A medical device system including an intracardiac pacemaker is configured to receive by an implantable medical device sensing module a first cardiac signal using a first pair of electrodes implanted outside the cardiovascular system and identify a P-wave from the first cardiac signal. The system transmits a wireless trigger signal to the intracardiac pacemaker in response to identifying the P-wave. The intracardiac pacemaker delivers a pacing therapy in response to the trigger signal.
