Rheumatic mitral stenosis: Background and pathophysiology
Many young women are not aware that they have rheumatic heart disease: the initial presentation of rheumatic mitral stenosis is often during pregnancy when women become symptomatic for the first time, so there is usually no opportunity to try to improve prepregnancy care or to treat the mitral stenosis preconception.
Mitral stenosis is particularly poorly tolerated in pregnancy because the tachycardia and increased stroke volume of pregnancy combined with impaired diastolic flow through the stenotic valve tend to increase left atrial pressure and impair cardiac output. The resulting dyspnea and pulmonary edema are further exacerbated if atrial fibrillation occurs. Furthermore, the development of pulmonary venous hypertension may precipitate right ventricular failure. Delivery and the immediate puerperium are particularly hazardous, since the tachycardia and rapid fluid shifts that occur may precipitate pulmonary edema.
A further significant risk factor is that rheumatic fever among people born in the UK is now very rare; those that have it are usually first-generation immigrants. They may already be socially disadvantaged, with poor access to health care and communication difficulties, all of which are independent risk factors for a poor pregnancy outcome.[3] Furthermore, with the decline in the incidence of rheumatic heart disease, a new generation of UK-trained doctors has little experience of diagnosing and treating mitral stenosis in either the pregnant or nonpregnant patient. This may lead to a delay in or failure of diagnosis, and/or to incorrect therapy, risking a poor outcome.
History and examination
There is frequently no known history of rheumatic fever. For those with known mitral stenosis, 40% experience worsening symptoms during pregnancy.[4] Exertional dyspnea can develop during the second trimester or even earlier, and exercise tolerance deteriorates as the pregnancy progresses and the circulating blood volume rises. Orthopnea, dry cough, paroxysmal nocturnal dyspnea, and pulmonary edema may develop, sometimes precipitated by tachyarrhythmia (usually atrial fibrillation). The average time of onset of pulmonary edema has been reported to be around 30 weeks of gestation.[4]
The woman may be breathless on minor exertion with a dry “high left atrial pressure” cough exacerbated by lying flat. Orthopnea is common, along with tachycardia, an elevated venous pressure, and classical signs of mitral stenosis.
Investigations
The chest radiograph may show pulmonary venous congestion or frank pulmonary edema and a dilated left atrium; it is useful to have a chest X-ray to exclude other lung pathology. The electrocardiogram (ECG) will confirm the rhythm; there may be signs of right atrial hypertrophy. Transthoracic echocardiography shows the severity of mitral stenosis and the suitability for balloon dilatation; it can also identify and quantify any associated lesions. It should be noted that valve area is a more reliable tool than pressure gradient for assessing mitral stenosis severity (Table 13.1) in pregnancy. Although the continuity equation for assessing severity of mitral stenosis is valid in pregnancy, the pressure half time method is influenced by loading conditions and thus may result in underestimating the severity of mitral stenosis in pregnancy.
| Severity | Mitral valve area (cm2) |
|---|---|
| Mild | >1.5 |
| Moderate | 1.0–1.5 |
| Severe | <1.0 |
Treatment
The mainstay of medical management is to reduce the heart rate to allow time for left ventricular filling. This is achieved in women with mild and moderate mitral stenosis by bedrest, oxygen therapy, beta-blockade, and a diuretic. If atrial fibrillation occurs, therapeutic-dose low-molecular-weight heparin anticoagulation should be given and the sinus rhythm restored promptly (see Chapter 18). Similarly, patients with prior embolic events or known left atrial appendage thrombus should be anticoagulated.[5]
The rheumatic mitral valve in women of childbearing age is usually suitable for balloon dilatation if there is no more than mild associated regurgitation. In experienced hands, the procedure has about a 95% success rate [6–8], although there is a small risk of embolism and stroke, and heparin anticoagulation is therefore advisable to cover the procedure. Procedural transesophageal echocardiography should be used to exclude left atrial appendage thrombus and reduce the need for fluoroscopy. Radiation doses to the fetus can be reduced a little further with maternal abdominal screening. With an experienced operator, fluoroscopy times should be limited to 5–8 min (see Chapter 8).[7–9] The risk of developing acute mitral regurgitation such that emergency mitral valve replacement is necessary is low in centers with high-volume experience; however, on-site facilities for emergency cardiac surgery must be available. Mitral valvotomy in pregnancy should only be undertaken by an experienced operator and women should be referred to a center in which the procedure is performed frequently.
Women with a mitral valve area of <1 cm2 will almost inevitably decompensate in pregnancy, and this is likely to result in a high-risk delivery of a preterm infant. If the mitral valve is suitable for balloon dilatation, then consideration should be given to intervening semielectively in the second trimester to allow a safer term delivery. The timing of intervention depends on the gestation at presentation, but once symptoms are controlled with medical therapy and the woman can lie fairly flat, early intervention will often convert a very high-risk and symptomatic pregnancy into one in which the woman feels well and has a much improved chance of a lower-risk term delivery.
