Mitral regurgitation

Question 1

Define mitral regurgitation

Answer 1

Retrograde flow of blood from LV to left atrium during systole

Question 2

What is the pathophysiology of mitral regurgitation?

Answer 2

Acute MR:
Regurgitated blood from LA enters back into LV → less space for more blood to enter from pulmonary veins and LA → pulmonary venous congestion (rapid) → pulmonary oedema

Chronic (compensated) MR:
Progressive dilation of the LV (eccentric hypertrophy) → increased volume capacity of the LV → allows more blood to enter from the pulmonary veins and LA (reduces congestion) → LV fills with more blood so higher preload → increases SV and CO

Chronic (decompensated) MR:
Eccentric hypertrophy → dilated cardiomyopathy → heart muscle cannot contract as efficiently → reduced SV and CO → left heart failure

LV cannot empty as efficiently → less space for more blood to enter from pulmonary veins and LA → pulmonary venous congestion → pulmonary oedema

(possibly: pulmonary oedema → pulmonary hypertension → right heart failure)

Question 3

What is the aetiology of mitral regurgitation?

Answer 3

• Rheumatic heart disease (most common)
• Infective endocarditis
• Mitral valve prolapse (inversion of mitral valve leaflets into the left atrium during systole)

Mitral valve prolapse can be caused by:

• MI → papillary muscle rupture
• Connective tissue disorders (e.g. osteogenesis imperfecta, Ehlers–Danlos syndrome, Marfan syndrome, SLE) → affects chordae tendinae
• Left ventricular dilation (left heart failure)
  → stretches mitral valve annulus → pulls apart valve leaflets → valve can’t close properly → regurgitation

Question 4

What is the epidemiology of mitral regurgitation?

Answer 4

Affects 􏰀approx. 5% of adults

Mitral valve prolapse is more common in young females

Question 5

What are the symptoms of mitral regurgitation?

Answer 5

Acute MR:
May present with symptoms of left ventricular failure (pulmonary oedema → DYSPNOEA)

Chronic MR:

• May be asymptomatic
• Exertional dyspnoea
• Fatigue
• Palpitations if in AF

Regurgitated blood from LA enters back into LV → less space for more blood to enter from pulmonary veins and LA → LA volume overload and dilation → fibrosis → promotes reentry circuits → AF

Mitral valve prolapse:

• Asymptomatic
• Atypical chest pain
• Palpitations (due to AF)

Question 6

What are the signs of mitral regurgitation?

Answer 6

Pulse:

• Normal
• Irregularly irregular if AF

Palpation:

• Apex beat may be laterally displaced and thrusting (left ventricular dilation)
• Murmur palpable as a thrill over mitral area

Auscultation:

General MR:
Pansystolic murmur
- loudest at apex
- radiating to axilla
- S1 is soft (because mitral valve does not close properly)
- S3 may be heard (in early diastole the ventricle fills rapidly as regurgitated blood from the LA flows back into the LV)

Pansystolic as blood flows back from LV to LA throughout the whole of systole

Mitral valve prolapse:

• Mid-systolic click (due to the leaflet inverting into the LA and being suddenly stopped by the chordae tendinae - stretched to its max)
• Late systolic murmur (due to bloodflow from LV to LA)

The click moves:

• towards S1 on standing
• away from S1 on lying down or squatting

Lying down → increased venous return to heart due to lack of effect of gravity → increased preload and LV dilation → maintains the tension in the chordae tendineae and keeps the valves closed for longer)

Question 7

What investigations would you do for mitral regurgitation?

Answer 7

1st line - echocardiogram and ECG

ECG:

• Normal
• Shows AF
• Broad bifid p wave (p mitrale) indicating delayed activation of LA (compared to RA) due to left atrial enlargement

Echocardiography:
Every 6–12 months for moderate to severe MR to assess:
- LV ejection fraction
- end-systolic dimension of the LV

CXR:

Acute MR:
May produce signs of left ventricular failure
(i.e. signs of pulmonary oedema)

Chronic MR:

• LA enlargement
• Cardiomegaly (caused by LV dilation)
• Mitral valve calcification in rheumatic cases (inflammation → calcification)