Interpretation

• The tachogram reveals the onset of a relatively unstable tachycardia at the beginning, inducing the change in diagnosis from VT to SVT and then a return to VT, followed by a perfect stability ultimately leading to an ATP sequence in the Slow VT zone with a return to a Slow rhythm.
• Analysis of the EGM of the onset of the tachycardia shows that after conducted PR cycles, a premature ventricular contraction noted 390 ms appears, followed by an As with a slightly shorter As-As interval (734 ms) than the basic As-As interval (757 ms). Of course, it is possible that a P’ wave may trigger the tachycardia, which would then be hidden in the post-ventricular atrial blanking of the last PR cycle, and the diagnosis would become supraventricular tachycardia. However, the ensuing ventricular tachycardia cycles are followed by a retrograde P wave: indeed, the variations in Vs-Vs intervals offset the As-As intervals (e.g., a 476 ms Vs-Vs interval precedes the As-As interval of same duration). Finally, although a less weighty argument, during the ATP, the atrial events follow the paced ventricular cycles. The diagnosis is indeed VT.

• This is a stable Slow VT with stable 1:1 association, but with initial ventricular acceleration.

• From the onset of the persistence, given the instability of the tachycardia, which is extremely common at the onset of ventricular tachycardia especially since the ventricular tachycardia rate is low, the diagnosis becomes SVT. The VT persistence counter is reset to zero.

• It is necessary to regain rhythm stability in order for the diagnosis to become VT again.
• The Slow VT persistence is started for 16 cycles. Since the rhythm is stable and non-dissociated (stable VT with retrograde 1:1 conduction), the device does not take into account long ventricular cycles. At the end of the persistence, the device verifies if the cycle, the majority and the persistence are all labelled “VT” before initiating its therapy. Therapy is triggered and terminates the tachycardia.

Comments

This case complements the previous case and demonstrates the delayed analysis without a study of the morphology in instances of tachycardias with 1:1 AV association.

In the previous case, the onset of the ventricular tachycardia is gradual and the P’ waves rapidly disappear in the blanking period, and the diagnosis is incorrect. In the present case, the onset of the tachycardia is clear, all P waves are visible, the analysis is easy and the diagnosis is reliable.

Message

The reading of the “Analysis” annotations is imperative to monitor the proper functioning of the algorithm, especially when the tachycardia includes a 1:1 AV association.