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A Unique Multimedia Interactive
Bauch, Terry D; Keller, J Walter Jr
Brooke Army Medical Center, San Antonio, Texas, United States
Cardiac electrophysiology may be best understood through interactions with live patients. Current computer technology has allowed realistic electrophysiologic modeling of the heart; with such methods we developed a practical real-time simulation to facilitate learning and research. The model divides the conduction system segments for the atria, AV node and junction, His bundle, right and left bundle branches, and the Purkinje system, and combines the output of timing clocks with parameters for conduction velocity and refractoriness to determine the sequence of depolarization. In normal or pathologic substrates, including accessory pathways, dual AV nodal physiology, or ischemic myocardium, the operator interactively adds or removes retrograde or antegrade blocks, and may modify the conduction velocity and refractory periods. Rate-dependant changes are specified separately for antegrade and retrograde AV conduction. Simulated drug infusions modify these parameters in real time based upon values stored on disk; users can modify these values to reflect updated knowledge, or to add new agents. The real-time display simultaneously shows the surface ECG, intracardiac electrograms, a ladder diagram, action potentials, and an animated diagram of the conduction system, which facilitates describing abnormalities of impulse formation and conduction. The model permits use of intracardiac electrodes for programmed stimulation, and pre-defined stimulation sequences allow users to observe the pathophysiology of initiation and termination of reentrant rhythms. The activation of single or dual chamber pacemaker simulations with timing ramp diagrams adjacent to the ECG promotes the understanding of clock timing and of difficult concepts like pacemaker-mediated tachycardia. The workstation can display anatomic and electrophysiologic diagrams; combining pre-defined model parameters with diagrammatic and textual explanations has facilitated self-instruction. This workstation has been applied in the instruction of cardiology fellows, medical residents, nurses, and medical students at our facility.
Our primary objective was to demonstrate that a practical interactive model of cardiac electrophysiology and current pacemaker technology could be programmed on a standard personal computer. A secondary objective was to determine if such models could accurately reproduce common pathophysiologic substrates, respond to programmed stimulation, and demonstrate pacemaker function and malfunction. In addition we sought to assess the impact of this technology on educating medical professionals in cardiac arrhythmias and pacemaker function.
Cardiac electrophysiology and mechanisms of arrhythmogenesis are complex topics that may be best understood in an interactive setting. The concepts behind advanced pacemaker technology, and its applications in various pathologic substrates, are difficult to convey without interactive teaching methods. Previous computer models of arrhythmogenic substrates have been successfully, but generally processed input parameters in a batch mode. Current computer technology can now support real-time cardiac electrophysiologic models, where the user can alter input parameters and directly observe the results.
MATERIAL AND METHODS
The programming language used was Quick Basic PDS Version 7 (Microsoft Corp, Redmond, WA). The cardiac conduction system was conceptually divided into segments representing the atria, interatrial pathways, AV node and junction, His bundle, bundle branches, the Purkinje system, and a right-sided accessory pathway. Timing clocks were created to represent the periodic activity of cardiac pacemaker cells, and to count time elapsed during each cardiac cycle. Clock outputs were used to initiate depolarization of the conduction segments, and interact with the parameters for conduction velocity and refractoriness to determine the sequence of depolarization through these segments. The largest time increment found to be practical for these clocks was 10 milliseconds.
The model was used to educate several different medical professional groups. These included paramedics in the U.S. Army, ICU nursing staff in Tuzla, Bosnia, fourth-year medical students at the University of Texas in San Antonio, and Internal Medicine residents at Brooke Army Medical Center in San Antonio.
Students were shown rhythm simulations from both normal and pathologic substrates including accessory pathways, dual AV nodal physiology, and ischemic myocardium. Retrograde and antegrade blocks were added in real-time and both conduction velocity and refractory periods were varied. Simulated drug infusions were also given, which modified these parameters based upon values stored on disk. A real-time simultaneous display of the surface ECG, intracardiac electrograms, ladder diagrams, and an animated diagram of the conduction segments were employed to illustrate arrhythmogenic mechanisms. Simulated programmed stimulation was used to initiate and terminate reentrant rhythms. Single and dual chamber pacemaker simulations were displayed during lectures on basic pacer function and pacemaker-mediated tachycardia.
. Indicates the components of the conduction system as viewed on the real-time display. The AV Node is expanded to permit visualization of AV nodal blocks or dual AV nodal physiology.
. Demonstrates a typical simultaneous display of a surface ECG, HIS bundle recording, expanded ladder diagram, and an animation of the conduction sequence which is indicating retrograde depolarization from an ectopic right ventricular focus (large arrow) to both atria and the sinus node. A compensatory pause results from this concealed retrograde conduction. A small retrograde P wave (small arrow) appears at the terminal portion of the ventricular beat.
. Shows a typical display during the simulation of a dual chamber pacemaker in a substrate with complete retrograde and antegrade AV block.
. Displays initiation of AV nodal reentrant tachycardia by an ectopic atrial beat in a substrate with dual AV nodal physiology.
Students and residents were informally polled following lectures utilizing this workstation. Fourth year medical students at the University of Texas felt that the ladder diagram explained macro and micro-reentrant circuits better than a standard textbook. Internal Medicine housestaff at Brooke Army Medical Center commented that the interactive pacemaker model was able to clarify dual-chamber pacing concepts.
Software simulation can successfully reproduce many aspects of cardiac electrophysiology and pathophysiology in a manner suitable for real-time display and instruction. The use of this interactive teaching tool may improve teaching efficiency and student comprehension. Further studies of the effectiveness of this teaching tool should be considered.
1. Josephson, M. Clinical Cardiac Electrophysiology: Techniques and Interpretation, 2nd ed.
2. Lea & Febiger. Philadelphia, 1992
3. Netter. Ciba V5 Heart. Ciba Publications, 1969
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