1. A device for reconstructing a surface electrocardiogram (ECG), the device comprising: a first linear filter receiving an input corresponding to endocardial or epicardial electrogram (EGM) signals; a second linear filter receiving the EGM signals squared, and/or a third linear filter receiving the same EGM signals cubed; and a linear combination of the filtered signals from the first, second and/or third linear filters of each EGM derivation, delivering as an output a reconstructed ECG signal.