Stimulus not properly stimulating

Question

Hi,
I have been working on a stimulus setup that is performing an extracellular stimulus (open or closed) of a large-tissue block submerged in a bath that is meant to mimic a piece of ventricular tissue. The mesh tissue has been tuned and has induced reentry using the psd function from the 02_EP_Tissue/21_reentry_induction example for 600ms, then I applied the stimulus to try to terminate the rotor. I have tried out the various configurations of both electrodes and types from the 02_EP_Tissue/02_stimulus example, but currently, the best result I got is seeing some slight effects on the tissue near the stimulation site, and they are not strong or sustained enough to significantly perturb or terminate the rotor. My current setup uses three different electrodes: a stimulus on the epicardial side selected from a grid based on electrical potential (crct type 2), some grounding electrodes across the bath face on the endocardial side (crct type 3), and aux electrodes on the endocardial side (crct type 0), and the stimulation strength is 1000 mV for 2ms, using Tomek20Land17_DynSarc ionic model, conduction velcority 0.57 and 0.24, tissue size 5cm by 5cm by 12mm, with 3mm bath, resolution 250 mircons. I wonder why my stimulation does not work and how the stimulation should be configured—whether through the electrode arrangement, grounding configuration, stimulation waveform, or other parameters—to produce a sufficiently strong and sustained effect that can successfully interrupt the rotor.

Answer 1

Hey,

Two things that come to my mind:

1. Are you actually solving bidomain?

The extracellular potential stimuli are only really active if you solve the bidomain equations. Check first if you set bidomain = 1 and that the bath/intra/extra regions are assigned properly.

2. Field strength is too low

Looking at the field gradient in the tissue (V/cm) is what matters here. If I understand it correctly, you want to defibrillate the tissue to stop or perturb the arrhythmia. Defibrillation scale capture needs somewhere in the area of 3-5 V/cm across the tissue. Your 1000mV across 5cm (assuming that's the endo-epi distance) is in the area of 0.2 V/cm, likely less since part of it drops across the bath and not the tissue.

So check if bidomain = 1. If yes, increase the voltage on your stimulating electrode quite a bit and measure the voltage drop across the tissue.

Best,

Tobias