Patient implanted with a single-chamber defibrillator (EnTrust VR) for dilated cardiomyopathy and hospitalised for palpitations; 3 detection zones were programmed with a VT zone between 400 and 320 ms.
- What diagnosis are you suggesting on this graph?
The graph shows an initial rhythm that appears normal, followed by a sudden acceleration, with evidence of a regular tachycardia detected in the VT zone and effectively treated by a burst of anti-tachycardia stimulation.
- What is your diagnosis?
On the EGM, there is a sudden acceleration with a regular tachycardia where all the cycles are detected in the VT (TS) zone; probable VT.
- What therapy is delivered?
After 16 consecutive cycles classified as TS, the device diagnoses VT; a burst is delivered; it is effective with a return to sinus rhythm and an end-of-episode diagnosis after 8 consecutive cycles classified as VS (stop).
Messages to remember
- The specific features of the VT counter must be perfectly integrated to allow optimum programming; in fact, for Medtronic devicesTM , the way of counting differs completely between the VT zone (consecutive cycles) and the VF zone (probabilistic counter), which is not the case for most of the competition's defibrillators.
- A cycle classified in the TV zone increments the TV counter by +1; a cycle classified in the FV zone does not modify the TV counter (no increment, no decrement); a long cycle classified VS resets the TV counter to 0.
- This counter has been specifically developed to provide optimal performance for tachycardias with a frequency of less than 200 beats/minute, with a dual objective: 1) to effectively detect episodes of regular, monomorphic ventricular tachycardia; 2) to provide a first level of "discrimination" during an episode of atrial fibrillation, which often includes one or more slow cycles that reset the counter to 0.
- The VT counter is filled after a programmable number of consecutive cycles classified in the VT zone (tolerance for VF cycles which do not modify the counter); the slightest cycle classified as SV resets the VT counter to 0, which has several consequences: 1) an inappropriate return of this counter to 0 occurs following ventricular under-detection (frequent in polymorphic ventricular tachycardias); this counter is therefore probably not appropriate for tachycardias of more than 200 beats/minute where some of the arrhythmias are polymorphic with signals of variable amplitude; 2) this counter improves the specificity of diagnoses, an episode of atrial fibrillation being readily associated with the existence of long iterative cycles (frequent return of the counter to 0).