MITRAL VALVE DISEASE

MITRAL STENOSIS Aetiology and pathophysiology Mitral stenosis is almost always rheumatic in origin, although in the elderly it can be caused by heavy calcification of the mitral valve apparatus. There is also a rare form of congenital mitral stenosis. In rheumatic mitral stenosis, the mitral valve orifice is slowly diminished by progressive fibrosis, calcification of the valve leaflets, and fusion of the cusps and subvalvular apparatus. The flow of blood from left atrium to left ventricle is restricted and left atrial pressure rises, leading to pulmonary venous congestion and breathlessness. There is dilatation and hypertrophy of the left atrium, and left ventricular filling becomes more dependent on left atrial contraction. Any increase in heart rate shortens diastole when the mitral valve is open, and produces a further rise in left atrial pressure; situations that demand an increase in cardiac output will also increase left atrial pressure. Exercise and pregnancy are therefore poorly tolerated. page 618 page 619 The mitral valve orifice is normally about 5 cm2 in diastole and may be reduced to 1 cm2 or less in severe mitral stenosis. Patients usually remain asymptomatic until the stenosis is approximately 2 cm2 or less. At first, symptoms occur only on exercise; however, in severe stenosis, left atrial pressure is permanently elevated and symptoms may occur at rest. Reduced lung compliance, due to chronic pulmonary venous congestion, contributes to breathlessness and a low cardiac output may cause fatigue. Atrial fibrillation due to progressive dilatation of the left atrium is very common. The onset of atrial fibrillation often precipitates pulmonary oedema because the accompanying tachycardia and loss of atrial contraction frequently lead to marked haemodynamic deterioration with a rapid rise in left atrial pressure. In contrast, a more gradual rise in left atrial pressure tends to cause an increase in pulmonary vascular resistance, which leads to pulmonary artery hypertension that may protect the patient from pulmonary oedema. Pulmonary hypertension may lead to right ventricular hypertrophy and dilatation, tricuspid regurgitation and right heart failure. Less than 20% of patients remain in sinus rhythm; many of these have a small fibrotic left atrium and severe pulmonary hypertension. All patients with mitral stenosis, and particularly those with atrial fibrillation, are at risk from left atrial thrombosis and systemic thromboembolism. Prior to the advent of anticoagulant therapy, emboli caused one-quarter of all deaths in this condition. Clinical features These are shown in Box 18.104. Symptoms 18.104 CLINICAL FEATURES OF MITRAL STENOSIS Symptoms Breathlessness (pulmonary congestion) Fatigue (low cardiac output) Oedema, ascites (right heart failure) Palpitation (atrial fibrillation) Haemoptysis (pulmonary congestion, pulmonary embolism) Cough (pulmonary congestion) Chest pain (pulmonary hypertension) Symptoms of thromboembolic complications (e.g. stroke, ischaemic limb)

Signs

Atrial fibrillation Mitral facies Auscultation Loud first heart sound, opening snap Mid-diastolic murmur Signs of raised pulmonary capillary pressure Crepitations, pulmonary oedema, effusions Signs of pulmonary hypertension RV heave, loud P2

Effort-related dyspnoea is usually the dominant symptom. Exercise tolerance typically diminishes very slowly over many years and patients often do not appreciate the extent of their disability. Eventually symptoms occur at rest. Acute pulmonary oedema or pulmonary hypertension can lead to haemoptysis. Systemic embolism may be a presenting feature.

Signs

The forces that open and close the mitral valve increase as left atrial pressure rises. The first heart sound (S1) is therefore often unusually loud and may even be palpable (tapping apex beat). An opening snap may be audible and moves closer to the second sound (S2) as the stenosis becomes more severe and left atrial pressure rises. However, the first heart sound and opening snap may be inaudible if the valve is heavily calcified.

Turbulent flow produces the characteristic low-pitched mid-diastolic murmur and sometimes a thrill (Fig. 18.89). The murmur is accentuated by exercise and during atrial systole (pre-systolic accentuation). Early in the disease, a pre-systolic murmur may be the only auscultatory abnormality, but in patients with symptoms, the murmur usually extends from the opening snap to the first heart sound. Coexisting mitral regurgitation causes a pansystolic murmur which radiates towards the axilla.

If pulmonary hypertension supervenes there may be a right ventricular heave at the left sternal edge (due to right ventricular hypertrophy) and accentuation of the pulmonary component of the second heart sound. Tricuspid regurgitation secondary to right ventricular dilatation causes a systolic murmur and systolic waves in the venous pulse.

The physical signs of mitral stenosis are often found before symptoms develop, and their recognition is of particular importance in pregnancy.

Investigations

18.105 INVESTIGATIONS IN MITRAL STENOSIS

ECG

Left atrial hypertrophy (if not in AF) Right ventricular hypertrophy

Chest X-ray

Enlarged left atrium Signs of pulmonary venous congestion

Echo

Thickened immobile cusps Reduced valve area Reduced rate of diastolic filling of LV

Doppler

Pressure gradient across mitral valve Pulmonary artery pressure Left ventricular function

Cardiac catheterisation

Assessment of coexisting coronary artery disease and mitral regurgitation

page 619

page 620

Figure 18.89 Mitral stenosis: murmur and illustration of the diastolic pressure gradient between left atrium and left ventricle. (Mean gradient is reflected by the area between LA and LV in diastole.) The first heart sound is loud, there is an opening snap (OS) and mid-diastolic murmur (MDM) with pre-systolic accentuation. Echocardiogram showing reduced opening of the mitral valve in diastole. Colour Doppler showing turbulent flow.

