Systems and methods for treating cardiac arrhythmias are disclosed. In one embodiment, an SICD comprises two or more electrodes, a charge storage device, and a controller operatively coupled to two or more of the electrodes and the charge storage device. In some embodiments, the controller is configured to monitor cardiac activity of the heart of the patient, detect an occurrence of a cardiac arrhythmia based on the cardiac activity, and determine a type of the detected cardiac arrhythmia from two or more types of cardiac arrhythmias. If the determined type of cardiac arrhythmia is one of a first set of cardiac arrhythmia types, the controller sends an instruction for reception by an LCP to initiate the application of ATP therapy by the LCP. If the determined type of cardiac arrhythmia is not one of the first set cardiac arrhythmia types, the controller does not send the instruction.
