Patient implanted with a triple-chamber ICD (Viva Quad CRT-D) for ischemic cardiomyopathy. A VF episode via the combined counter was stored in the device memory. The number of intervals in the VF zone for initial detection was programmed to 30/40. This tracing allows focusing on the value of a combined counter in order to avoid delaying the detection of an arrhythmia at the limit of the detection zone.
The graph initially shows a rhythm with 1:1 atrioventricular synchronization followed by an acceleration of ventricular rhythm with atrioventricular dissociation; the ventricular intervals oscillate between the VF zone and the VT zone; a burst is delivered and terminates the arrhythmia.
- a sinus rhythm with biventricular pacing is initially found on the EGM;
- onset of a ventricular arrhythmia;
- on this ventricular complex, there are 6 intervals classified as FS, which enables the activation of the combined counter;
- alternation between intervals classified as FS and TS;
- the combined counter is filled; indeed, there are 35 intervals classified as TS or FS (7/6 of 30 intervals); analysis of the last 8 intervals before diagnosis reveals at least one interval classified as VF leading to the diagnosis of VF;
- the first therapy of the VF zone (burst before the charge) is delivered;
- successful burst and end of the episode.
In a MedtronicTM ICD, VT and VF counters operate independently of each other, such that an interval classified as FS does not increment the VT counter as opposed to the functioning of certain competitors' devices. This may therefore theoretically lead to a delay in diagnosis when an arrhythmia fluctuates between the VT zone and the VF zone as observed in this example. The combined counter was designed to resolve this issue and is always active (non-deprogrammable) if a VT zone and VF zone have been programmed. The combined counter is triggered systematically after the detection of 6 intervals classified as FS (essential prerequisite); the combined counter sums the intervals classified as TS and FS and is filled when 7/6 (non-modifiable ratio) of the number of intervals required in initial detection in the VF zone have been detected; in this example, this parameter was programmed to 30/40, the combined counter was therefore filled after 35 intervals classified as TS or FS (7/6 of 30 = 35). When the combined counter is full, the device analyzes the last 8 ventricular intervals; if at least one of these intervals is classified as FS, the device diagnoses a VF and the first therapy of the VF zone is delivered; if the last 8 cycles are classified as TS, the device diagnoses a VT and the first therapy of the VT zone is delivered.
The combined counter therefore a delay in diagnosis when the tachycardia oscillates between the VT zone and the VF zone.