Pacing & Defibrillation

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VT in the VF zone treated by ATP one shot

Patient

This 75-year-old man in permanent atrial fibrillation received a Lumax 340 VR-T single chamber defibrillator for primary prevention in the context of ischemic cardiomyopathy with a depressed left ventricular ejection fraction. An event report (yellow color) was issued in the context of a classified VF.

Main programmed settings

  • VF zone (270 ms limit) and VT1 zone (370 ms limit)
  • 8 /12 cycles in the VF zone and 26 cycles in the VT1 zone were needed for the diagnosis
  • Maximum sensitivity programmed at 0.8 mV
  • VF zone: one ATP one shot (burst of 8 stimuli at 80% of the tachycardia cycle length), followed by 8 shocks of maximum strength (40 J); VT1 zone: 3 bursts, followed by 3 ramps, followed by 1 shock at 10 J, followed by 1 shock at 20 J, followed by 6 shocks of maximum strength
  • Effective discrimination in the VT zone
  • Pacing mode: VVI 60 bpm


Trace

Remote tracing

The 3 channels available are: 1) the markers with the time intervals, 2) the shock channel (FF =  far field) between the coil of the RV lead and the pulse generator, and 3) the RV sensing channel;

  1. atrial fibrillation (the Vs cycles are irregular, though their morphology does not vary);
  2. VES (the Vs cycles are short and their morphology varies);
  3. sudden onset of stable tachycardia detected in the VF zone; the morphology of the ventricular EGM is unlike the ventricular extrasystoles;
  4. classification of the episode in the VF zone after 8 cycles in the VF zone without interposed cycle classified VT1 or Vs (full 8/12 VF counter);
  5. the delivered ATP is not visible;
  6. termination of the arrhythmia; a dark horizontal line marking the interrupted charge is visible;
  7. end of the episode after 12 consecutive cycles classified Vs or Vp (12/16 cycles classified Vs or Vp);

Programmer tracing (same episode)

The 3 channels are the same as for the remote tracing.

  1. visible burst of 8 cycles at fixed rate;
  2. at the end of the burst, onset of the charge marked by the dark horizontal line;
  3. end of charge after 3 cycles classified Vs (3 slow cycles out of 4) as the device considered that the burst was successful;
  4. end of the episode after 12 consecutive cycles classified Vs or Vp (12/16 cycles classified Vs or Vp).

 

Comments

One of the priorities of device programming is to lower to a maximum the risk of delivery of an electrical shock while preserving the patient’s safety. A large number of fast tachycardias diagnosed in the VF zone are organized and monomorphic, thus likely to be terminated by ATP instead of an electrical shock.

The defibrillator first examines the rhythm stability (a criterion fulfilled in this case), before delivering an ATP sequence. At the end of the sequence, the charge of the capacitors begins. The burst was successful, the device diagnosed 3 consecutive Vs and interrupted the charge. Thus, the charge time is extremely short when ATP is successful, preventing a painful and prognostically detrimental shock, and saving energy.

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