How to assess a valve in a patient with a history of mechanical aortic valve replacement?

Assessment of Mechanical Aortic Valve Prosthesis

In patients with mechanical aortic valve replacement, urgent transthoracic echocardiography (TTE) is mandatory as the first-line assessment, followed by transesophageal echocardiography (TEE) in all cases except when TTE is entirely conclusive, with particular attention to prosthetic valve dysfunction including obstruction, regurgitation, and patient-prosthesis mismatch. 1

Initial Assessment Framework

Essential Pre-Imaging Information

Before performing echocardiography, document the following critical information:

• Prosthesis specifications: Type (mechanical valve model), size, and date of implantation 1
• Clinical presentation: Symptoms (heart failure, syncope, thromboembolism), presence of new murmur, fever, or signs of endocarditis 1
• Hemodynamic parameters: Current blood pressure and heart rate at time of examination 1
• Patient metrics: Height, weight, and body surface area for indexed calculations 1
• Review operative report: Confirms prosthesis brand, model, device number, and implantation technique 1

Multimodality Imaging Algorithm

Step 1: Transthoracic Echocardiography (TTE)

• 2D imaging assessment should evaluate:

  • Prosthetic valve leaflet/occluder morphology and mobility 1
  • Sewing ring integrity and stability (assess for rocking motion indicating dehiscence) 1
  • Left ventricular size, wall thickness, systolic and diastolic function 1
  • Presence of calcification or abnormal structures on valve components 1

• Doppler hemodynamic assessment must include:

  • Peak velocity and mean transvalvular gradient (normal mechanical aortic valve shows peak velocity >2 m/s with mean gradient typically <10 mmHg) 1, 2
  • Spectral Doppler envelope characteristics (normal shows triangular envelope with short acceleration time <80 ms) 1
  • Effective orifice area (EOA) calculation using continuity equation 1, 2
  • Doppler velocity index (DVI) calculation 1

Step 2: Transesophageal Echocardiography (TEE)

• TEE is required except when TTE is entirely conclusive 1
• Prosthetic valves must be evaluated by an expert in both TTE and TEE in emergency settings 1
• 3D TEE is now the preferred modality as it provides en face viewing of the entire prosthesis and sewing ring 1
• Mid-esophageal views at 45° and 120° provide optimal short- and long-axis visualization of valve closure, opening, and regurgitation 1

Step 3: Cardiac CT When Indicated

• CT should be considered when echocardiography cannot clearly delineate anatomy in suspected paravalvular infections 1
• CT is particularly useful for mechanical valves as it is less affected by shadowing artifacts than ultrasound 1
• CT allows evaluation of occluder motion and visualization of thrombus or pannus limiting valve function 1
• Fluoroscopy should be undertaken when doubt remains regarding mechanical prosthesis function 1

Specific Dysfunction Patterns to Assess

Prosthetic Valve Obstruction

Key diagnostic features:

• Increased mean transvalvular gradients with prolonged acceleration time (AT >100 ms) and AT/ejection time ratio >0.37 suggest obstruction 1
• Direct observation of restricted occluder motion on 2D imaging 1
• Obstruction typically due to thrombosis (most common in mechanical valves) or pannus formation 1
• Fluoroscopy and/or CT should be considered if obstruction is suspected to identify thrombus or pannus 1

Critical distinction: High gradients alone do not confirm obstruction—must distinguish from patient-prosthesis mismatch (PPM) by comparing measured EOA to normal reference values for that specific prosthesis model 2

Prosthetic Valve Regurgitation

Assessment approach:

• Paraprosthetic regurgitation is more common than transvalvular regurgitation in mechanical valves 1
• Abnormal mobility/rocking of the prosthesis sewing ring nearly always implies severe paraprosthetic regurgitation 1

Severity grading for paraprosthetic leaks:

