Prosthetic heart valves: Part 1

IMAGE OF THE WEEK 2014

IMAGE 5

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 4 structural components (Annulus, chordae, papillary muscles and 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 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 acquired aortic stenosis is one of progressive narrowing with a latent period of 10-20 years in which the patient remains asymptomatic. Once symptoms developed which consists of a triad of chest pain, heart failure and syncope, indicating moderate-to-severe aortic stenosis, the patient’s condition usually deteriorate rapidly and death can occurred within 3 years if left untreated, with a mortality of approximately 25% at 1 year and 50% at 2 years. Severe aortic stenosis is defined as an aortic valve orifice area of less than 1.2cm2/M2 or an LV to Ao gradient greater than 50mmHg.

Clinical signs of aortic stenosis include:

· Pulsus alternans due to presence of left ventricular systolic dysfunction

· Ejection click due to stiffness of aortic leaflets due to calcification which snaps open when force by the jet of blood passing through the aortic valve orifice

· Ejection systolic murmur

· Signs of LV hypertrophy includes ECG changes of large amplitude R wave, LBBB or RBBB, ST depression or T wave invertion.

· There may be signs suggestive of coronary artery disease

Aortic Valve Replacement

Indications for surgery is dependent on the severity of the aortic stenosis. For symptomatic patients, the aortic stenosis is usually moderate to severe and will need prompt aortic valve replacement to avoid sudden death or rapid deterioration. For mild aortic valve stenosis, operation is not urgent but patients should be regularly followed up to assess condition as disease progresses.

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 root and sinotubular dimension as well as in endocarditis for root abscess.

· Coronary angiogram to exclude coronary artery disease if indicated.

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

There are several choices of replacement valves and are indicated based on age (Table 2). The main categories are divided into 2 groups: mechanical and tissue valves.

Table 2: Choice of aortic valve replacement

Age	Valve Choice	Brand available
< 55years	Aortic allograft or pulmonary allograft (homograft)
55-75 years	Mechanical valves	St. Judes, Carbomedics, Metronic Hall, ATS Open Pivot valves and On-X and Conform-X valves.
>75 years	Bioprosthesis valves, stented or stentless	Carpentier-Edwards Porcine tissue valve, Carpentier-Edwards bovine perimont valves, Hancock aortic bioprosthesis.

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 AVR

· Early (hospital) mortality ranges from 3-6%

· 5-yr survival – 75%

· 10-yr survival – 60%

· 15-yr survival – 40%

Predictors of Survival

· Age – Advanced age significant predictor of survival and cardiac events

· Pre-op LV function

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:

Aortic stenosis, please visit this link http://emedicine.medscape.com/article/150638-overview#a0156

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