An implantable sensor circuit can be configured to generate a first sensor signal representative of mechanical activation of a first chamber of a heart of a subject and a second sensor signal representative of mechanical activation of a second chamber of the heart. A chamber synchrony measurement circuit can be configured to generate a measure of synchrony of the mechanical activations of the first heart chamber and the second heart chamber using the first and second sensor signals, a tachyarrhythmia detector circuit, and a control circuit. The control circuit can be configured to receive an indication of a detected episode of tachyarrhythmia, and to initiate, select, or adjust a device-based therapy at least in part using the measure of synchrony of the mechanical activations in response to the tachyarrhythmia detection.
