Ventricular Fibrillation is responsible for a majority of sudden cardiac death, but little is known about how ventricular tachycardia (VT) degenerates into ventricular fibrillation. Several clinical studies focused only on preventing VT with a class III antiarrhythmic drug resulted in many deaths. Our simulations investigate the interactions between an antiarrhythmic drug likely to suppress a VT and a Figure 8 reentry. A parameter AAR is introduced to increase the action potential duration and therefore simulate various Class III drugs. Simulations are (...) ran under several conditions (phases of the reentry, values of AAR, durations). They show that a VT can be suppressed whatever the phase of the reentry but it strongly depends on the duration of the effect. It confirms that a drug which can suppress a reentry can also worsen it. It also shows a great variety of activation patterns and thus the complexity of antiarrhythmic drugs effects. Simulations also demonstrate that suppressing VT is an increasing function of AAR. (shrink)

This study examined the quality of children's assent to a clinical trial. In subjects younger than 9 years of age, understanding of most aspects of the study was found to be poor to non-existent. Understanding of procedures was poor in almost all subjects. In addition, voluntariness may have been compromised in many subjects by their belief that failure to complete the study would displease others. If the fact that a child's assent has been obtained is used to justify the exposure (...) of that child to the potential harm of a non-therapeutic blood sample, the assent must be meaningful. In the nutrition study observed here, the quality of the assent of children younger than 9 years of age was very poor. The assent therefore did not provide a valid justification for requesting a blood sample from these children. This study indicates that most children younger than 9 years of age cannot be expected to consent or assent to clinical research in a meaningful way. The current age of 7 years for initiating assent (in addition to parental consent) is possibly not appropriate and should be reconsidered. (shrink)

A precise fomulation of the strong Equivalence Principle is essential to the understanding of the relationship between gravitation and quantum mechanics. The relevant aspects are reviewed in a context including General Relativity but allowing for the presence of torsion. For the sake of brevity, a concise statement is proposed for the Principle: An ideal observer immersed in a gravitational field can choose a reference frame in which gravitation goes unnoticed. This statement is given a clear mathematical meaning through an accurate (...) discussion of its terms. It holds for ideal observers (time-like smooth non-intersecting curves), but not for real, spatially extended observers. Analogous results hold for gauge fields. The difference between gravitation and the other fundamental interactions comes from their distinct roles in the equation of force. (shrink)

Objective: To determine whether the marks in the third year Objective Structured Clinical Examination were affected by the collusion reported by the students themselves on an electronic discussion board.Design: A review of the student discussion, examiners’ feedback and a comparison of the marks obtained on the 2 days of the OSCE.Participants: 255 third year medical students.Setting: An OSCE consisting of 15 stations, administered on three sites over 2 days at a UK medical school.Results: 40 students contributed to the discussion on (...) the electronic discussion board. The main points raised were perceived inequity between students who did, or did not, have prior knowledge of the station content, and the lack of honesty and professionalism of their peers. Most contributors claimed to have received, or knew of others receiving, prior knowledge, but none confessed to passing on information. No significant difference was observed in the overall mark for the OSCE on day 1 ) and day 2 ). On day 2, marks were considerably greater for four stations and markedly lower for three stations. It was not obvious why collusion should affect these station marks. A clear indication of the effects of collusion could only be obtained from a single subsection of an individual station where 82 students on day 2 incorrectly gave the diagnosis from day 1.Conclusion: Marks do not provide a sound inference of student collusion in an OSCE and may mask the aspects of professional development of students. (shrink)

We used computer simulations to study the possible role of the dispersion of cellular coupling, refractoriness or both, in the mechanisms underlying cardiac arrhythmias. Local ischemia was first assumed to induce cell to cell dispersion of the coupling resistance (Case 1), refractory period (Case 2), or both of them (Case 3). Our numerical experiments based on the van Capelle and Durrer model showed that vortices could not be induced by cell to cell variations. With cellular properties dispersed in a patchy (...) way within the ischemic zone, a single activation wave could give rise to abnormal activities. This demonstrates the stability of the wave front under small inhomogeneities. Probabilities of reentry, estimated for the three cases cited above showed that a severe alteration of the coupling resistance may be an important factor in the genesis of reentry. Moreover, use of isochronal maps revealed that vortices were both stable and sustained with an alteration of the coupling alone or combined with a reduction of the action potential duration. Conversely, simulations with reduction of the refractoriness alone, inducing only transient patterns, could exhibit functionally determined reentries. (shrink)