Induction of ventricular fibrillation by direct current

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.

Trace

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.

Trace

11. Rhythm detected in the atrium and biventricular stimulation (AS-BP);
12. Repeat delivery of DC for 2 sec;
13. Induction of ventricular arrhythmia; the initial cycles were unclassified;
14. 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;
15. The device switched to DDI mode during the episode;
16. Diagnosis of VF after 12 cycles that were detected and classified in the VF zone; onset of the capacitors charge;
17. 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);
18. Diagnosis of return to sinus rhythm after 5 consecutive VS and switch to the post-shock DDD pacing mode.