CT-Based Annulus Sizing Index Calculator

CT-Based Annulus Sizing Index: Explanation and Clinical Context The CT-Based Annulus Sizing Index is a quantitative parameter used to assess the relationship between the native aortic annulus size (derived from CT imaging) and the selected transcatheter heart valve (THV) size. It provides an objective measure of oversizing or undersizing during pre-procedural transcatheter aortic valve replacement (TAVR) planning. The annulus-derived diameter is calculated as the annulus perimeter divided by π, allowing for a circular-equivalent comparison to the nominal valve diameter.

The sizing index is expressed as a percentage: ((Valve Diameter – Annulus Derived Diameter) / Annulus Derived Diameter) × 100. Clinically, an oversizing index between 0–10% is generally considered optimal for balloon-expandable valves, while slightly higher values (up to 15%) are tolerated for self-expanding valves due to their gradual expansion and conformability. Excessive oversizing (>15%) may lead to annular rupture or conduction abnormalities, whereas undersizing (<0%) increases the risk of paravalvular leak and device migration.

CT-based annular sizing has become a cornerstone of modern TAVR planning, offering superior reproducibility and accuracy compared to echocardiography. Integration of perimeter and area-derived measurements enhances procedural safety and long-term valve performance.