Mitral Stenosis

Mitral stenosis is:

MS is classified:

Echocardiographic Grading of Mitral Stenosis
Measurement Mild Moderate Severe
MPG <5mmHg 6-10mmHg >10mmHg
Pressure half-time <139ms 140-219ms >220ms
Valve area 1.6-2.0cm2 1.5-1cm2 <1cm2

Epidemiology and Risk Factors

Important associations:

  • Rheumatic fever
  • Pregnancy
    Leads to early presentation with symptoms due to ↑ cardiovascular work and circulating volume.
    • Fixed CO-state leads to ↑ pulmonary hypertension
    • Cardiac failure typically occurs in third-trimester in patients with moderate-severe disease

Pathophysiology

  • ↑ Pressure gradient across the mitral valve
    Flow across mitral valve becomes the prime determinant of ventricular filling.
    • This leads to a fixed cardiac output state because:
      • ↓ Afterload does not improve subsequent ventricular filling
      • ↑ Contractility cannot improve output if the ventricle is not adequately filled prior to contraction
  • High LAP and PCWP
    • Development of class II pulmonary hypertension
    • Consequential RV dilation and RV failure
  • Low LVEDV and LVEDP
    • Typically results in LV remodelling and ↓ systolic function

Aetiology

Causes include:

  • Rheumatic Most common cause.
    • Rarer aetiology in developed countries
    • Typically worsens at the rate of 0.1-0.3cm2/year
      More rapid in cases of repeated infection.

Assessment

MS is typically well tolerated and has a long asymptomatic period that continues until LA dilation fails to compensate and pulmonary HTN ensures, leading to:

  • Pulmonary oedema
  • Fatigue

History

Examination

Diagnostic Approach and DDx

Investigations

Management

Goals of management

Resuscitation:

Specific therapy:

  • Pharmacological
    • Rate control of AF
      • β-blockers are mainstay of treatment
    • Diuresis and vasodilators (e.g. nitrates) for failure
  • Procedural
    • MVR
    • Percutaneous mitral commissurotomy
    • Balloon dilatation
  • Physical

Supportive care:

Disposition:

Preventative:

Anaesthetic Considerations

  • C
    • Maintain sinus rhythm
    • Low-normal HR to facilitate diastolic filling
    • Maintain preload
      Delicate balance.
      • Volume required due to diastolic dysfunction
      • Excessive volume will worsen pulmonary oedema
    • Maintain afterload
      As CO is fixed, reduced SVR will ↓ CPP.
    • Prevent ↑ in PVR
      Right heart function may be tenuous in the setting of pre-existing PHTN.
    • Systolic function often suppressed after replacement
      • Highly sensitive to preload changes

In mixed valvular disease, management should prioritise the most haemodynamically significant lesion. That said, in general:

  • In mixed AS and MS
    Progression is typically similar to that with pure MS and pulmonary hypertension. Considerations include:
    • Two fixed output lesions in series
    • Generally high burden of pulmonary disease
    • AS severity may be underestimated due to the ↓ AV flow
  • In mixed MS and MR
    Competing haemodynamic disease that is a common conundrum in rheumatic disease. In general:
    • In asymmetric disease, prioritise the most significant lesion
    • Otherwise aim maintenance of stable pre-induction haemodynamic parameters, i.e.:
      • Maintain normal afterload
      • Maintain normal HR
      • Maintain normal contractility
      • Avoid ↑ PVR
      • Provide adequate preload

ICU Considerations

Following MV repair or replacement:

  • Maintain preload due to existing diastolic dysfunction
  • Reduce afterload to improve forward flow
  • Right heart support may be required

Complications

  • AF
    Due to atrial dilation.
    • Leads to worsening symptoms due to:
      • Reduced diastolic time
      • Reduced atrial kick
  • Pulmonary hypertension
    Due to ↑ LAP.
  • Right heart failure
    Due to prolonged period of pulmonary hypertension.

Prognosis

  • Death
    Following symptom development there is:
    • 80% 1-year survival
    • 15% 10-year survival

References

  1. Holmes K, Gibbison B, Vohra HA. Mitral valve and mitral valve disease. BJA Educ. 2017;17(1):1-9. doi:10.1093/bjaed/mkw032