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.]]

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Symptoms of degenerative aortic stenosis manifest with progression of the disease. The first symptoms usually commence in the seventh or eight decade. Symptoms are typically noted on exertion. Dyspnoea on exertion is the most common encountered first symptom. Other symptoms are angina, precipitated by exertion and relieved by rest, syncope and heart failure. The findings on physical examination vary with the severity of the disease. On auscultation, a systolic ejection crescendo-decrescendo murmur, radiating to the neck is audible, often accompanied by a thrill. An elevated left ventricular pressure in patients with aortic stenosis, in conjunction with mitral annulus calcifications predisposes to rupture of mitral chordae tendineae, which may produce a regurgitant systolic murmur.<cite>Brener</cite> <cite>Mihaljevic</cite>

When stroke volume and systolic pulse pressures fall in severe aortic stenosis, a pulsus parvus (small pulse) may be present. A wide pulse pressure is also characteristic of aortic stenosis. A pulsus parvus et tardus (the arterial pulse is slow to increase and has a reduced peak) can be appreciated by palpating the carotid pulse of patients with severe aortic stenosis. The stenotic valve decreases the amplitude and delays the timing of the carotid upstroke. Rigidity of the vasculature may hamper this sign in the elderly.

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.  

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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The best non-invasive diagnostic tool to confirm the diagnosis of aortic stenosis, assess the number of cusps and the annular size, is ultrasonic examination of the heart. Quantification of valvular calcification is possible. In 1998, the American college of cardiology/American Heart Association (ACC/AHA) task force <cite>Bonow</cite> recommended the diagnostic use of echocardiography.

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Although the role of computed tomography (CT) in clinical management is currently not well defined, this imaging modality could improve assessment of the ascending aorta. CT has an established role in evaluating the presence and severity of aortic root and ascending aortic dilatation in patients with associated aortic aneurysms. The high sensitivity and specificity of CT in detecting high-grade coronary artery stenosis could be useful to preoperatively rule out coronary artery disease.

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Cardiac MRI (CMR) has an established role in evaluating aortic root and ascending aorta anatomy. It can be used to measure the aortic valve area, but the role of CMR in the management of aortic stenosis is currently not well defined.  

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Cardiac catheterization remains the gold standard to detect coronary artery disease. Currently, in patients with aortic stenosis, cardiac catheterization is most often performed to identify the presence of concomitant coronary artery disease (CAD). In patients with inconclusive noninvasive tests, hemodynamic abnormalities can be assessed by cardiac catheterization. Coronary angiography is recommended prior to aortic valve replacement.  

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Since aortic stenosis is a progressive disease, most common in the elderly population, many patients with aortic stenosis do not recognize gradually developing symptoms and cannot differentiate fatigue and dyspnea from aging and physical deconditioning. Lifestyle modification may mask symptoms. Although contraindicated in patients with severe aortic stenosis, Exercise testing is useful for risk stratification and eliciting symptoms. Under supervision, it is reasonable to propose exercise testing in patients >70 years who are still highly active.  

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For many years the standard of care for patients with significant aortic valve stenosis has been to provide antibiotic prophylaxis against infective endocarditis.  However, current AHA guidelines for prevention of infective endocarditis no longer recommend antibiotic prophylaxis for this group of patients. Exceptions are patients with a prior episode of endocarditis, patients with prosthetic valves or with additional complex cardiac lesions with a high risk for the development of endocarditis.  Patients who have had rheumatic fever should still receive antibiotic prophylaxis against recurrences of rheumatic fever  

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The infinitive treatment for aortic valve stenosis is aortic valve replacement.  

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In 2002, the first transcatheter aortic valve implantation was performed by Dr. Alain Cribier <cite>Cribier</cite>. A transcatheter aortic valve implantation is a less invasive treatment option for patients at prohibitive risk for conventional aortic valve replacement.  In this technique, the native valve is not excised. After balloon valvuloplasty, the prosthetic valve is implanted in the aortic position, with the frame of the prosthesis covering the native valve. The bioprosthesis can be implanted retrograde or antegrade. Currently 4 different approaches may be used in this technique. (table…). Transcatheter aortic valve implantation is assessed in randomized clinical trials and registries.  

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Aortic valve stenosis has a severe prognosis when any symptoms are present, with survival rates of only 15–50% at 5 years. Strongest predictors of poor outcome in the elderly population are  high New York Heart Association (NYHA) class (III/IV), associated mitral regurgitation and left ventricular dysfunction. Survival is only 30% at 3 years with the combination of these three factors.  

