Why is an ejection fraction of 30% a critical threshold for surgical intervention in patients with moderate mitral regurgitation undergoing Coronary Artery Bypass Grafting (CABG)?

Ejection Fraction of 30% as a Critical Threshold for Mitral Valve Surgery in Moderate Mitral Regurgitation During CABG

Surgery is indicated in patients with severe mitral regurgitation undergoing CABG when LVEF is >30%, but should only be considered in patients with LVEF ≤30% if there is evidence of myocardial viability. 1

Rationale for the 30% EF Threshold

The 30% ejection fraction threshold represents a critical decision point in surgical management for several important reasons:

For Patients with EF >30%:

• Better Surgical Outcomes: Patients with EF >30% have better tolerance of the combined procedure (CABG + mitral valve repair)
• Lower Operative Risk: Higher EF correlates with improved perioperative survival
• Greater Benefit from Mitral Repair: These patients show more significant improvement in ventricular remodeling after combined procedures

For Patients with EF ≤30%:

• Higher Surgical Risk: Combined procedures significantly increase operative mortality
• Uncertain Long-term Benefit: Limited evidence that mitral valve repair improves survival in this high-risk group
• Potential for Recovery with CABG Alone: Many patients with moderate MR and low EF show improvement in mitral regurgitation with revascularization alone 2, 3

Evidence-Based Management Algorithm

1. For severe MR with LVEF >30%:

   • Mitral valve surgery is indicated during CABG (Class I, Level C) 1

2. For moderate MR with LVEF >30%:

   • Mitral valve surgery should be considered during CABG (Class IIa, Level C) 1
   • Benefits include improved functional class and LV dimensions 4

3. For moderate MR with LVEF ≤30%:

   • CABG without mitral valve surgery may be considered if there is viability in the posteroinferior wall (Class IIb, Level B) 1
   • Mitral valve surgery may be considered only if there is evidence of viability (Class IIb, Level C) 1

4. For all patients with moderate MR:

   • Exercise echocardiography should be considered to determine the extent of ischemia and dynamic changes in regurgitation severity 1

Clinical Considerations and Caveats

Important Factors That Influence Decision-Making:

• Myocardial Viability: Critical factor for patients with EF ≤30% - surgery should only be considered with evidence of viable myocardium 1
• Comorbidities: Lower threshold for isolated CABG in high-risk patients
• MR Etiology: Functional vs. structural components of the regurgitation
• Surgical Expertise: Outcomes depend heavily on surgeon experience and center volume 1

Common Pitfalls to Avoid:

1. Overestimating Benefits: Adding mitral valve repair to CABG in patients with EF ≤30% without evidence of viability may increase mortality without improving outcomes
2. Underestimating Recovery: Some patients with moderate MR will show significant improvement after CABG alone, making additional valve surgery unnecessary 2, 3
3. Ignoring Dynamic Components: Failure to assess exercise-induced changes in MR severity may lead to inappropriate surgical decisions

Strength of Evidence

The guidelines from the European Society of Cardiology (ESC) and European Association for Cardio-Thoracic Surgery (EACTS) provide the strongest recommendations on this topic 1. These guidelines consistently identify 30% as the critical EF threshold for decision-making in patients with moderate MR undergoing CABG.

Several observational studies suggest that patients with moderate MR and severely reduced EF may benefit from CABG alone, as revascularization can improve LV function and reduce MR severity without the added risk of valve surgery 2, 3, 5.