An apparatus comprises a cardiac signal sensing circuit, a physiologic sensor circuit configured to provide a physiologic sensor signal representative of mechanical cardiac activity, a therapy circuit, and a control circuit. The control circuit includes a cardiac depolarization detection circuit, a tachyarrhythmia detection circuit, and a timer circuit. A time interval between a mechanical cardiac event and a detected fiducial electrical cardiac event is monitored. The control circuit is configured to correct the monitored time interval for variation with heart rate to form a corrected electromechanical time interval, initiate anti-tachyarrhythmia therapy when the corrected electromechanical time interval satisfies a specified time interval threshold value during a detected episode of tachyarrhythmia, and withhold anti-tachyarrhythmia therapy otherwise.
