Management of Cardiac Disease in Pregnancy

Introduction

Pregnancy makes a significant demand on the cardiovascular system. Therefore, it follows that women with cardiovascular compromise due to cardiac disease need specialist input and careful management pre-, peri-, and post-partum. In the latest CEMACH report, cardiac disease was the most common cause of indirect maternal deaths and the most common cause of death overall.[1] In particular, during 2003-5, there was an increase in deaths due to myocardial infarction, thoracic aortic dissection, and rheumatic mitral stenosis. The causes of maternal cardiac deaths in 2003-5 are summarized in Table 1.

Of particular relevance to anaesthesia and intensive care is that the majority of pregnant women who die of heart disease have not been identified as being 'at risk' before labour.[2] Maternal cardiac disease has the potential to remain undiagnosed during pregnancy, but presentation often occurs after 20 weeks gestation and frequently at the time of delivery or immediately post-partum. This is most likely to happen in women who have avoided, or not presented for, antenatal care. An appreciation of the issues involved in the care of the parturient with cardiac disease and an awareness of the signs and symptoms is therefore important.

Physiological Changes in the Cardiovascular System During Pregnancy

A thorough knowledge of the physiological changes that occur in the cardiovascular system during pregnancy is essential in order to understand the additional impact of cardiac disease. Peripheral vasodilation leading to a decrease in systemic vascular resistance is thought to be the first cardiovascular change associated with pregnancy (induced by progesterone). Cardiac output increases in response to this, by 20% at 8 weeks gestation and by up to 40-50% at 20-28 weeks gestation. This is achieved predominantly via an increase in stroke volume (due to an increase in ventricular end-diastolic volume, wall muscle mass, and contractility) but also by an increase in heart rate. Labour leads to further increases in cardiac output by 15% in the first stage and 50% in the second stage due to the combination of auto-transfusion of 300-500 ml of blood back into the circulation with each uterine contraction, and sympathetic stimulation caused by pain and anxiety. Cardiac output increases again immediately after delivery due to auto-transfusion of blood via uterine contraction and relief of aortocaval compression. This may increase cardiac output by as much as 60-80%, followed by a rapid decline to pre-labour values within 1 h.[3]

The impact of these physiological changes to a pregnant woman with cardiac disease will vary according to the type and severity of the disease. Women with the least ability to increase their cardiac output are at risk of decompensation earlier on in pregnancy and may present before the 28 week 'maximum pre-delivery' cardiac output is achieved. Those who tolerate the increase during pregnancy will be at further risk at the time of delivery and immediately post-partum due to the changes caused by sympathetic stimulation and auto-transfusion described above. These changes combined with the reduction in serum colloid osmotic pressure make women with cardiovascular compromise particularly susceptible to pulmonary oedema at the time of delivery and immediately post-partum. This risk is increased if the woman is given excessive i.v. fluid (causing an increase in cardiac preload) or if she also has pre-eclampsia (resulting in an increase in pulmonary capillary permeability).

General Principles of Management
Pre-delivery

In an ideal world, all women of reproductive age with congenital or acquired heart disease should have access to specialized multidisciplinary preconception counselling in order to empower them to make choices about pregnancy. Once they are pregnant, all women with heart disease should be assessed clinically as soon as possible by a multidisciplinary team and appropriate investigations undertaken. The core members of the team should include suitably experienced obstetricians, cardiologists, and anaesthetists; but midwives, neonatologists, and intensivists should also be involved in planning, when appropriate. Suitable arrangements for care should then be made at a district general hospital or tertiary unit according to the complexity of the heart disease, the risk assessment, and the locally available facilities and expertise.[2]

A clear plan for the management of labour and the puerperium in women with heart disease should be established in advance, well documented, and distributed widely (including to the woman herself) so that all personnel likely to be involved in the woman's intra- and post-partum care are fully informed.[2]

The main aims of management are: to optimize the mother's condition during the pregnancy (e.g. considering β-blockers, thromboprophylaxis, or pulmonary arterial vasodilators in appropriate cases); to monitor for deterioration; and minimize any additional load on the cardiovascular system from delivery and the post-partum period. Women with heart failure can be safely treated with diuretics, digoxin, and hydralazine, nitrates, or both as vasodilators to offload the left ventricle.[3] Additional fetal assessments may be needed in order to monitor for potential problems arising from pharmacological treatment of the mother (Table 2).

