PARIS – Real-time monitoring of von Willebrand factor during transcatheter aortic valve implantation shows promise as a means of detecting clinically significant aortic regurgitation, enabling interventionalists to make an on-the-spot fix and end up with a better result.
“We believe this is a nice way to expand the use of TAVI, to simplify the procedure, and to decrease the cost,” Dr. Eric Van Belle said at the annual congress of the European Association of Percutaneous Cardiovascular Interventions.
Clinically significant aortic regurgitation post-TAVI remains a major problem. It occurs in 10%-30% of patients who undergo TAVI to treat severe aortic regurgitation. It’s tough to identify and grade the severity of aortic regurgitation in the catheterization lab using echocardiography, angiography, and hemodynamic measurements, so the current standard is transesophageal echocardiography (TEE), typically performed under general anesthesia.
“It costs money for TEE under general anesthesia, and it lengthens the hospital stay,” observed Dr. Van Belle, professor of cardiology and head of the cardiac catheterization laboratory at Lille (France) University Hospital.
If this novel real-time monitoring of von Willebrand factor defects works out as well as it has in a new proof-of-concept study, it will essentially serve as a screening test for clinically significant aortic regurgitation. The need for TEE would then be limited to the minority of patients with evidence of moderate or severe aortic regurgitation on the screening test, he explained.
Dr. Van Belle and his coinvestigators have previously shown that patients with clinically significant aortic stenosis or valvular regurgitation exhibit high-molecular-weight multimers of von Willebrand factor defects and that these defects are corrected upon surgical valve replacement (Circ. Res. 2015;27:116:1193-201). Something that’s not widely known except among hematologists is that these defects can be monitored in real time by commercially available, bedside point-of-care platelet function analyzer closure time adenosine diphosphate(PFA-CADP) assays. Indeed, the cardiologist continued, hematologists use the PFA-CADP assay to screen for von Willebrand disease; a normal value is 114 seconds.
He presented a proof-of-concept study involving 88 consecutive patients who underwent TAVI with transfemoral delivery of the Sapien XT valve. All were monitored using the PFA-CADP assay, had their high-molecular-weight multimers of von Willebrand factor measured, and also underwent TEE to see how those definitive imaging results correlated with the assay findings.
The assay results were uniformly abnormal at baseline, prior to TAVI. The results normalized in most patients when PFA-CADP was measured 5 minutes after valve implantation, and TEE confirmed that patients with a normal assay result had only mild or no aortic regurgitation. Those with more than mild aortic regurgitation by TEE then underwent dilation with a larger balloon in an effort to correct the problem. Repeat PFA-CADP testing performed 5 minutes after the corrective procedure as well as TEE showed that the aortic regurgitation had been corrected.
One commentator said he’d really like to see evidence that the level of PFA-CADP reproducibly correlates with the degree of aortic regurgitation.
“If you could come up with a way of quantifying the degree of aortic regurgitation, that to me would be very, very appealing,” the cardiologist said.
Dr. Van Belle replied that “we’re relatively confident” that this is indeed the case, but an 88-patient study isn’t big enough to prove it. However, the study is ongoing, and with a planned 200 TAVI patients he says he believes it will be possible to demonstrate that the real-time assay discriminates between severe, moderate, and mild aortic regurgitation. Also, the investigators plan to evaluate the impact of PFA-CADP–guided interventions upon long-term clinical outcomes.
The study was funded by Lille University. Dr. Van Belle reported having no financial conflicts.