However, despite the negative results of the overall GALILEO study, results from the substudy that used 4DCT to evaluate function of the bioprosthetic aortic valves suggested rivaroxaban may have potentially beneficial effects on valve function.
The results showed that patients on the rivaroxaban and aspirin regimen had lower rates of subclinical reduced leaflet motion and leaflet thickening than patients on the antiplatelet strategy, said Dr. De Backer, reporting on behalf of the GALILEO-4D investigators.
The substudy evaluated 205 patients who had 4DCT 90 days after TAVR. The primary substudy endpoint was at least one prosthetic valve leaflet with a grade 3 or higher motion reduction, which 2 of 97 patients in the rivaroxaban group had (2.1%) versus 11 of 101 in the antiplatelet group (10.9%, P = .01).
“This indicated an 80% greater reduction of the primary endpoint in the rivaroxaban arm,” Dr. De Backer said. The chief secondary endpoint, the proportion of patients with at least one thickened leaflet, was met by 12.4% of the rivaroxaban group and 32.4% of the antiplatelet arm, “a 60% significant reduction by rivaroxaban,” Dr. De Backer said.
However, when the 10 patients in each group who didn’t adhere to the study drug regimen were excluded, he said, “then we see no single patient had reduced leaflet motion of grade 3 or more in the rivaroxaban arm.”
Another takeaway from the substudy is the ineffectiveness of transthoracic echocardiography as opposed to 4DCT in TAVR patients. Echocardiography (ECG) failed to show any significant differences in the mean valve gradient between the treatment groups, Dr. De Backer said.
Eleven patients who didn’t have leaflet thickening (7.3%) and 7 patients who did (15.9%) showed an increase of 5 mm Hg or more in the mean valve gradient on echo. ECG also showed a similar increase in the mean valve gradient in 14 patients who had no to moderate reduced leaflet motion (grade 3 or lower, 7.7%) and in four patients (30.8) who had grade 3 or higher reduced leaflet motion.
“This basically confirms results from observational studies that transthoracic echocardiography is often not good enough to detect these phenomena,” Dr. De Backer said.
The percentages of substudy patients who had major clinical events – major bleeding, thromboembolic events, or death at 90 days – were each less than 3%, he said. “There were too few clinical events to permit any assessment of the impact of leaflet thickening or reduced leaflet motion on clinical outcomes,” he said.
That lack of clarity with regard to clinical events is one of the questions the study leaves unanswered, said discussant, of Leiden University Medical Center in the Netherlands.
“With stroke or TIA, there are too few events to draw any conclusions,” she said of the substudy. “We don’t know when we need to use CT, when we need to evaluate these patients, or maybe when we should go for more advanced imaging techniques where we can see the biology of those changes in the leaflets.” Hopefully, she said, future studies provide those insights.
“CT can be more sensitive than ECG to see these subclinical changes,” she said, “but the open questions that we have are to see if there is a correlation between thrombosis rate on imaging versus the stroke rate.”
The substudy’s conclusion on ECG, however, has been borne out by previous retrospective studies, Dr. Delgado added.
, of Stanford Medicine, tried to put the seemingly conflicting findings of the main GALILEO study and the 4D substudy into context.
“There you have the disconnect between the mechanism and the clinical observation and those are sometimes difficult to reconcile because the assumption is that the mechanism leads to the clinical outcome.”
While the main study shows that routine anticoagulation after TAVR is not indicated, the findings raise questions about the risk of clots forming on bioprosthetic valves. “Yes, maybe there are clots forming on these valves, but maybe that’s not causing the bad clinical outcomes,” Dr. Harrington said.
The findings also raise questions about the use of newer anticoagulants to prevent stroke post TAVR, he said. “It appears that warfarin is better than the newer anticoagulants for reasons that aren’t entirely clear.”
Dr. Dangas, lead author of the main GALILEO trial, said the substudy results could help design future trials of even-lower doses of anticoagulation in a more selective group of TAVR patients.
“In order to decrease the clots, first of all you don’t need the full dose of anticoagulation; even a low dose may do the trick,” he said. Further investigations can evaluate the clinical significance of having a blood clot in the valve as an indication for anticoagulation versus antiplatelet therapy.
“Even though this obviously doesn’t mean you’re going to have a stroke in a year or two,” Dr. Dangas said, “could it perhaps mean that the valve is not going to have such a good durability later on?”
Perhaps future studies of anticoagulation in TAVR should concentrate on patients who actually have clotting in the valve, he said.
The trial was supported by Bayer and Janssen. Dr. Dangas reported receiving grants from Bayer during the conduct of the study, personal fees from Bayer and Janssen, grants and personal fees from Daiichi-Sankyo, and “other” funding from Medtronic outside the submitted work. Dr. De Backer reported receiving grants from Bayer during the conduct of the study and personal fees from Abbott and Boston Scientific outside the submitted work.
SOURCE: Dangas GD and De Backer O. AHA 19,.
This article also appears on Medscape.com.