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SAN FRANCISCO -- Early-developing subclinical leaflet thrombosis after surgical or transcatheter aortic valve replacement (TAVR) often resolved on its own, but its ultimate clinical significance remains unknown, results from the PARTNER 3 CT substudy indicated

Of the 10% of trial participants who had hypo-attenuated leaflet thickening (HALT) at 30 days, more than half had it resolve spontaneously and without anticoagulation by 1 year. On the other hand, about one in five among those without early HALT had it develop by year's end. Overall HALT incidence at 1 year was 24%.

Patients who did exhibit HALT at 30 days had numerically more adverse thromboembolic events out to 1 year. But none of these events were deaths or MIs, reported Raj Makkar, MD, of Cedars-Sinai Medical Center in Los Angeles, at this year's (TCT) conference.

"However, given the low total number of events, the data are inconclusive and only hypothesis-generating. Longer-term follow-up and larger data sets will further clarify the impact on clinical outcomes," Makkar said.

"Despite the high incidence of HALT and reduced leaflet motion, lack of a clear association with serious clinical events such as death, MI, and stroke does not justify the routine prophylactic use of anticoagulation in all patients," he emphasized.

Nor are routine CT scans justified after TAVR and surgical aortic valve replacement (SAVR), Makkar said: "CTs should be prompted by increased gradients or thromboembolic events."

That HALT resolved on its own means the device thrombus somehow embolized or dissolved, said discussion moderator Ajay Kirtane, MD, of Columbia University Medical Center/NewYork-Presbyterian Hospital in New York City, during a TCT press conference.

Embolic events are not always followed by clinical events, Kirtane cautioned. "When patients ask should they be scared, the answer is no."

HALT always came with partially restricted or largely immobile leaflets in the study. Such leaflet thickening was significantly more common after TAVR at 30 days (13.3% vs 5.0% with surgery, P=0.03) but not at 1 year (27.5% vs 20.2%, P=0.19).

"It may or may not have clinical significance but it conceivably could, so long-term data showing how this correlates with structural valve deterioration would be interesting," commented Robert Bonow, MD, of Northwestern University in Chicago, during the panel talk.

Bonow pointed to the Class IIa indication for oral anticoagulation up to 6 months after implant of a surgical bioprosthetic, which may partly explain the difference in early HALT rates between TAVR and SAVR.

Makkar surmised that the TAVR procedure may be causing microdamage to the leaflets during crimping and valve preparation in addition to changing the flow dynamics of the aortic route.

The PARTNER 3 substudy included more than 300 people at low surgical risk who had evaluable CTs at 30 days and 1 year. Scans were analyzed by a core lab.

Makkar's group reported that HALT and reduced leaflet motion resulted in minimal, clinically-insignificant increases in valve gradients.

This FDA-mandated substudy has "gone a long way but not answered" the question of TAVR valve thrombosis, according to panelist Michael Mack, MD, of Baylor Scott & White Health in Dallas.

Mack said he agreed with Makkar's recommendation to not give routine anticoagulation and called into question the guidelines for doing so with surgical valves. He cited the GALILEO trial of rivaroxaban (Xarelto) that had been stopped early due to an excess of early bleeding and thrombotic events after TAVR.

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