Multi-modal bicuspid aortic valve classification: diagnostic agreement and accuracy

Abstract Introduction Bicuspid aortic valves (BAV) exist in different valvular morphotypes. A recent International Consensus Classification and Nomenclature [1] was introduced, and includes 3 types of BAV: (i) the 3-sinus fused type, additionally divided into right-left (RL), right-non-coronary (RN) and left-non-coronary (LN) cusp fusion types, (ii) the 2-sinus type, divided into latero-lateral (LL) and antero-posterior (AP) forms, and (iii) the partial-fusion (or forme fruste) type. This classification serves as unified criteria to identify BAV phenotypes, possibly enabling improved prognostic and therapeutic considerations and a better knowledge of disease progression and clinical outcomes. Purpose To quantify the relative prevalence of BAV morphotypes following this recent classification and test the diagnostic accuracy as well as the inter-observer agreement on computed tomography (CT) and transthoracic echocardiography (TTE). Methods This is a secondary analysis of patients included in a recent clinical trial that included the acquisition of both TTE and contrast-enhanced CT [2]. Two blinded observers identified BAV morphotypes accounting for the number of Valsalva sinuses by CT. In case of disagreement, by discussion and consensus. Two observers also identified the number of sinuses, the fusion phenotypes and the presence of partial fusion in TTE studies. Results Data from 146 patients from 9 clinical centers were used. Patients were mostly middle-aged (median and inter-quartile age 45 [38-53] years) men (81%). Nineteen patients (13%) showed a two-sinus BAV. On CT, a 92.5% inter-observer agreement on the presence of 2 vs 3-sinus BAV was obtained. As compared with CT-based consensus, the diagnostic accuracy for 2 vs 3-sinus BAV on TTE was 88.4%. The errors consisted of missing 2-sinus BAV (over 17 errors, 16 (94%) where missing a 2-sinus form), resulting in a low sensitivity, as only 16% of 2-sinus BAV were correctly identified. Of note, both observers missed the same 16 2-sinus BAV on TTE, thus resulting in a 100% inter-observer agreement. The inter-observer agreement of 3-sinus fusion types on TTE was 93%, with disagreement mainly due to differences between RL and RN fusions (7/10 disagreements, 70%). The inter-observer agreement of partial fusion on TTE was 96.6%, with only 5 patients classified differently by the two experts. Conclusions The inter-observer agreement in the application of the new BAV International Consensus Classification and Nomenclature by TTE is high. However, given that a substantial number of 2-sinus BAV are missed by TTE, multi-modal imaging should be considered when this distinction has clinical relevance for decision-making.