6. Possible deleterious effect of antitachycardia pacing
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This clinical case illustrates the escalation of the applied therapies according to the zones in which the tachycardias are located, and according to their transition from one zone to another.
- Upon analyzing the tachogram, the initial variability of the RR cycles of the rhythm disorder can be clearly recognized, which rapidly changes the diagnosis over the course of the cycles. The tachograms cannot be spread out and therefore their respective reading is difficult since the annotations become intertwined. However, the succession of markers is the result of a tachycardia rate straddling the boundaries of the VT and VF zones, as well as the instability of the rhythm.
- At the beginning of the EGM, the rhythm is at times classified as stable in the VT zone and thus leads to a diagnosis of VT (markers n° 11, 14, 17, 19), at times classified as unstable in the VT zone and results in a diagnosis of SVT/ST (markers n° 13, 15), and at times classified as faster and leads to a diagnosis of VF (markers n° 12, 16, 18). Each SVT/ST majority will reset both the VT and VF persistence counters, and each VF cycle will increment the VF counter a well as the VT counter. The VT majority will reset the VF counter. The VF marker (16) triggers the respective persistence of 6 VF cycles, 12 VT cycles, and 30 Slow VT cycles. The first counter that is filled (threshold of 12) is the VT counter which defines the type of therapy that is ultimately initiated: an ATP sequence in the VT zone (ATP1 VT). This is a ramp given the programmed Autoswitch ATP function which we will address in Clinical Cases n°22 and 23.
- The ramp accelerates the tachycardia which, after 7 cycles, is classified as a VF, which triggers a persistence of 6 cycles, at the end of which the tachycardia is in the VF zone and is stable, in the FVT section,
- hence the triggering of the ATP sequence in the new FVT/VF zone (Fast VT ATP (22)). Indeed, with this latter ATP sequence in the FVT zone, we are now in the second line of therapies.
- This ATP leads to a new VF in redetection (VF (23)), which triggers the charging of the capacitors, the VF persistence counter having not being reset by the ATP.
- The charging of the capacitors is initiated (not marked in the platforms prior to Platinium !!!) which ultimately results in a shock of 42 Joules charged, 38.9 Joules delivered
- Termination of the episode is delayed, due to premature contractions in bursts during the redetection and which are classified in the VT zone with a first diagnosis of VT (6 out of 8 cycles) (marker 25),
- followed by the occurrence of 6 consecutive slow or paced cycles with diagnosis of Slow Rhythm and termination of the episode.
- It is necessary to revisit the counting in order to fully understand the functioning of the prosthesis and the delays in the initiation of therapies. The designers’ goal was to certify the diagnoses in order to apply the therapies that are consistent with the programming and therefore in keeping with the wishes of the physician.
- The principle of incrementing the VT and Slow VT counters in case of a VF majority is well illustrated in this example, as well as the resetting of all the counters in case of ST/SVT majority, and that of the VF counter in case of VT or Slow VT majority while maintaining a simple analysis based on a counting of 6 out of 8 cycles (we will see that this principle is also used for discrimination).
- In other words, the prosthesis will apply therapies depending on the zone in which it is detected at the end of its persistence. For the Slow VT/VT transition, when the tachycardia rate accelerates and enters the upper zone with the average of the last 4 persistence cycles in this upper zone, it is the therapy of the upper zone which is applied; similarly, if, when slowing down, the tachycardia enters the lower zone with the average of the last 4 persistence cycles in this lower zone, it is the therapy of the lower zone that is applied
- For the VT/VF transition, when the tachycardia rate accelerates and enters the upper zone (FVT/VF), the majority rhythm will change from VT to VF and after the counting of the FV persistence, it is the therapy of the upper zone that is applied; similarly, if, when slowing down, the tachycardia enters the lower zone (VT), it is the higher or equal therapy that will be applied, the FVT/VF ATP being considered « stronger » than the VT/Slow VT ATP.
- After a therapy, and in redetection, the same diagnosis as determined before the therapy increments the persistence and triggers the therapy planned in the program; if the diagnosis changes, a new persistence is restarted.
- The escalation of therapies, i.e. the progressive aggressiveness from one therapy to another in case of perpetuation of the tachycardia, applies in a same zone. It also applies from one zone to another: if the ATPs have been exhausted in a zone and the tachycardia changes zone, i.e. an upper zone or a lower zone, the called-upon therapy will necessarily be the next line programmed therapy in the new zone.
Are ramps more arrhythmogenic than bursts?
As ramps are more agressive than bursts (shorter pacing intervals), they are considered as more arrhythmogenic by most. However, in our study with over a 1000 confirmed VT episodes, we found no difference between burst and ramp arrythmogenicity or efficacy. Read the full article in Heart Rhythm or download the PDF here.
- Antitachycardia pacing may degrade a monomorphic ventricular tachycardia, particularly if the tachycardia to be treated is already fast.
- There is a progressive escalation of the therapies within a same tachycardia episode, ranging from mildly aggressive therapies to increasingly aggressive therapies.
- Review / Skip
A 56-year-old ischemic patient, with ejection fraction of 30% and symptoms of heart failure, implanted with an atrio-biventricular defibrillator (narrow QRS but with frequent episodes of Mobitz I second-degree AV block).
The EGMs are contiguous.
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