Causes

Congenital aortic stenosis

Congenital AS is usually due to a bicuspid valve. A bicuspid valve in itself does not give rise to significant hemodynamic abnormality, but it has a tendency to calcify and a predisposition to infective endocarditis (see Table 2).

Table 2

Clinical signs in aortic stenosis and aortic regurgitation.

Physical signs

• The carotid pulse is slow rising with reduced amplitude.
• The venous pressure is usually normal until late in the disease.
• The apex beat is sustained and can be doubled due to an additional atrial component.
• On auscultation, the second heart sound is single when the valve is calcified due to a lack of aortic component. The classic ejection systolic murmur, which can radiate to one or both carotids, is usually heard best over the aortic area. A soft, early diastolic murmur of aortic regurgitation (AR) often coexists.

Investigation and management

Echo is the diagnostic tool of choice for valve disease – in particular, Doppler measurement of valve gradients can quantify lesions. Significant hemodynamic changes do not occur until the aortic valve area has been reduced to a quarter of its normal size (the normal orifice is 3–4 cm²). AS is classed as:

• mild if the area is >1.5 cm²
• moderate if the area is 1–1.5 cm²
• severe if the area is <1 cm²

Severe stenosis causes a transvalvular pressure gradient of >50 mm Hg in the presence of normal transvalvular flow (ie, normal LV function). However, abnormally low pressure gradients are found in conditions of LV dysfunction, so the gradient alone is not a clear guide.

The natural history of AS is one of slow progression. Studies suggest that some patients exhibit a decrease in valve area of 0.1–0.3 cm²/year, although no progression is discernible in many patients. However, regardless of the individual variability, symptoms of angina, syncope, or heart failure generally develop after a latent period. At this point, the outlook changes dramatically. After the onset of symptoms, the average survival is less than 3 years. Thus, development of symptoms is the critical point in the natural history of AS and thereafter the benefits of surgery outweigh the risk. Consequently, asymptomatic AS patients should be monitored closely. Although there is no clear consensus, most cardiologists follow-up mild AS annually (together with 5-yearly echos); moderate AS every 6 months (together with 2-yearly echos); and severe AS more frequently (together with annual echos). If a patient with AS presents with a change in symptoms, their next appointment at the cardiology clinic should be expedited.

If a patient with severe AS is undergoing open chest bypass grafting for coexisting coronary artery disease (CAD), the opportunity should be taken to carry out aortic valve replacement (AVR) – regardless of whether or not AS symptoms are evident. The merit of carrying out a concomitant AVR is less clear for those with mild or moderate AS.

Cardiac catheterization is only indicated in AS for two reasons: (1) to perform coronary angiography before AVR in patients with risk factors for CAD; (2) to assess the severity of AS in symptomatic patients when AVR is planned or when noninvasive tests are inconclusive (catheterization allows accurate quantification of the orifice because it can account for transvalvular flow).

Contrary to popular belief, exercise testing is not contraindicated for mild to moderate AS patients and can give useful information with respect to exercise capacity, heart rate recovery, and exercise-induced rise in blood pressure.

Aortic valve replacement in the elderly

Due to the limitations of medical therapy and balloon valvotomy, AVR should be considered for all elderly patients with symptomatic AS. However, the decision as to whether to carry out AVR is rarely straightforward and must take into account the risks as viewed by both the surgeon and the patient. Comorbidity in the form of LVH or CAD greatly increases the risk associated with surgery. In addition, specific valve problems, such as heavy calcification and narrow LV outflow tract or annulus, make the procedure more complex. The decision is highly individual.

Acute aortic regurgitation

Acute AR is one hallmark of aortic dissection and is a medical emergency in its own right. A large regurgitant volume is suddenly imposed on an LV of normal size that has not had time to accommodate to the volume overload. The result is a reduction in stroke volume, compensatory tachycardia, pulmonary edema, and cardiogenic shock. Characteristic clinical findings are absent and an echo is essential to document the severity of the lesion. This is done by assessing the speed of equilibration of aortic and LV pressures in diastole. Useful echo measures are short regurgitant wave half time, short mitral deceleration time, and premature closure of the MV.

Mortality is high in acute severe AR and early surgical intervention is essential. Nitroprusside can be helpful in reducing preload and afterload, possibly in combination with dobutamine or dopamine. Intra-aortic balloon pumping is absolutely contraindicated (it increases aortic diastolic pressure and worsens the regurgitation), while β-blockers, often used in the management of dissection, should be used with caution in associated acute severe AR as they dampen the compensatory tachycardia.

Chronic aortic regurgitation

An early diastolic murmur is always justification for referral to a cardiologist for assessment and echo.

Causes

Rheumatic heart disease is the most common cause of MS, although it pre-dates the symptoms by at least 10 years. Other acquired causes are rare – eg, annular calcification, endocarditis, or granulomatous infiltration in association with eosinophilia.

