1. Simulating Initiation and Termination of Reentry in Cardiac Tissue Ena Xiao Mentor: David M. Chan

2. GOAL To understand the dynamic of a ring of excitable media that can be a cause of cardiac arrhythmia.

3. Background Arrhythmias - abnormal heart rhythms –Bradycardia - less than 60 beats per min. –Tachycardia - pace of the heart is faster than the regulatory signal from the sinus node (over 100 beats per min). Rapid heart beating in the ventricles can be life-threatening. (ex. Ventricular fibrillation - heart can’t pump any blood) Currently, over 2.2 million Americans are living with atrial fibrillation. (Estimated by American Heart Association)

4. Heart Diagram

5. Glossary Reentry: unidirectional recirculation of AP. UDC: unidirectional circulation Diastolic Interval (DI): recovering time between AP. Conduction Time (CT): the time required for an AP wave front to travel a specified distance. Action Potential Duration (APD): defined with respect to a threshold voltage. T1 / T2 / T3 / T4: Threshold

6. Ring-like Cardiac Tissue A schematic representation of a ring of cardiac tissue.

7. Adjacent cells’ Voltage

8. Restitution Curve (a) APD Restitution Curve(B) CT Restitution Curve

9. Thresholds In order to initiate and maintain reentry, the following thresholds must be satisfied. –Each cell requires a minimum DI for recovery of excitability. –The reentrant action potential must propagate around the ring slow enough for cell one to recover excitability –The reentrant action potential must propagate around the ring fast enough to excite cell one before the SA node

10. What I have done. Generating data from the model with different parameters, and looking at patterns. Studying different conditions that may cause lethal arrhythmia.

11. UDC vs. Reentry

23. Thank You! Dr. David Chan, Mentor Dr. Allison Johnson, Coordinator of HHMI Summer Scholar Program Hailan Liu