Valvular Heart Disease: Difference between revisions

The four cardiac valves consist of either cusps or leaflets that close to prevent the blood from flowing backwards. When pressure behind the valve builds up, the valve opens, after blood has passed through, the pressure is reduced and the valve closes, actively or passively.

Valvular heart diseases are a major burden to society and it is expected that the prevalence will increase.  

In developing countries, approximately 30 milion cases of rheumatic fever occur annually, in general before the age of 20.<cite>BurgeDeHoratius</cite>  Approximately 60% of patients will develop rheumatic heart disease, which becomes clinically evident 1 to 3 decades later.<cite>CarapetisCurrieMathews</cite> Rheumatic heart disease remains the most common cause of valvular heart disease in third world countries.  In western countries, rheumatic heart disease is the second most common cause of valvular heart disease

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All cardiac valves have similar well defined interstitial cell layers, covered by endothelium.  The three cell layers have specific features, and are named fibrose, spongiosa, and the ventricularis.  During the cardiac cycle, the spongiosa rich in glycosaminoglycans, facilitates the relative rearrangements of collagenous and elastic layers.  Valvular interstitial cells (VIC) are abundant in all layers of the cardiac valves and comprise a diverse, dynamic population of resident cells. Regulation of collagen and other matrix components is ensured by enzymes, synthesized by VICs. Integrity of valvular tissue is maintained by interaction of valvular endothelial cells (VECs) with VICs. Changes and remodeling of valvular interstitial and endothelium cell leads to changes in properties of the valve and potentially also valve function.  

[[Image:Aortic_valve_(1).gif‎|thumb|left|200px|This animation shows the aortic valve of a pig's heart.]]

The commissure between the left en non coronary leaflets is positioned along the area of mitro-aortic continuity.  The three cusps ascend towards the commissures and descend to the basal attachment with the aorta. Opening and closure of the aortic valve is a passive, pressure driven mechanism in contrast to the mitral valve.  Tissue of the aortic cusps is stretched via backpressure in diastolic phase with elongation and stretching of elastin. In the systolic phase, recoil of elastin ensures relaxation and shortening of the cuspal tissue.<cite>Rajamannan</cite> Optimal functioning of the valve requires perfect alignment of the three cusps.

The mitral valve was named after a Mitre, by Andreas Vesalius (De Humani Corporis Fabrica, 1543).<cite>Di</cite> This active valve is located at the junction of the left atrium and left ventricle. The mitral valve apparatus contains five functional components; leaflets, annulus, chordae tendineae, papillary muscles and subajacent myocardium.  The annulus is a junctional zone of discontinuous fibrous and muscular tissue that joins the left atrium and ventricle. The anterior leaflet spans about one third of the primary fibrous, anterior part of the annulus. Part of the mitral valve anterior leaflet is in direct fibrous continuity with the aortic valve annulus, the mitro-aortic continuity. The posterior, ventricular leaflet is attached to the posterior predominantly muscular half to two third of the annulus. Due to the asymmetric leaflets, the mitral valve orifice has a funnel shape.

The mitral valvular complex comprises the mitral valve apparatus and left atrial en ventricular myocardium, endocardium and the mitro-aortic continuity. It contributes to the formation of the left ventricular outflow tract. The timed passage of blood through the valve as well as the tight closure during systole is facilitated by combined actions of the mitral valvular complex.<cite>Muresian</cite>

The structure of the pulmonary valve is analogous to the aortic valve structure. The leaflets are semilunar shaped, with semilunar attachments. The pulmonary valve has no traditional annulus. Anatomically, three rings can be distinguished, superior at the sinotubular junction, at the musculoarterial junction and a third ring at the base of the sinuses.<cite>MillWilcoxAnderson</cite>

The tricuspid valve is located at the junction between the right atrium and right ventricle. The tricuspid valve apparatus consists of 3 leaflets, chordae tendinae, an anterior, posterior and often a third papillary muscle. The peripheral ends of the septal, anterosuperior and inferior or mural leaflets are referred to as commissures. The tricuspid valve has no well defined collagenous annulus. The three leaflets are attached to a fibrous elliptic shaped annulus. The direct attachment of the septal leaflet is a distinctive feature of the tricuspid valve. The prominent papillary muscles support the leaflets at the commissures.   

Valvular insufficiency, defined as reverse flow caused by failure of a valve to close completely, may result from either intrinsic disease of the valve cusps or from damage to or distortion of supporting structures without primary cuspal pathology

Chronic rheumatic valve disease is characterized by chronic, progressive deforming valvular disease. Anatomic lesions combine to varying degrees fibrous, or fibrocalcific distortion of leaflets or cusps, valve commissures and chordae tendineae, with or without annular or papillary muscle deformities.  

Stenosis results from fibrous leaflet and chordal thickening and commissural and chordal fusion with or without secondary calcification. Fusion of a commisure in an open position can cause regurgitation, as well as scarring induced retraction of chordae and leaflets.  

[[Image:Aortic stenosis rheumatic, gross pathology 20G0014 lores.jpg|thumb|400px|right|Gross pathology of rheumatic heart disease: aortic stenosis. Aorta has been removed to show thickened, fused aortic valve leaflets and opened coronary arteries from above. Autopsy, CDC/Dr. Edwin P. Ewing, Jr.]]

== Diagnostic options ==

=== Chest Radiography ===

In aortic stenosis, cardiac silhouette and pulmonary vascular distribution are normal unless cardiac decompensation is present. Post-stenotic dilatation of the ascending aorta is frequent. Calcification of the valve is found in almost all adults with severe aortic stenosis; however, fluoroscopy may be necessary to detect it. A late feature in patients with aortic valve stenosis is cardiomegaly. In patients with heart failure, the heart is enlarged, with congestion of pulmonary vasculature.  

=== Electrocardiography ===

In approximately 85% of patients with aortic stenosis, left ventricle hypertrophy, with or without repolarization abnormalities is seen on electrocardiography (ECG). Left atrial enlargement, left axis deviation and conduction disorders are also common. Atrial fibrillation can be seen at late state and in older patients or those with hypertension.  

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=== Diagnostic options ===

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Echocardiography is used to confirm the diagnosis of bicuspid aortic valve disease. Reported sensitivities and specificities of echocardiography for detecting BAV anatomy are 92% and 96% respectively. To establish the diagnosis, visualization of the aortic valve in systole in the short-axis view is essential. During diastole, the raphe can make the valve appear trileaflet. In the long-axis view, the valve often has an eccentric closure line and there is doming of the leaflets.  Transesophageal echocardiography may improve visualization of the leaflets in case of inconclusive transthoracic echocardiography.

In all patients, serial transthoracic echocardiography should be performed to evaluate the valve and disease progression.  Annual cardiac imaging is recommended for patients with significant valve lesions or with aortic root diameters >40 mm. Complete imaging of the thoracic aorta should be performed periodically for surveillance.<cite>SiuSilversides</cite>

The thoracic aorta is visualized by alternative imaging modalities such as cardiac magnetic resonance imaging (MRI) or computer tomography (CT). Both cardiac MRI and CT images can help to confirm the bicuspid anatomy of the aortic valve.   

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