1. A method for reconstructing electrocardiogram signals, the method comprising: obtaining at least one endocardial electrogram (EGM) signal, formed from a plurality of signal samples from at least one endocardial or epicardial derivation; obtaining a transfer function; and generating, with a time-delay type neural network, a first surface electrocardiogram (ECG) signal from the at least one EGM signal by simultaneously processing (A) the at least one EGM signal and (B) at least one delayed version of the of the at least one EGM signal, wherein the time-delay neural network is selected from a group comprising a focused time-delay neural network, a distributed time-delay neural network, and a recurrent time-delay neural network.