Interpretation

1. The present example is a VT initially detected in the VF zone after 6 cycles,
2. The tachycardia is stable with a rate below 240/min and after the 6 persistence cycles, a Fast VT burst is triggered with a coupling interval of 80% of the average coupling interval of the last 4 persistence cycles.
3. The burst is ineffective, leaving a slightly slower VT, which after the redetection phase, is classified in the VT zone, stable and dissociated.
4. A 12-cycle persistence phase is applied at the end of which the VT persists.
5. The capacitors start charging (not noted on this platform), which results in a shock of 18.8 J at the outset (shock 1 and not an ATP sequence, as programmed in the VT zone). The shock impedance is 41 Ohm.
6. The shock is unsuccessful, since after a 1-second blanking, the 6 redetection cycles lead to a diagnosis of VF and therefore to the charge of the capacitors after the counting of VF persistence (the initial counter having been reset to zero by the post-ATP VTLC majority), with a charge that will deliver 34 Joules in the VF zone.
7. However, due to the oscillation of the tachycardia cycles between the VF zone and the VT zone ((16) and (17)), the VT majorities reset the VF persistence counter, the VF and VT majorities increment the VT persistence counter. The VT persistence counter is incremented regularly, without diagnostic delay, and is the first to reach the programmed threshold where the annotation VTLC maj. (18) is indicated, such that it is the next shock of the VT zone that is delivered at 34 Joules (19) (shock 2). The impedance is stable at 40 Ohms.
8. The VT is terminated for 3 cycles and reappears with a 1st VF diagnosis (20) which persists and causes the capacitors to charge for a VF zone shock which would be of 34 Joules.
9. However, the tachycardia slows down such that a VT diagnosis (21) is now established after the 6 redetection cycles and persists sufficiently long to commit and apply a max shock in the VT zone (22) this time around, which does not terminate the tachycardia.
10. Two other max shocks are delivered in the VT zone, since in each instance, after a short termination of the tachycardia, it reappears in the VT zone with a VT diagnosis at the end of redetection.
11. Fortunately, the last max shock in the VT zone is effective with a return to slow rhythm and the end of the episode (SR).
12. At this time, the post-shock pacing program is underway in DDD mode at 70/min, at 4.5 V in the atrium and 7.0 V in the ventricle with pulse widths of 1 ms, for a total of 20 seconds (as programmed). Thereafter, the programmed permanent pacing parameters are applied.

Comments

1. The therapies applied are those programmed in the zone where the current tachycardia is confirmed and verified. This example shows that the first therapy is that of the VF zone, since it is in this zone that the tachycardia is initially detected, which fulfilled the diagnostic criteria necessary for the application of an ATP in the Fast VT zone (rate and stability). The tachycardia that follows this ineffective ATP is redetected in the VT zone, and it is therefore a VT therapy that will be initiated. The available VT therapy that will be applied must have a higher level of aggressiveness than that of ATP in the Fast VT zone (level 2). However the ATPs of the VT zones have a level 1 aggressiveness. The following available therapies are necessarily shocks (level 3 for the shock at 20 J and level 4 for the shocks at 34 J). It is therefore the programmed shock of 20 J which is charged and delivered in the zone where the VT is redetected, confirmed and verified.
2. There is therefore an escalation which triggers the therapies from the least aggressive to the most aggressive, although the latter is accelerated if the first diagnosis is a VF. This feature allows limiting the delivery time of effective therapies. This escalation can also be analysed after the very transient return of the sinus rhythm after the first shock of 31.4 J, since the following therapy is a maximum shock, since for the device, there was no termination of the episode.
3. This patient was fortunate since the tachycardia terminated after the 3rd maximum energy shock. Another ineffective maximum shock and no other therapy would have been applied on this VT since the device would have reached the end of the programmed therapies in the VT zone.
4. After the shocks, a post-shock pacing mode is programmable, with a mode and basic rate, possibly different from the permanent program, and above all a duration of application and pacing energies that are programmable at high levels. Indeed, after a shock, we readily witness a temporary elevation of the pacing thresholds.
5. The situation of this patient is critical since the shocks are insufficient in terms of energy to rapidly terminate the tachycardias. An ablation of arrhythmias triggering numerous episodes in this patient should be discussed.