory and requires only femoral access procedures. Unlike the IABP, the pVAD can generate ventricular unloading at flow rates of up to 4 L/min.The 1st described use of the pVAD was in 18 patients who experienced cardiogenic shock after myocardial infarction.⁵ The device provided adequate support that resulted in improved blood pressure, cardiac index, pulmonary capillary wedge pressure, and central venous pressure. Although the pVAD restored systemic perfusion, the high-risk group of patients experienced a 30-day mortality rate of 44%.The pVAD has also been used in the catheterization laboratory for hemodynamic support during high-risk coronary interventions.^6–11 In addition to its having provided successful temporary support for patients with acute myocarditis,^12,13 the TandemHeart has served as a bridge to cardiac transplantation in 1 patient.¹⁴Long-term implantable VADs, including the pulsatile pumps and the newer generation of axial-flow devices, can provide adequate support for patients with end-stage cardiomyopathy and can serve as a bridge to transplantation.¹⁵ However, these pumps have a less clear role in patients who are experiencing acutely decompensated heart failure. Available mechanical support options for these patients include extracorporeal pumps that require open surgical cardiac cannulation. In contrast, the TandemHeart can be placed percutaneously, and it affords immediate cardiac support.We studied the TandemHeart''s use in 5 patients who were experiencing end-stage cardiomyopathy and cardiogenic shock. Although this pVAD was intended to support these patients only until a longer-term device could be implanted, all experienced substantial improvement in cardiac function and were therefore listed for urgent cardiac transplantation.     

Asymmetrical Barkhausen Noise of a Hard Milled Surface

This study is focused on the asymmetrical Barkhausen noise emission of a hard milled surface during cyclic magnetisation. The Barkhausen noise is studied as a function of the magnetising voltage and the hard milled surface is compared with a surface after heat treatment. The asymmetry in the Barkhausen noise emission after hard milling occurs due to the typical “sandwich” structure and the different magnetic hardnesses of the different layers beneath the free surface. Furthermore, this asymmetry is also due to the preferential orientation of the matrix in the direction of the cutting speed and magnetostatic fields, which hinder or favour the premagnetising process.     

Left ventricular assist devices: an alternative to medical therapy for end-stage heart failure

Although aggressive medical therapy and ultimately cardiac transplantation have long been the therapeutic mainstays for patients with end-stage heart failure, the left ventricular assist device (LVAD), which was originally used clinically as a bridge to transplantation, may also be used as destination therapy. LVAD therapy for selected patients has been shown in the REMATCH trial to be superior to medical therapy in ameliorating symptoms and improving outcome in patients with terminal heart failure. LVAD therapy has also proved useful in improving native heart function by neuroendocrine modulation and reverse remodeling. Furthermore, current evidence suggests that when LVAD therapy is utilized to improve ventricular function, it may be further enhanced when combined with aggressive medical therapy.