Transcatheter Aortic Valve Implantation in Complex Anatomy: An Anatomy-Driven Framework for Bicuspid Stenosis, Pure Aortic Regurgitation, and the Small Annulus in the Era of Lifetime Management.

Background: Transcatheter aortic valve implantation is established for severe calcific tricuspid aortic stenosis, but its application in bicuspid aortic valve (BAV) stenosis, pure native aortic regurgitation (AR), and small aortic annulus anatomy remains limited by heterogeneous morphology, device-specific constraints, and uncertain long-term outcomes. These settings require decisions that extend beyond immediate procedural success to encompass coronary access, reintervention, valve durability, and associated aortopathy. This review synthesizes current evidence and proposes an anatomy-driven framework integrating imaging, device selection, procedural planning, and lifetime management. Methods: A structured narrative review was conducted in accordance with the Scale for the Assessment of Narrative Review Articles (SANRA) criteria. PubMed/MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials were searched from 1 January 2010 to 31 March 2026 for studies addressing TAVI in BAV stenosis, pure native AR, and small aortic annulus anatomy. Randomized trials, meta-analyses, multicenter registries, pivotal device studies, and guideline or consensus documents were prioritized. After screening 2663 records and assessing 330 full-text reports, 101 records were retained for qualitative synthesis. Evidence was appraised by anatomical substrate, imaging phenotype, device strategy, procedural hazards, and implications for lifetime management. Results: In BAV stenosis, contemporary registry and prospective cohort data support high device success and acceptable early and mid-term outcomes in carefully selected patients; however, calcified raphe, bulky asymmetric leaflet or left ventricular outflow tract calcification, annular eccentricity, and concomitant aortopathy identify higher-risk phenotypes that often favor surgery. Randomized evidence in younger low-risk BAV patients remains limited and exploratory, with the NOTION-2 trial showing a numerically higher 3-year composite event rate after TAVI than surgical aortic valve replacement (20.4% vs. 7.8%; hazard ratio 2.9, 95% confidence interval 0.9-9.0) in the small bicuspid subgroup. In pure native AR, lack of annular calcification and frequent root dilatation impair anchoring of conventional transcatheter heart valves, increasing risks of migration, embolization, residual AR, and second-valve implantation. Dedicated leaflet-anchoring devices have improved outcomes: in ALIGN-AR, the JenaValve Trilogy system achieved procedural success above 95% in high-surgical-risk patients, although evidence remains single-arm and nonrandomized. In small annuli, the strongest comparative evidence comes from the SMART trial, in which supra-annular self-expanding valves were non-inferior to balloon-expandable valves for the 12-month clinical composite and reduced moderate/severe prosthesis-patient mismatch at 30 days (11.2% vs. 35.3%). Across all three phenotypes, electrocardiography-gated computed tomography is fundamental for defining anchoring, sizing, calcium distribution, root and coronary anatomy, anticipated coronary re-access, and the feasibility of redo-TAVI. Surgery remains particularly relevant when aortic repair, annular/root enlargement, or a more durable lifetime strategy is required. Conclusions: TAVI is feasible in selected patients with BAV stenosis, pure native AR, and small aortic annuli, but the evidentiary strength and optimal procedural strategy differ substantially across these anatomies. Treatment should be guided by an anatomy-driven, computed-tomography-based Heart Team assessment that integrates immediate procedural feasibility with age, surgical candidacy, aortopathy, prosthesis-patient mismatch risk, coronary access, durability, and future reintervention options. Surgery remains the more established strategy for many younger, operable patients with unfavorable BAV morphology or aortopathy, AR with root dilatation, or very small annuli amenable to enlargement. Dedicated randomized trials, standardized imaging criteria, and long-term durability data are needed to refine lifetime management in complex aortic valve anatomy.