The role of computer modeling, optical imaging and MRI in ventricular arrhythmias

Mihaela Pop, M.Sc.

Abnormal cardiac rhythms (arrhythmias) are often a result of structural disease, such as chronic infarct. Many scars encase surviving bundles of heart muscle. This particular configuration is named a reentry circuit. It provides the substrate for an electrical excitation wave that can re-circulate around the scar and re-excite tissue to cause high heart rates (over150 beats per minute), a condition known as ventricular tachycardia or VT. The reentry circuits are often deep in the myocardium and are not identified, limiting the success of current radio-frequency ablation therapy.

Computer models can simulate the propagation of the electrical excitation wave through normal and diseased myocardium. I have built a 3-D theoretical model that predicts the inducibility of VT based on physical properties of the reentry circuits (i.e. geometry of the scars, tissue electrical conductivity and fibre directions).

To prove my hypothesis, I am developing an experimental framework using measurements of action potential from optical fluorescence images (based on a voltage-sensitive dye). The computer model is parametrized with anatomical information and fibre directions obtained via MR imaging. My current work is focused on building a pathological model of VT, for which the reentry circuit will be identified from MRI.

The theoretical model and its validation are being developed in collaboration with Dr. Maxime Sermesant and his ASCLEPIOS team at INRIA (France). The diffusion-tensor MR sequence for the fibre directions is implemented on our 1.5T scanner through collaboration with Dr. Elliot McVeigh of Johns Hopkins University (USA).

Publications

1. Pop M, Sermesant M, Lepiller D, Truong MV, McVeigh ER, Crystal E, Dick A, Delingette H, Ayache N, Wright GA; An experimental framework to validate 3-D models of cardiac electrophysiology via optical imaging and MR imaging (Medical Image Analysis – special issue FIMH 2008)
2. Pop M, Sermesant M, Dick A, Coudiere Y, Wright GA Modelling anatomic reentry – a 3-D simulation study on a virtual slab (conference paper accepted to Modelling and Simulation, IASTED, Quebec City, 2008)
3. Chung D, Pop M, Sermesant M , Wright GA. Stereo reconstruction of the epicardium for optical fluorescence imaging Technical Report MICCAI-2006 Workshop on Biophotonics Imaging for Diagnostics and Treatment. 2006 Oct; P33-40.