This is a portion of the transcript from Session III of the VetVine Mitral Valve Disease Masterclass Q&A segment:
Dr. Sheri Berger l VetVine: So, practically speaking, if someone's going to think about referring a case for an interventional V-clamp procedure, Dr. Ahern, at what point are we considering doing that? At what stage of heart disease?
Dr. Michael Aherne: So, regarding those interventional procedures, it depends a little bit on the individual patient. So, like I mentioned, the patients with very severely dilated hearts may simply be limited size. As I mentioned, if the size is too big to accommodate some of those devices then the device, itself, might not be able to grasp. So, it's not so much the size of the dog, it's the size of the heart in the dog.
So, that could be a limiting factor and, at least based on the published data from Colorado State University, it seems like a mitral annular size of about 20mm is about the upper limit of what we can currently consider with the V-clamp technique.
Dr. Sheri Berger l VetVine: So, you're able to discern that before even considering a referral for the procedure? Can we see that on an echocardiogram?.
Dr. Michael Aherne: For the most part, that should be able to be identified on echocardiography. Those patients that are kind of borderline, you know, kind of at the 20mm mark, it can be difficult to tell that from just a transthoracic echo - which is the typical echocardiogram that we perform. In those instances, it might need to be determined on a transesophageal echocardiogram. So, theoretically, a patient could get all the way to the point of being anesthetized for the procedure, and then that final measurement with a transesophageal echo - which is part of the procedure - could be the make or break as to whether or not they'll just meet the criteria for the device selection.
Dr. Sheri Berger l VetVine: And is it reasonable that a stage B2 dog would be a consideration for a V-clamp procedure, as far as treatment goes?
Dr. Michael Aherne: I think it's certainly reasonable. And if we think about the progression of the disease, those dogs in the earlier stages - those B1 and B2 dogs - are hopefully going to have a little bit less remodeling in the heart than the dogs in later stage B2 and stage C. So, it seems like the late B1 and early B2 - when there's minimal remodeling - is probably going to be the optimal type of case for these interventional procedures. But once we get significant remodeling, then the complication risks certainly increase. And, one other factor to consider is that we don't yet know what the long term benefits would be in those more advanced cases. Because we know that we can't address the annular dilation - which is something that can be addressed with direct open-heart repair while on bypass. And so some of these patients can still be left with a significant amount of regurgitation if they have a very dilated heart to begin with. So, it seems like the early B2s are probably going to be the best type of case from a risk-benefit scenario. And, certainly, once we've got evidence of remodeling, the likelihood is that we'll continue to have some remodeling.
And so the stage B1s, it certainly becomes a question as to whether the risk-benefit is there just yet, because we know - based on the survival times of those patients - that it could be years before their disease advances, and then more years beyond that before they would advance to stage C. So that would certainly be something for owners to consider very carefully, you know, with these patients in those earlier stages of the disease.
If they're already quite old and in a fairly mild stage of the disease, the likelihood of a long term benefit from these techniques might not be supported when we match it up against the potential risks of these techniques.
