General aspects of antenatal care

Maternal monitoring and investigation

Women who are known to have pre-existing heart disease should be advised to seek medical care as soon as pregnancy is confirmed, so that they can have a plan of care established by the multidiscip­linary team.

A detailed plan of care should be established and fully do cumented in the woman's notes, and shared with all relevant professionals in­cluding the family doctor. Women should carry their notes at all times so that key information is available in case of emergencies.

The women should be seen frequently by the obstetrician, usually every 2-4 weeks in the first half of pregnancy (depending on the se­verity of their lesion) and then weekly thereafter. Continuity of care is very important as it enables the detection of subtle signs of deteri­oration, such as increases in shortness of breath and palpitations. At each consultation, exercise tolerance should be assessed (watching the woman walk down the corridor to the consulting room can be informative) and enquiries should be made about any new symp­toms such as palpitations or shortness of breath. There should be a careful clinical examination at each consultation, assessing the pulse rate and rhythm, and the heart should be auscultated to detect any change in murmurs.

There should also be regular review by the multidisciplinary team, at a minimum for delivery planning once the baby has reached via­bility, and more frequently in high-risk cases. Echocardiography is a key investigation, and should be undertaken in all cases at the be­ginning of pregnancy, with further scans according to the nature and severity of the lesion. For example, it is usual in women with Marfan syndrome (a genetic deficiency in fibrillin structure leading to a loss of elasticity, most critically in the aortic root) to undertake measure­ment of the aortic root diameter at least every 8 weeks.

Women are increasingly being assessed and monitored using scoring systems such as that first described by the New York Heart Association in 1928 (Table 12.1).

This relatively simple system was updated in 2001 by incorporating the results of modern investigative techniques such as echocardiog­raphy to derive the CARPREG (‘CARdiac disease in PREGnancy')

Table 12.1 New York Heart Association scoring system

score, which was derived and then validated in a prospective multicentre study of 599 pregnancies in women with a variety of congenital and acquired heart disease (19).

In 2011, the Task Force on the Management of Cardiovascular Diseases in Pregnancy of the European Society of Cardiology modi­fied the World Health Organization classification to devise a new score related more closely to the nature of the cardiac lesion rather than just the overall maternal condition before pregnancy (20)— deterioration during pregnancy can be more rapid with some types of lesions than with others. For example, mitral incompetence is better tolerated during pregnancy than stenosis. This is because with incompetence, the percentage impairment varies little with the car­diac output, whereas with stenosis, the resistance to flow increases exponentially as cardiac output increases. This classification was fur­ther refined by Regitz-Zagrosek et al. in 2014 (21).

Fetal screening

Fetal assessment usually starts with an ultrasound scan at 10-14 weeks of gestational age. This is routinely done to assess whether the baby's size is consistent with the presumed gestational age, and to assess the nuchal thickness (thickness of the tissues at the back of the neck). This is done as part of screening for Downs syndrome, but a raised nuchal translucency (4 mm or more) is also associated with an increased risk of congenital cardiac dis­ease. Most women with congenital heart disease will have a risk of recurrence of the condition in their baby. For polygenic condi­tions such as tetralogy of Fallot, the recurrence risk is about 3-5% (compared with a background risk of congenital cardiac anomaly of 0.8%) (22). The risk is increased if the father of the baby has the same condition because it increases the likelihood of recur­rence of the particular combination of genes which produced the

Box 12.1 CARPREG score

• Prior episodes of heart failure, transient ischaemic attack, stroke be­fore pregnancy, or arrhythmias

• Baseline functional class greater than class II or cyanosis

• Left heart obstructive lesions

• Low systemic ventricular ejection fraction (in any pregnant woman presenting with chest pain.

All women presenting with chest pain in pregnancy should have an electrocardiogram (ECG) and this needs to be interpreted by someone who is used to interpreting it against the background changes seen during pregnancy. Because an initial ECG may be normal, ECGs should be repeated at least every 2 hours until the pain subsides. Serum troponin levels are important to confirm a suspected diagnosis; they need to be taken at least 3-4 hours after the onset of pain to avoid false-negative results. If they are ele­vated, there should be a low threshold for investigation by angiog­raphy. If the diagnosis is not clear, computed tomography (CT) or a magnetic resonance imaging (MRI) scan should be undertaken. Although there was concern at one time regarding the radiation exposure from CT scanning, the modern generation of scanners use substantially reduced amounts of X-rays and their use in demonstrating coronary anatomy has improved. MRI and CT scanning are both useful for detection of previously unsuspected aortic dissection.

