What causes murmur or palpitations due to a narrowing of the mitral valve opening, also known as mitral (mitral valve) stenosis?

Narrowing of the Mitral Valve Opening Causes Murmur and Palpitations

Mitral stenosis (MS) causes characteristic middiastolic murmurs and palpitations due to turbulent blood flow across the narrowed valve opening and subsequent hemodynamic consequences. 1

Pathophysiology of Mitral Stenosis

Mitral stenosis is characterized by obstruction of left ventricular inflow resulting from narrowing of the mitral valve orifice 2. This narrowing creates:

• Restricted valve opening during diastole
• Turbulent blood flow across the valve
• Increased left atrial pressure
• Potential left atrial enlargement

These changes lead to the classic auscultatory findings and symptoms associated with mitral stenosis.

Characteristic Murmur

The murmur of mitral stenosis has specific characteristics:

• Timing: Middiastolic, often extending into presystole (when in normal sinus rhythm)
• Quality: Low-pitched, rumbling sound
• Location: Best heard at the cardiac apex
• Radiation: Minimal radiation to surrounding areas
• Associated findings: Often accompanied by an opening snap 1

The murmur occurs because blood must flow through the narrowed valve opening during diastole, creating turbulence. The American College of Cardiology/American Heart Association guidelines emphasize that diastolic murmurs are virtually always pathological and require further cardiac evaluation 3, 1.

Causes of Palpitations

Palpitations in mitral stenosis result from several mechanisms:

1. Atrial fibrillation: The most common arrhythmia in mitral stenosis due to left atrial enlargement and pressure overload 4
2. Increased heart rate: Compensatory tachycardia to maintain cardiac output
3. Irregular heartbeats: Especially during conversion between normal rhythm and atrial fibrillation
4. Pulmonary hypertension: Late consequence of severe mitral stenosis causing right heart strain

Etiologies of Mitral Stenosis

The primary causes of mitral stenosis include:

• Rheumatic heart disease: Still the most common cause worldwide (>99% of cases) 5
• Degenerative/calcific changes: Increasingly common in developed countries, especially in elderly patients 2, 6
• Congenital abnormalities: Rare cause of mitral stenosis
• Severe mitral annular calcification: Can lead to functional mitral stenosis in the elderly 6

Diagnostic Evaluation

The definitive diagnostic tool for mitral stenosis is echocardiography, which can:

• Confirm the diagnosis
• Assess severity
• Evaluate valve morphology
• Determine the presence of associated conditions 1

Clinical Pearls and Pitfalls

• Distinguishing features: The murmur of mitral stenosis can be differentiated from other murmurs by its timing, duration, quality, and response to maneuvers 1

• Common pitfalls:

  • Confusion with Austin-Flint murmur (low-pitched diastolic murmur at the apex in severe aortic regurgitation)
  • Missing the murmur in patients with low cardiac output
  • Atrial fibrillation can alter the characteristics of the murmur
  • Overlooking degenerative mitral stenosis in elderly patients 1

• Response to maneuvers:

  • Left-sided murmurs like mitral stenosis are typically louder during expiration
  • Most murmurs decrease during Valsalva maneuver
  • Most murmurs become louder with squatting 3, 1

Understanding the relationship between mitral stenosis, its characteristic murmur, and associated palpitations is essential for proper diagnosis and management of this valvular condition.