1. A method for patient-specific planning and guidance of electrophysiological interventions, comprising: generating a patient-specific anatomical heart model from cardiac image data of a patient; generating a patient-specific cardiac electrophysiology model based on the patient-specific anatomical heart model and patient-specific electrophysiology measurements; performing a virtual electrophysiological intervention using the patient-specific cardiac electrophysiology model; and calculating an electrocardiogram (ECG) signal in response to the virtual electrophysiological intervention by: calculating extra-cellular potentials based on transmembrane potentials calculated using the patient-specific cardiac electrophysiology model at a plurality of points within the myocardium, calculating body surface potentials at a plurality of points on the torso based on the extra-cellular potentials, and calculating the ECG signal using the body surface potentials at points on the torso corresponding to ECG lead locations.