Response by Handa et al to letter regarding article, "Granger causality-based analysis for classification of fibrillation mechanisms and localization of rotational drivers" - Handa,BS; Li,X; Aras,KK; Qureshi,NA; Mann,I; Chowdhury,RA; Whinnett,ZI; Linton,NWF; Lim,PB; Kanagaratnam,P; Efimov,IR; Peters,NS; et al. (Circulation: Arrhythmia and Electrophysiology, 2020)