Combined counter - Viva Quad CRT-D

Patient

Patient implanted with a single-chamber defibrillator (Visia AF XT VR) for dilated cardiomyopathy.

Trace

1-2 What diagnosis is suggested by the interval plot?

Two detection zones were programmed: a VT zone from 360 ms and a VF zone from 280 ms; this episode was classified as VF (1) by the device; the interval plot shows a sudden acceleration with cycles detected at the limit of the VF zone; detection of a VF episode effectively treated by a burst (2).

3- What is your diagnosis?
The EGM shows a regular, monomorphic tachycardia, with detection alternating between the VT and VF zones.

4- What therapy is delivered?
The combined counter was full, with 35 cycles classified as TS or FS (7/6 of 30 cycles); analysis of the last 8 cycles before diagnosis showed at least one cycle classified as FV leading to a diagnosis of VF; the first therapy in the VF zone, a burst during charging, was delivered with termination of arrhythmia.

5- What is the diagnosis made by the system?
The diagnosis is VF via the combined counter.

Take home message

In a MedtronicTM defibrillator , the VT and VF counters operate independently, with a cycle classified as FS not incrementing the VT counter; this differs from the operation of some competitors’ devices and can lead to a delay in diagnosis when an arrhythmia fluctuates between the VT and VF zones, as in this example.
The combined counter has been designed to remedy this problem and is systematically active (cannot be programmed off) if a VT zone and a VF zone have been programmed.
The combined counter is systematically triggered after the detection of 6 cycles classified as FS (essential prerequisite); the combined counter sums up the cycles classified as TS and FS and is filled when 7/6 (non-modifiable ratio) of the number of cycles required for initial detection in the VF zone have been detected; in this example, this parameter was programmed at 30/40, so the combined counter was filled after 35 cycles classified as TS or FS (7/6 of 30 = 35).
When the combined counter is full, the device analyses the last 8 ventricular cycles; if at least one of these cycles is classified as FS, the device diagnoses VF and the first therapy in the VF zone is delivered; if the last 8 cycles are classified as TS, the device diagnoses VT and the first therapy in the VT zone is delivered.

Pacing & Defibrillation

ECG

Library

News