Tertiary units should offer a hotel-style facility to enable women who live some distance away to stay on site, in order to avoid delay in receiving appropriate care when they go into labour, and need to induce labour solely to avoid this risk.[2]
Mode of Delivery

Vaginal delivery is the preferred mode of delivery for most women with heart disease, unless there are specific obstetric indications or a deterioration in cardiac performance necessitating early delivery. The rate of Caesarean section is much higher for women with heart disease compared with the general population for this reason. In most cases, vaginal delivery is best achieved by aiming for spontaneous onset of labour, providing effective pain relief with low-dose regional analgesia and, if necessary, assisting vaginal delivery with instruments such as the ventouse or forceps, in order to limit or avoid maternal effort in 'pushing'. Regional analgesia during labour is usually recommended in order to reduce the further increases in cardiac output and myocardial oxygen demand caused by pain and anxiety. Good regional analgesia will also facilitate instrumental delivery. Induction of labour may be appropriate in order to optimize the timing of delivery in relation to anticoagulation and availability of specific medical staff, or because of deteriorating maternal cardiac function.[2]

General and regional anaesthesia (spinal, epidural, or combined spinal-epidural) have been used for Caesarean section. A recent 5 yr review of practice in an Australian hospital found that six of the seven parturients with NYHA grade IV symptoms received regional anaesthesia (three for Caesarean section and three for labour) and 12 out of 17 with NYHA grade III symptoms received regional anaesthesia (six for Caesarean section and six for labour).[4] There is no evidence to support any particular technique, but cardiovascular stability is the goal.

It is recommended that if oxytocin is required post-delivery, it should only be administered by infusion with the omission of a bolus. It has been argued that the cardiovascular effects of a post-partum haemorrhage in a patient with a fixed cardiac output, and the potential risk of overzealous i.v. fluid replacement in response, are worse than the potential cardiovascular effects of a slow infusion of oxytocin[5] (which include peripheral vasodilation, tachycardia, and fluid retention). Ergometrine should be avoided in severe cardiac disease as it leads to vasoconstriction and hypertension, and increases the risk of myocardial infarction and pulmonary oedema. Carboprost is not recommended in cardiac disease (see the British National Formulary) as it too has the potential to cause/exacerbate pulmonary oedema.

It should also be noted that the use of a glyceryl trinitrate infusion post-delivery may improve pulmonary oedema; however, it may also increase the risk of post-partum haemorrhage due to uterine relaxation.
Post-partum

In the post-partum period, high-level maternal surveillance is required until the main haemodynamic changes after delivery have resolved. For particularly unstable cardiac conditions, such surveillance may be required in hospital for up to 2 weeks. A recent review of parturients with heart disease found that the worst cardiac compromise did not always occur at the time of delivery. The occurrence of chest infection or development of peripartum cardiomyopathy (which may occur anytime from 1 month pre-delivery up to 5 months post-delivery) in some cases lead to worse compromise post-delivery.[4]

Specific High-risk Conditions
Myocardial Infarction

Myocardial infarction was a leading cause of cardiac death in 2003-5. All the women who died had identifiable risk factors including obesity, older age and high parity, smoking, diabetes, pre-existing hypertension, and a family history. A low threshold for diagnosis of myocardial infarction and acute coronary syndrome in women with risk factors is recommended and appropriate intervention in the form of coronary angiography, emergency coronary intervention, and thrombolysis should not be withheld in the pregnant or puerperal woman.[1] Thrombolysis at the time of delivery, however, carries a significant risk of haemorrhage and management therefore needs to be on an individual basis. The first choice for treatment of acute coronary syndrome in pregnant women is percutaneous coronary intervention.[2]

There are several case reports in the literature describing the management of delivery in women with coronary artery disease, ranging from spontaneous delivery with or without epidural analgesia to elective Caesarean under combined spinal-epidural anaesthesia[6] or elective Caesarean under general anaesthesia.[7] The need for anti-platelet medications (e.g. clopidogrel) would at present preclude the use of regional analgesia or anaesthesia.
Aortic Dissection

Aortic dissection is a particular risk in women with Marfan's syndrome; however, it can also occur in previously apparently normal women. The risk is thought to be highest near full-term or the immediate post-partum period, in particular in the presence of systolic hypertension. In the recent CEMACH report, an inappropriate emphasis on the treatment of diastolic hypertension led to failure to treat systolic hypertension in some of the women who died from aortic dissection.[1] In three out of the nine deaths from aortic dissection, there may also have been undiagnosed Marfan's syndrome.

The management of women with known Marfan's syndrome should include pre-pregnancy counselling if possible. If the aortic root diameter is > 4-4.5 cm, the risk of aortic dissection is greatly increased, so aortic root replacement should be offered before pregnancy. β-Blockers should be continued or started in pregnant patients with Marfan's syndrome who have aortic dilatation or hypertension as they have been found to reduce the rate of aortic dilatation.[3] Monitoring during pregnancy will normally include regular (e.g. every 4-8 weeks) transthoracic echocardiography to assess aortic root diameter. The timing of delivery will be dependent on the root diameter and the rate of dilatation, and also any other complicating factors (see Table 2 for a summary of the potential effects of cardiovascular drugs on the fetus).

