1. A method for locating an indwelling medical device within a vasculature of a patient, the method comprising: identifying an endovascular ECG waveform complex from an endovascular ECG signal associated with the indwelling medical device; calculating an absolute value of the energy of the endovascular ECG waveform complex over a predetermined segment thereof; and determining a position of the medical device within the vasculature by observation of the absolute value of the energy of the predetermined segment of the endovascular ECG waveform complex.