What factors based on CT (Computed Tomography) findings determine the choice of TAVI (Transcatheter Aortic Valve Implantation) valve?

CT-Based Factors for TAVI Valve Selection

The choice of TAVI valve type and size is primarily determined by annular dimensions (area, perimeter, and diameters), coronary artery heights, sinus of Valsalva dimensions, sinotubular junction measurements, valve morphology, and calcium distribution patterns on CT imaging. 1

Core Anatomical Measurements for Valve Selection

Annular Dimensions (Primary Determinant)

• Annular area (mm²) is the most critical measurement for prosthesis sizing and should be measured at the annular plane defined by the lowest insertion points of the aortic valve cusps 1
• Annular perimeter (mm) and minimum/maximum diameters provide additional sizing information 1
• Measurements should be obtained in systole (10-20% of cardiac cycle) to capture maximal dimensions, as significant dimensional changes occur throughout the cardiac cycle 2
• The circumference-derived diameter shows maximum dimension at 20% of the cardiac cycle 2

Coronary Artery Assessment

• Left main coronary artery height (mm) and right coronary artery height (mm) must be measured to assess risk of coronary obstruction 1
• Low coronary heights (<10-12 mm) represent adverse root features that may influence valve type selection 1
• Coronary ostia at 8 mm or less height carry increased risk of over-stenting 3

Aortic Root Geometry

• Sinus of Valsalva (SoV) averaged diameter (mm) should be measured across all three sinuses; for symmetric anatomies, the three values can be averaged 1
• Sinotubular junction (STJ) diameter and height must be assessed, particularly when using balloon-expandable devices 1
• When STJ diameter is smaller than anticipated transcatheter heart valve (THV) diameter, there is increased risk for STJ injury, which may favor self-expanding valve selection 1

Valve Morphology and Calcium Distribution

Morphological Classification

• Valve morphology must be categorized: tricuspid, congenital bicuspid (using Sievers classification), or functional/acquired bicuspid 1
• Bicuspid valve anatomy requires modified measurement techniques, identifying the annular plane using the two most basal cusp insertion points 1

Calcium Pattern Analysis

• Calcium distribution should be characterized as symmetric versus asymmetric, and crescent non-protruding versus bulky protruding 1
• Bulky calcification at the free edge or intramural calcification patterns influence valve type selection 1
• Presence and extent of annular and subannular calcification with specific location documentation affects deployment strategy 1

Vascular Access Considerations

Iliofemoral Assessment

• Minimal vessel diameters with location, extent of calcification (mild/moderate/severe), and tortuosity determine feasibility of transfemoral approach and may influence valve delivery system selection 1
• Horseshoe or circumferential calcium patterns at the common femoral artery access site are adverse features 1
• Anterior common femoral artery calcium has implications for closure system selection 1

Valve-Specific Selection Algorithm

Balloon-Expandable vs Self-Expanding Valves

For balloon-expandable valves:

• Require precise annular measurements with particular attention to STJ dimensions 1
• Less suitable when STJ diameter is significantly smaller than required valve size 1
• Better suited for symmetric, less calcified anatomies

For self-expanding valves:

• More accommodating for anatomies with STJ constraints 1
• May be preferred in heavily calcified or asymmetric anatomies
• Better conformability to irregular annular geometry

Special Considerations for Valve-in-Valve Procedures

Pre-VIV CT Assessment

• Determine if surgical valve is stented versus stentless, as this fundamentally changes the assessment approach 1
• For stented valves: assess relationship of uppermost aspect of surgical valve struts to STJ and coronary ostia 1
• Virtual THV to coronary (VTC) distance must be measured if stent posts extend to or above coronary ostia level 1
• VTC <4 mm indicates increased risk of coronary obstruction and may contraindicate certain valve choices 1
• When surgical valve struts end below coronary ostia level, VTC measurements are not required 1
• Stentless surgical valves should be assessed as native TAVI cases regarding coronary occlusion risk 1

Imaging Protocol Requirements

• Full cardiac cycle imaging with retrospective ECG gating is essential for accurate measurements 2
• Systolic phase (10-20% of cardiac cycle) captures maximal dimensions critical for sizing 2
• Contrast-enhanced acquisition covering at least the aortic root through iliofemoral vessels 4
• Three-dimensional volume rendering for optimal projection angle determination 3

Critical Pitfalls to Avoid

• Never measure annular dimensions in diastole only, as this underestimates true maximal dimensions and risks prosthesis undersizing 2
• Prosthesis size selection can differ in 25-75% of cases depending on which measurement method is used 2
• In bicuspid valves, failure to properly identify the annular plane using the two most basal insertion points leads to inaccurate sizing 1
• Overlooking bulky calcification patterns may result in paravalvular leak or deployment complications 1
• Inadequate assessment of coronary heights, particularly in valve-in-valve cases, risks catastrophic coronary obstruction 1