Saturday, February 18, 2012
Exhibit Hall A-B1 (VCC West Building)
Background: A cardiac arrhythmia is an abnormal heartbeat. Certain types of arrhythmias - in particular, very fast or irregular `reentrant' heartbeats - can be fatal if left untreated. It is accepted that these potentially fatal cardiac arrhythmias can arise due to an electrical problem with a piece of heart tissue. This situation can be modeled by one or more `spiral waves' in a system of excitable media. Mechanisms for the appearance of spiral waves due to anatomical inhomogeneities - for example, damaged tissue or scar tissue - have been well-studied. However, patients can present with these arrhythmias yet have no permanently damaged or dead tissue. How can spiral waves appear in seemingly undamaged cardiac tissue? Methods: A standard two-variable model of excitable media - the FitzHugh Nagumo system - is used to simulate a two-dimensional rectangle of heart tissue with the commercial software MATLAB. The traditional situation of a piece of damaged tissue requires an anatomical blemish, which is modelled by a spatially inhomogeneous domain. My novel approach considers a spatially homogeneous medium - undamaged tissue - and instead explores how transient conditions can lead to spiral wave activity. Results: Simulations indicate that it is possible to generate spiral waves in a spatially homogeneous medium by imposing a temporarily refractory region (a condition on one of the variables). Moreover, this mechanism is robust; the refractory region can vary over a range of sizes and shapes. Conclusions: This work explores a previously unasked question: how can spiral waves appear in a homogenous medium? This is tantamount to asking how a reentrant arrhythmia can arise in a seemingly healthy heart. I provide proof-of-concept simulations of how a transiently refractory region can result in spiral wave activity. Moreover, this is also a physiologically reasonable idea as this type of functional barrier can indeed appear in healthy heart tissue.