What are the risks, assessment criteria, and alternative options to consider before performing redo mitral valve surgery?

Redo Mitral Valve Surgery: Risk Assessment and Management

Redo mitral valve surgery carries significantly elevated operative mortality (11.1% vs 6.5% for primary surgery) and morbidity, but can be performed safely with careful patient selection, risk stratification, and consideration of minimally invasive or transcatheter alternatives in appropriate candidates. 1

Key Risk Factors for Poor Outcomes

The following factors independently predict major morbidity and 30-day mortality in redo mitral valve surgery:

• Cardiogenic shock increases risk 10-fold (OR 10.3) and represents the highest-risk scenario 1
• Severe tricuspid insufficiency more than doubles mortality risk (OR 2.3) 1
• Urgent or emergent status increases risk by 80% (OR 1.8) 1
• Concurrent CABG increases risk 2.4-fold 1
• NYHA Class IV symptoms significantly predict 30-day mortality 2
• Active infective endocarditis predicts both short and long-term mortality 2
• Need for postoperative dialysis strongly predicts 30-day mortality 2
• Higher STS risk scores predict long-term mortality 2

Preoperative Assessment Criteria

Mandatory Evaluation

Transthoracic echocardiography must document:

• Left ventricular ejection fraction (LVEF), with dysfunction defined as <60% in primary MR patients 3, 4
• Left ventricular end-systolic dimension (LVESD ≥40 mm indicates need for intervention) 3
• Pulmonary artery systolic pressure (>50 mmHg is concerning and warrants closer evaluation) 3, 4
• Severity and mechanism of recurrent mitral pathology 5

Additional required studies:

• BNP/NT-proBNP levels to assess ventricular dysfunction, with markedly elevated levels and LVEF <25% representing a relative contraindication 5
• CT angiography to assess vascular anatomy, identify patent grafts, evaluate chest wall thickness, and detect calcified aorta 5, 6
• Transesophageal echocardiography if TTE is inadequate or complex pathology suspected 5

Risk Stratification Categories

Low-risk patients (can proceed with standard care):

• Asymptomatic with stable prosthetic valve function 4
• LVEF >50% 4
• No pulmonary hypertension 4
• Controlled atrial fibrillation 4

Moderate-risk patients (require enhanced monitoring and cardiology input):

• Mild symptoms (NYHA Class I-II) 4
• LVEF 30-50% 4
• Mild-moderate pulmonary hypertension 4

High-risk patients (mandatory cardiology consultation, consider deferring if unstable):

• NYHA Class III-IV symptoms 4, 2
• LVEF <30% 4, 2
• Severe pulmonary hypertension 4
• Prosthetic valve dysfunction 4
• Active endocarditis 2
• Cardiogenic shock 1

Alternative Surgical Approaches

Minimally Invasive Right Thoracotomy

This approach should be strongly considered for redo mitral surgery because it:

• Avoids sternal re-entry and risk of injury to cardiac structures or patent grafts 6
• Requires limited dissection of adhesions 6
• Achieves good repair rates with low mortality 6
• Uses a 3-4 cm right minithoracotomy in the fourth intercostal space 6

Key technical considerations:

• Femoral cardiopulmonary bypass with transthoracic aortic occlusion 5
• Meticulous preoperative CT angiography to assess vascular anatomy 5
• Careful de-airing to prevent cerebrovascular injury 5
• Deliberate inspection of all ports before closure to prevent hemorrhage 5

On-Pump Beating Heart Technique

For high-risk redo patients, beating heart technique offers advantages:

• Maintains physiologic cardiac conditions throughout the procedure 7
• Uses normothermic bypass without aortic cross-clamping for mitral procedures 7
• Demonstrates lower perioperative mortality than conventional cardioplegic arrest 7
• Particularly beneficial in patients with patent grafts or calcified aorta 7

Transcatheter Options

Transcatheter mitral valve repair (TMVR) may be considered for:

• Severely symptomatic patients (NYHA Class III-IV) with chronic severe primary MR 3
• Patients with reasonable life expectancy but prohibitive surgical risk due to severe comorbidities 3
• Appropriate valve anatomy on transesophageal echocardiography 3

Critical anatomic criteria for TMVR:

• LVEF 20-50% 3
• LVESD ≤70 mm 3
• Pulmonary artery systolic pressure ≤70 mmHg 3

Repair vs Replacement Decision

Mitral valve repair remains preferred over replacement when feasible because:

• Operative mortality for repair is approximately half that of replacement 3
• LV function is better preserved with repair 3
• Repair avoids prosthetic valve-related complications (thromboembolism, anticoagulation bleeding, structural deterioration) 3

However, replacement should be chosen over a poor repair, particularly when:

• Unfavorable morphological characteristics exist 8
• High risk of MR recurrence is anticipated 8
• Active endocarditis with extensive tissue destruction is present 2

For ischemic MR specifically:

• Repair with small undersized rigid annuloplasty ring is recommended 3, 8
• Chordal-sparing techniques should be used during replacement to preserve ventricular function 8

Specific Clinical Scenarios

Prosthetic Valve Dysfunction

• Valve thrombosis and endocarditis are primary indications for reoperation following prior MVR 9
• Bioprosthetic valve degeneration typically occurs after 10-15 years 9
• Mechanical valve thrombosis despite good anticoagulation control mandates bioprosthetic valve at reoperation 3

Concomitant Procedures

• Isolated redo SMVR has significantly lower mortality than procedures requiring concomitant interventions 2
• Concurrent CABG increases operative risk 2.4-fold 1
• Severe tricuspid insufficiency should be addressed but increases mortality risk 1

Critical Pitfalls to Avoid

Do not proceed with elective redo surgery when:

• Patient is in cardiogenic shock without stabilization 1
• Active endocarditis is uncontrolled 2
• LVEF <30% without optimization of medical therapy 4
• Urgent/emergent status can be converted to elective with medical management 1

Technical hazards specific to redo surgery:

• Patent coronary grafts are at high risk for injury during sternal re-entry 6
• Dense adhesions complicate valve exposure through median sternotomy 6
• Calcified aorta increases risk of embolic events 6

Outcomes and Expectations

Contemporary results show improvement over time:

• Observed-to-expected mortality ratios improved from 1.44 to 0.72 in recent era 1
• Volume of redo mitral surgery increasing 10% per year 1
• Operative mortality ranges from 3.4-11.1% depending on patient selection 2, 1
• One-year mortality approximately 25.9% in high-risk cohorts 2

For valve repair specifically:

• Expected operative mortality <1% in ideal candidates at high-volume centers 5
• Freedom from reoperation 95% at 15-20 years 5
• Freedom from recurrent moderate-severe MR >80% at 15-20 years 5