NetLogo User Community Models
by Asymptote (Submitted: 01/09/2008)
WHAT IS IT?
HearSim is a (vastly simplified) simulation of the electrical activity in the human heart. As simplified as it is, it is still capable of producing many of the rhtyhms observed in real hearts (normal sinus rhythm, ventricular tachycardia, ventricular fibrillation, atrial flutter, atrial fibrillation, heart block, etc.)
HOW IT WORKS
Each patch in the model represents a cell in the virtual heart. Every patch does double duty both as an atrial cell and a ventricular cell. A cell fires when a turtle (an electrical "spark") passes over it. A spark cannot pass over a cell which is in its refractory (post-firing) state. A cell passes into this state every time a spark successfully passes over it.
HOW TO USE IT
Set the parameters and press "Go." If an arrythmia occurs and doesn't self-terminate, then use the "Defibrillate" button.
NOTE: Setting "refract-length" below about 20 is not advisable. It causes the electrical waves to degenerate very quickly, leading to a rather uninteresting chaotic mess.
THINGS TO NOTICE
Note the spiral nature of the electrical waves in many of the simulated arrythmias. These are the same kind of "deadly spirals" observed in real cardiac arrythmias.
Note also how arrythmias don't occur with any real frequency when refract-length is set above about 35. Thus, the higher the refract-length, the healthier the heart.
THINGS TO TRY
Exercise stress test: Simulate an exercise stress test by gradually turning down the "sinus-rate" slider. An unhealthy heart will degenerate into arrythmia as the rate gets higher and higher. Note also how heart block (see below) causes bradycardia during the "stress test."
Heart block: Simulate heart block by setting the "AV-delay" parameter very high. Note how, when this is done, not all of the atrial impulses are conducted to the ventricles. This will result in a very slow heart rate and a poor ventricular rate response to exercise (see above), which results in the exercise intolerance frequently seen in AV blocks.
CREDITS AND REFERENCES
HeartSim created by Asymptote (firstname.lastname@example.org)
A Java version of the model will eventually be available through http://www.asymptote.wordpress.com.
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