Male implanted with a triple-chamber defibrillator (Cobalt Quad CRTD) for ischaemic cardiomyopathy.
Trace
What is the diagnosis made by the defibrillator?
This episode has been classified SVT-AF by the system.
Which programmed zone appears on the graph?
Two detection zones have been programmed with a VT zone of 340 to 280 ms.
What diagnosis does the interval plot suggest?
The graph shows a tachycardia detected in the VT zone with atrial activity faster than ventricular activity and an irregular ventricular response; the graph favours conducted AF.
How many discrimination parameters are programmed?
The discrimination parameters (PR Logic and Wavelet) are programmed with a SVT V. Limit of 260 ms.
How does the VT counter work?
Some cycles fall within the VT zone, others do not; cycles classified as VS systematically reset the VT counter to 0.
What is the diagnosis made by the defibrillator?
The tachycardia accelerates and stabilises in the VT zone; after 16 consecutive cycles classified as VT, the VT counter is full; PR Logic classifies the episode as AF.
What are the results of Wavelet?
Wavelet is not used because it is superseded by PR Logic; if used, it would have led to the diagnosis of VT because only 2 ventricular complexes are classified as similar to the reference.
Take home message
This patient presented with multiple episodes of AF correctly discriminated by PR Logic; this tracing allows us to discuss the conditions for Wavelet intervention.
The sequence used by PR Logic to diagnose AF is identical to the previous tracing: 1) the atrial rhythm is faster than the ventricular rhythm (V<A); 2) the sensed atrial signals correspond to atrial activation (no far-field R wave oversensing); 3) the AF counter is greater than 6; 4) the ventricular rhythm is irregular.
When PR Logic and Wavelet are programmed simultaneously and PR Logic concludes SVT-AF, the Wavelet results cannot change the diagnosis, which is desirable in this example since the Wavelet data favoured the diagnosis of VT.
