Mitral regurgitation

Mitral regurgitation

Etiology and pathology

• Mitral valve apparatus-
  • Papillary muscles
  • Chordae tendineae
  • Leaflets
  • Annulus
• Common causes of MR-
  • Rheumatic
  • MVP
  • CAD
  • Cardiomyopathy (dilated, hypertrophic)
  • IE
  • Annular calcification
• List of causes of MR-
  • Papillary muscles-
    • CAD (ischemia, MI)
    • Severe anemia
    • Shock
    • Amyloidosis
    • Sarcoidosis
    • Abscess
    • Granuloma
    • Neoplasm
    • Dilated cardiomyopathy
    • Trauma
    • Rupture (MI)
    • Parachute mitral valve
  • Chordae tendineae-
    • Idiopathic rupture
    • Myxomatous degeneration (MVP, Marfan syndrome, Ehlers-Danlos syndrome, Pseudoxanthoma elasticum)
    • Osteogenesis imperfect
    • Relapsing polychondritis
    • IE
    • Acute LV dilation due to any cause
    • Acute rheumatic fever
    • Blunt chest trauma
    • Following PTMC
  • Leaflets-
    • Rheumatic
    • Myxomatous degeneration (MVP, Marfan syndrome, Ehlers-Danlos syndrome, Pseudoxanthoma elasticum)
    • IE
    • SLE
    • Scleroderma
    • Mitral valve clefts or fenestrations
    • Trauma
    • Following PTMC
    • Atrial myxoma
  • Annulus-
    • Abscess (IE)
    • Annular calcification
    • Dilation of annulus- dilated cardiomyopathy
    • LV submitral aneurysm
  • Other causes-
    • SAM- HCM
    • Prosthetic valve-
      • Suture interruption due to surgical technique or IE
      • Strut fracture
      • Immobilized disc
      • Immobilized ball
      • Biological valve cusp perforation or degeneration
    • Hypereosinophilic syndrome
    • Endomyocardial fibrosis
• Associations of parachute mitral valve-
  • Endocardial cushion defects
  • Endocardial fibroelastosis
  • TGA
  • Anomalous origin of left coronary
• Causes of MR in IE-
  • Leaflet perforation
  • Vegetations preventing leaflet coaptation
  • Chordal rupture
  • Annular abscess
  • Chordal rupture
  • Valve retraction during healing phase
• Causes of MR in RHD-
  • Leaflet rigid and retracted
  • Chordae shortened
• Causes of MR in blunt chest trauma-
  • Leaflet damage
  • Chordal rupture
• Mitral annulus
  • Normal diameter is 10 cm
  • Normally constricts during systole
• LV submitral aneurysm-
  • Sub-Saharan Africa
  • Posterior
• Mitral annular calcification-
  • More in women
  • Risk factors for development- HT, DM, DLP
  • Increases morbidity and mortality due to associated coronary and carotid atherosclerosis
  • Causes-
    • Atherosclerosis
    • Marfan syndrome
    • Hurler syndrome
    • CRF
    • Hyperparathyrodism
    • Rheumatic heart disease
  • Mechanism of MR-
    • Lack of systolic constriction
    • Immobilization of leaflets
  • May involve conduction system- AV block, IVCD
• Chordal rupture is more common in the posterior chordae
• Posterior papillary muscle gets ischemic more commonly than the anterior one as it gets only one supply (PDA) while the latter gets two (LAD & LCx).
• Causes of MR in CAD-
  • RWMA causing tethering of PML
  • Papillary muscle ischemia
  • LV failure (see below)
• Causes of MR in LV failure-
  • Alteration of spatial relation between papillary muscles
  • Annular dilation
  • Poor annular systolic constriction
• Ischemic MR has poorer prognosis than other causes of MR- due to associated ischemia

Pathophysiology

• Factors determining regurgitant volume-
  • Regurgitant orifice
  • LV-LA pressure gradient
• Regurgitant orifice can be increased by-
  • Increasing preload
  • Increasing afterload and
  • Decreasing LV contractility
• LV-LA pressure gradient can be increased by increasing SVR.
• 50% of MR occurs before aortic valve opening

The progression of an MR with a regurgitant fraction of 50% are shown below.

