Oral anticoagulants reduced CT-detected valve clots after TAVI in randomized trial

A randomized Norwegian trial has found that oral anticoagulant monotherapy reduced imaging evidence of blood-clot formation on replacement aortic valves compared with aspirin during the first year after transcatheter aortic valve implantation, or TAVI.

The ACASA-TAVI findings were presented at the European Society of Cardiology Congress and published in JAMA on August 30. They address an increasingly consequential question as TAVI expands into younger, lower-risk populations: whether post-procedure medication can protect the implanted valve without creating unacceptable bleeding risk.

The answer remains provisional. The trial demonstrated an effect on a CT-detected marker of leaflet thrombosis, not longer valve life or fewer disabling cardiovascular events.

A 360-person randomized comparison

Investigators enrolled 360 adults ages 65 to 80 who had undergone successful TAVI for severe aortic stenosis at three Norwegian centers. Their mean age was 74.5 years, and 37% were women. Patients with a separate indication for anticoagulant or antiplatelet therapy were excluded.

Participants were randomly assigned to 12 months of monotherapy with a factor Xa inhibitor oral anticoagulant or aspirin. The study was open-label, meaning participants and clinicians knew the assignment, but endpoint assessment was blinded.

The co-primary efficacy endpoint was hypoattenuated leaflet thickening, an imaging sign consistent with subclinical thrombus on the implanted valve, measured by cardiac CT at 12 months. The co-primary safety endpoint combined bleeding, stroke, myocardial infarction and death from any cause.

Leaflet thickening occurred in 27 of 167 evaluable participants receiving an anticoagulant, or 16.2%, compared with 48 of 168 receiving aspirin, or 28.6%. That corresponded to a risk ratio of 0.55, with a 95% confidence interval from 0.37 to 0.82.

The safety composite occurred in 13 of 174 participants in the anticoagulant group, or 7.5%, and 19 of 180 in the aspirin group, or 10.6%. The result met the study’s statistical criterion for noninferiority, indicating that the trial did not detect an unacceptable increase in the combined safety outcome with anticoagulation.

Why the safety conclusion needs restraint

The safety-event rate was substantially lower than investigators had anticipated. That produced a wider relative noninferiority margin than originally expected and limits how firmly the trial can establish comparable safety.

The study was also not powered to assess individual clinical outcomes. Although two participants assigned to anticoagulation died compared with 10 assigned to aspirin, the researchers classified that mortality difference as exploratory. Stroke and myocardial-infarction counts were small, and no distinct between-group differences emerged for most secondary outcomes.

Forty-seven participants had treatment deviations, including crossover, interrupted treatment or therapy discontinuation. Baseline differences were also present in sex and several medical conditions, although supporting adjusted analyses produced results consistent with the primary analysis.

An imaging result, not proof of longer valve life

Subclinical leaflet thrombosis is considered relevant because it may impair leaflet motion, contribute to embolic events or progress toward structural valve deterioration. However, its causal relationship with those outcomes remains uncertain. ACASA-TAVI followed participants for only 12 months and did not show that reducing the CT finding makes replacement valves last longer.

Current guidelines generally discourage routine anticoagulation after TAVI when patients have no independent reason to receive it. ACASA-TAVI adds evidence specifically about anticoagulant monotherapy, rather than regimens combining anticoagulants with antiplatelet drugs, but one modest-sized trial should not be interpreted as an immediate practice change.

The practical result is a clearer research direction: longer and larger trials must determine whether preventing early leaflet thrombosis preserves valve performance or improves patient outcomes without adding clinically important bleeding. Until then, the study supports a potential strategy for selected patients, not routine anticoagulation for everyone after TAVI.