A method and apparatus to detect anomalies in the conductors of leads attached to implantable medical devices based on the dynamical electrical changes these anomalies cause. In one embodiment, impedance is measured for weak input signals of different applied frequencies, and a conductor anomaly is detected based on differences in impedance measured at different frequencies. In another embodiment, a transient input signal is applied to the conductor, and an anomaly is identified based on parameters related to the time course of the voltage or current response, which is altered by anomaly-related changes in capacitance and inductance, even if resistance is unchanged. The method may be implemented in the implantable medical device or in a programmer used for testing leads.