What are the considerations for Transcatheter Aortic Valve Implantation (TAVI) in patients with a small aortic annulus and left ventricular outflow tract (LVOT) calcification?

TAVI in Small Annulus and LVOT Calcification

TAVI remains feasible in patients with small annular dimensions and LVOT calcification, but requires meticulous pre-procedural CT planning, careful valve sizing with potential oversizing adjustments, and heightened awareness of annular rupture risk—particularly with protruding calcification below the non-coronary cusp. 1

Anatomical Feasibility and Device Selection

Small Annulus Considerations

• Acceptable annular dimensions are 18-25 mm for balloon-expandable valves and 20-27 mm for self-expandable devices 1, 2
• Small annular anatomy (annular size <21 mm) actually favors TAVI over SAVR in the ACC/AHA framework, as surgical annular enlargement procedures carry additional risk 1
• For annuli at the lower size limits, self-expandable valves may offer advantages given their slightly broader size range (20-27 mm vs 18-25 mm) 1
• CT-based area and perimeter measurements are mandatory over 2D echocardiographic diameter measurements alone, as the annulus is non-circular and 2D measurements systematically underestimate size 1

LVOT Calcification Assessment

LVOT calcification should be qualitatively graded as none, mild, moderate, or severe based on three key features: 1

• Circumferential extent (what percentage of the LVOT perimeter is involved)
• Depth of extension into the LVOT (upper 4-5 mm is the critical landing zone)
• Morphology: flat/adherent versus protruding nodules

The location and morphology of LVOT calcification matter more than the overall burden: 1, 3

• Calcification below the non-coronary cusp (including the intervalvular fibrosa) carries the highest risk of annular rupture 1
• Protruding nodules extending >1 mm into the LVOT lumen confer significantly higher rupture risk than flat, mural calcification 1, 4
• Calcification immediately below the annular plane is more dangerous than calcification deeper in the LVOT 1

Procedural Risks and Mitigation Strategies

Annular Rupture Risk

Annular rupture is the most feared complication in patients with LVOT calcification, with mortality rates approaching 50% when it occurs 1

Risk factors that compound each other include: 1

• Female sex
• Balloon-expandable valves (higher radial force)
• Aggressive prosthesis oversizing
• Moderate-to-severe subannular calcification, especially protruding nodules below the non-coronary cusp
• Prior chest radiation therapy

Mitigation strategy: 1

• In patients with protruding LVOT calcification, reduce the degree of oversizing or consider self-expandable valves which exert lower radial force
• Document the exact location and morphology of protruding calcification in the pre-procedural report to guide valve selection 1

Paravalvular Regurgitation

LVOT calcification independently predicts paravalvular regurgitation (PVR) after TAVI 5, 3, 4

• Moderate-to-severe LVOT calcification increases the need for pre-dilation and post-dilation to optimize valve seating 5
• Despite this, recent data from the SOLVE-TAVI trial showed no difference in 30-day or 1-year outcomes between self-expandable and balloon-expandable valves in patients with moderate-to-severe LVOT calcification 5
• Both valve types are acceptable, but asymmetric LVOT calcification (unequal distribution across cusps) is an independent predictor of significant PVR 4

Practical approach: 5, 4

• Plan for higher likelihood of pre-dilation in patients with moderate-to-severe LVOT calcification
• Accept longer fluoroscopy times as these patients require more meticulous positioning 5
• Post-dilation should be performed cautiously given the competing risks of PVR versus annular injury

Device Sizing in the Presence of LVOT Calcification

Standard oversizing principles must be modified: 1

• Systolic CT measurements of annular area and perimeter are the gold standard for sizing 1
• In patients with protruding LVOT calcification, aim for the lower end of recommended oversizing ranges (typically 10-15% by area for balloon-expandable, 5-10% for self-expandable) 1
• Never rely on 2D echocardiographic measurements alone in small annuli, as these underestimate annular size by a mean of 1.36 mm compared to TEE 1

Contraindications and When to Favor SAVR

Absolute contraindications to TAVI that may coexist with small annulus/LVOT calcification: 1, 2

• Bicuspid aortic valve (risk of incomplete deployment) 1, 2
• Asymmetric heavy valvular calcification that may compress coronary arteries 1, 2
• Apical LV thrombus 1, 2

Relative indications favoring SAVR over TAVI despite small annulus: 1

• Subaortic (LVOT) calcification is explicitly listed as favoring SAVR in the ACC/AHA framework 1
• However, this recommendation predates recent data showing equivalent outcomes with modern valve platforms 5
• In practice, extensive protruding LVOT calcification with annular dimensions at the extreme lower limit (<18-20 mm) should prompt serious consideration of SAVR with annular enlargement 1

Imaging Protocol

Mandatory pre-procedural imaging includes: 1

• Gated cardiac CT with multiphasic reconstruction to identify the systolic phase with largest annular dimensions and sharpest contour definition 1
• Qualitative description of annular and subannular calcification including morphology (flat vs protruding), circumferential extent, and relationship to each cusp 1
• Coronary ostial heights measured perpendicular from the annular plane to assess risk of coronary obstruction 1
• TEE if CT measurements are borderline or if there is concern about LVOT obstruction from septal hypertrophy 1

Clinical Outcomes

Recent high-quality data provide reassurance: 5

• The 2022 SOLVE-TAVI post-hoc analysis found that moderate-to-severe LVOT calcification (present in 34% of patients) did not increase 30-day composite adverse events or 1-year mortality with either valve type 5
• This challenges older guideline statements that listed LVOT calcification as favoring SAVR 1
• Both self-expandable and balloon-expandable valves are acceptable options, with no significant interaction between LVOT calcification severity and valve type for clinical outcomes 5

Common Pitfalls

• Undersizing the valve due to reliance on 2D echo measurements in small annuli leads to PVR; always use CT-based area/perimeter 1
• Aggressive oversizing in the presence of protruding LVOT calcification dramatically increases annular rupture risk; reduce oversizing targets 1
• Failing to document the specific location of protruding calcification (especially below the non-coronary cusp) prevents informed valve selection 1
• Assuming LVOT calcification is a contraindication to TAVI—modern data show equivalent outcomes with appropriate technique 5