Cardiomyopathy

The wide variety of proposed aetiologies for cardiomyopathy has already been alluded to earlier in this chapter. A key distinction is whether the cardiomyopathy was already present/diagnosed before pregnancy, or whether it was detected for the first time during preg­nancy. The pregnancy prognosis for pre-existing cardiomyopathy (the most common form of which is idiopathic dilated cardiomy­opathy) is very dependent upon the cardiac ejection fraction (24). This is the proportion of the left ventricular volume which is ejected with each heartbeat, and it should normally be 60% or more (as the heart does not collapse completely during each beat, there is always a substantial amount of blood left in the ventricular cavity at the end of each contraction). The majority of women with previously diagnosed cardiomyopathy will have an ejection fraction of ap­proximately 45% or more, and their prognosis is relatively good.

Peripartum cardiomyopathy (cardiomyopathy appearing for the first time in relation to pregnancy or in the puerperium) has a highly variable incidence according to racial origin (25), with par­ticularly high rates in women of black African origin. It is usually diagnosed when a woman presents with rapidly increasing short­ness of breath and pulmonary oedema; diagnosis is by echocardiog­raphy and the demonstration of a severely reduced ejection fraction. There is currently some optimism that treatment with bromocrip­tine can prevent or ameliorate peripartum cardiomyopathy (26-28). Management is in other respects supportive (the use of diuretics to combat pulmonary oedema, inotropic agents to improve cardiac contractility). The most important prognostic feature in relation to the outlook for future pregnancies is the rate and completeness of the recovery of cardiac function. If after 12 months cardiac func­tion has returned to entirely normal, then the risk of recurrence of heart failure in a future pregnancy is about 20%, but the mortality is low.

Mitral stenosis

The majority of mitral stenosis cases are secondary to rheumatic fever. It is common for it to present for the first time during preg­nancy, particularly in immigrants who have never had any form of cardiac assessment previously and who are unaware that they have had rheumatic fever (in the developing world, non-specific fevers are common and the diagnosis of rheumatic fever is frequently missed). A simple ‘rule of thumb' for severity is that the normal mi­tral valve area is 8 cm², a value less than 4 cm² is abnormal, a value less than 2 cm2 is concerning, and a value less than 1 cm2 is likely to require intervention during pregnancy. As explained previously, the obstruction to blood flow increases exponentially with stenosis, and therefore the clinical status of most women with mitral sten­osis will deteriorate during pregnancy because of the increased cir­culating blood volume and cardiac output. The reduction in output from the left side of the heart results in the blood ‘backing up' in the lungs, leading to pulmonary oedema. This can occur acutely if the left atrium (which is commonly dilated due to the back pressure from the constricted valve) starts to fibrillate. Symptoms are com­monly those of orthopnoea, a dry cough, and paroxysmal nocturnal dyspnoea. Diagnosis is readily made using echocardiography.

Treatment is bed rest (reduces cardiac output), oxygen therapy, beta-blockade, and a diuretic (29). As with cardiomyopathy, treat­ment anticoagulation with low-molecular-weight heparin should be given if there is atrial fibrillation. In severe cases with a valve area less than 1 cm2, a balloon valvotomy or even an open valvotomy may be needed.

Aortic stenosis

Most aortic stenosis is secondary to bicuspid aortic valve disease, a congenital lesion. A common method of assessment is to measure the gradient across the valve using Doppler echocardiography. A normal gradient is less than 5 mmHg, but it can be as high as 25 mmHg with only mild stenosis. The gradient commonly doubles during pregnancy because of the increased blood flow, and therefore a gradient up to about 60 mmHg during pregnancy suggests mild- to-moderate stenosis only. Values above 60 mmHg are likely to be clinically significant, and values above 80 mmHg are commonly as­sociated with symptoms and morbidity (29). The majority of women with aortic stenosis will have a congenital aetiology and therefore should have had preconception counselling. Ideally, in severe cases, there will have been prepregnancy treatment to improve function during pregnancy. One such treatment is the Ross procedure, where the mother's tricuspid valve is used to replace the damaged aortic valve, and a tissue homograft/xenograft (from a human, pig, or cow) is placed in the tricuspid position. The value of this exchange is that the native tissue will survive longer in the high pressure of the left heart than a tissue homograft or xenograft, while the latter will sur­vive longer in the low pressure of the right heart. Unlike with the mitral valve, surgical valvotomy commonly results in severe regurgi­tation and thus valve replacement is preferable. This requires the use of cardiopulmonary bypass, and in its usual form this has a high fetal mortality (20-30%). This can be reduced by using higher perfusion pressures than would usually be used with non-pregnant patients, and avoiding the use of hypothermia; this makes the technique par­ticularly challenging during pregnancy, as does the need for full anticoagulation during the procedure (30).

