How to prepare a patient with a mitral mechanical valve for surgery?

Preparing a Patient with a Mitral Mechanical Valve for Surgery

For patients with mechanical mitral valves undergoing elective surgery, discontinue warfarin 5 days preoperatively and bridge with therapeutic-dose low molecular weight heparin (LMWH) or unfractionated heparin, with the last dose given 12-24 hours before surgery, then resume anticoagulation within 24-48 hours postoperatively using IV heparin bridging to warfarin with target INR 2.5-3.5. 1, 2, 3

Risk Stratification

Patients with mechanical mitral valves are inherently high-risk for thromboembolism due to valve position and require aggressive perioperative anticoagulation management 2, 3:

• Mechanical mitral valves carry higher thrombotic risk than aortic position valves, necessitating target INR 2.5-3.5 (range 2.5-3.5) for tilting disk and bileaflet valves in the mitral position 2, 3
• Additional risk factors that further elevate thrombotic risk include: atrial fibrillation, prior systemic embolism, left atrial thrombus, heart failure, or LVEF <30% 1, 2
• If history of systemic embolization exists, target INR should be 2.5-3.5 combined with low-dose aspirin 75-100 mg daily 2, 3

Preoperative Anticoagulation Management

Warfarin Discontinuation Timeline

• Stop warfarin 5 days before surgery to allow INR to normalize to <1.5 for safe surgical hemostasis 3, 4
• Check INR 1-2 days before surgery to confirm it is <1.5; if still elevated, consider low-dose vitamin K (1-2 mg oral) 3

Bridging Anticoagulation Strategy

Initiate bridging anticoagulation when INR falls below therapeutic range (typically 2-3 days after warfarin discontinuation) 3, 4:

• Preferred option: Therapeutic-dose LMWH administered subcutaneously at home (e.g., enoxaparin 1 mg/kg twice daily or 1.5 mg/kg once daily), which was selected by 87.5% of expert clinicians for high-risk mitral valve patients 4
• Alternative: Inpatient IV unfractionated heparin with aPTT target 1.5-2.0 times control (60-80 seconds), initiated with 80 U/kg bolus followed by 18 U/kg/hour infusion 1, 3
• Discontinue LMWH 24 hours before surgery (for twice-daily dosing) or 12 hours before (for once-daily dosing) 4
• Discontinue IV heparin 4-6 hours before surgery 3

Preoperative Evaluation Requirements

Cardiac Assessment

• Transthoracic echocardiography (TTE) to assess mechanical valve function, gradients, presence of pannus or thrombus, LVEF, and pulmonary artery pressures 1, 5
• Transesophageal echocardiography (TEE) is mandatory if TTE suggests valve dysfunction, to exclude left atrial thrombus, or if complex pathology suspected 1, 5
• CT angiography to assess vascular anatomy, particularly if peripheral cannulation anticipated for cardiopulmonary bypass 1, 5

Laboratory Studies

• Complete preoperative panel within 7 days of surgery: CBC, comprehensive metabolic panel, coagulation studies (PT/INR, aPTT), type and screen 5
• BNP/NT-proBNP levels to assess ventricular function; markedly elevated levels with LVEF <25% represent relative contraindication 5
• Baseline INR to confirm subtherapeutic level (<1.5) immediately preoperatively 3

Intraoperative Considerations

• Intraoperative TEE is mandatory to assess valve function, detect air emboli during de-airing, and evaluate for complications 1, 5
• Meticulous de-airing protocols are critical to prevent cerebrovascular air embolism in patients with mechanical valves 5
• Cerebral oximetry monitoring should be used to detect hypoperfusion 1

Postoperative Anticoagulation Resumption

Immediate Postoperative Period

Resume anticoagulation within 24-48 hours postoperatively once adequate hemostasis is confirmed and bleeding risk is acceptable 1, 2, 3:

• Initiate IV unfractionated heparin (no bolus) at 18 U/kg/hour, titrated to aPTT 1.5-2.0 times control, which is safer than subcutaneous LMWH in the immediate postoperative period 1
• Begin oral warfarin within 24-48 hours postoperatively, overlapping with heparin until therapeutic INR achieved for 2 consecutive days 1, 2, 3
• Initial warfarin dosing: 2-5 mg daily (lower doses for elderly >70 years: 3 mg; younger patients <70 years: 4 mg) 2, 3

Achieving Therapeutic Anticoagulation

• Target INR for mechanical mitral valves: 2.5-3.5 2, 3
• Morning administration (10 AM) of warfarin may achieve therapeutic INR faster than evening dosing (mean 7.4 vs 8.4 days) 6
• Continue IV heparin until INR is therapeutic (2.5-3.5) for 2 consecutive days, then discontinue heparin 1, 2
• Monitor INR every 2-3 days initially until stable therapeutic range achieved, then weekly for 1 month, then monthly if consistently therapeutic 7

Common Pitfalls and Caveats

Critical Warnings

• Never use aspirin alone as bridging anticoagulation in mechanical mitral valve patients—this is inadequate and carries unacceptable thrombotic risk 1, 2
• Avoid large loading doses of warfarin postoperatively (>5 mg), as this increases bleeding risk without faster therapeutic benefit 2
• Do not delay heparin initiation beyond 48 hours postoperatively in stable patients, as thrombotic risk escalates rapidly 1, 3
• Mechanical mitral valves require lifelong anticoagulation regardless of rhythm; even with left atrial appendage closure, anticoagulation cannot be discontinued 1, 7, 2

Special Considerations

• If atrial fibrillation is present, lifelong anticoagulation is mandatory with target INR 2.5-3.5 1, 2
• For emergency surgery where bridging is not possible, consider intraoperative heparin and aggressive early postoperative anticoagulation 3
• Valve thrombosis risk is highest in the first 3 months postoperatively and during any period of subtherapeutic anticoagulation 3, 8

Follow-Up Monitoring

• Baseline TTE before hospital discharge to establish reference for future comparisons and assess valve function 5, 7
• Follow-up TTE at 3 months to reassess valve function and detect complications 5, 7
• Annual echocardiographic surveillance to monitor for pannus formation, valve dysfunction, or other complications 1, 8
• Lifelong INR monitoring with target 2.5-3.5 for mechanical mitral valves 1, 2, 3