Signs

Symptoms of MS generally occur during exertion, infection, stress, or with the onset of atrial fibrillation (AF) with a rapid ventricular response. This is because a left atrial (LA) pressure that is normal at rest rises with an increase in transmitral flow or a decrease in the diastolic filling time.

The most common manifestation is breathlessness, but a reduction in exercise tolerance or symptoms of right-sided congestion can also occur. The typical physical signs are described in Table 4. Figure 4 demonstrates MS in echo, electrocardiography pressure tracing, and a chest x-ray.

Table 4

The typical physical signs of mitral stenosis.

Figure 4

Mitral stenosis demonstrated by (a) echocardiography (showing thickened leaflets that no longer open), (b) electrocardiography pressure tracing in the left atrium versus left ventricle demonstrating the gradient between the two cavities (and therefore (more...)

Natural history

The disease takes a slow course with progressive acceleration later in life. In developed countries, the lag period from the time of rheumatic fever to the onset of symptoms is 20–40 years, and there is another 10 years before these symptoms become disabling. The 10-year survival rate is high for asymptomatic patients (>80%), but low for those with symptoms (0%–15%). Asymptomatic patients with mild MS (MV area >1.5 cm²) require no further evaluation and do not need to be followed up more than annually.

Percutaneous and surgical therapy

Decisions on therapy are made by joint consideration of symptoms and MV morphology (including hemodynamics and pulmonary artery pressure). Therapeutic options include MV repair (open/closed commissurotomy), MV replacement, and percutaneous valvotomy.

Both repair and percutaneous valvotomy acutely result in a doubling of the valve area and a 60% reduction in transmitral gradient. However, open commissurotomy and percutaneous valvotomy produce better long-term hemodynamic results. The current recommendations for percutaneous and surgical therapy are outlined in Table 5.

Table 5

Current recommendations for surgical therapy.

Medical therapy

Prophylaxis against rheumatic fever and endocarditis should be considered for all patients with MS. Agents with negative chronotropic properties, such as β-blockers or calcium-channel blockers, may benefit those in sinus rhythm with symptoms relating to exertional tachycardia.

Atrial fibrillation

AF develops in 40% of patients with symptomatic MS and should be treated according to standard protocols (see Chapter 8, Arrhythmia). The value of anticoagulation therapy for those with AF and those with a prior embolic event with or without AF is clear. However, there is no evidence that oral anticoagulation is beneficial in those with MS who have neither AF nor a prior embolic event. The frequency of embolic events does not seem to be related to the severity of MS, the size of the LA, or the presence of symptoms. There is some controversy over whether percutaneous mitral valvotomy should be performed in patients with new-onset AF and moderate or severe MS who are otherwise asymptomatic.

Acute mitral regurgitation

In acute severe mitral regurgitation (MR), the hemodynamic changes are not tolerated and the result is generally acute decompensation. Without time for compensatory LV and LA dilatation, the increase in ventricular preload leads to a decreased stroke volume and pulmonary congestion. However, examination findings may not be typical:

• there may be no hyperdynamic apex beat
• the systolic murmur may be short
• there may be a fourth heart sound

The most common cause of acute MR is papillary muscle rupture secondary to myocardial infarction (MI) (see Figure 5). In this situation, the principal differential diagnosis is ventricular septal defect and an echo is required to differentiate between the two. Ventricular septal defect is more likely with:

Figure 5

(a) Transesophageal echocardiography showing a tear in the papillary muscle (the most common cause of acute mitral regurgitation). (b) The same scene with a color jet from the left ventricle into the left atrium, demonstrating "blood flow" in the wrong (more...)

• right-sided radiation of murmur
• raised jugular venous pressure (JVP)
• anterior MI (inferior MI is more likely to cause acute MR)

The goal of medical therapy in acute severe MR is to diminish regurgitation, increase stroke volume, and reduce pulmonary congestion. As such, nitroprusside alone or in combination with dobutamine (if blood pressure is low) can be effective. Intra-aortic balloon pumping can also help to achieve these goals. In many cases, emergency surgery is warranted. If so, prior transesophageal echo helps to characterize the anatomy and severity of the lesion. Cardiac catheterization should be performed if the patient is at high risk for CAD.

Chronic mitral regurgitation

Causes

• Degenerative MV disease is common in the elderly. The valve leaflets are thickened, redundant, increased in area, and they prolapse into the LA in systole. The chordae may become elongated, thinned, and tortuous – predisposing to rupture.
• Infective endocarditis is a major cause of chronic MR. Vegetations developing on the cusp vary from small nodules along the line of apposition to large friable masses of up to 10 mm or more (see Figure 6). "Jet" lesions on the anterior cusp of the MV can also occur in association with aortic valve endocarditis.
• Ischemia.

Figure 6

Echocardiogram showing a vegetation on the mitral valve (arrow).