	EDV	ESV	EF	TSV	FSV	LAP
N	120	50	60	70	70	10
a/c MR	140	40	70	100	50	25
c/c MR	200	60	70	140	70	15
c/c MR decom	220	100	55	120	60	25

• In acute phase, LA is non-compliant. This allows only a slight increase in EDV. ESV is decreased, though only slightly, due to low afterload as LV is able to eject into the LA which is low pressured compared to the aorta. The total stroke volume increases to a lesser degree than it does in chronic MR where the large EDV due to the compliant LA leads to a large increase. Since TSV increases only slightly, forward stroke volume falls.
• In the chronic phase, LA compliance increases and hence EDV rises. ESV rises to normal. The high EDV allows normal forward stroke volume.
• In longstanding cases, LV may decompensate due to prolonged hemodynamic overload. Then, due to incomplete LV emptying ESV increases. Also, due to drop in total stroke volume, forward stroke volume decreases.

The changes in preload and afterload are as below.

	Preload	Afterload
N	N	N
a/c MR	Increase	Decrease
c/c MR	Increase	N
c/c MR decom	Increase	Increase

• In all phases of MR, preload is increased due to increase in EDV. In acute MR, the increase is slight, in chronic MR there is a prominent increase while in chronic decompensated MR, it increases further as EDV increases further.
• Afterload is decreased in acute MR due to ejection into the LA which has lower pressure compared to the aorta. In chronic MR, due to LV dilation, the afterload increases to normal. In decompensated chronic MR, it increases to above normal.
• LV wall tension is very low in acute MR while in chronic compensated MR it is normal or high.
• MR begets MR due to increased EDV causing annular dilation.
• Myocardial oxygen demand is not much increased in MR due to normal wall tension. So myocardial ischemia is less likely in MR than in AR or AS.
• In MR, due to reduced afterload, EF is increased (EF is afterload dependent). So EF less than 60% indicates LV dysfunction.
• Increased ESV/ESD is another indicator of LV dysfunction in MR.
• LA pressure-
  • Tall v wave
  • Rapid y descent (unless coexistent MS)
  • Early diastolic pressure more than LV pressure (reason for mitral MDM)
  • Late diastolic pressure less than LV pressure (higher if coexistent MS)
  • Higher LA pressure in acute MR than in chronic MR
• LA compliance-
  • Normal or reduced-
    • Usually seen in acute MR
    • Hypertropied atrial wall
    • PVR increases in 6 to 12 months
  • Marked increase –
    • Usually seen in chronic severe MR
    • Atrial wall has little muscle, more fibrous tissue
    • PVR normal
    • AF always present
    • COP may be low
    • Moderate increase-
  • Commonest group

Symptoms

• Fatigue- due to low cardiac output
• Dyspnoea- more likely in acute MR and in chronic decompensated MR
• Right heart failure symptoms like ascites and edema- more likely in acute MR and in chronic decompensated MR
• It is important to understand that chronic MR may become symptomatic only after the onset of irreversible LV dysfunction.

Physical examination

• Sharp upstroke of pulse
• Hyperdynamic LV apex
• Palpable S3 may be present
• Parasternal late systolic impulse due to LA enlargement
• If leaflet disease is the cause of MR- soft S1
• Wide split S2- due to early A2 due to reduced LVET
• Loud P2 if PAH
• S3 – not a sign of heart failure in MR
• Mitral MDM- not a sign of heart failure in MR
• PSM-
  • Begins with S1 and extends beyond A2
  • Flat topped
  • High pitched & blowing
  • Radiates to left axilla or base (PML prolapse) or spine (AML prolapse)
  • No change with AF or VPCs
  • Little correlation between intensity of murmur and severity of MR
• Severe MR with soft or no murmur- silent MR-
  • LV dilation
  • Acute MR
  • Paraprosthetic MR
• Late systolic murmur-
  • Seen in MVP and papillary muscle dysfunction
  • Usually MR is not severe
  • S1 is not soft
• Early systolic murmur-
  • Acute MR (due to large LA v wave)
• Dynamic auscultation-
  • Non-MVP MR murmur is distinguished from MVP murmur by increase with squatting and decrease with standing (opposite with MVP).
  • MR murmur is distinguished from AS/HCM murmur by increase with isometric handgrip (opposite for AS/HCM).

