A system comprising: a subcutaneous implantable cardioverter defibrillator (SICD) comprising a first set of electrodes and configured to: sense a first electrical signal from a heart of a patient via the one or more first electrodes; detect a tachyarrhythmia within the sensed first electrical signal; and determine, based on the detected tachyarrhythmia, to deliver anti-tachyarrhythmia shock therapy to the patient to treat the detected arrhythmia; and a leadless pacing device comprising a second set of electrodes and configured to be implanted within the heart of the patient, wherein the LPD is configured to: receive communication from the SICD requesting the LPD deliver anti-tachycardia pacing to the heart; sense a second electrical signal from the heart of the patient via the second set of electrodes; and determine, based on the second electrical signal, whether to deliver anti-tachycardia pacing to the heart; and wherein the LPD is configured to: determine, based on the second electrical signal, not to deliver anti-tachycardia pacing, and in response to the determination not to deliver anti-tachycardia pacing, transmit, to the SICD, communication identifying the determination not to deliver anti-tachycardia pacing; and wherein the SICD is configured to: receive the communication from the LPD identifying the determination not to deliver anti-tachycardia pacing; and overturn, based on the received communication identifying the determination not to deliver anti-tachycardia pacing, the determination to deliver anti-tachyarrhythmia shock therapy to the patient. a subcutaneous implantable cardioverter defibrillator (SICD) comprising a first set of electrodes and configured to: sense a first electrical signal from a heart of a patient via the one or more first electrodes; detect a tachyarrhythmia within the sensed first electrical signal; and determine, based on the detected tachyarrhythmia, to deliver anti-tachyarrhythmia shock therapy to the patient to treat the detected arrhythmia; and sense a first electrical signal from a heart of a patient via the one or more first electrodes; detect a tachyarrhythmia within the sensed first electrical signal; and determine, based on the detected tachyarrhythmia, to deliver anti-tachyarrhythmia shock therapy to the patient to treat the detected arrhythmia; and a leadless pacing device comprising a second set of electrodes and configured to be implanted within the heart of the patient, wherein the LPD is configured to: receive communication from the SICD requesting the LPD deliver anti-tachycardia pacing to the heart; sense a second electrical signal from the heart of the patient via the second set of electrodes; and determine, based on the second electrical signal, whether to deliver anti-tachycardia pacing to the heart; and receive communication from the SICD requesting the LPD deliver anti-tachycardia pacing to the heart; sense a second electrical signal from the heart of the patient via the second set of electrodes; and determine, based on the second electrical signal, whether to deliver anti-tachycardia pacing to the heart; and wherein the LPD is configured to: determine, based on the second electrical signal, not to deliver anti-tachycardia pacing, and in response to the determination not to deliver anti-tachycardia pacing, transmit, to the SICD, communication identifying the determination not to deliver anti-tachycardia pacing; and determine, based on the second electrical signal, not to deliver anti-tachycardia pacing, and in response to the determination not to deliver anti-tachycardia pacing, transmit, to the SICD, communication identifying the determination not to deliver anti-tachycardia pacing; and wherein the SICD is configured to: receive the communication from the LPD identifying the determination not to deliver anti-tachycardia pacing; and overturn, based on the received communication identifying the determination not to deliver anti-tachycardia pacing, the determination to deliver anti-tachyarrhythmia shock therapy to the patient. receive the communication from the LPD identifying the determination not to deliver anti-tachycardia pacing; and overturn, based on the received communication identifying the determination not to deliver anti-tachycardia pacing, the determination to deliver anti-tachyarrhythmia shock therapy to the patient.