VT or SVT? That's the question...

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Hello everyone,

66 years old male.

Anterior myocardial infarction 84

First implant after SCD in 2008.

Paroxysmal AF

Current device Medtronic Evera XT VR

Determining the origine of a fast ventricular event in a single chamber device is often tricky. In the present case what are the arguments in favor of VT/SVT? What change (if any) of the defibrillator programming would you suggest?

Thanks for your imputs. Please share your thoughts and make this forum alive!

S Ploux

Hello Sylvain,

Interesting case!

The patient has 2 different tachycardias during this episode! The algorithm decides this is a VT. It does so because it considers the onset to be sudden, the arrythmia to be stable, and the morphology to be different to the template.

Although VT is very likely, these criterias could also be met in the case of an organized SVT (ATach, AVRT or AVNRT).

Different things can be noticed :

1) After the failed ATP salvos, the return cycle is 550ms, which yields a PPI-CL of approx. 190ms, in favor of VT. (The patient has probably a left-sided isthmus given his underlying substrate, which explains why the PPI is not shorter.)

2) We notice that during the second (slower) tachy, a couple of beats are different from the predominant morphology. These beats can be either PVCs during an SVT or captured beats during VT. If we look at the morphology of these extra beats and compare it to the morphology after the tachycardia (seen after the succesfull ATP), they look highly similar. This makes a captured supraventricular beat likely. We notice that each one of these beats is not followed by an equivalent pause, and therefore resets the tachycardia. (This is clearly visible on the plot on the first page (@20-35s in the episode) that displays dots 50ms below the tachy line and only a couple ms above it immediately afterwards). This reseting means the tachycardia isthmus has been captured, which means the ventricle is likely part of the circuit and makes an ATach or an AVRNT very unlikely. It is surprising that such a captured beat would reset the tachycardia almost every time. Maybe this is in favor of an isthmus close to the intrinsic conduction pathways ? (which would also explain the narrow QRS appearance in VT).

We also see that the arrythmia accelerates again after 2 morphologicaly different ventricular beats, which is again in favor of ventricular involvement.

3) The ATP manages to stop the tachy, which is in favor of VT.

I would go for 2 different VTs with similar circuits!