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Stuck Mitral Valve (Prosthetic Mitral Valve Thrombosis) - CICU Overview

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Incidence & Risk

• Mechanical valve thrombosis: 0.3-1.3% per patient-year in high-income countries; up to 6% per patient-year in low/middle-income settings
• Mitral and tricuspid positions are more prone than the aortic position
• Risk is similar (~2%/year) for mechanical and biologic valves when anticoagulation is adequate

• Sub-therapeutic anticoagulation (most common trigger) - low mean INR
• Atrial fibrillation
• Left atrial enlargement
• LV systolic dysfunction
• Hypercoagulable states
• Prior thromboembolism
• Valve type and design

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Symptoms

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Signs on Examination

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Diagnosis

1. Clinical Suspicion

• New symptoms + subtherapeutic INR
• Absent or muffled prosthetic valve sounds

2. Echocardiography (Primary Tool)

• Elevated transvalvular gradients (mean mitral gradient >5 mmHg suggests obstruction)
• Restricted leaflet/disc motion
• Visible thrombus (not always seen)
• Reduced valve area
• Elevated PASP

• Better visualization of thrombus size and location (anterior vs. posterior)
• Thrombus area measurement (critical for management: <0.8 cm² vs. ≥0.8 cm²)
• Assesses leaflet excursion directly
• Important: TEE may be negative if thrombi are small or if thrombus has embolized - an embolic event in a prosthetic valve patient is presumed related to the prosthesis even with negative TEE

• For mechanical valves: directly visible immobile disc/leaflet
• For bioprosthetic/TAVR valves: increased transvalvular velocity, decline in proximal-to-valve velocity ratio, leaflet thickening (HALT - hypo-attenuating leaflet thickening)

3. Cinefluoroscopy (Fluoroscopy of the Valve)

• Non-invasive, rapid, widely available
• Directly visualizes leaflet/disc opening and closing angles over several cardiac cycles
• Valve imaged en face AND at 90° angle
• Compares measured angles to manufacturer-specified normal opening/closing angles
• Fixed or restricted leaflet = diagnostic of obstruction

• Harrison's Principles of Internal Medicine 22E, Fig. 249-4, p. 1951

4. ECG-Gated Cardiac CT

• Excellent for visualizing thrombus vs. pannus
• Detects hypo-attenuating leaflet thickening (HALT) in bioprosthetic valves
• Used when echo is inconclusive

5. Laboratory

• INR - confirm sub-therapeutic anticoagulation
• CBC, renal and hepatic function
• BNP/NT-proBNP (severity of heart failure)
• Troponin (if ischemia suspected)
• Blood cultures if endocarditis considered

Thrombus vs. Pannus Differentiation

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Management

Risk Stratification (Determines Treatment)

1. Thrombus size: <0.8 cm² (small) vs. ≥0.8 cm² (large)
2. NYHA functional class / hemodynamic status

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Algorithm

Suspected PMVT
       |
  ┌────┴────┐
Shock/NYHA   NYHA I-II
III-IV        Stable
  |               |
Emergency    TEE → measure
Surgery*     thrombus size
              ┌────┴────┐
           <0.8 cm²   ≥0.8 cm²
           Small      Large
              |           |
         Fibrinolysis  Fibrinolysis
         OR UFH       (if surgery
                       not available)
                       or SURGERY

• Left-sided PMVT + cardiogenic shock
• NYHA class III-IV symptoms
• Large thrombus burden ≥0.8 cm² on TEE
• Braunwald's Heart Disease, 15th Ed., p. 821

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Fibrinolytic (Thrombolytic) Therapy

• Recent onset (<2 weeks) + NYHA class I-II + small thrombus (<0.8 cm²)
• Sicker patients with larger thrombi when surgery is not available or is too high-risk
• Right-sided PMVT (first-line)

• Slow infusion, low-dose fibrinolytic (e.g., tPA 10 mg IV bolus then 90 mg over 2 hrs; or streptokinase/urokinase regimens)
• Followed by continuous UFH infusion during transition to VKA

• Recent stroke (<2 months)
• Active internal bleeding
• Large thrombus (high embolic risk)
• NYHA III-IV with available surgery

• Serial TTE/TEE to assess response
• Monitor INR, PTT
• If unsuccessful with UFH alone → convert to fibrinolytic therapy

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Anticoagulation

• UFH infusion for small, asymptomatic or minimally symptomatic thrombi as initial therapy
• Transition to VKA (warfarin) - targeting higher INR range than baseline
• Add low-dose aspirin if not already prescribed
• Review for drug interactions and compliance
• Optimize INR to therapeutic range

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Post-Treatment

• After any fibrinolytic course: continuous UFH then transition to VKA at higher target INR ± aspirin
• Serial TTE to assess treatment response
• Long-term: compliance counseling, regular INR monitoring, patient education

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Key Points Summary for CICU

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• Braunwald's Heart Disease, 15th Ed. (Prosthetic Valve Thrombosis, p. 821)
• Harrison's Principles of Internal Medicine 22E (Cinefluoroscopy, p. 1951)
• Rosen's Emergency Medicine (Valve Thrombosis, p. 2065)
• Textbook of Clinical Echocardiography (Prosthetic Valve Thrombosis, p. 442)