Termination by ATP?
Patient
A 56-year-old ischemic patient, with ejection fraction of 30% and symptoms of heart failure, implanted with an atrio-biventricular defibrillator.
Programming
EGM
Interpretation
- The counting of events is very clear in this example: The first tachycardia cycle is 609 ms and is therefore not in the VT zone. For the system, the tachycardia begins on the following cycle, the one noted 398 ms, which is excluded from the counting, as is the next cycle noted 320 ms
- The next 6 cycles are detected in the VT zone, and a first VT diagnosis is made (VTLC)
- Which triggers the persistence of 20 cycles, each cycle validating the VT majority, and perpetuating the persistence
- Once the persistence fulfilled, the first scheduled ATP sequence in the program is delivered, a burst
- The tachycardia terminated shortly after the second ATP but first we see a few premature contractions
- 6 out of 8 cycles are in the slow zone, and the episode ends.
Comments
- This tracing reveals the proper analysis behaviour of the defibrillator: the counting is simple, the discrimination correctly resulted in the diagnosis of VT with a persistence of exactly 20 cycles as programmed, the therapy of the zone was applied.
- This therapy is effective, certainly, but with a result that is not as clear-cut as in the previous example.
- One may wonder if a longer burst would have allowed to better penetrate the tachycardia loop and obtain a faster result. On the other hand, extrasystoles with varying cycle interval are often seen after ATP and may themselves be a sign of
tachycardia destabilisaiton and ultimately termination. The exact number of fast ventricular events between ATP and termination to be tolerated and allow the therapy to be called succesful is not known.
- In addition, due to an onset mode seemingly always identical with the presence of many premature contractions which have a morphology ostensibly identical to that which triggers the tachycardia, an indication of ablation of the tachycardia should be
discussed with this patient by targeting the triggering premature contractions circuit.
Take home message
It takes several cycles before the paced cycles of a burst fully capture the ventricular events and have a chance to enter the tachycardia circuit.
It is recommended to program at least eight cycles for every burst.
