1. A method for reconstructing a surface electrocardiogram (ECG), the method comprising: receiving, a plurality of inputs, corresponding to a plurality of signals from endocardial or epicardial electrograms, each of the plurality of signals acquired on a respective channel of a plurality of channels; filtering each of the plurality of inputs with a corresponding non-linear, digital Volterra type filter, each of the corresponding non-linear, digital Volterra type filters having a transfer function including a linear term and at least one quadratic and/or cubic term(s); and combining each of the filtered plurality of inputs to reconstruct at least one reconstructed surface electrocardiogram ECG signal.