What is mitral regurgitation in patients, particularly older adults or those with a history of heart disease?

What is Mitral Regurgitation?

Mitral regurgitation (MR) is a common valvular heart disease where blood flows backward from the left ventricle into the left atrium during systole, caused by failure of the mitral valve to close properly, leading to significant morbidity and mortality if left untreated. 1, 2

Fundamental Pathophysiology

The mitral valve consists of two leaflets (anterior and posterior), each divided into three scallops, and normal function requires perfect coordination between the leaflets, subvalvular apparatus, mitral annulus, and left ventricle. 2 When this coordination fails, blood regurgitates backward during ventricular contraction, creating a pressure gradient between the left ventricle and left atrium throughout systole. 3

The backward flow causes elevated left atrial and pulmonary venous pressures, leading to pulmonary congestion and shortness of breath. 4 This chronic volume overload causes left ventricular dilation and progressive contractile dysfunction, ultimately resulting in biventricular failure and death without treatment. 5

Two Distinct Disease Entities

Primary (Organic) Mitral Regurgitation

• This is a disease of the mitral valve itself, where the valve apparatus is directly pathologic. 2, 6
• Mitral valve prolapse and Barlow disease (myxomatous degeneration with excessive leaflet tissue) represent the most common causes in developed countries. 2
• Other causes include chordal rupture, papillary muscle rupture (particularly post-myocardial infarction), and infective endocarditis. 2

Secondary (Functional) Mitral Regurgitation

• This is a disease of the left ventricle, not the valve, occurring despite structurally normal leaflets. 2, 6
• Results from left ventricular enlargement and remodeling that leads to reduced leaflet closing due to geometric distortion of the subvalvular apparatus and global dilatation. 1, 7
• Differentiating between primary and secondary MR is crucial because treatment strategies differ fundamentally. 1

Clinical Presentation

Patients may be asymptomatic or present with exertional dyspnea, orthopnea, paroxysmal nocturnal dyspnea, fatigue, and heart rhythm disturbances. 4, 5 The severity of shortness of breath typically correlates with the degree of MR, though even mild-to-moderate regurgitation can cause significant symptoms in some patients, especially during exertion. 4

Physical Examination Findings

• A holosystolic murmur at the apex that begins with S1 and extends through systole, often radiating to the axilla, is the hallmark finding. 3
• A third heart sound (S3) is commonly present in severe MR due to rapid early diastolic filling from the volume-overloaded left ventricle. 3
• A diastolic flow rumble may be audible at the apex in severe MR, reflecting increased flow across the mitral valve during diastole. 3
• The combination of a holosystolic murmur, diminished S1, and an S3 at the apex strongly suggests severe mitral regurgitation. 3

Critical Diagnostic Pitfalls

In acute severe MR, the murmur may be soft or even absent despite hemodynamic catastrophe, because the non-compliant left atrium rapidly equalizes pressure with the left ventricle. 3 Any new murmur in a patient with acute cardiorespiratory symptoms mandates immediate echocardiography—do not wait. 2

Eccentric jets that impinge on the atrial wall can lose energy and may appear mild on color Doppler despite severe regurgitation—a loud holosystolic murmur and S3 should raise suspicion that echocardiography has underestimated severity. 3

Misdiagnosing shortness of breath as asthma or attributing it solely to other conditions rather than considering mitral regurgitation is a common pitfall. 4 Underestimating the severity based on echocardiography alone, particularly with eccentric jets, can lead to inadequate treatment. 4

Diagnostic Approach

Transthoracic echocardiography is the most commonly used and preferred diagnostic test for MR, answering four critical questions: mechanism, severity, cardiac effects, and suitability for intervention. 1, 2, 5 Transesophageal echocardiography is often needed to better define morphology and MR severity, and is essential for guiding transcatheter therapies. 1

Echocardiography should assess:

• The severity of regurgitation using multiple parameters
• Left ventricular and left atrial size
• Left ventricular ejection fraction (even mild reduction may indicate reduced ventricular reserve and should be taken seriously) 4
• Direction and characteristics of the regurgitant jet
• Suitability of the valve for repair versus replacement 1, 2

Cardiac magnetic resonance has been recommended by recent guidelines to quantify MR severity when the distinction between moderate and severe MR is indeterminate by echocardiography. 1

Life-Threatening Acute Presentations

Suspect papillary muscle rupture in any post-MI patient with sudden hemodynamic deterioration, even if the murmur is soft or absent. 2 This causes sudden hemodynamic deterioration with cardiogenic shock and pulmonary edema and requires emergency surgery. 2

Chordal rupture in degenerative disease presents as acute decompensation in previously stable patients. 2 Infective endocarditis can cause rapid valve destruction with acute severe MR and high risk of embolism. 2

Intra-aortic balloon pump placement is the most effective bridge to surgery in acute severe MR with cardiogenic shock—place early while preparing for definitive intervention. 2

Treatment Implications

Surgery is the only treatment proven to improve symptoms and prevent heart failure in severe MR. 2, 5 Valve repair improves outcome compared with valve replacement and reduces mortality in patients with severe organic MR by approximately 70%. 2

Shortness of breath in mitral regurgitation indicates hemodynamic significance and should prompt evaluation for potential intervention. 4 Early recognition and timely referral for mitral valve surgery significantly improve symptoms and long-term survival. 5

For secondary MR, effective medical therapy leading to reverse remodeling of the left ventricle may reduce functional mitral regurgitation, and every effort should be made to optimize medical treatment in these patients. 1 The role of isolated mitral valve surgery in patients with severe functional MR and severe LV systolic dysfunction who cannot be revascularized remains questionable. 1