What are mitral stenosis and mitral regurgitation?

Mitral Stenosis and Mitral Regurgitation: Definitions and Clinical Implications

Mitral stenosis is a pathologic narrowing of the mitral valve orifice that restricts blood flow from the left atrium to the left ventricle, while mitral regurgitation is the backward flow of blood from the left ventricle into the left atrium due to imperfect functioning of the mitral valve. 1

Mitral Stenosis

Definition and Pathophysiology

• Mitral stenosis is characterized by a reduction in the effective mitral valve area, which creates resistance to blood flow from the left atrium to the left ventricle during diastole
• Severity is classified based on three key parameters:

  Severity	MVA (cm²)	Mean Gradient (mmHg)	PASP (mmHg)
  Mild	>1.5	<5	<30
  Moderate	1.0-1.5	5-10	30-50
  Severe	<1.0	>10	>50

Clinical Manifestations

• When stenosis is mild or moderate, tachycardia can lead to severe pulmonary congestion due to reduced diastolic filling time
• Significant mitral stenosis increases the risk of heart failure 1
• Symptoms typically include dyspnea, fatigue, and potentially hemoptysis in advanced cases

Management Considerations

• Heart rate control is crucial during perioperative periods for patients with mild to moderate stenosis 1
• Balloon mitral valvuloplasty is appropriate for patients with favorable valve morphology (particularly with commissural fusion) 1
• Surgical intervention is indicated when:
  • Stenosis is severe and the patient is symptomatic
  • The patient is undergoing left-sided valve intervention 1

Mitral Regurgitation

Definition and Pathophysiology

• Mitral regurgitation is the backward flow of blood from the left ventricle into the left atrium during systole
• Can be classified as:
  • Primary (organic): Due predominantly to valvular pathology (e.g., leaflet prolapse)
  • Secondary (functional): Due mainly to ventricular remodeling and annular dilatation 1

Common Causes

• The two most common causes are:
  1. Mitral valve prolapse resulting from myxomatous degeneration
  2. Functional mitral regurgitation that complicates post-infarction left ventricular remodeling 1

Clinical Manifestations

• Severe mitral regurgitation is often manifested by:
  • Apical holosystolic murmur
  • Third heart sound
  • Diastolic flow rumble 1
• Can lead to left atrial enlargement, pulmonary hypertension, and eventually right heart failure

Management Considerations

• Patients with severe mitral regurgitation benefit from:
  • Afterload reduction
  • Diuretic administration to optimize hemodynamic stability before high-risk surgery 1
• Important to note that even mild reduction in left ventricular ejection fraction (LVEF) in patients with mitral regurgitation may indicate reduced ventricular reserve 1
• Surgical intervention is indicated for:
  • Symptomatic patients with severe primary mitral regurgitation without severe RV dysfunction
  • Asymptomatic patients with severe primary mitral regurgitation and progressive RV dilatation 1

Clinical Pearls and Pitfalls

Important Considerations

• When both mitral stenosis and regurgitation coexist, management follows recommendations for the predominant lesion 1
• The interaction between different valve lesions must be considered in assessment and management 1
• Mitral regurgitation may lead to underestimation of aortic stenosis severity due to decreased stroke volume 1

Perioperative Management

• In patients with atrial fibrillation at high risk for thromboembolism, perioperative anticoagulation with intravenous heparin or low-molecular-weight heparin should be considered 1
• Patients with mechanical prosthetic valves require careful anticoagulation management during procedures 1

Diagnostic Challenges

• Exercise or stress echocardiography provides valuable information about the hemodynamic significance of mitral stenosis 2
• A mean gradient <10 mmHg does not exclude severe mitral stenosis, particularly in patients with atrial fibrillation, enlarged left atrium, or impaired left ventricular diastolic function 2

By understanding the definitions, pathophysiology, and management principles of mitral stenosis and mitral regurgitation, clinicians can better address these conditions to reduce morbidity and mortality and improve quality of life for affected patients.