Clinical signs

The clinical signs of chronic MR are outlined in Table 6. With severe MR, the regurgitant murmur is usually short and stops at the same time as aortic valve closure. Occasionally, the murmur can hardly be heard due to early equalization of atrioventricular pressures. The signs and causes of MR are outlined in Table 3.

Table 6

The clinical signs of chronic mitral regurgitation.

Natural history

In chronic MR, the increased preload and decreased afterload of the LV (caused by ejection of some of the stroke volume into the LA) are compensated for by LV and LA dilatation, and the total stroke volume is increased (the EF is also maintained). This compensated phase of chronic MR may last for years. Eventually, however, the volume overload causes sufficient dilatation to push the LV onto the downward portion of the Frank–Starling curve and dysfunction results (see Figure 7). Importantly, the loading conditions mean that this dysfunction might not be reflected in an abnormal EF (the EF in a patient with MR and normal LV function is >60%).

Figure 7

Frank–Starling curve showing left ventricular (LV) dysfunction.

Asymptomatic patients with mild MR and no evidence of LV dilatation or dysfunction can be followed on a yearly basis and undergo echo less frequently than that. Asymptomatic patients with moderate MR should have an echo annually. Asymptomatic patients with severe MR should be followed up every 6–12 months and undergo echo to detect silent LV dysfunction. Exercise testing is useful to document changes in exercise tolerance.

The timing of surgery is determined by the EF, LV end systolic dimension (LVESD), the presence of AF, and symptoms. It is indicated for those with:

• class II–IV symptoms, EF >60%, LVESD <45 mm
• EF 30%–60%, LVESD 45–55 mm (regardless of symptoms)
• asymptomatic patients with AF and normal EF
• symptomatic patients with normal EF and pulmonary hypertension (>50 mm Hg)
• asymptomatic patients with EF 50%–60% and LVESD <45 mm, or EF >60% and LVESD 45–55 mm
• patients with EF <30% and/or LVESD >55 mm in whom the chordae tendineae are likely to be intact (ie, no previous MI in that territory)

The operation of choice is MV repair. In many patients, however, replacement of the valve together with removal of part or all of the MV apparatus (chordae) is required. The repair procedure leads to better postoperative LV function and survival.

There is no generally accepted medical therapy for chronic MR. Although vasodilators might seem a sensible choice, in fact, in compensated chronic MR the afterload is decreased (since the LV has two routes of ejection); as such, drugs that reduce the afterload further are unlikely to be beneficial.

Chronic MR can also occur due to a primary ischemic cause, relating either to LV dysfunction or to chordal ischemia – revascularization or stenting can eliminate the episodes.

Clinical signs

Physical examination is key to the diagnosis of tricuspid regurgitation. Typical signs are:

• gross fluid retention
• significant peripheral edema
• ascites that may result in nausea
• raised JVP with a prominent systolic wave and sharp Y descent
• parasternal heave and loud P2, suggesting pulmonary hypertension as a cause
• an enlarged, tender, pulsatile liver and, occasionally, mild jaundice
• a pansystolic murmur at the left lower sternal edge that is increased by inspiration

Management

Severe tricuspid regurgitation resulting from any cause is associated with a poor long-term outcome due to RV dysfunction and systemic venous congestion. The timing of surgery and the most suitable operation remain controversial, although chordal reconstruction and annuloplasty have become established in recent years. Annuloplasty involves the use of a prosthetic ring to support the endogenous dilated annulus. Valve replacement is also possible.

Medical management treats fluid retention and AF. Standard protocols are used, although high doses and combination diuretics are often required.

Mitral stenosis

Penicillin prophylaxis should be continued in pregnant women with MS. The cautious use of diuretics and β-blockers in those with mild to moderate disease can prevent tachycardia and optimize diastolic filling. For women with severe disease, a percutaneous balloon valvotomy prior to conception should be considered. Those who develop class III–IV symptoms during pregnancy should also undergo valvotomy. This can be achieved with very limited fluoroscopy or appropriate shielding.

Mitral regurgitation

The usual cause of MR is MVP; this rarely requires treatment.

Aortic stenosis

The most likely cause of AS in a woman of childbearing age is congenital bicuspid disease. Mild to moderate obstruction can be managed conservatively throughout pregnancy, whereas those with severe disease (eg, gradient >50 mm Hg, LV function likely to be normal) should be advised to delay conception until treatment is obtained.

Aortic regurgitation

AR can usually be managed medically with a combination of diuretics and vasodilator therapy. As with MR, surgery should be contemplated during pregnancy for the control of class III–IV symptoms.

Anticoagulation in pregnancy

Warfarin crosses the placenta and has been associated with an increased incidence of spontaneous abortion, fetal deformity, prematurity, and stillbirth. The incidence is probably around 5%–10%. In contrast, heparin does not cross the placenta and is generally safer. However, it is associated with a higher degree of thromboembolic complications. The evidence base for decision making is not good, and the decision should be made in partnership with the patient after explaining the risks involved. Most change from warfarin to heparin at week 36 in anticipation of labor.