Hello, I'm Dr Lee from Seoul National University Hospital, Seoul, Korea. And today my talk is about CSP non-responder in patients with heart failure who need cardiac resynchronization therapy.

How do current guidelines address patient selection for conduction system pacing for cardiac resynchronization therapy in heart failure patients, and what are the gaps in these recommendations?

At this moment the current guideline did not much mention about the CSP CRT. Patients who had LBBB, reduced ejection fraction and wider QRS. Biventricular pacing as a classic one got a Class 1 recommendation. In this population, CSP CRT got a Class 2B recommendation, and when the physician failed the classic biventricular pacing, CSP CRT as an option alternative option for Class 2A recommendation. But all these CSP CRT recommendations are based on level of evidence D.

What are the key clinical and ECG indicators that suggest a patient might not respond to conduction system pacing?

Actually, there is not much data for the patients who will be non-responder for the CSP CRT. We can get one clue in the ECG than classic typical LBBB patients got more benefit from CSP CRT. And when patients have IVCD, those patients are likely to poorer or non-responder to the CSP CRT.

And one more clue we can get from cardiac MRI and patients who had much scar on diffuse myocardium or patients who have septal scar, the CSP CRT can be technically challenging. And also in that case, patients receive less benefit from the CSP CRT. It is not much data for the clinical factors or ECG factors for the patients who will be non-responder on CSP CRT. But the principle is when patients have conduction dyssynchrony, they can get more benefit from CSP CRT.

So one important clue from ECG then typical LBBB pattern, patients have typical LBBB pattern these patients have higher chance to respond from CSP CRT, but patients with IVCD, those patients would be the non-responder or poor responder from CSP CRT.

And we can get one more clue from cardiac MRI. So the CSP CRT the lead usually placed in the septal area. So in patients who have transmural septal scar or fibrosis, the procedure can be more challenging and the results of the CSP CRT would be poor, or patients who have diffused scar on their LV myocardium, they're the kind of patients also easily to be the non-responder or [illegible] responder.

What comorbidities are associated with reduced benefit from conduction system pacing?

That kind of things are not fully evaluated in CSP CRT field. But we can get some clues from the observational study and RCT that patients who had LBBB and non-ischemic cardiomyopathy that characteristics is typical responder from CSP CRT.

Otherwise in patients with ischemic cardiomyopathy who had severe disease on proximal LAD or diffuse [illegible] disease, that patients might be non-responder because they have a dense scar in a place that CSP lead usually placed. And whichever the etiology of heart failure is, patients who had high burden of myocardial scar or progressive nature of their disease that can be non-responder from the CSP CRT as well as the biventricular CRT.

What procedural challenges might lead you to determine a patient is not suitable for conduction system pacing?

With the adoption of growing LBB area pacing, the target zone of LBB area pacing is important to achieve good results of our procedures and the patients who had dense fibrosis or transmuter scar on their septal area. It makes the technical challenging to penetrate the septal area and achieve true conduction system capture and achieve good response for the CSP CRT.

Another consideration is the patient who has very large chamber especially in the right atrium that makes it very challenging because we have almost fixed the curved tool at this time point. So that kind of anatomical challenge makes it difficult to achieve the good position of the LBB area pacing in heart failure patients.

How has your approach to patient selection evolved with increased clinical experience and emerging data?

At this time point in our centre, we tried LBB area pacing first in patients with the typical LBBB and non-ischemic cardiomyopathy. And in that procedure, when we achieve the perfect LBB area pacing capture, then we switched our strategy to biventricular pacing. And if biventricular pacing cannot achieve a good result in procedure, we back up the hybrid approach— for example, last CRT kind of things. Then we just tried everything in one procedure to achieve best outcome.

What changes would you like to see in future guidelines to better clarify which patients should not undergo conduction system pacing?

Non-responder in biventricular pacing is quite well characterised because we have many data from the biventricular pacing RCTs. So in CSP CRT field we don't have that kind of large size and long history data. So we need from the big trials, like left versus left kind of things, we can find some clues that which patients need which strategy first.

So I don't think CSP CRT versus biven CRT there is some kind of absolute winner between two. Some patients need CSP CRT more and some patients need biven CRT more or some patients need the hybrid approach for the best outcome. So in future study we can delineate that by patient specific characteristics. We can choose the first option for the cardiac resynchronization therapy.