Interpretation

1. The battery is new, the leads work perfectly, the maximum rate-responsive pacing rate (120 bpm) and the Slow VT zone (110 bpm) overlap (a pioneering specifies of Microport: the Brady Tachy Overlap).
2. The programming of the therapies is very surprising and will need to be corrected: the number of ramps and bursts in the Slow zone is too elevated, the lower boundary of the VT zone should be higher, the first shock in this same zone should be maximum, the number of persistence cycles in the VT zone and VF zone should be much higher, there is no Fast VT zone enabling a burst to terminate a stable Fast VT, the alternating polarity is useless, since a shock through the anode in the RV is more effective than a reverse shock.
3. The tachogram reveals an alternation of the duration of the ventricular cycles, but with a 1:1 ratio between atria and ventricles (1). The explanation is given by reading the markers and the EGM.

Comments

1. This is indeed a SafeR mode. The alternating AP-Vs and Ap-Vr cycles evokes two possible diagnoses: either an atrio-ventricular crosstalk or a ventricular bigeminism. The second hypothesis is the most plausible since we clearly observe the emergence of two bigeminal premature contractions on the ventricular EGM with a short Ap-Vr, followed by a T wave. The premature contraction is denoted « Vr » since falling in the safety window. In the SafeR mode, there is no pacing at the end of a safety window. Prior to opening the EGM window, when only markers are available, it is impossible to distinguish between crosstalk and bigeminism.
2. The onset of the tachycardia is seen to begin by an atrial event.
3. However, the criterion that led to the initial SVT diagnosis is the instability of the rhythm, which is the first discrimination criterion of the PARAD algorithm.
4. Since the detection rate is set to 110/min (545 ms), the first cycle that activates the Tachy Detection Algorithm is the cycle with the 539 ms coupling interval, i.e. the third tachycardia cycle. It therefore has for reference the previous cycle whose coupling interval is 554 ms. The sudden acceleration criterion cannot be fulfilled; the 539 ms coupling interval is not less than the acceleration reference: 75% of the 554 ms coupling. The algorithm continues to diagnose SVT on the following criteria: stable 1:1 rhythm without sudden onset.
5. As a reminder, the device only specifies annotations (SVT/VT/VF/SR) upon classification changes. Since the n°1 annotation SVT/ST, the sliding diagnosis (6/8) has consistently remained SVT/ST even if the attained discrimination criteria evolved during the tachycardia.
6. The basic problem of this clinical case is the age of the patient, an age when, usually, the issue is rather the stopping of the therapies, or of not changing a defibrillator with another. The indication was made after a staff discussion given the physiological state of the patient. Once the medical decision is proposed, the patient must in this instance be involved in the final decision

Message

1. Analysis of the « Analysis » dialog boxes is always essential to understand what the defibrillator has taken into account for its diagnosis, in order to properly correct a possible faulty analysis by reprogramming the right parameter to its proper value.
2. The stability criterion is the first criterion of the decision tree of the PARAD+ algorithm.