A general method for estimating deformation and forces imposed in vivo on bioprosthetic heart valves with flexible annuli: in vitro and animal validation studies

BACKGROUND AND AIM OF THE STUDY: The use of flexible structures within cardiovascular prostheses such as valves, stents and vascular grafts has been proposed as a means of more closely modeling native mechanics, and thereby reducing the biomechanical problems associated with rigid materials. However, the design of such materials has been hampered by the paucity of quantitative information on the in-vivo behavior of such structures. The aim of this study was to explore the use of 3D ultrasound imaging coupled with finite element analysis (FEA) as a tool to estimate deformation and forces imposed in vivo on a novel bioprosthetic valve design. METHODS: The method was first tested using in-vitro static loading conditions, where good agreement between displacements seen on video and those obtained from application of the identical force within the finite element program was seen. The method was then tested in a porcine model with valves implanted in the mitral position. Images of the deforming annular ring were obtained over the cardiac cycle using 3D intravascular ultrasound; these images were fed into the FEA program for calculation of reaction forces. RESULTS: Results in vitro showed that a force of 2.7-8.0 Newtons (N) was required to produce a deformation of between 1.0 and 3.0 mm in the radial direction. A time history of deformation and force around the ring of the valve stent could be obtained for the in-vivo conditions. These results revealed a maximum deformation of 0.5-1.7 mm along the short axis (anteroposterior) of the mitral valve. Coupled to this, a peak reaction force of 4.4-13.9 N was found at the points corresponding to maximal deflection. Both deformation and reaction force reached maximum during atrial contraction. CONCLUSION: This method provides an accurate means of estimating deformation and corresponding forces imposed in vivo on intracardiac prostheses. The results provide information on the dynamic behavior of the mitral valve annulus. Such information should be useful in the design of flexible cardiovascular prostheses.     

Society position statement

Purpose

There are more than 200,000 Canadians living with permanent pacemakers or implantable defibrillators, many of whom will require surgery or invasive procedures each year. They face potential hazards when undergoing surgery; however, with appropriate planning and education of operating room personnel, adverse device-related outcomes should be rare. This joint position statement from the Canadian Cardiovascular Society (CCS) and the Canadian Anesthesiologists?? Society (CAS) has been developed as an accessible reference for physicians and surgeons, providing an overview of the key issues for the preoperative, intraoperative, and postoperative care of these patients.

Principal findings

The document summarizes the limited published literature in this field, but for most issues, relies heavily on the experience of the cardiologists and anesthesiologists who contributed to this work. This position statement outlines how to obtain information about an individual??s type of pacemaker or implantable defibrillator and its programming. It also stresses the importance of determining if a patient is highly pacemaker-dependent and proposes a simple approach for nonelective evaluation of dependency. Although the document provides a comprehensive list of the intraoperative issues facing these patients, there is a focus on electromagnetic interference resulting from electrocautery and practical guidance is given regarding the characteristics of surgery, electrocautery, pacemakers, and defibrillators which are most likely to lead to interference.

Conclusions

The document stresses the importance of preoperative consultation and planning to minimize complications. It reviews the relative merits of intraoperative magnet use vs reprogramming of devices and gives examples of situations where one or the other approach is preferable.     

Neuroleptic malignant syndrome in a child

Neuroleptic malignant syndrome (NMS) is an uncommon condition, characterized by the insidious onset of fever, muscle rigidity, elevated creatine kinase, tachycardia, haemodynamic instability, altered level of consciousness, tachypnoea, diaphoresis and leucocytosis over a period of days to weeks. This condition occurs almost exclusively in patients receiving antipsychotic medications. We present a case of an eight-year-old boy who developed a condition that was suggestive of neuroleptic malignant syndrome after receiving oral haloperidol for control of athetoid movements. NMS is of particular importance to the anaesthetist since its clinical presentation may be confused with malignant hyperthermia (MH). Patients who had been treated for NMS have been reported as having a muscle biopsy positive for MH.     

A case against the specificity of "cardiac" troponin-T.

A case of a spurious rise in cardiac troponin-T in an 85 year old Caucasian man with myelodysplastic syndrome and multiple malignancies but with intact cardiac and renal function is reported. The patient presented to the accident and emergency department with fever and chest pain. Inconsistent laboratory findings in biochemical markers diagnostic of myocardial infarction were observed. Discrepant findings included a rise in the concentration of the cardiac specific marker troponin-T in the absence of an increase in creatine kinase (CK) isoenzyme MB activity. Somewhat surprisingly, there was a significant and consistent increase in CK isoenzyme BB activity. Awareness of the increase in troponin-T concentrations in patients with multiple clinical non-cardiac problems may prevent an erroneous diagnosis of myocardial infarction and avert institution of unduly aggressive treatment.     

Immunopathogenic mechanisms in tourette syndrome: A critical review

Tourette syndrome (TS) has a multifactorial etiology, in which genetic, environmental, immunological and hormonal factors interact to establish vulnerability. This review: (i) summarizes research exploring the exposure of TS patients to immune‐activating environmental factors, and (ii) focuses on recent findings supporting a role of the innate and adaptive immune systems in the pathogenesis of TS and related disorders. A higher exposure prior to disease onset to group A β‐haemolytic streptococcal (GABHS) infections in children with tics and obsessive‐compulsive (OC) symptoms has been documented, although their influence upon the course of disease remains uncertain. Increased activation of immune responses in TS is suggested by changes in gene expression profiles of peripheral immune cells, relative frequency of lymphocyte subpopulations, and synthesis of immune effector molecules. Increased activity of cell‐mediated mechanisms is suggested by the increased expression of genes controlling natural killer and cytotoxic T cells, increased plasma levels of some pro‐inflammatory cytokines which correlate with disease severity, and increased synthesis of antineuronal antibodies. Important methodological differences might account for some inconsistency among results of studies addressing autoantibodies in TS. Finally, a general predisposition to autoimmune responses in TS patients is indicated by the reduced frequency of regulatory T cells, which induce tolerance towards self‐antigens. Although the pathogenic role of immune activation in TS has not been definitively proven, a pathophysiological model is proposed to explain the possible effect of immunity upon dopamine transmission regulation and the generation of tics. © 2009 Movement Disorder Society     

Using bioscience knowledge in nursing: actions, interactions and reactions

This paper draws on empirical data from a study undertaken to explore the outcomes of the applied physiology component of a post-registration diploma in nursing (DN). Most students completing the DN were utilizing their new bioscience knowledge in clinical practice, and reported increased participation in interprofessional discussions and team decisions. Respondents found themselves better able to monitor and evaluate doctors' decisions and this led to friction with some medical colleagues. However, the strongest resistance came from senior nurses, very few of whom had completed advanced nursing courses in bioscience and who were generally unwilling to allow respondents to develop new roles. General managers were also perceived as a major barrier to change. There is little evidence of tangible benefits to the nurses themselves: most saw the DN qualification as a way of protecting their status as professional nurses in the face of managerially driven organizational change, rather than as a route to occupational advancement.