[[Image:Heart bicuspid aortic valve.svg|thumb|right|400px|Heart bicuspid aortic valve anatomy by Patrick J. Lynch, medical illustrator, 2006]]  

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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Life expectancy in adult patients with bicuspid aortic valve disease is not shortened when compared to the general population. 10-year survival in asymptomatic adults with bicuspid aortic valve disease with a spectrum of valve function, was 96%.<cite>Tzemos</cite> In asymptomatic adults with bicuspid aortic valve disease without significant valve dysfunction the 20-year survival was 90%.<cite>Michelena</cite>

A variety of aetiologies can cause aortic regurgitation by preventing proper coaptation of the aortic valve leaflets with a subsequent diastolic reflux of blood from the aorta into the left ventricle. Etiology of aortic regurgitation can be primary valvular, or it can be primarily caused by aortic root or disease.   

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Surgical intervention can improve the functional capacity and long-term survival of patients with mitral stenosis substantially. Survival rates of 96% and freedom from valve-related complications of 92% at 15 years have been reported.<cite>Antunes</cite> Surgery should be performed before New York Heart Association (NYHA) class III symptoms are present.  

Mitral valve regurgitation results from inadequate mitral leaflet coaptation during systole. This allows the systolic regurgitation of blood from the high-pressure LV to the normally low-pressure LA. The regurgitating volume depends on both the size of the regurgitant orifice and the pressure gradient between the left ventricle and the left atrium. In primary mitral regurgitation, inadequate mitral leaflet coaptation results from an abnormality in any of the functional components of the mitral apparatus. Secondary or functional mitral regurgitation results from left ventricle disease and remodeling.  

For most patients, mitral valve surgery is performed for the relief of symptoms or to prevent worsening of asymptomatic left ventricular dysfunction.   

Tricuspid stenosis (TS) is most commonly of rheumatic origin and combined with tricuspid regurgitation. The anatomical characteristics are similar to those of mitral stenosis, including fibrous leaflet thickening and fusion and shortening of the subvalvular apparatus. The preponderance of cases is in young women. Other aetiologies of right atrial obstruction are rare and include congenital tricuspid atresia, right atrial tumors and carcinoid syndrome

The normal valve area of the tricuspid valve is 7–8cm2. Reduction of valve area to <2 cm2 causes a pressure gradient. A small diastolic pressure gradient (<5 mmHg), gradient between the right atrium and ventricle can be present due to tricuspid stenosis. The gradient is increasing on inspiration. A mean pressure gradient >5mmHg is considered indicative of significant TS and is usually associated with symptoms  

A tricuspid opening snap and a characteristic mid-diastolic murmur may be audible along the left sternoid border on auscultation. Carvallo’s sign, an increase of murmur intensity on inspiration, may be present. Distention of jugular veins, ascites, pleural effusion and peripheral edema may be present due to increased right atrial pressures.

The therapeutic approach for tricuspid regurgitation is dictated by the aetiology of the regurgitation and overall condition of the patient.  In a limited number of patients percutaneous balloon tricuspid dilatation has been performed. This is a treatment option in cases of isolated and pure tricuspid stenosis, but it frequently induces regurgitation.<cite>Vahanian1</cite> Tricuspid balloon valvotomy, combining commissurotomy leaflet augmentation and annuloplasty, can be used to treat tricuspid stenosis; however, with this treatment the potential for inducing severe tricuspid regurgitation still exists. A biological prosthesis is preferred in case of tricuspid valve replacement,since it heas satisfactory long-term durability and mechanical prosthesis caries a higher risk of thrombosis.

Functional tricuspid regurgitation results from distortion of the architecture and coordinated actions of the tricuspid leaflets, annulus, chords, papillary muscles, and right ventricular (RV) wall. This distortion is most commonly caused by right ventricular dilation and dysfunction from left sided heart disease with pressure/volume overload conditions.  

Surgical options for tricuspid regurgitation include annuloplasty or valve replacement with a mechanical valve or bioprosthesis. Functional tricuspid regurgitation may be repaired by suture annuloplasty (De Vega procedure) or by ring annuloplasty. Longterm outcomes of ring annuloplasty are superior to those of suture annuloplasty. Annuloplasty can be optimized by the use of intraoperative transesophageal echocardiography. Bioprostheses are generally preferred above mechanical prostheses for the tricuspid position, as mentioned in the section about tricuspid stenosis.

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Pulmonary valve replacement is indicated if the patient is not suitable for balloon valvuloplasty or surgical valvotomy.  

   

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