An implantable medical device may comprise a therapy module configured to generate pacing therapy for a heart of a patient and a control module configured to control the therapy module. The control module may also be configured to detect a condition indicative of the presence of a magnetic resonance imaging (MRI) device and switch operation from a first pacing therapy program to a second pacing therapy program in response to detecting the condition indicative of the presence of the MRI device. While operating in the second pacing therapy program, control module may control the therapy module to generate a pacing pulse to an atrium of the heart of the patient during a time period between the end of an atrial refractory period of a previous atrial depolarization and the end of a ventricular refractory period of a previous ventricular depolarization corresponding to the previous atrial depolarization.