  Cardiac diseases are the principal cause of human morbidity and mortality in
the western world. The electric potential of the heart is a highly complex
signal emerging as a result of nontrivial flow conduction, hierarchical
structuring and multiple regulation mechanisms. Its proper accurate analysis
becomes of crucial importance in order to detect and treat arrhythmias or other
abnormal dynamics that could lead to life-threatening conditions. To achieve
this, advanced nonlinear processing methods are needed: one example here is the
case of recent advances in the Microcanonical Multiscale Formalism. The aim of
the present paper is to recapitulate those advances and extend the analyses
performed, specially looking at the case of atrial fibrillation. We show that
both ECG and intracardial potential signals can be described in a model-free
way as a fast dynamics combined with a slow dynamics. Sharp differences in the
key parameters of the fast dynamics appear in different regimes of transition
between atrial fibrillation and healthy cases. Therefore, this type of analysis
could be used for automated early warning, also in the treatment of atrial
fibrillation particularly to guide radiofrequency ablation procedures.
