10. Tachycardia inducing various types of therapies
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- At first, the rhythm is 1:1 atrioventricular associated without premature contraction
- Then a tachycardia begins suddenly, visibly unstable and at the boundary between the VT zone and the VF zone, explaining the multiple annotations, which are impossible to read on the tachogram
- An ATP is triggered, which is ineffective, followed by VF and a second ATP
- The tachycardia is terminated with the return to slow rhythm after a few premature contractions
- 1: The 1st tachycardia cycle is associated with atrial pacing (Ap)
- 2: For the prosthesis, the 1st tachycardia cycle is as follows (367 ms), which is ignored (a ventricular far-field signal is visible on the atrial canal, which is not detected), as well as the next cycle (273ms) with a P wave falling in the blanking period
- 3: Then, the following 6 cycles lead to the diagnosis of SVT. Indeed, the rhythm is in the VT zone but unstable. Scrolling at 50 mm/s allows a better reading of the markers
- 4: The « Analysis » function provides details on the elements of the diagnosis and is very useful for understanding the discrimination function. It was indeed the instability that led to the diagnosis of SVT/ST.
- 5: At the next cycle, the diagnosis becomes VF, since among the 8 cycles preceding this diagnosis, 6 are in the VF zone. Indeed, remember that the counters operate in parallel, SVT, VT, VF, and are competing.
- 6: Then, the diagnosis is once again labelled SVT since the rhythm is in the VT zone and is unstable. The VF and VT counters are therefore reset to zero.
- 7: At the next cycle, the diagnosis becomes VT. Indeed, 6 out of 8 cycles preceding this diagnosis are in the VT zone, are stable and not associated.
- 8: Then once again, the rhythm is unstable two cycles later, with a return to an SVT diagnosis with reset of the VT counter.
- 9: One cycle later, the diagnosis of VT is once again made, since 6 out of the 8 cycles preceding this diagnosis are stable and dissociated. VT persistence is initiated.
- 10: The tachycardia accelerates and leads to the diagnosis of VF, which generates a counting in the VF zone which also implements the VT counter.
- 11: Before reaching the end of the VF counter (which would have led to a VF zone therapy), the tachycardia slows down and enters into the VT zone, which induces a VT diagnosis. However, the VT counter has been running since annotation n°6. Since the VF counter has also incremented the VT counter, this cycle marked n°8 is sufficient to fulfil this VT counter and thus induce the first therapy in the VT zone, a burst.
- 12: However, the burst (marker n°9) does not terminate the tachycardia. A redetection is initiated, ignoring the 1st cycle following the last paced ATP cycle, and the diagnosis of VT is confirmed, stable, and dissociated (marker n°10)
- 13: This VT accelerates and enters the VF zone, fast VT section (marker n°11). It is stable, which is why it is a burst in the fast VT zone which is applied.
- 14: If the VF had been unstable, or displayed a rate greater than 255/min, then the applied therapy would have been a shock.
- 15: Once again, the tachycardia does not terminate instantly, a burst of spontaneous premature contractions occurs which could have generated a true VF and therefore a shock. Perhaps this burst in the Fast VT zone should include more cycles to better penetrate the tachycardia circuit, although more cycles could also possibly degenerate this tachycardia into a true VF … Or maybe next time, this same tachycardia will be terminated « cleanly » with the same burst …
- This tracing is complex but perfectly illustrates the diagnostic modifications of the device during the course of the tachycardia cycles.
- This tachycardia was indeed unstable, which explains the delay in initiating therapy. This occurrence is linked to the absence of the V>A conduction diagnostic criterion as a basic criterion for the diagnosis of a ventricular tachycardia, as is the case with other platforms from competing manufacturers. This choice is deliberate and results on the one hand, on possible detection failures of atrial events, in particular due to atrial arrhythmia, which creates a false diagnosis of VT as opposed to a poorly detected supraventricular tachycardia, and on the other hand, the refusal to take into account « atrial » events falling in the post-ventricular atrial blanking period, most often linked to ventriculo-atrial crosstalk, and which lead to false diagnoses of supraventricular arrhythmia, whereas it is in fact a ventricular tachycardia.
- The first reason for this choice is likely to result in inappropriate therapies by the devices of this brand, while the second reason will be perfectly managed. The designer therefore created a diagnostic algorithm which takes into account atrial detection failures.
- Finally, in keeping with this logic, a morphology algorithm would thus be welcome to aid in the discrimination between supraventricular tachycardia and ventricular tachycardia.
- In addition, this tracing illustrates once again the escalation of the therapies when moving from one zone to another.
- The 75% of cycles rule to validate a counting or discrimination criterion applies everywhere: the counting for the diagnosis of tachycardia and for the first diagnosis of the type of tachycardia, change in zone, stability, AV association, return to sinus rhythm.
- For the Microport brand, the first discrimination criterion is the stability of the tachycardia. Any instability leads to the SVT diagnosis which resets the VT and VF counters which precede that of the SVT.
- The therapy applied is that of the zone of the last diagnosis (majority and persistence) and as a function of the average rate of the last 4 persistence cycles which was triggered following the diagnosis.
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A 56-year-old ischemic patient, with ejection fraction of 30% and symptoms of heart failure, implanted with an atrio-biventricular defibrillator despite a narrow QRS, due to frequent episodes of Mobitz I second–degree AV block.
The shaded areas are the portions of the EGM that are the repetitions of the end of the previous image.
Same tracing, scrolling speed 50 mm/sec
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