Aortopathies

There is a wide range of congenital and acquired aortopathies, many of which have a genetic component. The most common is probably Marfan syndrome, and there are about 10,000 individuals with this syndrome in the United Kingdom, associated with approximately 150 pregnancies per year (31). It is due to a defect (at least a dozen different defects have been identified) in the gene responsible for the production of fibrillin-1. This is associated with an increase in a pro­tein called transforming growth factor beta, which causes problems in connective tissues throughout the body. Those affected tend to be very tall and slim, with a span (width from the tip of the fingers of an outstretched arm to the tips of the fingers on the other side) which exceeds their height. Other signs include eye problems, particularly dislocation of the lens. The expression of the defect is very variable from one individual to another. From the perspective of pregnancy complications, the main problem is excessive dilatation of the aortic root. The interquartile range of the aortic root diameter at the level of the sinuses of Valsalva in healthy women is from 26 to 34 mm (32). Some dilatation occurs in pregnancy due to the circulatory volume expansion; the likelihood of dissection during pregnancy is generally said to be no more than 1% if the aortic root diameter is less than 40 mm, but increases to 10% if the diameter is greater than this (33). Of course there is no sudden jump in the likelihood of dissection between 39 mm and 41 mm; the risk is probably also in­creased if there is a sudden expansion even within the normal range. There is no specific management other than a recommendation for the woman to take beta-blockers to reduce the cardiac impulse and thus limit the stretch on the aortic root, and careful monitoring of the aortic root diameter with elective delivery if it shows a worrying increase. Elective aortic root replacement is then recommended during the puerperium (34).

Right heart lesions

These comprise a wide variety of conditions including systemic right ventricles (transposition of the great arteries after an atrial switch op­eration (Mustard or Senning)), or congenitally ‘corrected' transpos­ition of the great arteries), functionally univentricular hearts with or without a Fontan-type operation, atrial septal defects, tetralogy of Fallot, and Ebstein's anomaly of the tricuspid valve. Accordingly, the risk of an adverse outcome depends very much on the specific lesion and associated factors such as arrhythmia, impaired cardiac output due to tricuspid regurgitation, heart failure, cyanosis, myocardial dysfunction, and the severity of outflow tract obstruction.

Tetralogy of Fallot is the most common cyanotic congenital heart lesion (it comprises up to 10% of cases of congenital heart disease) and consists of a large ventricular septal defect, right ventricular out­flow tract obstruction, right ventricular hypertrophy, and overriding of the aorta. Genetic testing should be offered before pregnancy, as the recurrence risk of DiGeorge syndrome is 50%. In its absence, the risk for recurrence in the fetus is about 2-3%. Repair is usually to relieve the outflow tract obstruction with a transannular patch, re­sulting in free pulmonary valve regurgitation (35). In pregnancy, the degree of pulmonary regurgitation is the main variable influencing the degree of fetal growth restriction, with which it is commonly associated (36). Tetralogy of Fallot can be part of the DiGeorge syn­drome (present in 15% of tetralogy of Fallot patients). Pulmonary valve regurgitation is also the main concern with Ebstein's anomaly.

Women who rely on a systemic right ventricle need to be observed carefully for any signs of decompensation during pregnancy. This will be manifest as a decrease in blood pressure and signs of pul­monary oedema.

