Heart Disease and Pregnancy, 2nd edn. ed. Philip J. Steer and Michael A. Gatzoulis. Published by Cambridge University Press.
© Cambridge University Press 2016.
Chapter
Practical practice points
1. Severe valvular stenosis is poorly tolerated in pregnancy.
2. Rheumatic mitral stenosis is the leading cardiac cause of maternal death in the developing world.
3. Th e initial presentation of many women with rheumatic mitral stenosis occurs when pregnancy precipitates symptoms for the fi rst time.
4. Diuretics and beta-blockers are useful in medical management, but balloon mitral valvuloplasty has a high success rate and is the mainstay of treatment for severe mitral stenosis in pregnancy .
5. Bicuspid aortic valve is the commonest cause of aortic stenosis in women of childbearing age.
6. Preconception assessment is important to determine whether a woman with moderate or severe aortic stenosis is likely to tolerate pregnancy well, or whether she should undergo prepregnancy aortic valve replacement.
7. Th e severely stenotic bicuspid aortic valve in adulthood is oft en unsuitable for balloon valvotomy, so surgical aortic valve replacement may be necessary if a woman with severe aortic stenosis decompensates during pregnancy .
Section 4: Antenatal Care: Specifi c Maternal Conditions
the UK in the twenty-fi rst century, and in most other developed countries, maternal aortic stenosis (aortic stenosis) is usually congenital, whereas mitral stenosis is usually rheumatic in origin .
Rheumatic mitral stenosis: Background and pathophysiology
Many young women are not aware that they have rheu- matic heart disease: the initial presentation of rheumatic mitral stenosis is oft en during pregnancy when women become symptomatic for the fi rst time, so there is usu- ally 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 fl ow through the stenotic valve tend to increase left atrial pressure and impair cardiac output. Th e resulting dyspnea and pulmonary edema are further exacerbated if atrial fi brillation 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 fl uid shift s that occur may precipitate pulmonary edema .
A further signifi cant risk factor is that rheumatic fever among people born in the UK is now very rare;
those that have it are usually fi rst-generation immi- grants. Th ey may already be socially disadvantaged, with poor access to health care and communication diffi culties, all of which are independent risk factors for a poor pregnancy outcome.[ 3 ] Furthermore, with the decline in the incidence of rheumatic heart dis- ease, a new generation of UK-trained doctors has little experience of diagnosing and treating mitral stenosis in either the pregnant or nonpregnant patient. Th is may lead to a delay in or failure of diagnosis, and/or to incorrect therapy, risking a poor outcome .
History and examination
Th ere 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 preg- nancy progresses and the circulating blood volume rises.
Orthopnea, dry cough, paroxysmal nocturnal dysp- nea, and pulmonary edema may develop, sometimes
precipitated by tachyarrhythmia (usually atrial fi brilla- tion). Th e average time of onset of pulmonary edema has been reported to be around 30 weeks of gestation.[ 4 ]
Th e woman may be breathless on minor exertion with a dry “high left atrial pressure” cough exacerbated by lying fl at. Orthopnea is common, along with tachy- cardia, an elevated venous pressure, and classical signs of mitral stenosis .
Investigations
Th e 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. Th e electrocardiogram (ECG) will confi rm 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 assess- ing mitral stenosis severity ( Table 13.1 ) in pregnancy.
Although the continuity equation for assessing sever- ity of mitral stenosis is valid in pregnancy, the pressure half time method is infl uenced by loading conditions and thus may result in underestimating the severity of mitral stenosis in pregnancy .
Treatment
Th e mainstay of medical management is to reduce the heart rate to allow time for left ventricular fi lling. Th is is achieved in women with mild and moderate mitral ste- nosis by bedrest, oxygen therapy, beta-blockade, and a diuretic. If atrial fi brillation 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 ]
Th e rheumatic mitral valve in women of child- bearing age is usually suitable for balloon dilatation if there is no more than mild associated regurgitation.
Table 13.1 Classifi cation of the severity of mitral stenosis Severity Mitral valve area (cm 2 )
Mild >1.5
Moderate 1.0–1.5
Severe <1.0
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 fl uoroscopy. Radiation doses to the fetus can be reduced a little further with maternal abdominal screening. With an experienced operator, fl uoroscopy times should be limited to 5–8 min (see Chapter 8 ) . [ 7 – 9 ] Th e risk of developing acute mitral regurgitation such that emergency mitral valve replacement is nec- essary is low in centers with high-volume experience;
however, on-site facilities for emergency cardiac sur- gery 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 cm 2 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 dilata- tion, then consideration should be given to intervening semielectively in the second trimester to allow a safer term delivery. Th e timing of intervention depends on the gestation at presentation, but once symptoms are controlled with medical therapy and the woman can lie fairly fl at, early intervention will oft en 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 ] Th is situation will rarely arise in the UK: fi rst, because cath- eter 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 aft er preg- nancy carries a higher risk to the mother than when performed in the nonpregnant state. Th e 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
Th e major risk factors for maternal morbidity are severe mitral stenosis and a history of prepregnancy cardiac events.[ 4 ] Th e risk of maternal complications rises from 26% in mild mitral stenosis to 38% and 67% for moderate and severe mitral stenosis, respec- tively. Maternal mortality may be up to 2%, depend- ing on the severity of the mitral stenosis and the level of antenatal and intrapartum care.[ 4 , 11 ] Other car- diac and noncardiac conditions should also be con- sidered 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 ]
Th e risk of adverse fetal outcome, including pre- term 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 preg- nancy because there may be other associated con- genital lesions, and the options for intervention may be limited. Parachute mitral valve is the commonest cause of congenital mitral stenosis. Th ere is a single papillary muscle, so the valve is funnel-shaped with its orifi ce displaced toward the narrow end. Stenosis due to this pathology cannot be relieved by balloon valvuloplasty, since to do so would result in disrup- tion of the valve architecture and severe regurgitation.
In addition, the valve is oft en not amenable to repair, so women presenting for the fi rst 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 oft en exists as part of Shone syndrome, with a series of coexisting left -sided obstructive lesions that may include supramitral ridge, bicuspid aortic valve, aor- tic 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 aff ected fetuses may have any combination of left -sided obstructive lesions, includ- ing, at the worst end of the spectrum, hypoplastic left heart syndrome .
Section 4: Antenatal Care: Specifi c Maternal Conditions