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WASHINGTON -- Bioprosthetic aortic valves implanted during transcatheter aortic valve replacement (TAVR) and surgical aortic valve replacement (SAVR) "frequently" developed subclinical leaflet thrombosis in a registry study, according to researchers.

After a median of 83 days from valve placement to CT, 11.9% of eligible enrollees in the RESOLVE and SAVORY registries had subclinical leaflet thrombosis (3.6% for SAVR valves and 13.4% for transcatheter valves, P=0.001), according to , of Cedars-Sinai Heart Institute in Los Angeles, at a late-breaking trial session at the annual American College of Cardiology conference here.

Makkar's group defined subclinical leaflet thrombosis as the presence of reduced leaflet motion on CT imaging, with corresponding hypoattenuating lesions. Their results also appeared .

Subclinical leaflet thrombosis was not associated with significantly more strokes (4.2 versus 1.92 per 100 person-years, P=0.10), but patients who developed it did have more transient ischemic attacks (4.18 versus 0.60 per 100 person-years, P=0.0005). Combining strokes and TIAs yielded a significant difference as well (7.85 versus 2.36 events per 100-person years, P=0.001).

TAVR valves had much thicker leaflets (5.01 mm versus 1.85 mm for SAVR valves, P=0.0004) and more restricted leaflet motion (71.0% versus 56.9%, P=0.004), suggestive of more severe thrombosis with these devices.

On multivariable analysis, age was a predictor of reduced leaflet motion (OR 1.04, 95% CI 1.01-1.07). Protective effects appeared to be tied mainly to surgical versus transcatheter valve (OR 0.33, 95% CI 0.11-0.96) and anticoagulation (OR 0.24, 95% CI 0.10-0.58).

Leaflet thrombosis was less likely among patients who were on anticoagulants (4% versus 15% for no anticoagulation, P<0.0001). Within anticoagulants, NOACs were on par with warfarin (3% versus 4%, P=0.72).

Reduced leaflet motion was especially prominent with dual and monoantiplatelet therapy (14.9% and 15.6%, P<0.0001 for comparison with anticoagulation).

All patients initiating anticoagulation showed resolution of leaflet thrombosis, as did 89.1% of patients on antiplatelets (P<0.0001).

"Anticoagulation (both NOACs and warfarin), but not dual antiplatelet therapy was effective in prevention or treatment of subclinical leaflet thrombosis. Despite excellent outcomes after TAVR with the new-generation valves, prevention and treatment of subclinical leaflet thrombosis might offer a potential opportunity for further improvement in valve hemodynamics and clinical outcomes," the authors suggested.

"Patients with elevated gradients were more likely to have reduced leaflet motion than were those without elevated gradients; however, most patients with reduced leaflet motion detected with CT scanning had echocardiographic gradients of less than 20 mm Hg, which is considered to be within the normal range," they added.

Their data came from those enrolled in the RESOLVE registry in 2014-2017 at Cedars-Sinai Heart Institute and another cohort in the SAVORY registry enrolling during 2014-2016 at Denmark's Rigshospitalet. Altogether, the study population counted 931 patients, 890 of whom had interpretable CT scans.

There are many questions regarding bioprosthetic leaflet thrombosis that are yet to be answered, , of Leiden University Medical Center in the Netherlands, and , of Columbia University Medical Center and the Cardiovascular Research Foundation in New York, emphasized in an .

They asked: "Given the risks of chronic anticoagulation, should all patients be offered such therapy, or should patient selection be guided by imaging (and should this imaging be CT or echocardiography, and at what interval)? What is the optimal duration of treatment? Are NOACs preferred or as good as warfarin? Should repeat imaging be systematically done at given timepoints? And will such therapy safely enhance net clinical benefit (a greater reduction in stroke and valve deterioration than an increase in major bleeding)?"

Several sources of confounding remain suspect. Importantly, TAVR patients got CT much earlier (58 days versus 162 days for SAVR, P<0.0001) and tended to be older (time to CT did not turn out to be a predictor of subclinic leaflet thrombosis in multivariate analysis, however). The SAVR group had fewer comorbidities such as hypertension, hyperlipidemia, and congestive heart failure.

Bax and Stone suggested that other confounders such as frailty or immunological factors were at play.

Another point of contention, according to the pair: "Dynamic four-dimensional CT imaging was used for detection of subclinical thrombosis. Consensus definitions and quantification of leaflet thrombosis with CT need to be established before prospective study and clinical use."

"A second issue relates to the discrepancy between CT and echocardiographic findings. Investigators of previous small studies reported a 10% to 15% prevalence of subclinical thrombosis with CT, whereas elevated gradients (a mean gradient of >20 mm Hg) with echocardiography were infrequent. Similar findings were present in the large RESOLVE and SAVORY registries."

"These observations imply that CT detects early subclinical thrombosis, whereas echocardiography detects the late consequences of thrombosis -- i.e., valvular stenosis. These results also indicate that not all thrombosis results in valve degeneration and stenosis -- i.e., early thrombosis might resolve without permanent clinical sequelae," the editorialists suggested.

"The optimal CT timing after valve implantation to detect meaningful leaflet thrombosis is thus unknown."