My name's Professor Pier Lambiase. I'm a consultant cardiologist and electrophysiologist at Bart's Heart Centre in London and University College London. And I'm going to discuss VT substrate ablation.

What are the key challenges or limitations that still exist in accurately identifying VT substrates?

There are two main challenges: one is in the electrophysiological mapping and the other is actually in the imaging. So if we start, perhaps more simply with imaging, we rely very heavily now on MRI to look for scar and we use gadolinium late enhancement. But often you can get equivocal images where there may be intramural scar you can't see clearly. And that's really important when it comes to mapping and planning a VT ablation procedure, because it's these intramural scars that can be the most challenging to ablate.

Having said that, MRI has been extremely useful in delineating areas of interest to target. From the electrophysiological point of view, we've become increasingly sophisticated in how we map. And, originally, we were simply using voltage mapping areas of scar, ablating around scar, doing lots of lesion sets. Now we're undertaking functional substrate mapping where we try and stimulate the myocardium and cause delays and pick out late potentials which are delayed, called delayed evoke potentials, and those, in principle, that's a really elegant strategy and gives good results in terms of targeting.

But the challenge is actually seeing these late potentials often with what we describe as far field signals, which can drown out those potentials. So it's the ability to map more precisely and distinguish the important signals, which is a real electrophysiological challenge.

What are the most significant recent advancements in techniques or technologies for identifying VT substrates, and how do they improve upon previous methods?

The main advancements have been really related to the mapping catheters we've been using over the past three to five years, particularly high-density, multi-electrode catheters and the software that's being used to process the signals.

So one approach that's been quite transformative has been the omnipolar approach where one can distinguish wave fronts that both move at right angles, perpendicularly and parallel to the grid, but also diagonally across the grid. And we can pick out these signals very, very clearly now where before we were essentially blind to seeing them. So we were misled thinking they were scar areas when they were viable myocardium.

The other thing has been the processing of these signals and the important thing really has been to look at the frequency of the signals. We can pick out high frequency or peak frequency signals which can delineate the critical isthmuses or the corridors of conduction which are supporting ventricular tachycardia. And the sophistication of the processing of the signals means we can hone in on important areas to target for ablation much more precisely than we could before. So it's actually simplifying the process, provided we understand better how to utilise the software.

How are these new insights into VT substrate identification influencing current clinical practices in the management and treatment of VT?

Yeah, so essentially by two strategies—one is using these deep delayed evoke potentials, so we're doing more focused ablation, targeting areas of conduction delay induced by pacing. But also using the peak frequency approach, we can isolate the isthmus into the VT more precisely and that actually can potentially shorten the procedure. There's very nice work from Della Bella's lab that's shown if you target frequencies over 400 Hz in VT, you can terminate the VT within about five seconds.

So this is a very superficial component of the circuit, very amenable to ablation, and that can be also utilized for substrate mapping as well. So that's potentially shortening the procedure once you characterise the substrate that you need to target. And we're getting very good results simply with delayed evoked potential mapping using HD grid mapping in these patients—80% reductions or 80% free of ventricular tachycardia as a result.

How do these advancements in VT substrate identification directly benefit patients, particularly in terms of treatment outcomes and quality of life?

So first of all, they're shortening the procedures because they can be more targeted. And second of all, we've seen in our hands much better outcomes, certainly for ischemic VT ablation, which used to be about 50% up to 80% success in terms of preventing further ventricular arrhythmias.

What are the most promising areas of research or development in VT substrate identification, and how might they shape the future of arrhythmia management?

Well, I think the key thing that's probably the most exciting that certainly came out of the VT symposium that we've known about for the past two to three years really is the utilisation of computational modelling. So if we use an MRI scan to identify scar and determine the slow conduction, use computer simulation essentially to predict where the circuits are likely to run, you can actually predict where the circuits are likely to come from. You can use the MRI to then target ablation using in silico prediction prior to the procedure. And that's probably the most exciting development that we've seen.

So we know it's substrate that's likely to support re-entry and likely to support VT. And there's very elegant work from Trayanova's lab demonstrating this work working with Magdi Saba in London at St George's Hospital. So that's going to simplify the procedures and make them much more tailored to the substrate and individual patients.