Definitions of small aortic annuli on transcatheter aortic valve implantation from the TOTO-TAVI study

Background Small aortic annuli (SAA) have long been recognised as a risk factor for patient-prosthesis mismatch (PPM) and a poor prognostic factor. However, while 430 mm², as analyzed by multi-detector computed tomography (MDCT), is frequently used to define SAA, a clear definition remains scarce. Furthermore, previous studies have often used the same 430 mm² definition for all individuals without considering regional variations in aortic valve anatomy. Purpose This study aimed to redefine SAA and to clarify the impact of SAA on outcomes following transcatheter aortic valve implantation (TAVI). Methods The TOTO-TAVI study included patients who underwent TAVI in a university hospital and a clinic, from March 2024 to September 2025. The primary endpoint was the early safety. A subgroup analysis was performed to identify the independent risk factors of short-term outcomes using multivariate analysis. Results A total of 790 patients (385 from Japan and 405 from France) were included. When the definition of SAA in France was less than 430 mm², 189/405 (47%) cases met the criteria for SAA. Therefore, in this study, SAA was defined as less than 385 mm² to ensure that SAA patients constituted 47 % (180/385) in Japan. Overall, Japan and France showed differences in all patient background factors, with notable variations observed in age (83.9±6.1 vs. 82.8±6.2), gender (male: 42.6 % vs. 57.8 %), body mass index (22.3±3.8 kg/m² vs. 27.3±5.1 kg/m²), STS-PROM score (6.6 [3.7-10.3] % vs. 3.5 [2.3-5.7] %), and left ventricular ejection fraction (62.0±10.7 % vs. 59.1±11.6 %). Regarding anatomical differences by MDCT, patients in Japan demonstrated smaller anatomy than those in France in the annulus, left ventricular outflow tract, sinotubular junction, sinus of valsalva, both coronary arteries height, and both femoral arteries diameter (all p<0.001). However, considering annulus-perimeter-derived diameter adjusted for height, patients in Japan showed larger than those in France (14.6±1.1 mm/m vs. 14.5±1.2 mm/m, p=0.024). The early safety was comparable between patients in Japan and in France, both overall and in the SAA group (overall: 81.3 % vs. 77.5 %, p=0.19; SAA: 76.7 % vs. 75.7 %, p=0.82). The other in-hospital outcomes, including mortality and the incidence of PPM, showed no significant differences between Japan and France, both overall and in the SAA group. For subgroup analysis, SAA was not significantly associated with independent risk factors for the early safety (odds ratio: 1.4; 95% confidence interval: 0.84-2.4, p=0.19). Conclusions Considering body size, the definition of SAA for patients in Asia should be used as less than 385 mm². Given that short-term outcomes after TAVI between Asia and France showed no significant difference, including safety endpoints and the incidence of PPM, TAVI has the potential for highly favourable results even in patients with SAA.