How is patient-prosthesis mismatch (PPM) assessed intraoperatively?

Intraoperative Assessment of Patient-Prosthesis Mismatch

Patient-prosthesis mismatch (PPM) should be assessed intraoperatively by calculating the predicted indexed effective orifice area (iEOA) using the normal reference EOA of the selected prosthesis divided by the patient's body surface area, with severe PPM defined as iEOA <0.65 cm²/m² and moderate PPM as iEOA 0.65-0.85 cm²/m². 1

Preoperative Planning to Prevent PPM

The most critical assessment occurs before valve implantation, not after:

• Calculate the predicted iEOA using the normal reference EOA value for the specific prosthesis model and size being considered, divided by the patient's body surface area 1, 2
• Target an iEOA >0.85 cm²/m² to avoid clinically significant PPM 1, 3
• If the calculated iEOA will be ≤0.85 cm²/m², consider alternative strategies before proceeding 1

Intraoperative Prevention Strategies

When preoperative calculations predict PPM, implement one of these approaches:

• Select a newer generation prosthetic valve with superior hemodynamic performance and larger EOA for the same annular size 2
• Perform annular enlargement procedures to accommodate a larger prosthetic valve 1, 3
• Consider TAVR instead of surgical AVR, particularly in patients with small (<21 mm) aortic annulus, as transcatheter valves have thinner stents that minimize obstruction and reduce PPM incidence 3, 4

Immediate Post-Implantation Assessment

After valve deployment, perform echocardiographic assessment to establish baseline hemodynamics:

• Measure mean transvalvular gradient (should typically be <10 mmHg for aortic prostheses) 3
• Calculate effective orifice area using the continuity equation (stroke volume/VTI across prosthesis) 3
• Assess indexed EOA by dividing EOA by body surface area 3
• Evaluate prosthetic valve leaflet morphology and mobility to ensure normal function 2

Distinguishing PPM from Prosthetic Valve Stenosis

Critical intraoperative differentiation:

• PPM characteristics: High transprosthetic velocity and gradients with normal EOA relative to prosthesis specifications, small iEOA, and normal leaflet morphology and mobility 2
• Prosthetic stenosis characteristics: High gradients with reduced EOA compared to normal reference values for that prosthesis, and abnormal leaflet morphology or restricted mobility 2, 3

Common Pitfalls

• Bileaflet mechanical valves may show high velocities due to complex flow patterns and pressure recovery, particularly in small aortic diameters—this should not be mistaken for PPM or stenosis 3
• Failure to use prosthesis-specific reference values when calculating EOA leads to misdiagnosis; always compare measured EOA against the normal reference value for that specific prosthesis model and size 3, 2
• Inadequate LVOT measurements compromise EOA calculation accuracy; ensure LVOT diameter and velocity are recorded from the same anatomical location 3