Echocardiography

• Mitral annular calcification is seen between mitral valve apparatus and posterior wall.
• TEE is useful to see if repair is possible in MVP.
• Features of severe MR-
  • Effective regurgitant orifice 0.4 cm2 or more
  • Regurgitant volume 60 ml or more
  • Regurgitant fraction 50% or more
  • MR jet reaching LA posterior wall (with high aliasing velocity of course!)
  • Pulmonary vein systolic flow reversal
• MVP is defined as more than 2 mm systolic displacement of mitral leaflet into LA

ECG

• LAE, LVE

Radiography

• LAE (more than in MS)
• Interstitial edema is seen with acute MR, chronic decompensated MR or with coexistent MS.
• Annular calcium is seen as a C shaped opacity in posterior third of heart in lateral or RAO.

Cardiac MRI-

• Useful for MR quantification when echo is suboptimal

LV angiography-

• Qualitative estimation of MR- by LA opacification
• Quantitative estimation of MR- by finding total stroke volume from LV angio and forward stroke volume by Fick method; then the difference is found

Disease course

• Asymptomatic severe MS-
  • Yearly risk of cardiac death- 4%
  • 5 year chance of needing surgery- 30%
  • 10 year chance of needing surgery- almost all
  • Main series- Sarano, Rosenhek, Rosen
• MR needing surgery, but not undergoing surgery- 5 year survival is 30% – Horstkotte
• Poorer outcome in MR due to flail leaflet- annual mortality rate of 6.3%- Ling

Medical management

• Acute MR- afterload reduction with nitroprusside.
• Chronic MR- ACE inhibitors and nifedipine are used, but have not been proven to be effective in studies.

Surgery-

• Conditions in which repair of mitral valve is possible-
  • MVP
  • Chordal rupture
  • Papillary muscle dysfunction
  • Annular dilation
  • Leaflet perforation due to IE
  • Rheumatic MR in the young
• Steps of mitral valve repair in PML prolapse-
  • Reduction excision of posterior leaflet
  • Reattachment of posterior leaflet
  • Repair of posterior leaflet
  • Insertion of annuloplasty ring
• Annuloplasty ring-
  • As part of MVP repair
  • For MR due to dilated cardiomyopathy
  • For MR due to regional LV dysfunction with annular dilation
• Disadvantages of mitral replacement-
  • LV dysfunction due to loss of annular-chordal-papillary muscle continuity
  • IE risk
  • Mechanical prosthesis- thrombus, hemorrhage
  • Bioprosthesis- deterioration
• Operative mortality (STS database)-
  • Repair- 2%
  • Replacement- 6%
  • Replacement with CABG- 10 to 13%
  • Replacement in elderly- 14%
• Percutaneous mitral repair-
  • Edge to edge technique
  • Coronary sinus approach to mitral annuloplasty
• MV repair or replacement in MR with LV dysfunction-
  • Improvement in LV function- usual
  • Same LV function- less common
  • Deterioration of LV function- uncommon
• Indications for surgery-
  • Symptoms present-
    • EF > 30% + ESD ≤ 55 mm (class I)
    • EF < 30% or ESD > 55 mm + chordal preservation possible (class IIa)
  • No symptoms-
    • EF ≤ 60% (class I)
    • ESD ≥ 40 mm (class I)
    • New onset AF (class IIa)
    • Pulmonary HT (class IIa)
    • Successful MV repair highly likely (class IIa)

Acute MR

• Clinical features
  • Murmur-
    • Decrescendo- ends before A2
    • Low pitched
    • Soft
  • LV S4
  • PAH is common
  • PA v wave may cause early P2 leading to paradoxical split of S2
• Echo-
  • Severe MR jet
  • No LA or LV dilation
  • Prominent systolic motion of LV
• Medical management-
  • Afterload reduction with IV nitroprusside
  • If hypotension, all dobutamine also
  • IABP
• Surgery-
  • Needed as an emergency
  • If MI is causing papillary muscle dysfunction, if possible, defer surgery for 4 to 6 weeks. For rupture, immediate surgery is needed.