A non-second-gradient model for nonlinear elastic bodies with fibre stiffness.

In the past, to model fibre stiffness of finite-radius fibres, previous finite-strain (nonlinear) models were mainly based on the theory of non-linear strain-gradient (second-gradient) theory or Kirchhoff rod theory. We note that these models characterize the mechanical behaviour of polar transversely isotropic solids with infinitely many purely flexible fibres with zero radius. To introduce the effect of fibre bending stiffness on purely flexible fibres with zero radius, these models assumed the existence of couple stresses (contact torques) and non-symmetric Cauchy stresses. However, these stresses are not present on deformations of actual non-polar elastic solids reinforced by finite-radius fibres. In addition to this, the implementation of boundary conditions for second gradient models is not straightforward and discussion on the effectiveness of strain gradient elasticity models to mechanically describe continuum solids is still ongoing. In this paper, we develop a constitutive equation for a non-linear non-polar elastic solid, reinforced by embedded fibers, in which elastic resistance of the fibers to bending is modelled via the classical branches of continuum mechanics, where the development of the theory of stresses is based on non-polar materials; that is, without using the second gradient theory, which is associated with couple stresses and non-symmetric Cauchy stresses. In view of this, the proposed model is simple and somewhat more realistic compared to previous second gradient models.

El desfibrilador automático implantable: actualización para médicos de urgencias / The implantable automatic defibrillator: an update for emergency physicians

El desfibrilador automático implantable (DAI) constituye una opción terapéutica de reciente adquisición para el tratamiento y prevención de las arritmias ventriculares y la muerte súbita de origen cardíaco. Durante los últimos años se ha producido una relevante ampliación de sus indicaciones y, dado el creciente número de pacientes en los que hoy se puede identificar un riesgo elevado de padecer estas gravísimas situaciones, también a un aumento exponencial del número de implantes de dispositivos. Por último, los dispositivos más actuales incorporan otras funciones además de la posibilidad de liberar descargas de corriente, como la del registro de eventos arrítmicos, las funciones de estimulación antitaquicardia o antibradicardia y la función de resincronización cardíaca. Todo ello ilustra la importancia de conocer esta nueva arma terapéutica en los escenarios clínicos de la fase aguda. En la presente actualización se discuten los aspectos de mayor interés para los médicos de urgencias relativos a los fundamentos clínicos y electrofisiológicos, funcionamiento e indicaciones actuales de los DAI (AU)

The implantable automatic defibrillator (IAD) represents a recentlyacquired therapeutic option for the prevention and management of ventricular arrhythmias and cardiac sudden death. A significant increase of the indications for its use has occurred over the last few years and, considering the increasing number of patients in whom an increased risk of these most severe complications may today be identified, there has been also an exponential increase in the number of device implantations. Finally, the currently most advanced devices incorporate further functions beyond that of triggering electric discharges, such as arrhythmia event recording, anti-tachycardia or anti-bradycardia stimulation functions, or cardiac resynchronisation therapy. It is thus of utmost importance for the emergency physician to know the possibilities of this new therapeutic tool in all acute-phase clinical scenarios. The present review paper addresses those aspects with the greatest interest for the emergency physicians in the context of clinical and electrophysiological background, device function and current IAD indications (AU)

Manejo de los pacientes portadores de un desfibrilador automático implantable en los servicios de urgencias hospitalarias / Management of emergencies in patients with implantable cardioverter defibrillator

