Induction of ventricular fibrillation by direct current

N° 2
Manufacturer Abbott Device ICD Field Implantation

This 54-year-old man suffering from ischemic dilated cardiomyopathy, with a 30% LVEF and 120-ms QRS, underwent implantation of a Unify triple chamber ICD. VF was induced by DC at the end of the implantation procedure.

Main device programming (during the induction procedure)

  • Single VF zone for rates >187 bpm
  • 12 cycles in the VF zone were needed for the diagnosis
  • Sensitivity programmed at 0.5 mV
  • First shock at 25 J, second shock at 40 J (maximum strength).
Graph and trace

Text (trace 2a)

The narrative suggests the occurrence of a non-sustained VF episode at a rate of 292 bpm, which is the mean rate of the last 4 cycles before the trigger and the arrhythmic diagnosis; the shock therapy was cancelled.


  1. Rhythm detected in the atrium and biventricular stimulation (AS-BP);
  2. DC delivered for 2 sec;
  3. A 600-ms blanking period follows the induction;
  4. Ventricular arrhythmia; the first 3 short cycles are unclassified (-): the analyzed intervals and the 4 previous averaged intervals are not concordant;
  5. First interval classified in the VF zone (F) (concordance between instantaneous and average intervals);
  6. At the third cycle in the VF zone, the device switched to DDI mode, the programmed mode during the episode;
  7. VF episode detected after 12 ventricular cycles in the VF zone, and trigger of the EGM recording (Trigger); start of the capacitors charge;
  8. Spontaneous termination;
  9. Diagnosis of return to sinus rhythm made by the ICD and interruption of the capacitors charge; in this patient 5 VS or BP cycles were needed; the nominal programming of  “sinus return” is 3, 5 or 7 cycles;
  10. Interruption of the EGM 4 sec after the diagnosis of sinus return.

Text (trace 2b)

The narrative suggests the occurrence of VF at a rate of 279 bpm. A 25 J shock was delivered; the programming and the measurements describing the shock are shown; the programming was nominal and the shock was biphasic, with a fixed tilt (65% for both phases), the anode in the right ventricle and the shock delivered between the right ventricle and the pulse generator; the shock impedance was 75 Ohms, the charge time 4.4 sec, and the pulse duration 7.7 ms.


  1. Rhythm detected in the atrium and biventricular stimulation (AS-BP);
  2. Repeat delivery of DC for 2 sec;
  3. Induction of ventricular arrhythmia; the initial cycles were unclassified;
  4. A cycle marked “-“, occurred after a cycle that was undetected because of low amplitude. This caused the measurement of a long (359 ms) cycle, which was outside the VF zone. However the average of the 4 previous cycles remained in the VF zone. Because of this non-concordance that cycle remained unclassified;
  5. The device switched to DDI mode during the episode;
  6. Diagnosis of VF after 12 cycles that were detected and classified in the VF zone; onset of the capacitors charge;
  7. Delivery of 25 J shock after confirmation (the shock was synchronized with the second cycle following the end of the charge, the instantaneous and averaged interval of the last cycle in the VF zone);
  8. Diagnosis of return to sinus rhythm after 5 consecutive VS and switch to the post-shock DDD pacing mode. 

Depending on the manufacturer, 3 different methods can be used to induce VF during implantation of an ICD:

  1. Delivery of a low-amplitude electrical shock during the vulnerable period (the peak of the T wave). In order to induce VF, the number or length of the pacing cycles, the delay between the shock and the preceding paced QRS, or the shock amplitude may need to be varied;
  2. Very rapid pacing: 30 Hz pulses, i.e. at 33 ms cycle length, are delivered until VF is triggered; the duration of pacing may be prolonged before the successful induction of VF;
  3. Delivery of low-voltage DC across the defibrillation electrodes; the duration of current needed to trigger VF may also need to be modulated. This highly effective means of triggering VF rarely requires >2 sec of DC delivery.