Systems and methods are disclosed to determine a P wave window for a patient using cardiac acceleration information of the patient, including a determined time of an S4 heart sound. Correlations between an S4 template and cardiac acceleration information in an S4 window having a duration longer than the S4 template can be determined. An S4 centroid can be determined as a peak of the determined multiple correlations, and the P wave window can be determined using the determined S4 centroid and an electromechanics delay.