Fast VT and the combined counter - Cobalt DR

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Male implanted with a dual-chamber defibrillator (Cobalt DR) for ischaemic cardiomyopathy.

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What diagnosis is suggested by the interval plot?
Three detection zones were programmed: a VT zone from 360 ms, a FVT zone from 310 ms and a VF zone from 280 ms; the episode was classified as FVT by the device (1);
the plot shows probable VT with atrioventricular dissociation (2) with cycles oscillating between the limit of the VT-FVT zones; a burst is used to terminate the arrhythmia
What is your diagnosis?
The EGM shows a regular, monomorphic tachycardia, alternately detected in the VT zone and the FVT zone; the combined counter is full, with 35 cycles classified as
TS or TF. (7/6 of 30 cycles); analysis of the last 8 cycles before diagnosis shows at least one cycle classified as TF leading to the diagnosis of FVT; the first therapy in
the VF zone (a burst) is delivered with termination of the arrhythmia.
What is the diagnosis made by the system?
The diagnosis is that of FVT via the combined counter

This plot shows another example of how the combined counter works.
The tachycardia oscillates between the VT zone and the FVT zone programmed
via VF; therefore the 2 VT and VF counters increment in parallel.
The combined counter has been developed to avoid delaying therapy in this
scenario.
When the combined counter is filled (35 TS or TF cycles in this example), the
device analyses the last 8 intervals; here, no cycle is classified as FS, but at least
one of the cycles is classified as TF, leading to a diagnosis of FVT.