El desfibrilador automático implantable (DAI) constituye una de las principales opciones terapéuticas en los pacientes con arritmias ventriculares malignas, muerte súbita cardiaca o elevado riesgo de desarrollarlas. Por ello, el número de implantes de DAI y, por consiguiente, el número de pacientes portadores de DAI que presentan alguna complicación relacionada con el mismo ha aumentado significativamente en la última década. Estos pacientes se han convertido en frecuentadores potenciales de los Servicios de Urgencias Hospitalarios (SUH), hecho que, sin duda, se verá incrementado en los próximos años. El panel de consenso del Grupo de Trabajo de DAI de la Sección de Electrofisiología y Arritmias de la Sociedad Española de Cardiología (SEC) y el Grupo de Arritmias Cardíacas de la Sociedad Española de Medicina de Urgencias y Emergencias (SEMES) han elaborado un documento en el que se detallan las recomendaciones para el manejo de las principales situaciones urgentes que pueden presentar estos pacientes. El objetivo del mismo es mejorar la atención médica de éstos y promover un uso más racional de los recursos en los SUH. En él se hace especial hincapié en la evaluación inicial del paciente con DAI en el SUH y en las causas y manejo de las principales complicaciones: descargas del DAI esporádicas y múltiples, parada cardiaca, ausencia de intervención durante una arritmia ventricular, proarritmia inducida por el DAI, fallo de estimulación, síncope, infección del dispositivo, trombosis venosa asociada al DAI, interferencia con técnicas diagnósticas y terapéuticas, síndromes psiquiátricos en pacientes con DAI, alarmas acústicas, palpitaciones no asociadas a descargas y recomendaciones en pacientes terminales (AU)

Implantable cardioverter-defibrillators (ICD) have become one of the most important therapeutic options for patients with or with high risk of having life-threatening ventricular arrhythmias. Therefore, the number of device continues to grow and an increasing number of patients are experiencing complications related to ICD. Because these patients are potentials users of Emergency departments the number of visits related to ICD will be increase in the next years. The Consensus panel of the Working Group on ICD of the Electrophysiology and Arryhtmia Section of the Spanish Society of Cardiology and the Working Group on Cardiac Arrhythmia of the Spanish Society of Emergency Medicine has developed a Consensus Document in which the main recommendations on the diagnosis and management of the emergency situations that could present these patients are reviewed. Its main objective is to facilitate delivery of optimal care for these patients and to promote a more rational use of the Emergency departments. In this document, special emphasis is done on the initial evaluation for the ICD patient at the Emergency department and on the causes and management of the main complications: single and multiple shocks, cardiac arrest, ventricular tahcyarrhythmias without ICD intervention, ICD-induced proarrhythmia, pacing malfunction, syncope, ICD system infection, venous thrombosis associated to ICD, interferences with diagnostic and therapeutic procedures, psychiatric syndromes in patients with ICD, acoustic alarms, palpitations not related to ICD shocks and terminal care issues (AU)

[The clinical practice guidelines of the Sociedad Española de Cardiología on the automatic implantable defibrillator]. / Guías de práctica clínica de la Sociedad Española de Cardiología sobre el desfibrilador automático implantable.

Since the first implantation in man in 1980 implantable cardioverter defibrillator technology has greatly improved and the number of devices implanted has increased considerably every year. Non thoracotomy lead systems and biphasic shocks are now the approach of choice, offering an almost 100% success rate. This document reviews the recommendations for qualification of personnel and for the centres implanting and carrying out follow-ups on defibrillators. The current indications for the implantation of implantable cardioverter defibrillator are also addressed.

[The determinants of exercise tolerance in patients with hypertensive cardiopathy]. / Determinantes de la tolerancia al ejercicio en pacientes con cardiopatía hipertensiva.

A study was made of 45 patients with arterial hypertension, no prior angina or myocardial infarction, mean age 64 +/- 5 years, and ejection fraction > 50%. Twenty (group I) had congestive heart failure while 25 (group II) were asymptomatic. Testing following remission of symptoms revealed impaired exercise tolerance (VO2 max < 20 ml/kg/min) in 22 (subgroup A-80% from group I), and normal tolerance in 23 (subgroup B). Of ventricular function indexes, only peak filling rate correlated significantly with VO2 max (r = 0.65). Of 32 patients with thallium-201 negative in ergometric tests, the 12 in subgroup A had a higher degree of hypertrophy (p > 0.01). Nine thallium-positive patients had lower VO2 max (p > 0.05) than did 17 thallium-negative patients with a similar degree of hypertrophy. Thus, in hypertensive patients, exercise tolerance depends on prior congestive heart failure, diastolic dysfunction, degree of hypertrophy and silent regional ischemia.