Bentall procedure in the small aortoannular complex: impact of the implantation plane on prosthesis upsizing and early outcomes—a retrospective cohort study

Proximal conduit geometry may affect prosthesis accommodation during Bentall surgery for severe aortic stenosis and a small aortoannular complex. We compared subannular-supported supra-annular conduit implantation (SSSC) with supra-annular-supported annular conduit implantation (SSAC) for nominal size gain and early outcomes. This retrospective cohort included 402 adults undergoing mechanical Bentall surgery between January 2020 and April 2026 (SSSC, n = 164; SSAC, n = 238). After leaflet excision and annular debridement, the largest manufacturer sizer accepted before suture/pledget placement defined the presuture expected size; repeat sizing after interrupted pledgeted sutures guided final conduit selection. The primary endpoint was implanted nominal size minus presuture expected size. Preoperative computed tomography characterized anatomy without conversion to nominal size, and body-size variables were recalculated from corrected measurements. Routine transthoracic echocardiography on postoperative days 5–7 measured continuity-equation effective orifice area (EOA), indexed EOA (EOAi), prosthesis–patient mismatch (PPM), and Doppler gradients. The 24-patient narrow sinotubular junction–proximal ascending aorta subgroup was analyzed separately. SSSC yielded larger implanted size (23.4 ± 1.4 vs. 22.0 ± 1.1 mm) and nominal size gain (3.3 ± 1.1 vs. 1.9 ± 0.9 mm; both p < 0.001). After adjustment for corrected body size, baseline anatomy, and patient characteristics, SSSC remained associated with 0.99 mm greater gain (95% CI, 0.78–1.19; p < 0.001), higher EOA (+ 0.108 cm²) and EOAi (+ 0.063 cm²/m²), and lower odds of moderate PPM (adjusted odds ratio, 0.15; all p < 0.001). The adjusted mean-gradient difference was nonsignificant and the peak-gradient difference small. Permanent pacemaker implantation was more frequent after SSSC (7.9% vs. 2.1%; p = 0.007), whereas mortality was similar. SSSC was associated with approximately 1 mm greater adjusted nominal size gain and more favorable early prosthesis–patient hemodynamics than SSAC, without demonstrated overall clinical superiority. The higher pacemaker rate warrants longer-term evaluation. Not applicable. This retrospective observational study did not prospectively assign participants to a health-related intervention.