Absence of discrimination in a pacemaker-dependent patient

Tracing N° 2
Boston Scientific Devices: ICD

This 68-year-old man underwent implantation of a Cognis triple chamber defibrillator in the context of ischemic cardiomyopathy with left bundle branch block. He had undergone ablation of the His bundle for permanent AFib. He was seen for a routine ambulatory visit.

Graph and trace
  1. AFib accurately detected by the device; rate responsive, paced ventricular rhythm;
  2. sudden onset of regular tachycardia;
  3. 8 out of 10 criterion fulfilled;
  4. at the end of Duration, the arrhythmia persisted; detection of an episode of VT without other discriminator;
  5. burst of 8 cycles of ATP;
  6. successful burst and termination of the arrhythmia.

Episode of tachycardia diagnosed in the VT zone without programmed discriminator other than the rate. A burst of ATP was delivered


This patient had undergone ablation of the His bundle and was entirely dependent on his defibrillator. No discrimination should be programmed in this context, as all spontaneous rapid rhythms can only be ventricular in origin. The discriminators (Onset/Stability or Rhythm ID) are, therefore, systematically deactivated in patients with complete AV block, whether spontaneous, drug-induced or after ablation of the conduction pathways.

Theoritical features / Basic concepts

Sensing and detecting episodes Detection zones SENSING AND DETECTING EPISODES Auto-adjusting sensitivity The effective operation of an Implantable Cardioverter Defibrillator (ICD) relies on its ability to detect both fast ventricular signals and low amplitude ventricular fibrillation signals without detecting T waves or extra-cardiac signals when the patient is in sinus rhythm. In order to ensure appropriate sensing, the device should be programmed with a high sensitivity (low detection threshold) and short refractory periods. Unlike a pacemaker the detection threshold is not programmed to a fixed value. The detection threshold automatically adjusts based on the amplitude of the preceding R-wave. Following a sensed or paced ventricular event the detection circuit starts a blanking period...