Fig. 10.1
Flow chart describing the management of women with aortic stenosis according to different phases (Phase 1–5). AVR aortic valve replacement, TTE transthoracic echocardiography, ET exercise test, BNP brain natriuretic peptide, FU follow-up, EF ejection fraction
10.3.1 Phase 1: Preconception Evaluation
All women with known aortic stenosis should have preconception evaluation. This evaluation should be done by an interdisciplinary team of obstetricians and cardiologists and should include careful history and family history, physical examination, electrocardiography and echocardiography. To assess the functional state, an exercise test in asymptomatic women may be helpful [7].
10.3.1.1 Echocardiography
Transthoracic echocardiography (TTE) is a safe and quick diagnostic tool and it is mandatory for the diagnosis of aortic stenosis. It allows morphological assessment of the valves and provides information on the aetiology of the disease. The morphological assessment of the aortic valve (AoV) is best performed in a parasternal short-axis view (SAX) (Fig. 10.2a). Congenital AS is typically encountered in the form of a bicuspid AoV. To establish the diagnosis, the valve has to be visualised in the SAX in systole where the orifice has a characteristic “fish-mouth” appearance (Fig. 10.2b).
Fig. 10.2
(a) Normal tricuspid aortic valve in short axis. (b) Bicuspid aortic valve in short axis. (c) Transoesophageal echocardiography of a bicuspid aortic valve with typical “doming” of the cusps. (d) TTE of a severe aortic stenosis
In rheumatic valve disease, the valve is characterised by thickening at the edges of the cusps and commissural fusion, and in most cases, also the mitral valve (MV) is affected. The quantification of stenosis includes predominantly the measurement of transaortic jet velocities and gradients as well the calculation of the aortic valve area, thus combining flow-dependent and relatively flow-independent variables.
The normal aortic valve area is in the range of 3–4 cm2. Under normal conditions and also during pregnancy, the transvalvular flow has a peak flow velocity typically <2 m/s. With increasing narrowing of the AoV orifice, the transaortic jet velocities increase [1, 7]. Transaortic jet velocities are measured by recording of the maximal transaortic flow signal using continuous wave (CW) Doppler, and gradients can be derived from flow velocities using the simplified Bernoulli equation. The mean gradient can be determined by averaging the instantaneous gradients over the entire systole.
There are some pitfalls to watch for when measuring transaortic velocity and gradients. For an accurate measurement of the transaortic jet velocity, the Doppler beam needs to be aligned with the stenotic aortic jet. Alignment errors, which can frequently occur in pregnant women with atypical heart position or congenital aortic stenosis, lead to an underestimation of the true velocity and consequently of the calculated gradients resulting in underestimation of AS severity. As a consequence, a meticulous search of the highest transvalvular velocity is required. This necessitates a comprehensive Doppler study that is not only limited to the apical window but also includes right parasternal, suprasternal and sometimes (if possible in pregnant women) subcostal approaches using a small, dedicated CW Doppler transducer (pencil probe). It is not unusual that significantly higher aortic jet velocities can be recorded from these acoustic windows.
Transaortic jet velocities and gradients are highly flow dependent. In the presence of associated aortic regurgitation, high cardiac output states such as pregnancy, anaemia, hyperthyroidism, or transaortic flow velocities will further increase.
Aortic valve area, calculated using the continuity equation, is a relatively – although not entirely – flow-independent variable. Even if carefully performed, one major limitation of this method remains the LVOT area calculation from its diameter. Since the LVOT shape is rather elliptical than circular, this will result in flow underestimation and therefore valve area underestimation [8, 9]. Any discrepancy in the measurement of the LVOT diameter will be squared, leading to errors in the calculation of the AVA.
Planimetry of the valve area, primarily by 2D TEE, has also been proposed. However, the orifice of a stenotic aortic valve, especially in a doming bicuspid aortic valve (Fig. 10.2c), frequently represents a complex three-dimensional structure that cannot be reliably assessed with a planar 2D image.
As stenosis severity encompasses a continuous spectrum of disease, its assessment needs to be viewed in a continuous way. In clinical practice, peak transaortic jet velocities, mean gradients and valve areas (calculated by the continuity equation) should be estimated and the findings are ideally concordant (Table 10.1).
Table 10.1
Quantification of aortic stenosis severity
Mild aortic stenosis | Moderate aortic stenosis | Severe aortic stenosis | |
|---|---|---|---|
Peak aortic jet velocity (m/s) | 2.5–2.9a | 3.0–3.9a | ≥4.0a |
Mean gradient (mmHg) | <20a | 20–39a | ≥40a |
Aortic valve area (cm2) | >1.5 | 1.0–1.5 | ≤1.0 |
Indexed valve area (cm2/m2 BSA) | ≤0.6 cm2/m2 |
Classification of AS severity is not difficult when measurements of velocity, gradient and valve area are concordant but becomes challenging when conflicting values of these indices are found. Because pressure gradients are flow dependent, gradients by itself may provide misleading information about the severity of aortic stenosis during pregnancy. The situation of a peak velocity >4 m/s and mean gradient >40 mmHg despite a valve area greater than 1.0 cm2 can be found in the presence of a high transvalvular flow, especially in pregnancy. The increased heart rate during pregnancy may also influence the peak and mean systolic gradients (as calculated from the Bernoulli equation) but should not affect the calculated valve area as calculated by the continuity equation. Until now it is unclear which parameter during pregnancy, gradient or valve orifice, describes best the haemodynamic situation.
