Dual-chamber discrimination, atrial tachycardia
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Patient
- 76-year-old man; ischemic cardiomyopathy with wide QRS; implanted with a triple-chamber defibrillator
Summary
- episode diagnosed in VT zone with atrial rate = ventricular rate
- programmed discrimination: Onset/stability
EGM layout
- rapid ventricular rate with A/V ratio 1/1, on the edge of the VT zone (RVS marker)
- slight acceleration of the rhythm into the VT zone (VT zone limit: 375 ms)
- criterion 8/10 met; analysis of onset of arrhythmia favors sinus tachycardia (Gradl: gradual onset)
- at the end of the duration, the rhythm is considered stable; no therapy delivered in the presence of a stable rhythm with gradual onset
- cycle-by-cycle analysis of stability continues; the rhythm is still considered stable and therapies are inhibited
Take home message
- this episode is diagnosed as sinus tachycardia in the presence of a stable rhythm with gradual onset; therapies are therefore inhibited
- the purpose of the Onset parameter is to inhibit ventricular therapies for the lowest tachycardia zone when the heart rate increase is gradual; its application is limited to the lowest rate zone of a multi-zone configuration; when a detection window is satisfied, the device starts Sudden Onset calculations in two steps; step 1 measures the ventricular intervals preceding the start of the episode and locates the pair of adjacent intervals (pivot point) where the cycle length has decreased the most; if the decrease in cycle length is equal to or greater than the programmed Onset value, step 1 declares the onset to be sudden; step 2 then compares other intervals; if the difference between the average interval preceding the pivot point and 3 of the first 4 intervals following the pivot point is equal to or greater than the programmed Onset threshold, step 2 declares the onset to be sudden.
- the Onset parameter can be programmed as a percentage of cycle duration or as an interval duration (in ms); the programmed Onset value represents the minimum difference that must exist between intervals above and below the lowest programmed rate threshold.
- this episode corresponds to an episode of sustained atrial tachycardia with 1/1 AV conduction; the tachycardia frequency oscillates around the lower limit of the VT zone, which explains why the onset is considered gradual; in fact, the ventricular rate varies very little but oscillates between the sinus and VT zones; this patient’s rhythm initially went from its resting rate (60 beats/minute) to a rate of 165 beats/minute; gradually, the tachycardia rate then accelerated to reach the VT zone; there was therefore a sudden onset that was not diagnosed by the device; paradoxically, the fact that the sudden onset parameter was implemented avoided the patient having to receive inappropriate therapies
- 1/1 atrial tachycardia is not correctly discriminated by the combination of V>A (atrial rate is equal to ventricular rate in 1/1 atrial tachycardia as in VT with 1/1 retrograde conduction), abrupt onset (onset is usually abrupt in atrial tachycardia as in VT) and stability (ventricular rate is usually stable in atrial tachycardia as in VT).
- in this patient, it is advisable to raise the lower limit of the VT zone to avoid overlap between the diagnostic zone and the zones of his clinical atrial tachycardia; similarly, it may be advantageous to use discrimination based on the Rhythm ID
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