Myocardial infarction (MI) during pregnancy is uncommon, with a reported incidence of ~2-6 per 100,000 deliveries; these figures do not, however, include unstable angina. In the 2016 report of the Confidential Enquiries into Maternal Deaths (CEMD), ischaemic heart disease accounted for over a fifth of all cardiac deaths. The risk of coronary syndromes is increased fourfold in pregnancy, owing to altered physiology such as hypercoagulability, increased myocardial demand and vascular dysfunction.
Ischaemic heart disease in the antenatal population may result from atherosclerotic coronary artery disease or acute coronary artery dissection. Risk factors include smoking, obesity, hypertension, older maternal age and the use of illegal drugs, particularly crack cocaine, which can cause hypertension, left ventricular hypertrophy and coronary artery vasospasm. Postpartum MI has been reported as a complication of pre-eclampsia. Women who have had previous MI, with or without previous coronary artery bypass grafting, may also present to the obstetrician and obstetric anaesthetist.
Problems and special considerations
A high index of suspicion is necessary. Myocardial ischaemia may not be considered in the differential diagnoses of a pregnant woman presenting with chest pain, and the presentation may be atypical. The woman who has been using cocaine is frequently an unreliable historian, and may conceal or deny her drug abuse. Clinical examination and investigations may be difficult to interpret; a systolic murmur is common during pregnancy, and it should be remembered that left axis deviation with non-specific ST and T wave changes is commonly seen in the healthy pregnant patient. Serial ECGs to detect dynamic changes are useful, as is cardiac troponin I since it is unaffected by pregnancy, labour and delivery.
Maternal mortality of acute MI during pregnancy has been reported to be as high as 30-50%, with the highest mortality associated with MI during the third trimester and also delivery within two weeks of an MI. Recent studies suggest a lower mortality rate, of under 10%.
Myocardial ischaemia and infarction caused by cocaine are associated with a high incidence of cardiac arrhythmias.
Antenatal considerations include: the use of antiplatelets and anticoagulants; planning of place, time and mode of delivery; use of intrapartum invasive monitoring; and choice of analgesia and anaesthesia for delivery.
Management options
These women should be managed by a multidisciplinary team. Reported treatments include drug therapy, percutaneous coronary intervention, the use of intra-aortic balloon counterpulsation and coronary artery bypass grafting.
Mode of delivery
There is no consensus of opinion in the literature about the preferred mode of delivery of a woman who has had an antenatal MI, nor about the method of anaesthesia. Vaginal delivery eliminates the stress of surgery and the need to provide anaesthesia. The risk of peripartum thromboembolism is also reduced, as is the potential for obstetric haemorrhage. However, induction of labour carries an increased risk of further obstetric intervention, whereas allowing spontaneous onset of labour is unpredictable. Pushing in the second stage should be limited. Caesarean delivery can be optimally timed to permit senior staff from all concerned specialties to be involved. There is adequate time to institute full invasive monitoring and to organise cardiovascular support, but surgical intervention increases the risks of complications. Blood loss may precipitate cardiac ischaemia in women with preexisting coronary artery disease.
Monitoring
Most authorities suggest using intra-arterial pressure monitoring, pulse oximetry and continuous electrocardiographic monitoring. The use of pulmonary artery pressure monitoring is now not advised as it is associated with significant risks that may outweigh potential benefits. Central venous catheterisation allows infusion of cardioactive drugs as well as an additional mode of monitoring, albeit of right-sided pressures only.
Analgesia and anaesthesia
For analgesia in labour, epidural analgesia minimises haemodynamic instability caused by the pain and stress of labour. Use of low-dose local anaesthetic and opioid infusions or boluses avoids the risk of hypotension. Combined spinal-epidural analgesia would also be a suitable alternative.
Both ‘cardiac’ (high-dose opioid) general anaesthesia and epidural anaesthesia have been used successfully for caesarean section. The major concerns with general anaesthesia are the uncontrolled hypertensive response to tracheal intubation, the risks of potentially life-threatening arrhythmias (particularly in cocaine users) and the need for postoperative ventilatory support because of the high doses of opioids used.
The major concern with regional anaesthesia is haemodynamic instability caused by rapid onset of sympathetic blockade. For this reason, if a regional technique is chosen, a slow incremental technique is preferred to single-shot spinal anaesthesia; epidural, continuous spinal, and combined spinal-epidural anaesthesia have been used successfully.
Oxytocic drugs
Ergometrine causes acute hypertension and is contraindicated in women with ischaemic heart disease; its use has been implicated in maternal deaths in recent CEMD reports. Large intravenous boluses (> 5 U) of oxytocin cause transient hypotension and may compromise coronary filling; it is therefore preferable to use an intravenous infusion of oxytocin during management of the third stage of labour. Carboprost can cause significant haemodynamic effects and is often avoided in patients with known cardiac disease. Non-pharmacological methods of haemostasis should be considered early, to avoid major blood loss and reduce the use of drugs that may cause haemodynamic compromise.
Puerperium
The fluid shifts that occur during the early postpartum period contribute to potential haemodynamic instability at this time. High-dependency nursing and medical care is mandatory; intensive cardiovascular monitoring should be maintained for at least 24-48 hours after delivery. Epidural opioids are recommended for provision of postoperative analgesia. The use of prophylactic anticoagulants should be considered for 3-6 months post-delivery.
Key points
• Myocardial infarction during pregnancy has a high maternal mortality.
• The association between myocardial infarction and cocaine consumption should be considered.
• Management of labour and delivery is based on maintaining haemodynamic stability and minimising myocardial oxygen consumption.
Further reading
Bush N, Nelson-Piercy C, Spark P, et al. Myocardial infarction in pregnancy and postpartum in the UK. Eur JPrev Cardiol 2013; 20: 12-20.
Fryearson J, Adamson DL. Heart disease in pregnancy: ischaemic heart disease. Best Pract Res Clin Obstet Gynaecol 2014; 28: 551-62.
Kealey A. Coronary artery disease and myocardial infarction in pregnancy: a review of epidemiology, diagnosis, and medical and surgical management. Can J Cardiol 2010; 26: 185-9.
Knight M, Nair M, Tuffnell D, et al.; MBRRACE-UK. Saving Lives, Improving Mothers’ Care: Surveillance of maternal deaths in the UK 2012-14 and lessons learned to inform maternity care from the UK and Ireland Confidential Enquiries into Maternal Deaths and Morbidity 2009-14. Oxford: National Perinatal Epidemiology Unit, University of Oxford, 2016.
Roth A, Elkayam U. Acute myocardial infarction associated with pregnancy. J Am Coll Cardiol 2008; 52: 171-80.