Optimising Large Animal Models of Sustained Atrial Fibrillation: Relevance of the Critical Mass Hypothesis

From Frontiers via Jisc Publications RouterHistory: collection 2021, received 2021-04-04, accepted 2021-05-24, epub 2021-06-15Publication status: PublishedBackground: Large animal models play an important role in our understanding of the pathophysiology of atrial fibrillation (AF). Our aim was to determine whether prospectively collected baseline variables could predict the development of sustained AF in sheep, thereby reducing the number of animals required in future studies. Our hypothesis was that the relationship between atrial dimensions, refractory periods and conduction velocity (otherwise known as the critical mass hypothesis) could be used for the first time to predict the development of sustained AF. Methods: Healthy adult Welsh mountain sheep underwent a baseline electrophysiology study followed by implantation of a neurostimulator connected via an endocardial pacing lead to the right atrial appendage. The device was programmed to deliver intermittent 50 Hz bursts of 30 s duration over an 8-week period whilst sheep were monitored for AF. Results: Eighteen sheep completed the protocol, of which 28% developed sustained AF. Logistic regression analysis showed only fibrillation number (calculated using the critical mass hypothesis as the left atrial diameter divided by the product of atrial conduction velocity and effective refractory period) was associated with an increased likelihood of developing sustained AF (Ln Odds Ratio 26.1 [95% confidence intervals 0.2–52.0] p = 0.048). A receiver-operator characteristic curve showed this could be used to predict which sheep developed sustained AF (C-statistic 0.82 [95% confidence intervals 0.59–1.04] p = 0.04). Conclusion: The critical mass hypothesis can be used to predict sustained AF in a tachypaced ovine model. These findings can be used to optimise the design of future studies involving large animals

Golden Eagles in a multiple land-use environment: A case study in conflict management

Volume: 36Start Page: 55End Page: 6

An Observational Review and Analysis of Qualitative Data to Explore the Benefits of Equine Assisted Learning in Improving the Engagement of Adolescents with Complex Learning Needs, within the Educational Setting

The study determined whether Equine Assisted Learning (EAL) acted as a positive influence to improve the engagement of adolescents with complex learning needs, within their educational setting. The past two years has seen a continuous increase in the number of pupils with complex learning needs in the UK, from 1,244,255 in January 2017 to 1,276,215 in January 2018, an increase from 14.4% to 14.6%. These increasing figures provide a clear rationale for the requirement for a greater utilisation of various learning intervention tools, to begin to meet the dynamic needs of these learners. Seven participants engaged in six EAL sessions over six weeks and were involved in an array of unmounted EAL activities. Questionnaires were formulated with reference to the “Student Engagement (SE) Survey” and were presented to both staff and parents at three points throughout the study, along with Carpenters approved engagement scale for staff to complete weekly, within the lesson following the EAL session. Furthermore, observational research was conducted by the researcher to generate a supportive discussion for the obtained results. Through the quantitative data formulated no significant difference was shown, however a moderate positive correlation between the before and after results of staff and parent questionnaires was presented (Staff Questionnaire p =.119366. Parent Questionnaire p = .145547). Further trends also began to emerge, with correlations forming between improved engagement and specific EAL activities, providing a direction for future research

Calcium in the Pathophysiology of Atrial Fibrillation and Heart Failure

Atrial fibrillation (AF) is commonly associated with heart failure. A bidirectional relationship exists between the two—AF exacerbates heart failure causing a significant increase in heart failure symptoms, admissions to hospital and cardiovascular death, while pathological remodeling of the atria as a result of heart failure increases the risk of AF. A comprehensive understanding of the pathophysiology of AF is essential if we are to break this vicious circle. In this review, the latest evidence will be presented showing a fundamental role for calcium in both the induction and maintenance of AF. After outlining atrial electrophysiology and calcium handling, the role of calcium-dependent afterdepolarizations and atrial repolarization alternans in triggering AF will be considered. The atrial response to rapid stimulation will be discussed, including the short-term protection from calcium overload in the form of calcium signaling silencing and the eventual progression to diastolic calcium leak causing afterdepolarizations and the development of an electrical substrate that perpetuates AF. The role of calcium in the bidirectional relationship between heart failure and AF will then be covered. The effects of heart failure on atrial calcium handling that promote AF will be reviewed, including effects on both atrial myocytes and the pulmonary veins, before the aspects of AF which exacerbate heart failure are discussed. Finally, the limitations of human and animal studies will be explored allowing contextualization of what are sometimes discordant results