The differential diagnosis of aortic dissection includes pulmonary embolism, pneumonia, pneumothorax, myocardial ischaemia, pericarditis, and musculoskeletal pain. A recent case report demonstrates the difficulty of differentiating between some of these in the acute situation.[8] The occurrence of severe chest pain requiring opioid analgesia should always prompt investigation, including CT scan or transoesophageal echocardiogram where aortic dissection is suspected.
Valvular Heart Disease

The valvular condition which carries the highest risk in pregnancy is mitral stenosis. Although rare in the UK, rheumatic heart disease is still common in less developed countries and often complicates pregnancy. Therefore, a high index of suspicion should be maintained, particularly in immigrant women, and those with symptoms of heart failure should be investigated carefully. Pregnant women with mitral stenosis should be managed in tertiary centres with expertise in this condition.[1] The greatest risk associated with mitral stenosis is pulmonary oedema at the time of delivery due to the increase in cardiac output. This risk of pulmonary oedema is considerably increased if pre-eclampsia develops (increased pulmonary capillary permeability).

Women with severe mitral stenosis associated with a large left atrium will often be started on β-blockers and heparin in pregnancy to prevent atrial fibrillation. Early admission is advised and, if vaginal delivery is planned, invasive arterial monitoring is recommended early in labour, before slow and careful institution of epidural analgesia (e.g. 5 ml boluses of bupivacaine 0.1% with fentanyl 2 µg ml-1). IV fluid administration should be avoided; if necessary, it should be given in small (100-200 ml) boluses. Regional anaesthesia for Caesarean section has been described using low-dose combined spinal-epidural anaesthesia[9] and continuous spinal analgesia.[10] Management using general anaesthesia has also been described in a patient with severe aortic and mitral stenosis whose pregnancy was also complicated by pre-eclampsia.[11]

The management of other valvular conditions in pregnancy will largely be governed by the severity of the condition, using the general principles of management described above. In particular, both mitral and aortic regurgitation are usually well tolerated in pregnancy, provided there is no significant left ventricular dysfunction.[3] This is because the decrease in systemic vascular resistance in pregnancy is usually associated with a reduction in regurgitant flow across the affected valve. However, the onset of pre-eclampsia may lead to decompensation.

The general principle of anaesthesia for a parturient with severe aortic stenosis is to avoid sudden decreases in systemic vascular resistance. Whether this is done via careful regional or general anaesthesia will depend on the particular situation and preferences of those involved.

Thromboprophylaxis in women with metallic prosthetic heart valves remains controversial. Warfarin provides the best protection against thrombosis, but increases the risk of fetal teratogenicity and miscarriage. Low molecular weight heparin is much safer for the fetus but carries a greater risk of valve thrombosis to the mother. The method of thromboprophylaxis is therefore usually determined after discussion with the mother.

Percutaneous catheter interventions are safe in the management of mitral and pulmonary stenosis during pregnancy. However, balloon dilatation for aortic valve disease should only be considered in high-risk cases as it carries a lower success rate and a higher risk. Cardiac surgery during pregnancy should only be considered in cases refractory to medical treatment or when there is no catheter-based intervention alternative. Hypothermic cardiopulmonary bypass carries a risk of 30% mortality to the fetus; however, if hypothermia is avoided and perfusion pressures maintained at a relatively high level, fetal mortality can be reduced to 10%.[2]

Pulmonary Hypertension. Pulmonary arterial hypertension carries a very high risk during pregnancy (30-50% mortality). If possible, this needs to be discussed pre-conception. If this has not been possible, it is appropriate in most cases for the question of termination to be raised and discussed with the mother, ideally by the multidisciplinary team who has carried out her risk assessment and who can advise on further management. If the decision is made to continue with the pregnancy, efforts will be made to optimize her condition, usually including the use of a pulmonary arterial vasodilator such (e.g. sildenafil) and plans made for the rest of the pregnancy and delivery as described above.

Owing to the increased risk of mortality at delivery, most units tend to opt for elective Caesarean section under a 'cardiac' general anaesthetic, as this allows control over ventilation, permits more invasive monitoring (e.g. transoesophageal echocardiography), and may lead to greater cardiovascular stability. However, successful management using regional anaesthesia for Caesarean section has also been described in pulmonary hypertension.[9]

Peripartum Cardiomyopathy. Peripartum cardiomyopathy is defined as the presence of heart failure without any other obvious cause in a pregnant woman occurring anytime from 1 month pre-delivery up to 5 months post-partum. If any pregnant or post-partum woman has unexpected and persistent dyspnoea or is noted to be unusually tachypnoeic or tachycardic, and pulmonary embolus has been excluded, she may have peripartum cardiomyopathy and should be investigated further by a cardiologist and usually by echocardiography.[2]

Source : http://www.medscape.com/viewarticle/590859