Prosthetic heart valves: Part 2 - Mitral valve stenosis

IMAGE OF THE WEEK 2014

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HEART VALVES REPLACEMENT: PART 2 - MITRAL VALVE STENOSIS

Figure 1: Chest xray of a woman who had undergone open heart surgery (presence of central sternal wires) with 2 metalic rings structures inside the heart, one verticle ring and another a horizontal disc, just above the ring to indicate both mitral and aortic valves replacement respectively.

(Click on image to enlarge)

Mitral stenosis is a condition characterised by a narrowing of the opening of the mitral valve, resulting in an obstruction of left ventricular inflow tract. Unlike the aortic valve, the mitral valve consists of 5 structural components (Annulus, chordae, papillary muscles, left ventricular wall and valvular leaflets) which can be individually affected causing stenosis but in most cases, are a combination of abnormalities of 2 or more structures. The aetiologies of mitral valve stenosis can be classified into 2 groups as shown in the table 1 below:

Table 1: Aetiologies of aortic stenosis

Neonate/Infant/Children	Acquired
Congenital mitral stenosis	Rheumatic mitral stenosis
Cor Triatriatum	Infective endocarditis with large vegetation
	non-rheumatic mitral annular calcification
	Rheumatic heart disease
	Ball valve thrombus
	malignnant carcinoid disease
	SLE
	Rheumatoid arthritis
	mucopolysaccharidosis of the Hunter-Hurler phenotype
	Fabry disease
	Whipple disease
	Methysergide therapy

The natural history of mitral valve stenosis arising from Rheumatic fever is one of life-long progressive narrowing with a latent period of 20-40 years in which the patient remains asymptomatic. From the onset of symptoms to development of disability may take up to 10 years. Normal mtral valve area is 4.0-5.0 cm². Symptomatic mitral stenosis occur when orifice area decreased down to 1.4-2.5 cm², with critical mitral stenosis occurring when orifice area is less than 1.0 cm². Signs and symptoms of mitral valve stenosis is shown in table 2.

Table 2: Signs and Symptoms of Mitral stenosis

Symptoms	Signs
Dyspnoea	Loud first heart sound
Fatigue	Diastolic murmur
Palpitation	Opening snap murmur best heard over the apex, which occurs when the leaflets are mobile. This disappears when the leaflets are rigid and calcified
Haemoptysis	Signs of right ventricular failure - RV heave, tricuspid regurgitation, hepatomegaly, ascites,
Paroxysmal Nocturnal dyspnoea	Atrial Fibrillation
	thromboembolic events (20%)

Mitral Valve Replacement

Indications for surgery is dependent on the severity of the mitral stenosis. Asymptomatic patients are not recommended for operation and should be follow up regularly to monitor progession of their disease. Symptomatic patients who are otherwise healthy should be advised to undergo surgical correction. Patients presenting with critical mitral stenosis should undergo urgent operation.

Preoperative preparations

· Blood investigations: FBC, Renal panel, LFTs, coagulation screen, cross match.

· ECG, Echocardiography to assess severity of stenosis and LV function, TOE for better assessment particularly of leaflet structures, annulus, chordae and papillary muscles.

· Coronary angiogram to exclude coronary artery disease if indicated.

· Dental check -up to repair or extract decayed tooth and resolve all dental caries.

Surgical procedures for mitral valve stenosis can be classified into 4 types as shown below in table 3:

Table 3: Choice of surgical procedures for mitral valve stenosis

Types of procedures
1) Catheter based mitral valvotomy
2) Open or closed surgical commisurotomy
3) Mitral valve repair
4) Mitral valve replacement (cases with thick anterior leaflet, calcification, mitral regurgitation, thick short chordae)	mechanical prosthesis, Bioprosthesis (stented porcine) or mitral homograft.

As shown in the chest radiograph Figure 1 and Figure 2 (annotated), this patient has bivalve replacement using both mechanical St Judes Mechanincal valves as indicated by the opaque sewing ring and 2 parallel hinge points where the carbon leaflets are attached.

Figure 2: Annotated image of Figure 1 with white arrow pointing at the aortic valve which sits horizontally to the base of the heart while the mitral valve appears as a ring and sits vertical to the base of the heart (red arrow).

(Click on image to enlarge)

Survival after MVR

· Early (hospital) mortality ranges from 2.5 - 4.0%

· 5-yr survival – 80%

· 10-yr survival – 50-80%

Predictors of Survival

· Coincident coronary artery disease (mortality 6-12%)

· Left ventricular ejection fraction

Post operative management

· Maintain INR of 2.5 – 3.5 using Warfarin for mechanical valves,

· For bioprosthesis, depending on units protocol, may need Warfarin for the first 3 months to allow for the sewing ring to endothelise before stopping Warfarin

· Cover with antibiotic Amoxycillin 1.2 g for invasive procedures where breach of epithelium may occur.

For more information on:

Mitral stenosis, please visit this link http://emedicine.medscape.com/article/155724-overview

Prosthetic heart valve, please visit this link http://emedicine.medscape.com/article/780702-overview

Images and text contributed by

Dr Ian Bickle, Department of Radiology,RIPAS Hospital

and

Dr Chong Chee Fui, Department of Surgery, RIPAS Hospital