1. A method for estimating capture thresholds for one or more alternate pacing vectors of an implantable cardiac device, comprising: measuring a capture threshold of at least one initial vector; measuring an impedance of the at least one initial pacing vector; measuring an impedance of at least one alternate vector, the at least one initial vector and the at least one alternate vector having an electrode in common, the common electrode having the same polarity for both the initial and alternate vectors; and estimating a capture threshold for the at least one alternate vector based on the measured capture threshold of the at least one initial vector, the measured impedance of the at least one initial vector, and the measured impedance of the at least one alternate vector.