What is functional mitral regurgitation?

Functional Mitral Regurgitation

Functional mitral regurgitation is a condition where mitral valve regurgitation occurs despite structurally normal valve leaflets, resulting from abnormalities in left ventricular function or geometry that prevent proper leaflet coaptation during systole.

Definition and Mechanism

Functional mitral regurgitation (FMR) differs fundamentally from primary mitral regurgitation:

• In primary MR: The valve itself is structurally abnormal (e.g., myxomatous degeneration, rheumatic disease)
• In functional MR: The valve leaflets are structurally normal, but fail to coapt properly 1

The pathophysiology involves:

1. Left ventricular dysfunction causing:

   • Reduced closing forces on the leaflets
   • Systolic tethering of leaflets into the LV
   • Either global LV dilation/dysfunction or focal wall motion abnormalities 1

2. Mitral annular dilation due to:

   • Left ventricular enlargement
   • Left atrial dilation (especially in chronic atrial fibrillation) 1

Classification

Functional MR can be classified based on the underlying mechanism:

1. Ventricular Functional MR:

   • Most common form (especially in ischemic heart disease)
   • Involves LV remodeling and tethering of mitral leaflets
   • Typically shows Carpentier Type IIIb dysfunction (restrictive leaflet motion) 1
   • Can be:
     • Asymmetric pattern: More common with posterior infarction
     • Symmetric pattern: Seen in dilated cardiomyopathy or multiple infarctions 1

2. Atrial Functional MR:

   • Due to severe left atrial dilation
   • Seen in chronic atrial fibrillation or restrictive cardiomyopathy 1

Diagnostic Features

Key echocardiographic findings include:

• Structurally normal mitral valve leaflets
• Tethering of leaflets into the LV during systole
• "Seagull sign" - traction on the anterior leaflet by secondary chordae (in ischemic MR) 1
• Anterior leaflet override of the posterior leaflet (often misinterpreted as prolapse) 1
• Incomplete coaptation of leaflets
• Mitral annular dilation 1

Clinical Significance

Functional MR has significant clinical implications:

• Associated with poor long-term survival 1
• Often progresses slowly with gradual worsening of symptoms
• Can lead to irreversible left ventricular dysfunction
• Contributes to heart failure morbidity and mortality 1
• Creates a vicious cycle: LV dysfunction → MR → volume overload → further LV dilation → worsening MR

Proportionate vs. Disproportionate MR

An important concept in functional MR is whether the degree of regurgitation is proportionate or disproportionate to the degree of LV dilation:

• Proportionate MR: The degree of MR corresponds to the extent of LV dilation
• Disproportionate MR: The MR is more severe than would be expected for the degree of LV dilation 1

This distinction has therapeutic implications, as disproportionate MR may benefit more from valve-directed interventions.

Treatment Approaches

Treatment of functional MR focuses on both the valve regurgitation and the underlying ventricular dysfunction:

1. Medical therapy:

   • Guideline-directed medical therapy (GDMT) for heart failure is the first step
   • Includes ACE inhibitors/ARBs, beta-blockers, MRAs, SGLT2 inhibitors 1

2. Device therapy:

   • Cardiac resynchronization therapy (CRT) in eligible patients with LV dyssynchrony 1

3. Interventional approaches:

   • Transcatheter edge-to-edge repair (TEER) with MitraClip for selected patients with persistent severe MR despite optimal medical therapy 1
   • Surgical repair or replacement in selected cases

Conclusion

Functional mitral regurgitation represents a complex interplay between valvular function and ventricular geometry/performance. Unlike primary MR, the valve itself is structurally normal, with regurgitation resulting from abnormal coaptation due to ventricular or atrial pathology. Understanding this distinction is crucial for appropriate management, as treatment must address both the valve regurgitation and the underlying cardiac dysfunction.