What is the cause of left-sided weakness in a patient post mitral valve (MV) repair with a normal computed tomography (CT) scan?

Post-Operative Stroke with Normal CT After Mitral Valve Repair and Maze Procedure

The most likely diagnosis is an embolic stroke that is either too small to detect on standard CT or occurred too early for CT visualization, with the primary sources being perioperative thromboembolism from atrial fibrillation, left atrial appendage manipulation during the Maze procedure, or air embolism during surgery. 1

Primary Diagnostic Considerations

Embolic Stroke Not Yet Visible on CT

• Standard CT scans may not detect acute ischemic strokes within the first 6-24 hours, particularly small embolic events, which is the most common timeframe for post-cardiac surgery neurological complications 1
• Brain MRI with diffusion-weighted imaging (DWI) is far more sensitive than CT for detecting acute ischemic stroke and should be obtained immediately if not already done 1
• Studies show that 58-100% of patients undergoing cardiac valve procedures have new brain lesions on MRI that are not visible on CT 1

Thromboembolic Sources Specific to This Surgery

Left Atrial Appendage and Maze Procedure:

• The Maze procedure involves extensive atrial manipulation and creates multiple surgical lesions that can serve as thrombogenic surfaces in the immediate post-operative period 1
• Incomplete left atrial appendage closure or residual peridevice leak occurs in 26-57% of cases and is associated with increased thromboembolism risk 1
• Blood stasis from loss of atrial contraction post-Maze, combined with surgical trauma, creates a prothrombotic state 1

Mitral Valve Repair-Related Emboli:

• Air embolization during valve repair is a well-documented cause of stroke, particularly if de-airing techniques were inadequate 1
• Debris from valve manipulation, including fibrin, calcium particles, and tissue fragments, can embolize to the brain 1
• Device-related thrombus formation can occur in 2-5% of cases, typically within 180 days post-procedure 1

Atrial Fibrillation-Related Thromboembolism:

• Even with the Maze procedure, persistence of atrial fibrillation occurs in 80% of patients who had pre-operative atrial fibrillation ≥3 months 1
• The immediate post-operative period carries the highest thromboembolism risk due to inadequate anticoagulation, inflammatory state, and potential atrial stunning 1

Immediate Diagnostic Algorithm

Step 1: Advanced Neuroimaging

• Obtain urgent brain MRI with DWI sequences to detect acute ischemic changes not visible on CT 1
• If MRI is contraindicated or unavailable, repeat CT in 24-48 hours as infarcts become visible with time 1

Step 2: Cardiac Source Evaluation

• Perform transesophageal echocardiography (TEE) to assess for:
  • Left atrial or left atrial appendage thrombus 1
  • Valve-related thrombus or vegetation 1
  • Adequacy of Maze procedure and atrial appendage closure 1
  • Patent foramen ovale or atrial septal defect 1
• Check current rhythm status and review telemetry for atrial fibrillation episodes 1

Step 3: Assess Anticoagulation Status

• Review perioperative anticoagulation adequacy - check INR, aPTT, and anti-Xa levels if on heparin 1
• Verify that therapeutic anticoagulation was achieved post-operatively 1

Critical Management Considerations

Anticoagulation Strategy:

• Warfarin with target INR 2.5-3.5 is recommended for at least 3 months post-mitral valve repair if atrial fibrillation persists 1
• The Maze procedure does not eliminate the need for anticoagulation in the immediate post-operative period, particularly if pre-operative atrial fibrillation duration was >3 months 1
• Two patients in one study developed left ventricular thrombus despite DOAC therapy, suggesting vitamin K antagonists may be superior in this population 2

Common Pitfall:

• Do not assume a normal CT rules out stroke - CT has poor sensitivity for acute ischemic stroke in the first 24 hours and misses small embolic events entirely 1
• Do not attribute neurological deficits to "post-operative delirium" without excluding stroke with MRI 1

Additional Rare Considerations:

• Metallic embolus from mechanical valve components or suture material (Cor-Knot fasteners) can occur, though this would typically be visible on CT 3
• Hypoperfusion injury from intraoperative hypotension during rapid pacing for valve deployment, though this typically causes watershed infarcts rather than focal weakness 1

Prognosis and Follow-up:

• Most post-cardiac surgery brain lesions visible on MRI disappear by 3 months, but clinical significance of subclinical lesions remains unclear 1
• Patients with severely depressed LV function (EF <30%) have a 4.4% prevalence of LV thrombus formation post-mitral valve procedures 2