Dual chamber discrimination: V>A
This 44-year-old patient, recipient of a Abbott Atlas dual chamber ICD, implanted for primary prevention in the context of ischemic cardiomyopathy and a 27% LVEF, was seen for routine follow-up.
Main programmed parameters
- VF zone at 231 bpm and VT zone at 160 bpm
- 12 cycles in the VF and 12 cycles in the VT zone are needed for the diagnosis
- Effective discrimination programmed in the VT zone (dual chamber discrimination)
- V<A: if one of the criteria is fulfilled: morphology (60%, 5 out of 8), stability (50 ms, with 30 ms delta AV association, 12 intervals)
- V=A: if all criteria are fulfilled; morphology (60%, 5 out of 8), sudden onset (20%)
Episode of VT diagnosed in the V>A arm; no additional analysis needed and VT was diagnosed, prompting an 8-complex burst of ATP at a fixed rate.
- sinus rhythm;
- late ventricular extrasystole;
- ventricular undersensing with spuriously long cycle (VS), which delayed the diagnosis of VT;
- first T classified cycle;
- mode episode AAI;
- VT diagnosis in the V>A arm; the tachycardia starts suddenly, regular with a different morphology than the reference QRS (x, 0). These single chamber discrimination parameters are not included in the discrimination process. Atrioventricular dissociation is present, with a faster ventricular rate (calculated over the last 12 cycles before the diagnosis) than the atrial rate (calculated over the same cycles). No additional discrimination is needed for the diagnosis of VT;
- burst of 8 stimuli;
- successful burst; termination of VT and diagnosis of return to sinus rhythm.
In a dual chamber ICD of this manufacturer, the comparison between atrial and ventricular rate represents the first discriminator. When the ventricular rate (corresponding to the median of 12 ventricular cycles of an episode of tachycardia) is faster than the atrial rate (corresponding to the median atrial interval over the same cycles), as on this tracing, the tachycardia is classified as VT and no other discrimination criterion is taken in consideration.