A cardiac rhythm management (CRM) system delivers anti-tachyarrhythmia therapies and uses patient-specific and/or tachyarrhythmia event-specific information to automatically set and adjust one or more arrhythmia detection durations. In one embodiment, the CRM system initializes and updates the one or more arrhythmia detection durations using patient-specific information such as medical history and recent medical trends. In another embodiment, the CRM dynamically adjusts the one or more arrhythmia detection durations using the patient's hemodynamic performance. One example of such an arrhythmia detection duration is a sustained rate duration (SRD) that starts when a tachyarrhythmia such as a supraventricular tachyarrhythmia is detected. An anti-tachyarrhythmia therapy is delivered only if the tachyarrhythmia sustains throughout the SRD.