Increasing counters and preventing avoidable therapies - Visia AF XT VR

Patient

Patient implanted with a single-chamber defibrillator (Visia AF XT VR) for congenital long QT syndrome; episode of syncope.

Comments

What diagnosis are you suggesting on this graph?

The graph shows a sudden acceleration of the ventricular rate with irregular cycles detected in the VF zone; the initial VF counter is completed (Detection) but no therapy is delivered following a probable spontaneous reduction.

What type of arrhythmia is it?

This is probably a very rapid and irregular ventricular arrhythmia; the shock canal shows the polymorphic character with a torsadiform appearance.

How is the initial detection counter in the FV zone programmed?

The initial counter is set to 30/40.

What does abandonment mean?

The capacitors are charged when the initial VF counter is completed; during charging, the arrhythmia stops spontaneously and after 4 consecutive slow cycles, the therapy is abandoned; note that the shock channel makes it possible to recover a very elongated QT aspect.

Take home message

This episode of arrhythmia corresponded to a torsade de pointes which lasted around fifteen seconds and reduced spontaneously with abandonment of the charge at the end of the charge; this tracing illustrates the importance of the confirmation phase during and at the end of the charge to avoid delivering a shock when the tachycardia has reduced.
One of the main objectives of defibrillator programming is to reduce as far as possible the number of inappropriate or avoidable therapies; the systematic programming of an initial counter at 30/40 is a step in this direction; in the VF zone, the initial counter is filled after approximately 7 to 8 seconds; if we add the charging time and confirmation at the end of the charge, the total time in arrhythmia is at least 15-17 seconds before delivering a shock, which encourages spontaneous reduction.
Treating an episode of malignant ventricular arrhythmia with an electric shock remains the only option for restoring viable haemodynamics; however, the latest recommendations, based on all recent studies, suggest the need to avoid treating ventricular arrhythmias that can reduce spontaneously too early and too aggressively; an electric shock can save a life but is associated with a deleterious effect of its own and should therefore be avoided wherever possible when spontaneous reduction is possible or less aggressive therapy can be effective.
It is therefore advisable: 1) not to systematically programme treatment zones that are too low for primary prevention; 2) to lengthen the initial detection counters in the VT zone, but also in the VF zone, to avoid treating episodes of arrhythmia that would have reduced spontaneously (appropriate but avoidable therapies); 3) to favour first-line treatment with anti-tachycardia pacing, even for very rapid tachycardias (limit to 230-250 beats/minute).

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