The ECG (Box 18.105) may show either the bifid P waves (P mitrale) associated with left atrial hypertrophy, or atrial fibrillation. There may also be evidence of right ventricular hypertrophy (pulmonary hypertension). The chest X-ray (Fig. 18.9, p. 530) may show enlargement of the left atrium and its appendage, enlargement of the main pulmonary artery and enlargement of the upper pulmonary veins and horizontal linear shadows in the costophrenic angles.

Doppler echocardiography provides the definitive evaluation of mitral stenosis (Box 18.105 and Fig. 18.89). Cardiac catheterisation has a role in assessing coexisting mitral regurgitation and coronary artery disease.

Management

Patients with minor symptoms should be treated medically, but the definitive treatment of mitral stenosis is by balloon valvuloplasty, mitral valvotomy or mitral valve replacement. Intervention should be considered if the patient remains symptomatic despite medical treatment or if pulmonary hypertension develops.

Medical management

This consists of anticoagulants to reduce the risk of systemic embolism, a combination of digoxin, β-blockers or rate-limiting calcium antagonists to control the ventricular rate in atrial fibrillation (or to prevent a rapid ventricular rate if atrial fibrillation should develop), diuretics to control pulmonary congestion, and antibiotic prophylaxis against infective endocarditis (Box 18.125, p. 633).

Mitral balloon valvuloplasty

This is the treatment of choice if the appropriate criteria are fulfilled (Box 18.106 and Fig. 18.14, p. 533). Closed or open mitral valvotomy may be used if the facilities or expertise for valvuloplasty are not available. Patients who have undergone mitral valvuloplasty or valvotomy should receive antibiotic prophylaxis against infective endocarditis and should be followed up at 1-2-yearly intervals because restenosis may occur. Clinical symptoms and signs are a guide to the severity of mitral restenosis, but Doppler echocardiography provides a more accurate assessment.

18.106 CRITERIA FOR MITRAL VALVULOPLASTY

Significant symptoms Isolated mitral stenosis No (or trivial) mitral regurgitation Mobile, non-calcified valve/subvalve apparatus on echo Left atrium free of thrombus

For further information see http://www.acc.org" target="_blank">www.acc.org, which has comprehensive guidelines on valvular heart disease.

page 620

page 621

18.107 CAUSES OF MITRAL REGURGITATION

Mitral valve prolapse Dilatation of the left ventricle and mitral valve ring (e.g. coronary artery disease, cardiomyopathy) Damage to valve cusps and chordae (e.g. rheumatic heart disease, endocarditis) Damage to papillary muscle Myocardial infarction

Mitral valve replacement

Valve replacement is indicated if there is substantial mitral reflux, or if the valve is rigid and calcified (p. 633).

MITRAL REGURGITATION

Aetiology and pathophysiology

Rheumatic disease is the principal cause of mitral regurgitation in countries where rheumatic fever is common, but elsewhere, including in the UK, other causes are more important (Box 18.107). Mitral regurgitation may also follow mitral valvotomy or valvuloplasty.

Chronic mitral regurgitation causes gradual dilatation of the left atrium with little increase in pressure and therefore relatively few symptoms. Nevertheless, the left ventricle dilates slowly and the left ventricular diastolic and left atrial pressures gradually increase as a result of chronic volume overload of the left ventricle; breathlessness and pulmonary oedema eventually supervene. In contrast, acute mitral regurgitation tends to cause a rapid rise in left atrial pressure (because left atrial compliance is normal) and marked symptomatic deterioration.

Mitral valve prolapse

This is also known as 'floppy' mitral valve and is one of the more common causes of mild mitral regurgitation. It is caused by congenital anomalies or degenerative myxomatous changes and is sometimes a feature of connective tissue disorders such as Marfan's syndrome (p. 605).

In the mildest forms of mitral prolapse, the valve remains competent but bulges back into the atrium during systole, causing a mid-systolic click but no murmur. Occasionally, multiple clicks are audible. In the presence of a regurgitant valve, the click is followed by a late systolic murmur which lengthens as the regurgitation becomes more severe. A click is not always audible and the physical signs may vary with both posture and respiration.

Progressive elongation of the chordae tendineae may lead to increasing mitral regurgitation, and if chordal rupture occurs, regurgitation may suddenly become severe. These complications are rare before the fifth or sixth decade of life.

Haemodynamically significant mitral valve prolapse can predispose to infective endocarditis and requires antibiotic prophylaxis. Mitral valve prolapse is also associated with a variety of typically benign arrhythmias, atypical chest pain and a very small risk of embolic stroke or transient ischaemic attack. Nevertheless, the overall long-term prognosis is good. An echocardiogram of mitral valve prolapse is shown in Figure 18.90.