Where balloon mitral valvotomy is not available, closed mitral valvotomy is a safe alternative, since it avoids the need for cardiopulmonary bypass.[10] This situation will rarely arise in the UK: first, because catheter techniques are now widely available; and second, because few, if any, surgeons now have experience of closed mitral valvotomy.
Mitral valve replacement during or soon after pregnancy carries a higher risk to the mother than when performed in the nonpregnant state. The risk of fetal loss is up to 30%. Cardiac surgery in pregnancy and the puerperium are discussed below.
Mode of delivery
Vaginal delivery with epidural analgesia is preferred for the majority of women. Invasive monitoring should be used for symptomatic women and those with severe mitral stenosis.
Risk factors for a poor outcome in mitral stenosis
The major risk factors for maternal morbidity are severe mitral stenosis and a history of prepregnancy cardiac events.[4] The risk of maternal complications rises from 26% in mild mitral stenosis to 38% and 67% for moderate and severe mitral stenosis, respectively. Maternal mortality may be up to 2%, depending on the severity of the mitral stenosis and the level of antenatal and intrapartum care.[4,11] Other cardiac and noncardiac conditions should also be considered when assessing risk. It should be noted that coexisting severe mitral and aortic regurgitation does not appear to increase the risk of pregnancy in mild mitral stenosis.[4]
The risk of adverse fetal outcome, including preterm delivery, fetal growth restriction, and death, is directly related to the severity of mitral stenosis.
Congenital mitral stenosis
Congenital anomalies of the mitral valve that result in stenosis do not commonly present in adulthood, but are important to consider in relation to pregnancy because there may be other associated congenital lesions, and the options for intervention may be limited. Parachute mitral valve is the commonest cause of congenital mitral stenosis. There is a single papillary muscle, so the valve is funnel-shaped with its orifice displaced toward the narrow end. Stenosis due to this pathology cannot be relieved by balloon valvuloplasty, since to do so would result in disruption of the valve architecture and severe regurgitation. In addition, the valve is often not amenable to repair, so women presenting for the first time in pregnancy with severe mitral stenosis may have to undergo valve replacement during pregnancy if the gestational stage does not permit delivery. Parachute mitral valve often exists as part of Shone syndrome, with a series of coexisting left-sided obstructive lesions that may include supramitral ridge, bicuspid aortic valve, aortic coarctation or interruption, and hypoplastic aortic arch. In women who are pregnant or contemplating pregnancy, these lesions must be sought and managed appropriately. Shone syndrome has an approximately 10% recurrence rate, and affected fetuses may have any combination of left-sided obstructive lesions, including, at the worst end of the spectrum, hypoplastic left heart syndrome.
Aortic stenosis: Introduction and pathophysiology
In the UK, significant aortic stenosis is usually secondary to bicuspid aortic valve disease. Coexisting congenital cardiac lesions such as bicuspid aortopathy, aortic coarctation, and Shone syndrome should be considered when assessing the risk and management of pregnancy. Severe rheumatic aortic stenosis is not common in women of childbearing age; if present, it will almost certainly be in association with severe rheumatic mitral valve disease.
Pregnancy is usually well tolerated in women with isolated mild and moderate aortic stenosis with good ventricular function. However, the increased circulating and stroke volumes of pregnancy result in an increase in left ventricular pressure and in pressure gradients across the stenotic aortic valve. This may result in a failure to increase coronary blood flow with consequent compromise to myocardial perfusion. Thus, pregnant women with severe aortic stenosis are at risk of developing symptoms for the first time, including dyspnea, angina, syncope, pulmonary edema, left ventricular failure, and sudden cardiac death.
The risk of maternal death in severe aortic stenosis has been quoted as 17%, with a fetal mortality rate of 30%;[12] however, more recent data are encouraging,[13] with no pregnancy-related deaths in a series published in 2009.[14] Women with moderate or severe aortic stenosis, especially if symptomatic, are at an increased risk of needing aortic valve intervention within the first postpartum year.[14]
Prepregnancy assessment of isolated aortic stenosis
As long as left ventricular dimensions and function are normal, coexistent aortic regurgitation does not appear to increase the risk of pregnancy in women with aortic stenosis.
A history of symptoms including exertional dyspnea, chest tightness, or light-headedness in a woman with aortic stenosis is highly significant and suggests that aortic valve replacement should be performed before pregnancy. However, the majority of women with aortic stenosis seeking prepregnancy counseling are asymptomatic; they require careful assessment of their valve, ventricular function, and response to exercise (the latter being a surrogate for the increased cardiovascular demands of pregnancy).
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