Arrhythmogenicity of cardiac fibrosis: fractal measures and Betti numbers.

Infarction- or ischaemia-induced cardiac fibrosis can be arrythmogenic. We use mathematcal models for diffuse fibrosis ($\mathcal{DF}$), interstitial fibrosis ($\mathcal{IF}$), patchy fibrosis ($\mathcal{PF}$), and compact fibrosis ($\mathcal{CF}$) to study patterns of fibrotic cardiac tissue that have been generated by new mathematical algorithms. We show that the fractal dimension $\mathbb{D}$, the lacunarity $\mathcal{L}$, and the Betti numbers $\beta_0$ and $\beta_1$ of such patterns are \textit{fibrotic-tissue markers} that can be used to characterise the arrhythmogenicity of different types of cardiac fibrosis. We hypothesize, and then demonstrate by extensive \textit{in silico} studies of detailed mathematical models for cardiac tissue, that the arrhytmogenicity of fibrotic tissue is high when $\beta_0$ is large and the lacunarity parameter $b$ is small.