Fast VT complicated by syncope

Tracing
N° 9
Manufacturer Abbott Device ICD Field Sensing
Patient

This 60-year-old man presenting with hypertrophic cardiomyopathy received a Current dual chamber ICD for secondary prevention of VT. He was seen after he had sustained 2 episodes of syncope complicated by physical injury.

Main programmed parameters

  • VF zone at 222 bpm, VT-2 zone at 200 bpm, VT-1 zone at 171 bpm
  • 12 cycles in each the VF, the VT-2 and the VT-1 zones were needed for the diagnosis
  • Maximum sensitivity programmed at 0.5 mV
  • VF zone: six 36-J shocks (maximum strength); VT-2 zone: 4 bursts of ATP followed by a single 10-J shock, followed by a single 25-J shock, followed by 2 shocks of maximum strength; VT-1 zone: set on monitor
  • Effective discrimination in the VT-1 and VT-2 zones
  • DDD episode pacing mode at 60 bpm; DDI post-shock pacing mode at 60 bpm
Graph and trace

Narrative

The text confirmed the occurrence of 3 VT/VF episodes; the analyzed episode was detected in the VF zone, was non-sustained and lasted 12 sec; the shock therapy was aborted.

Tracing

  1. Atrial paced, ventricular sensed rhythm (AP-VS);
     
  2. Frequent ventricular extrasystoles (VES) with pairs; retrograde atrial activation was sensed after the VES; however no marker is visible, because it fell in the post-ventricular atrial refractory period (a thin dash is visible under the marker chain);
     
  3. Fast VT (more ventricular than atrial events) in the VF zone; the initial cycles are unclassified; after 3 F classified cycles: DDI episode pacing mode;
     
  4. Diagnosis of VF (after 12 F cycles) and onset of the capacitors charge; the first therapy programmed in the VF zone was a 36-J shock (maximum strength; long duration of charge);
     
  5. After 11 seconds of arrhythmia, spontaneous termination before the end of the capacitors charge;
     
  6. End of the capacitors charge;
     
  7. At the very end of the charge, return of sinus rhythm was not confirmed by the device, as 3 VS were needed. A shock cannot be delivered on a VS cycle; when a third VS fills the return to sinus rhythm counter the shock is aborted.
Comments

This tracing also raises the issue of the delays that are observed between onset of fast ventricular arrhythmias and delivery of electrical shocks. In the VT zone, ATP sequences are delivered immediately after the initial detection phase. In the VF zone, the capacitor charge time is added before delivery of the shock. This programming must be flawless, in the VF zone particularly, because even a short delay in the treatment of a very fast ventricular tachyarrhythmia can be the cause of devastating symptoms. Conversely, as illustrated on the previous tracing, the programming of an excessively short detection time causes unnecessary and energy wasting charge of the capacitors for non-sustained tachyarrhythmias. In this patient, the rate of the ventricular arrhythmia was above 300 bpm and rapidly caused syncope. This leaves 2 choices: 1) leave the programming unchanged and the arrhythmia end spontaneously, with a risk of syncope, fall and physical injury, or 2) shorten the delay between the onset of arrhythmia and the shock delivery, which might prevent the loss of consciousness. Abbreviating this delay by shortening the detection time does not seem feasible. However, the strength of the first shock can be decreased, shortening the charge time and hastening its delivery. On the other hand, if the shock is too weak and ineffective, a second, stronger shock will be needed, the charge time of which is added to the redetection delay, lengthening the overall arrhythmia duration.

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