Failure of ATP one shot and electrical shock
Patient
This 48-year-old man underwent implantation of a Lumax 540 VR-T single chamber defibrillator 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 (250 ms limit) and VT1 zone (340 ms limit)
- 18/24 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 40 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;
- atrial fibrillation with probable VES (the morphology of the short cycles is different from that of the long cycles on the FF channel);
- sudden onset of tachycardia initially detected in the VT1 zone, then in the VF zone; irregular and polymorphous tachycardia;
- cycles classified VT1;
- stabilization of the arrhythmia in the VF zone;
- classification of the episode in the VF zone after 18 out of 24 cycles (3 VT1 cycles) in the VF zone;
- the delivery of ATP and the shock are not visible;
- termination of the arrhythmia;
- end of the episode after 12 consecutive cycles classified Vs or Vp.
Programmer tracing (same episode)
The 3 channels are the same as for the remote tracing.
- detection of VF and delivery of burst of 8 stimuli;
- at the end of the burst, onset of the charge of the capacitors (dark horizontal line);
- unsuccessful burst, cycles classified VF and continuation of the charge;
- end of the charge;
- synchronized 40-J shock at 78-Ohm impedance, delivered on the first cycle classified VF after the end of the charge;
- successful shock.
Comments
This tracing illustrates the operation of the defibrillator when ATP one shot is ineffective. The arrhythmia was sensed as stable, at the limit of the programmed threshold. ATP did not terminate the arrhythmia. Compared with the programming of an electrical shock delivered outright, the charge of the capacitors is delayed only by the duration of an ATP sequence (~ 1 sec).
