Dual chamber discrimination: V>A

Tracing N° 46
Abbott Devices: ICD Field: Discrimination

This 77-year-old man, recipient of a St Jude medical CRT-D implanted for idiopathic dilated cardiomyopathy, a LVEF at 30%, a wide QRS and a prolonged PR, was seen for a routine follow-up. 

Main programmed parameters

  • VF zone at 231 bpm, VT-2 zone at 181 bpm, a VT-1 zone at 160 bpm
  • 12 cycles in the VF zone, 12 cycles in the VT-2 zone and 12 cycles in the VT-1 zone are needed for the diagnosis
  • Effective discrimination in the VT-1 and VT-2 zones (dual chamber discrimination)
  • V<A: if one of the criteria is fulfilled; morphology (60%, 5 out of 8), stability (50 ms, with 60 ms delta AV association, 12 intervals)
  • V=A: if all criteria are fulfilled; morphology (60%, 5 out of 8), sudden onset (20%)
Graph and trace


Episode of VT-1 in the V>A arm; no additional analysis and diagnosis of VT-1; ramp of 12 stimuli; probable success with slowing of the rate (740 ms coupling interval).


  1. atrial and biventricular (AP-BP) pacing at sensor-indicated rate (SIR);
  2. tachycardia starts suddenly with atrioventricular dissociation; first cycles unclassified;
  3. DDI mode episode after 3 T1 classified cycles; it is noteworthy that the ventricular morphology is strictly identical to that of the reference QRS (v, 100);
  4. diagnosis of VT in the V>A arm; ventricular rate faster than the atrial rate; no additional discrimination needed for the diagnosis of VT;
  5. ramp of 12 stimuli;
  6. successful ramp and diagnosis of return to sinus rhythm.

This tracing illustrates the likelihood of a conflict between single chamber and dual chamber discrimination parameters. The diagnosis of VT is clearly apparent from the presence of AV dissociation; the episode was accurately identified in the V>A arm. In contrast, the morphology criterion was misleading (100% similarity with the reference complex). In this patient, who was continuously biventricular paced, the device probably chose an ectopic complex as its reference.