A transvascular electrode system includes an expandable electrode-carrying anchor. The anchor is intravascularly advanced in a compressed position to a first site in a blood vessel. A first portion of the anchor expands to position an electrode against the vessel wall, while a second portion remains is compressed. Mapping is performed by delivering stimulation energy from the electrode and measuring the response (e.g. blood pressure, heart rate, and/or related parameters). The first portion is at least partially collapsed and the electrode system is moved to a second site. The first portion is expanded to position the electrode into against the vessel wall, while the second portion remains compressed. Additional mapping is performed. The process is repeated until the anchor electrode position is optimized, at which point the second portion of the anchor is expanded to chronically retain the electrode in the vessel.