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CHICAGO -- Hemodynamics offers clues on which low-risk patients benefit more from transcatheter aortic valve replacement (TAVR) than surgical aortic valve replacement (SAVR) -- and why.

So found secondary analyses of the Evolut Low Risk and PARTNER 3 trials presented here at the Cardiovascular Research Foundation's .

Both trials scored recent wins for TAVR overall in low-risk patients with severe aortic stenosis, whose potentially longer, more active lives present a bioprosthetic valve durability concern.

Evolut Low Risk investigators had showed non-inferiority of the self-expanding CoreValve line of TAVR bioprostheses compared against surgery, whereas the main finding of PARTNER 3 was that use of the Sapien 3 device resulted in significantly fewer events than with a surgical valve.

Echocardiographic data now available from both trials underscore the importance of prosthesis-patient mismatch -- even though its correlation with clinical outcomes may not emerge until 5 years, said session co-moderator Martin Leon, MD, of Columbia University Medical Center/NewYork-Presbyterian Hospital in New York City.

Hemodynamics in the Evolut Low Risk Trial

Gradients were lower, effective orifice areas (EOAs) were larger, and prosthesis-patient mismatch less common 1 year following TAVR than with SAVR, according to an analysis of the Evolut Low Risk Trial.

Better hemodynamics were observed at 30 days as fewer TAVR than SAVR patients showed moderate-or-severe prosthesis-patient mismatch (11.0% vs 19.9%, P<0.001) and increased mean aortic valve gradients (16.4% vs 32.3%, P<0.001), reported Mubashir Mumtaz, MD, of the University of Pittsburgh Medical Center, at a late-breaking trial session.

At 1 year, TAVR maintained numerically lower aortic valve gradients (8.6 vs 11.2 mm Hg) and higher EOAs (2.3 vs 2.0 cm²). The Doppler velocity index also favored this group at 1 year (0.6 vs 0.5, P<0.01).

The main finding from the Evolut Low Risk Trial was that TAVR was non-inferior (but not superior) to surgery in terms of combined deaths and disabling strokes at 24 months (5.3% vs 6.7%, posterior probability of noninferiority >0.999).

Mumtaz's secondary analysis included 850 trial participants (mean age around 74 years, about one-third women) who were stratified by annular size: small (<23 mm), medium (23-26 mm), and large (>26 mm).

Notably, the greatest advantage for TAVR appeared to be in smaller annuli. The surgical arm had increasing rates of prosthesis-patient mismatch (P=0.031 for trend) and increased gradients (P=0.0001 for trend) with smaller annular sizes.

TAVR treatment and larger aortic annulus perimeter independently predicted less 30-day prosthesis-patient mismatch and lower likelihood of elevated mean gradients, according to the investigators.

However, Mumtaz cautioned that each annular size group had too few patients for this to be a definitive finding, and suggested that the 33% rate of sutureless valve use in the SAVR arm might have lowered the incidence of prosthesis-patient mismatch.

In addition, the trial's Bayesian design meant that the primary endpoint was assessed when 850 out of 1,402 implanted patients reached 1-year follow-up. The full cohort dataset should be available by December, Mumtaz said.

Hemodynamics and More in PARTNER 3

Echocardiographic parameters may also help explain the superiority of TAVR in PARTNER 3, a separate presentation showed.

More TAVR patients had mild aortic regurgitation and fewer had trace regurgitation or none at 1 year compared with SAVR. However, this did not translate into more combined deaths, strokes, and rehospitalizations, according to Philippe Pibarot, DVM, PhD, of the University of Laval in Quebec.

Instead, these clinical events at 1 year were more common with characteristics more often seen in the SAVR arm:

• Flow was lower after SAVR (40.1 vs 43.2 ml/m² for TAVR, P<0.001), with a trend for more clinical events with low stroke volume index (17.0% <30 vs 10.0% for 30+, log-rank P=0.06).
• Higher valvulo-arterial impedance seen with SAVR (3.93 vs 3.73 mmHg/mL/m², P=0.0001) was associated with more events (13.5% vs 9.0% with Zva 4+ vs less, log-rank P=0.04).
• Worse right ventricular (RV) systolic function seen with SAVR (1.6 vs 2.1 cm, P<0.0001) was associated with events (13.6% vs 9.3% tricuspid annular plane systolic excursion under vs over 1.6, log-rank P=0.04).

Moderate-or-greater paravalvular aortic regurgitation, severe prosthesis-patient mismatch, and high residual gradients at 30 days were not associated with primary outcome events at 1 year, Pibarot told the audience during the TVT session.

TAVR likely came out on top for multiple reasons, which may include better remodeling, better preservation of RV function, and perhaps some recovery of RV diastolic function, Pibarot said.

This 950-person analysis of PARTNER 3 was based on the as-treated TAVR and SAVR arms. The main finding of the trial was a reduction in combined deaths, strokes, or rehospitalizations at 1 year with TAVR compared to SAVR (8.5% vs 15.1%, P=0.001 for superiority).

Operators reported similar baseline patient (mean age just over 73 years, more than two-thirds men) and echocardiography characteristics between treatment groups. However, the surgery arm required longer procedure times, more concomitant procedures, and some use of aortic root enlargement.

Valve size distributions suggested that the PARTNER 3 surgeons were more aggressive than usual about sizing larger (compared to the experience in PARTNER IIA, for instance), the presenter noted.

While there were significant between-group differences in mean gradient, aortic valve area, and Doppler velocity index at 30 days, they did not translate into more events at 1 year.

Pibarot acknowledged that the assessment of structural and hemodynamic valve deterioration won't come until after the investigators complete a 10-year follow-up on these patients.