Devices and methods obtain and use endovascular electrograms in a number of clinical applications and settings. In one embodiment, methods for triggering analysis of an endovascular ECG waveform are based on the detection of a peak in a skin-based ECG waveform in order to determine a location of an indwelling medical device, such as a catheter. In another embodiment, the position of a catheter or other medical device within the vasculature can be determined by analysis of the energy profile of a detected P-wave. In yet other embodiments, magnetic connecting devices are used for establishing an operable connection through a sterile field.