Dual-chamber discrimination and atrial fibrillation

Summary

• Episode diagnosed in the VT zone with atrial rate greater than ventricular rate
• Programmed discrimination: Onset/stability
• Initially, inhibition of therapies due to unstable rhythm with diagnosis of AF
• Secondly, therapies delivered (bursts, ramps, then 1 maximum output shock)

• This episode corresponds to conducted AF, initially well discriminated by the device; the atrial rhythm is rapid, the ventricular rhythm is considered unstable and therapies are inhibited; in a second phase, the ventricular rhythm stabilizes, which is relatively classic for conducted AF with ventricular rates exceeding 160 beats/minute; unsure between conducted AF and dual tachycardia, the device favors sensitivity over specificity and delivers the programmed therapies.
• The stability criterion has been deceived; it was programmed at the nominal value of 20 ms; it is possible to make it less sensitive and more specific (setting discriminators is always a balancing act between sensitivity and specificity) by increasing this value (to 30 or 40 ms, for example)

When discrimination is set to Onset/Stability

• If the onset is considered sudden and the rhythm is stable, therapies are delivered
• If the onset is considered gradual, the AF criterion is satisfied and the rhythm is stable, the therapies are also delivered
• The setting of the stability parameter and the setting of the rate threshold for AF are decisive:
• When the AF threshold (nominally 170 beats/minute) is set too low (young patient): risk of inappropriate therapies for rapid sinus tachycardia (gradual onset, AF+ criteria, stable rhythm)
• When the stability criterion is programmed too low (20 ms in nominal): risk of inappropriate therapies (as in this example) if conducted AF stabilizes over a few cycles; there is the option of adapting the stability criterion (reprogramming to 30 ms, 40 ms, etc.)