Other causes of mitral regurgitation

Mitral valve function depends on the chordae tendineae and their papillary muscles; dilatation of the left ventricle distorts the geometry of these and may cause mitral regurgitation. Dilated cardiomyopathy and the impaired ventricular function that results from coronary artery disease are common causes of so-called 'functional' mitral regurgitation. Ischaemia or infarction of the papillary muscles may also cause mitral regurgitation. Endocarditis may lead to distortion or perforation of the valve leaflets and is an important cause of acute mitral regurgitation.

Clinical features

These are summarised in Box 18.108.

The symptoms depend on how suddenly the regurgitation develops. Chronic mitral regurgitation produces a symptom complex that is similar to that of mitral stenosis, but sudden-onset mitral regurgitation usually presents with acute pulmonary oedema.

The regurgitant jet causes an apical systolic murmur (Fig. 18.90) which often radiates into the axilla, and may be accompanied by a thrill. The first heart sound is quiet because valve closure is abnormal. Increased forward flow through the mitral valve may give rise to a loud third heart sound and even a short mid-diastolic murmur. The apex beat feels active and rocking due to left ventricular volume overload and is usually displaced to the left as a result of dilatation of the left ventricle.

18.108 CLINICAL FEATURES OF MITRAL REGURGITATION

Symptoms

Dyspnoea (pulmonary venous congestion) Fatigue (low cardiac output) Palpitation (AF, increased stroke volume) Oedema, ascites (right heart failure)

Signs

Atrial fibrillation/flutter Cardiomegaly-displaced hyperdynamic apex beat Apical pansystolic murmur ± thrill Soft S1, apical S3 Signs of pulmonary venous congestion (crepitations, pulmonary oedema, effusions) Signs of pulmonary hypertension and right heart failure

Investigations

These are shown in Box 18.109 and include chest X-ray, ECG and Doppler echocardiography. Atrial fibrillation is common, as a consequence of atrial dilatation. At cardiac catheterisation the severity of mitral regurgitation may be indicated by the size of the v (systolic) waves in the left atrial or PAW pressure trace, or by left ventriculography; however, this is not always reliable, as left atrial compliance may vary. In practice, a common problem lies in deciding on the extent to which cardiac failure is due to mitral regurgitation as opposed to impaired left ventricular function.

page 621

page 622

Figure 18.90 Mitral regurgitation: radiation of the murmur to the axilla and illustration of systolic wave in left atrial pressure. The first sound is normal or soft and merges with a pansystolic murmur (PSM) extending to the second heart sound. A third heart sound occurs with severe regurgitation. The left atrium and ventricle become dilated. A transoesophageal echocardiogram shows an example of mitral valve prolapse, with one leaflet bulging towards the left atrium (LA; arrow). This results in a jet of mitral regurgitation on colour Doppler (arrow).

18.109 INVESTIGATIONS IN MITRAL REGURGITATION

ECG

Left atrial hypertrophy (if not in AF) Left ventricular hypertrophy

Chest X-ray

Enlarged left atrium Enlarged left ventricle Pulmonary venous congestion Pulmonary oedema (if acute)

Echo

Dilated LA, LV Dynamic LV (unless myocardial dysfunction predominates) Structural abnormalities of mitral valve (e.g. prolapse)

Doppler

Detects and quantifies regurgitation

Cardiac catheterisation

Dilated LA, dilated LV, mitral regurgitation Pulmonary hypertension Coexisting coronary artery disease

Management

page 622

page 623

18.110 MEDICAL MANAGEMENT OF MITRAL REGURGITATION

Diuretics Vasodilators, e.g. ACE inhibitors (p. 549) Digoxin if atrial fibrillation is present Anticoagulants if atrial fibrillation is present Antibiotic prophylaxis against infective endocarditis

Mitral regurgitation of moderate severity can be treated medically (Box 18.110). In all patients with mitral regurgitation, high afterload may worsen the degree of regurgitation and hypertension should be treated with vasodilating drugs such as ACE inhibitors. Patients should be reviewed at regular intervals because worsening symptoms, progressive radiological cardiac enlargement or echocardiographic evidence of deteriorating left ventricular function are indications for surgical intervention (mitral valve replacement or repair). Mitral valve repair can be used to treat most forms of mitral valve prolapse and offers many advantages when compared to mitral valve replacement. Indeed, it is now advocated for severe regurgitation even in asymptomatic patients because results are excellent and early repair has been shown to prevent irreversible left ventricular damage. Commonly, mitral regurgitation accompanies the ventricular dilatation and dysfunction that accompany coronary artery disease. If such patients are to undergo coronary bypass graft surgery it is common practice to repair the valve and restore mitral valve function by inserting an annuloplasty ring to overcome annular dilatation and to bring the valve leaflets closer together. A common dilemma in patients with ventricular dilatation and mitral regurgitation is to determine which of the two abnormalities is the predominant problem. If, for example, ventricular dilatation is the underlying cause of mitral regurgitation, then mitral valve repair or replacement may actually worsen ventricular function as the ventricle can no longer empty into the low-pressure left atrium.