John J. Lee

Characteristics of wave fronts during ventricular fibrillation in human hearts with dilated cardiomyopathy : Role of increased fibrosis in the generation of reentry

OBJECTIVES We sought to evaluate the characteristics of wave fronts during ventricular fibrillation (VF) in human hearts with dilated cardiomyopathy (DCM) and to determine the role of increased fibrosis in the generation of reentry during VF. BACKGROUND The role of increased fibrosis in reentry formation during human VF is unclear. METHODS Five hearts from transplant recipients with DCM were supported by Langendorff perfusion and were mapped during VF. A plaque electrode array with 477 bipolar electrodes (1.6-mm resolution) was used for epicardial mapping. In heart no. 5, we also used 440 transmural bipolar recordings. Each mapped area was analyzed histologically. RESULTS Fifteen runs of VF (8 s/run) recorded from the epicardium were analyzed, and 55 episodes of reentry were observed. The life span of reentry was short (one to four cycles), and the mean cycle length was 172 +/- 24 ms. In heart no. 5, transmural scroll waves were demonstrated. The most common mode of initiation of reentry was epicardial breakthrough, followed by a line of conduction block parallel to the epicardial fiber orientation (34 [62%] of 55 episodes). In the areas with lines of block, histologic examination showed significant fibrosis separating the epicardial muscle fibers and bundles along the longitudinal axis of fiber orientation. The mean percent fibrous tissue in these areas (n = 20) was significantly higher than that in the areas without block (n = 28) (24 +/- 7.5% vs. 10 +/- 3.8%, p < 0.0001). CONCLUSIONS In human hearts with DCM, epicardial reentrant wave fronts and transmural scroll waves were present during VF. Increased fibrosis provides a site for conduction block, leading to the continuous generation of reentry.

Effects of Procainamide on Wave-Front Dynamics During Ventricular Fibrillation in Open-Chest Dogs

BACKGROUND There is increasing evidence that both functional reentrant wave fronts and multiple wavelets are present during ventricular fibrillation (VF). However, the effects of procainamide on the characteristics of activation waves during VF are poorly understood. METHODS AND RESULTS Seven dogs were studied; six underwent subendocardial chemical ablation procedures. A plaque with 317 to 480 bipolar electrodes was sutured to the right ventricular free wall, and the patterns of activation were registered with a computerized mapping system. VF was electrically induced, and the patterns of activation were registered at baseline and during procainamide infusion (serum concentration, 9.3+/-1.9 microg/mL). Among the six dogs that had their subendocardium ablated, reentrant wave fronts were present in 6 of the 108 runs of VF at baseline and in 6 of the 100 runs of VF during procainamide infusion. By analyzing the wave fronts, we found that the cycle length, refractory period, conduction velocity, and wavelength at baseline were 101+/-9 ms, 54+/-5 ms, 0.93+/-0.21 mm/ms, and 51+/-16 mm, respectively, and during procainamide infusion, values became 125+/-11 ms (P<.001), 119+/-7 ms (P<.001), 0.42+/-0.02 mm/ms (P<.001), and 50+/-4 mm (P=.8), respectively. The vast majority of the activation waves do not form organized reentry. These activation waves broke up more frequently at baseline than during procainamide administration. The number of activation waves was 7.25+/-1.39 s(-1) x cm(-2) at baseline and 4.45+/-1.80 s(-1) x cm(-2) during procainamide administration (P<.001). The dog without subendocardial ablation had similar results. CONCLUSIONS Procainamide decreases the number of wavelets during VF by preventing spontaneous wave breaks. This represents a novel mechanism of antiarrhythmic drug action.

Assessment Methodology for Computer-Based Instructional Simulations

Computer-based instructional simulations are becoming more and more ubiquitous, particularly in military and medical domains. As the technology that drives these simulations grows ever more sophisticated, the underlying pedagogical models for how instruction, assessment, and feedback are implemented within these systems must evolve accordingly. In this article, we review some of the existing educational approaches to medical simulations, and present pedagogical methodologies that have been used in the design and development of games and simulations at the University of California, Los Angeles, Center for Research on Evaluation, Standards, and Student Testing. In particular, we present a methodology for how automated assessments of computer-based simulations can be implemented using ontologies and Bayesian networks, and discuss their advantages and design considerations for pedagogical use.

Assessing Cognitive Readiness in a Simulation-Based Training Environment

This chapter describes progress toward developing and validating an assessment of cognitive readiness for Tactical Action Officer performance in a simulated Combat Information Center. In this chapter we describe the simulation environment and scenarios, the constructs defined to measure cognitive readiness, an approach to measurement, and a computer-based assessment tool that operationalizes the measures and supports data collection and reporting. The preliminary results provide evidence that the measures are meaningful indicators of the constructs, but the confirmatory factor analysis and convergent validity results were mixed, depending on the nature of the scenario. The chapter closes with a discussion of the implications for future research.

Design and Development of Training Games: Learning Game Disciplines

Abstract As you get started on your project to create a serious game for learning, it is important for you to recognize that you and your team will likely need the skills of several different disciplines to achieve success. Usually, this means that you will be working with colleagues who have been trained in a different field from yours. By better understanding what the key concerns and methods of their disciplines are, you will better understand where your teammates are coming from and the processes they are used to. We introduce the standard methods used in the supporting fields of instructional system design, software development, game design, assessment development, and story creation and discuss some of the main strengths of each area as well as some of the typical challenges that practitioners in each area face. Introduction So, you’re thinking of developing a game to help teach some valuable knowledge and/or skills. How do you go about designing and developing your learning game efi ciently? What steps are involved? Who needs to be involved? What are the gotchas to be aware of and how do you address those issues effectively? How do you ensure that your learning game successfully engages your learners while effectively teaching them?