A method for sensing cardiac activity in an atrium of a patient's heart includes delivering a pulse to the atrium using an electrode configuration that includes at least a cathode electrode; sensing cardiac activity in the atrium using a unipolar electrode configuration to provide a sensed signal wherein the unipolar electrode configuration does not include the cathode electrode; determining the duration during which the voltage of the sensed signal falls below a threshold voltage; and comparing the determined duration to a parameter to determine whether the pulse caused an atrial evoked response.