• Measure extent of prosthetic circumference showing leakage on short-axis views 1
• >20% of circumference indicates severe regurgitation 1
• Premature mitral valve closure indicates catastrophic aortic prosthetic regurgitation 1
• New paraprosthetic leakage in acute setting is predominantly due to endocarditis, though vegetations are frequently absent 1

Imaging technique:

• Parasternal short-axis view best determines origin (central vs. paravalvular) 1
• Posterior jets may be masked by prosthetic shadowing in parasternal views—carefully examine apical views 1
• 3D TEE provides en face view enabling accurate determination of number and location of dehiscence areas 1

Patient-Prosthesis Mismatch (PPM)

Diagnostic criteria:

• Suspect PPM when persistent symptoms occur after valve replacement with high prosthetic velocity/gradient (mean >20 mmHg) and small indexed EOA (≤0.85 cm²/m²) 2
• Severe PPM defined as iEOA <0.65 cm²/m²; moderate PPM as iEOA 0.65-0.85 cm²/m² 2

Assessment algorithm:

1. Calculate EOA using continuity equation from TTE 2
2. Index EOA to body surface area 2
3. Compare to normal reference values for specific prosthesis model 2
4. If TTE inadequate or discordant, proceed to TEE 2
5. Assess left ventricular hypertrophy regression and function 2

Prosthetic Valve Endocarditis

High-risk indicators requiring urgent evaluation:

• Persistent fever without bacteremia or new murmur in prosthetic valve patient 1
• TEE has lower sensitivity for prosthetic endocarditis compared to native valve endocarditis—serial studies are paramount 1
• CT is reasonable to evaluate paravalvular abscess extent and anatomic consequences when TEE is equivocal 1
• New paraprosthetic regurgitation with valve instability, even without visible vegetations, suggests endocarditis 1

Common Pitfalls and How to Avoid Them

Technical Pitfalls

• Bileaflet mechanical valves show high velocities due to complex flow patterns and pressure recovery—do not mistake for stenosis or PPM 2
• Failure to use prosthesis-specific reference values when calculating EOA leads to misdiagnosis 2
• Inadequate LVOT measurements compromise EOA calculation accuracy—use multiple views and careful technique 2
• Anterior regurgitant jets may be under-detected on TEE due to shadowing—obtain multiple views 1

Clinical Pitfalls

• Normalization of septal motion in presence of dynamic LV with pulmonary edema/shock suggests left-sided prosthetic dysfunction 1
• Modest regurgitant volume developing acutely can cause severe symptoms despite appearing hemodynamically mild 1
• In low cardiac output states, severely stenotic valves may show only mildly elevated gradients—use acceleration time and AT/ET ratio 1
• Positive pressure ventilation significantly alters hemodynamics and echocardiographic findings 1

Diagnostic Algorithm Pitfalls

• Never rely on single imaging modality—use parallel diagnostic techniques when uncertainty exists 1
• Always compare to previous post-operative baseline studies when available 1
• In critically ill patients requiring extracorporeal support, even minor aortic regurgitation may be important and requires expert evaluation 1

Recommendations for Specific Clinical Scenarios

Acute Presentation with Hemodynamic Instability

• Urgent TTE is mandatory to define extent and mechanism of dysfunction 1
• Suspect massive prosthetic obstruction or regurgitation, plus prosthetic endocarditis if septic 1
• Look for normalization of septal motion with dynamic LV and pulmonary edema features 1
• TOE required except when TTE entirely conclusive 1

Routine Surveillance

• Establish baseline "fingerprint" study early after hospital discharge 1
• Comprehensive study indicated for new murmur or symptoms possibly related to prosthesis 1
• Document all hemodynamic parameters for longitudinal comparison 1

Pre-Intervention Planning

• Review all available imaging from different modalities as each provides valuable information on different dysfunction aspects 1
• Serial imaging allows early detection of valve degeneration 1
• Consider invasive hemodynamic assessment with high-fidelity pressure wire if non-invasive assessment remains inconclusive 3