The ascending aorta should be routinely assessed in women with AS since a dilation of the ascending aorta is frequently observed especially in patients with bicuspid valves. The assessment is performed in a PLAX view at early systole and includes measurements at the levels of the aortic annulus, the sinuses of Valsalva, the sinotubular junction and the ascending aorta. In case of an aortic diameter greater than 50 mm (or >27 mm/m2 BSA), surgery before pregnancy should be considered [2].
Supravalvular AS is a rare congenital lesion (e.g. in Williams-Beuren syndrome) in which the ascending aorta is narrowed. Subvalvular AS consists of a fixed obstruction below the aortic valve level in the left ventricular outflow tract and can be due to a thin fibrous membrane or a fibromuscular narrowing. Both forms are fixed stenosis with similar pathophysiological consequences as in valvular stenosis. Hypertrophic obstructive cardiomyopathy represents a dynamic obstruction of the left ventricular outflow tract and is usually well tolerated during pregnancy [10, 11].
10.3.1.2 Other Tests
Exercise testing is recommended in asymptomatic patients before pregnancy to confirm asymptomatic status and evaluate exercise tolerance, blood pressure response and arrhythmias [2]. In addition, electrocardiography (ECG) is recommended to exclude, among other findings, arrhythmias. To what extent an elevated brain natriuretic peptide adds prognostic information in this setting remains unclear.
10.3.2 Pre-pregnancy Counselling/Risk Estimation
Pre-pregnancy counselling has to address how pregnancy may affect not just the mother but also the fetus. This means women should be given information on maternal and fetal morbidity and mortality associated with pregnancy. This allows women to make an informed choice whether to accept the risk associated with pregnancy.
Several risk scores for predicting cardiac complications in patients with acquired or valvular heart disease have been proposed. They try to predict cardiac and obstetric complications in different forms of heart disease and are therefore not specific for women with aortic stenosis.
The CARPREG risk score is the most popular one [12]. It classifies the different heart conditions in three risk categories [13]. To categorise these women, the study identifies four predictors of primary cardiac events (each one point):
Prior cardiac event (heart failure, transient ischaemic attack or stroke before pregnancy) or arrhythmia
Baseline NYHA class >II or cyanosis
Left heart obstruction (mitral valve area <2 cm2, aortic valve area <1.5 cm2 or peak left ventricular outflow tract gradient >30 mmHg by echocardiography)
Reduced systemic ventricular systolic function (ejection fraction <40 %)
The estimated risk of a cardiac event in pregnancies with 0, 1 and >1 points was reported to be 5 %, 27 % and 75 %, respectively.
The current European Heart Society guidelines have extended the modified World Health Organization (mWHO) score to assess maternal risk. The score classifies patients in four categories indicating the risk of cardiovascular complications and the consequences for management during pregnancy. Women in mWHO class I have a low risk; class II, small risk of complications; and class III, significant risk of complications. Women in class IV have such a high risk of morbidity and mortality that they should be advised against pregnancy [2].
According to the modified WHO classification of maternal cardiovascular risk, patients with severe symptomatic aortic stenosis are assigned to class IV, whereas all other forms of aortic stenosis are assigned to classes II–III. Aortic dilatation between 45 and 50 mm associated with a bicuspid aortic valve (without significant dysfunction of the valve) is assigned to class III, aortic dilatation >50 mm to class IV.
Patients with a low- or moderate-risk condition (WHO I–III) should be seen by the end of the first trimester and a follow-up plan with time intervals for review and investigations such as echocardiograms defined. The follow-up plan should be individualised taking into account the severity of aortic stenosis, aortic dilatation and clinical status of the patient.
10.3.3 Phase 2: Care During Pregnancy
As many general cardiologists or obstetricians will see only a few women with aortic stenosis, referral to a specialist centre for counselling is advisable. Management of pregnant patients with aortic stenosis should be ensured by experienced multidisciplinary teams. The follow-up frequencies depend on the severity of stenosis with at least monthly visits and echocardiographic assessments in patients with severe stenosis.
Symptoms due to severe aortic stenosis such as dyspnoea, angina pectoris, dizziness or syncope on exertion usually become apparent in the second trimester or early third trimester when the haemodynamic load on the heart significantly increases. Onset of symptoms related to AS before this stage seems to be a poor prognostic sign. It could be a diagnostic challenge to decide if shortness of breath is related to an aggravation of aortic stenosis or just to physiological changes during pregnancy [14].
10.3.4 Echocardiography During Pregnancy
TTE should be done regularly during pregnancy. The frequency depends on symptoms and severity of stenosis. Particular attention should be given to the evaluation of left ventricular function, accompanying valvular lesions and changes of aortic stenosis severity. In women with more than mild AS, an increase in pressure gradients over the stenotic valve is usual [15]. In contrast to that, aortic valve area, which is less flow dependent, should stay constant throughout pregnancy. Concerning left ventricular function, ejection fraction should not show significant changes unlike longitudinal strain, which decreases during normal pregnancy [16]. Any drop in ejection fraction during pregnancy in women with AS should be a warning sign.
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