High Rate Timeout is nominally programmed Off in dual (DR) and triple (CRT-D) chamber high power devices (ICDs). It can be programmed to specific amounts of time separately for All Zones and VF Zone Only.

• All Zones – Applies to discriminators applied in all zones currently programmed On. High Rate Timeout is not applied to rates in the VT Monitor zone.
• VF Zone Only – Applies to the discriminators in the VF and FVT via VF zone only. Rates must stay in these zones continuously or the timer will start over.

• VF Zone Only is programmed nominally On at 0.75 mins or 45 seconds. 
• All Zones in these devices is nominally Off.

To program this feature, go to Params -> Detection.

Programming both High Rate Timeout periods: If both timeout periods are programmed, the shorter timeout is applied first. The VF Zone Only timeout would normally be programmed with the shorter duration.

High Rate Timeout allows the device to deliver therapy for any ventricular tachyarrhythmia that continues beyond a programmed length of time by overriding an SVT discrimination algorithm’s decision to withhold therapy. Although High Rate Timeout negates the effect of SVT discriminators, it may be appropriate for certain patients.

The High Rate Timeout feature can be programmed separately for All Zones and VF Zone Only.

• All Zones – If programmed, the device starts the programmed High Rate Timeout period when VF, FVT, or VT detection occurs or is withheld by an SVT discrimination feature. If the tachyarrhythmia continues beyond the programmed timeout period, the device suspends all SVT discrimination features and allows for therapy delivery.
• VF Zone Only – If programmed, the device starts the programmed High Rate Timeout period when VF or FVT via VF detection occurs or is withheld by an SVT discrimination feature. If the tachyarrhythmia continues beyond the programmed timeout period, the device suspends all SVT discrimination features and allows for therapy delivery. Note that PR  Logic™and Wavelet are the only SVT discriminators that are impacted by the VF zone if the SVT Limit is programmed into the VF zone.

In the following example, the device uses PR Logic™ to classify the arrhythmia as AF and therapy is withheld. The High Rate Timeout feature is programmed to All Zones. The programmed High Rate Timeout period expires during the episode and therapy is delivered. Therefore, the stored EGM for that episode (shown below) includes the HT Decision Channel annotation at the point when the High Rate Timeout period expires. Additionally, the Initial Type field in the episode text would include the text “High Rate Timeout–All Zones.”