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The Mechanism of Reflection Type Reentry: A Simulation Study.

ABSTRACT: Reflection is a special type of reentry in which an electrical wave front travels in a forward direction through tissue that is then re-excited by a wave front that propagates backward. This type of reentry has been studied computationally in 1-dimensional fibers and verified experimentally. Different hypotheses explaining reflected reentry have been proposed based on the structure and heterogeneity of the tissue properties, but the mechanism remains uncertain.We used the bidomain model to represent cardiac tissue and the Luo-Rudy model to describe the active membrane properties. We consider an ischemic region in a volume of ventricular myocardium. Our results show that a slow depolarization in the ischemic border zone caused by electrotonic coupling to depolarized tissue in the normal region creates a delay between proximal and distal regions that produces enough electrotonic current in the distal region to re-excite the proximal region.Our simulation shows that an early afterdepolarization (EAD) is not the source of the reflection. It depends on the pacing interval and stimulus strength necessary to maintain enough time delay between proximal and distal regions.

SUBMITTER: Kandel SM

PROVIDER: S-EPMC4701638 | biostudies-literature | 2015 Dec

REPOSITORIES: biostudies-literature

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The Mechanism of Reflection Type Reentry: A Simulation Study.

Kandel Sunil M SM Roth Bradley J BJ

Journal of cardiovascular electrophysiology 20150926 12

<h4>Introduction</h4>Reflection is a special type of reentry in which an electrical wave front travels in a forward direction through tissue that is then re-excited by a wave front that propagates backward. This type of reentry has been studied computationally in 1-dimensional fibers and verified experimentally. Different hypotheses explaining reflected reentry have been proposed based on the structure and heterogeneity of the tissue properties, but the mechanism remains uncertain.<h4>Methods an ...[more]

PMID: 26269355

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Project description:IntroductionIn recent years, researchers have recognized the need to examine the relative effectiveness of different simulation approaches and the experiences of physicians operating within such environments. The current study experimentally examined the reflective judgments, cognitive processing, and clinical reasoning performance of physicians across live and video simulation environments.MethodsThirty-eight physicians were randomly assigned to a live scenario or video case condition. Both conditions encompassed two components: (a) patient encounter and (b) video reflection activity. Following the condition-specific patient encounter (i.e., live scenario or video), the participants completed a Post Encounter Form (PEF), microanalytic questions, and a mental effort question. Participants were then instructed to re-watch the video (i.e., video condition) or a video recording of their live patient encounter (i.e., live scenario) while thinking aloud about how they came to the diagnosis and management plan.ResultsAlthough significant differences did not emerge across all measures, physicians in the live scenario condition exhibited superior performance in clinical reasoning (i.e., PEF) and a distinct profile of reflective judgments and cognitive processing. Generally, the live condition participants focused more attention on aspects of the clinical reasoning process and demonstrated higher level cognitive processing than the video group.ConclusionsThe current study sheds light on the differential effects of live scenario and video simulation approaches. Physicians who engaged in live scenario simulations outperformed and showed a distinct pattern of cognitive reactions and judgments compared to physicians who practiced their clinical reasoning via video simulation. Additionally, the current study points to the potential advantages of video self-reflection following live scenarios while also shedding some light on the debate regarding whether video-guided reflection, specifically, is advantageous. The utility of context-specific, micro-level assessments that incorporate multiple methods as physicians complete different parts of clinical tasks is also discussed.

Project description:Patients with an accessory pathway (AP) have an increased propensity to develop atrial fibrillation (AF), but the mechanism is unknown.The purpose of this study was to identify crucial risk factors and to test the hypothesis that reflection and/or microreentry of atrial impulses propagating into the AP triggers AF.Five hundred thirty-four patients successfully treated with radiofrequency ablation of AP at two university hospitals were evaluated. Patients were separated into those with concealed vs those with manifest AP in terms of their propensity to develop AF. To investigate AF triggering mechanisms, linear and branched two-dimensional models of atrium-to-ventricle propagation across a heterogeneous 1 x 6 AP using human ionic kinetics were simulated.A history of AF was twice as common in patients with manifest AP vs concealed AP irrespective of AP location. AF was more likely to occur in older males and in patients with larger atria. There was no correlation between AF history and AP refractory measures. However, the electrophysiologic properties of APs seemed to fulfill the prerequisites for reflection and/or microreentry of atrially initiated impulses. In the linear AP model, repetitive atrial stimulation resulted in progressively larger delay of atrium-to-ventricle propagation across the passive segment. Eventually, sufficient time for repolarization of the atrial segment allowed for reflection of an impulse that activated the entire atrium and by wavefront-wavetail interaction with a new atrial stimulus AF reentry was initiated. Simulations using the branched model showed that microreentry at the ventricular insertion of the AP could also initiate AF via retrograde atrial activation as a result of unidirectional block at the AP-ventricle junction.Propensity for AF in patients with an AP is strongly related to preexcitation, larger atria, male gender, and older age. Reflection and microreentry at the AP may be important for AF initiation in patients with manifest (preexcited) Wolff-Parkinson-White syndrome. Similar mechanisms also may trigger AF in patients without an AP.

Project description:BackgroundSimulation in healthcare attempts to create relevant representations of patient encounters. It provides experiential learning, bridging typical classroom activities and clinical practice. This study aims to investigate whether the principle of Peer-Assisted Learning can be used in simulation by letting simulation-experienced paramedic students prepare, deliver, and debrief their own simulations, with minimal faculty assistance. This could be a way to support student learning by being involved in teaching, and it might at the same time optimise the cost-effectiveness of simulation-based training.MethodsThis observational non-inferiority study compared reflection levels between facilitator-led and student-led simulation and debriefing, between scenario types, and compared the number of turns in which students are involved in both settings. Third-year Bachelor in Paramedic Science students' debriefings were filmed and transcribed. The degree of reflection in students' statements was rated according to a modified version of Fleck's analytical framework of reflection levels, assigning scores from lowest (R0 description) to highest (R4 critical reflection). Facilitator-led and student-led debriefings were compared using chi-square tests. Scenarios were also analysed according to type (paediatric emergencies and complex assessments) regardless of who led the simulation.ResultsTen facilitator-led and 12 student-led debriefings were analysed. Students gave 682 (49%) contributions in the facilitator-led debriefings, and 702 (51%) contributions in student-led debriefings. Comparison of reflection levels between facilitator-led and student-led debriefings was respectively: R0-level 32.7% vs 33.8%, R1-level 44.0% vs 44.3%, R2-level 14.7% vs 17.1%, R3-level 0.1% vs 1.3%, and R4-level 0.1% vs 0.1%. There were no statistically significant differences in reflection levels between facilitator-led and student-led debriefings (p = 0.178). Comparing the reflection levels between the scenarios on "paediatric emergencies" and "complex assessments", the results were respectively: R0-level 35.4% vs. 31.7%-level, R1-level 45.3% vs. 43.3%-level, R2-level 13.4% vs. 17.8%, R3-level 0.5% vs. 0.9%, and R4-level 0.0% vs. 0.3%. These differences were statistically significant (p = 0.010). No significant differences in engagement were found between debriefings led by a student or a facilitator, when measuring the number of turns in the conversations.ConclusionsFacilitator-led and student-led debriefings resulted in equivalent reflection levels amongst students. Student-led simulation is potentially a cost-effective supplement to regular simulation within a healthcare degree program. Since complex scenarios provided higher reflection levels than paediatric, scenario design might influence reflection levels.

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The Mechanism of Reflection Type Reentry: A Simulation Study.

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The Mechanism of Reflection Type Reentry: A Simulation Study.

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