A method and system that includes an implantable cardioverter defibrillator (ICD) determining signal characteristics of a cardiac signal within a signal evaluation window positioned along a first portion of a cardiac cycle and determining whether a P-wave occurs within the signal evaluation window associated with the first portion of the cardiac cycle. The signal evaluation window is adjusted to be positioned along a second portion of the cardiac cycle in response to the P-wave not occurring within the signal evaluation window and signal characteristics of the cardiac signal are determined within the adjusted signal evaluation window. A determination is made as to whether a P-wave occurs in response to the signal characteristics determined within the adjusted signal evaluation window, and the ICD delivers a trigger signal to a leadless pacing device instructing delivery of ventricular pacing therapy by the leadless pacing device whenever a P-wave is determined to occur.