Pulmonary hypertension

Although pulmonary hypertension is relatively rare, it is one of the most serious conditions in women who become pregnant, because it limits severely their ability to adapt to the cardiovascular changes of pregnancy. The outcome for the fetus is also commonly poor, with high rates of preterm delivery, fetal growth restriction, and peri­natal mortality (37). Until the beginning of the twenty-first century, maternal mortality rates of 50% were sometimes quoted, and pul­monary hypertension was widely regarded as a complete contraindi­cation to pregnancy. However recent series show some improvement in outcomes, with a mortality of perhaps only (!) 20% (37, 38). This improvement has been attributed to new therapies, such as the routine use of sildenafil, and the use of prostanoids such as intra­venous prostacyclin. These therapies have a specific vasodilator in action in the lungs, helping to reduce the impedance to blood flow. Specific pregnancy care involves routine full anticoagulation with low-molecular-weight heparin, monitored by the measurement of antifactor Xa levels (target 0.6-1). In the typical case, failing fetal growth and increasing maternal compromise at about 34 weeks of pregnancy mandate delivery, which is then usually by caesarean section under either regional block or general anaesthetic.

Arrhythmias

The most common arrhythmia is extrasystole; these often occur in healthy individuals. They increase in frequency during pregnancy because of the increase in myocardial excitability, and commonly become noticeable to the woman because of the increased stroke volume associated with the pregnancy circulatory expansion. They are readily investigated by the use of 24-hour ECG recording (com­monly called the Holter test). As a rule of thumb, up to 10,000 iso­lated unifocal ventricular extrasystoles per day can be regarded as normal; above this number it is wise to investigate further with an echocardiogram. The largest number the author has seen recorded in a single day in a woman who was subsequently normal on all in­vestigations was 24,000. Runs of ventricular tachycardia of no more than seven consecutive beats occur less frequently but provided they only occur occasionally and are associated with an otherwise normal ECG do not usually justify further investigation unless they are associated with symptoms such as syncope. Other common conduction disturbances including the Wolff-Parkinson-White syndrome are relatively common and generally innocuous during pregnancy. However, there are rare but serious conditions such as the long QT syndrome and Brugada syndrome which are associated with sudden cardiac arrest and may require the insertion of an im­planted cardiac defibrillator. Chronic atrial fibrillation can lead to embolism of clot from the poorly contracting atria and therapeutic anticoagulation with low-molecular-weight heparin is therefore indicated. Persistent arrhythmia is increasingly being treated suc­cessfully with catheter thermoablation, when the abnormal myo­cardium where the arrhythmia originates is destroyed (39). pregnancy straightforward and relatively low risk. Unfortunately, the tissue has to be denatured before being implanted so that it does not create an immune response, and therefore is not self-repairing. This means that it gradually wears out and after about 12-15 years a tissue valve on the left (high pressure) side of the heart usually needs replacing. This means once again undergoing major open­heart surgery, which even in the best hands carries a 1-2% mor­tality rate. A metal valve on the other hand will usually last a lifetime. Unfortunately, its mechanical structure makes it prone to act as a focus for the formation of thrombus, with the potential for embolus. On the left side of the circulation, this embolism can be to the brain, causing a disabling stroke. As a result, permanent anticoagulation, usually with warfarin, is required. Unfortunately, warfarin crosses the placenta and in the first trimester, once the placental circulation has formed, it can cause warfarin embryopathy (this has many fea­tures but typically comprises epiphyseal stippling, nasal hypoplasia, limb abnormalities, and developmental delay) and miscarriage. It also anticoagulates the fetus, and in the second trimester this can result in intracranial haemorrhage and death of the fetus. If the baby survives, it may have neurological disability (40). The alter­native to warfarin is therapeutic low-molecular-weight heparin. Unfortunately, this is less effective as an anticoagulant than warfarin, and results in a 5-10% risk of valve thrombosis, requiring an urgent repeat valve replacement with associated morbidity and mortality, especially during pregnancy.

A 2015 study in the journal Circulation reported on the outcomes of pregnancy in 212 women with mechanical valves and 134 women with tissue valves (41). Although mortality was similar (1.4% vs 1.5%), complications were more common with mechanical valves (42% vs 21%), largely due to miscarriage (28.6% vs 9.2%), haemor­rhage (23.1% vs 4.9%), and late fetal loss (7.1% vs 0.7%).

Currently, the balance of counselling tends to encourage the use of tissue valves in young women who have expressed an intention to have one or more pregnancies with the aim of completing their preg­nancies and then when their tissue valve needs replacement, chan­ging to a metal valve. However, if they already have a metal valve when they become pregnant, the choice of anticoagulant is very dif­ficult as there is no entirely satisfactory solution. Therefore, current practice is to explain to women the pros and cons of each approach and allow them to choose (42).