The parturient with heart disease, whether congenital or acquired, represents a challenge even for the experienced anaesthesiologist. The main goal in the management of these patients is to prevent further derangement of cardiac function during labour in a heart which is already stressed by the "physiological" changes of pregnancy. This can be accomplished by effective anxiolysis, analgesia and anaesthesia. Ultimately, the aim of any anaesthetic intervention is to ensure the wellbeing of both the mother and the fetus.

Pregnancy induces an increase in cardiac output (30-40%), which reaches its maximum by the end of the 10th week and which is maintained for the remainder of the gestational period. The increase in cardiac output results from an increase in both heart rate and stroke volume. There is a concomitant decrease in peripheral vascular resistance (PVR), which reflects the hormonally-induced vasodilation seen in pregnancy (1). Circulating blood volume increases by about 1 litre as a result of an increase in plasma volume and, to a lesser extent, an increase in red cell mass.

Labour itself is associated with additional cardiovascular stresses. The pain of labour can lead to a sustained increase in cardiac output of about 45 percent as compared to the pre-labour value. The parturient can be exposed to wide variations in ventricular preload. - During each uterine contraction preload increases as a result of autotransfusion from the uterine vascular bed. Conversely, preload can be decreased as a result of caval compression, haemorrhage (average blood loss during a vaginal delivery is about 500mls and during caesarean section about 1000mls) or the sympatholytic effects of neuraxial blockade (Chapter 82). The effects of the Valsalva manoeuvre (which occurs during pushing) are complex. All of these physiological changes have the potential to precipitate acute cardiac failure in patients whose cardiac performance is already compromised.

Drugs used during obstetric analgesia or anaesthesia can affect cardiovascular performance either directly or indirectly through the autonomic nervous system. If an appropriate analgesic or anaesthetic technique is selected for a parturient, the haemodynamic consequences of the chosen method can sometimes be used to the advantage of the parturient with cardiovascular disease.

Accurate cardiovascular monitoring during labour and in the puerperium is essential in the management of all parturients with heart disease. Monitoring of ECG, BP (preferably invasive) and Sa02 is mandatory in patients with severe disease.

Parturients with Valvular Disease:
The general principles of regional blockade in a patient with valvular disease are outlined in Chapter 108. Mitral Stenosis
This condition is usually the result of rheumatic heart disease. The main haemodynamic features are pulmonary congestion and reduced left ventricular diastolic filling. Epidural analgesia for labour has been successfully used in these patients and has been shown to have little influence (and sometimes beneficial effects) on the haemodynamic picture. Pulmonary artery pressure monitoring (Swan-Ganz catheter) is strongly recommended by some authors (8) in patients with moderate-to-severe mitral stenosis. Many authors recommend epidural block as the technique of choice in providing anaesthesia for caesarean section in these patients (2, 9, 10). Great care is needed in the administration of the block and its cephalad spread should be restricted at T5 level.

Mitral Regurgitation
In these patients an increase in systemic vascular resistance should be prevented. Epidural block is the technique of choice (3, 11, 12) for analgesia in labour as well as for anaesthesia for caesarean delivery (3).

Aortic Stenosis.
The key to the anaesthetic management of these parturients is the maintenance of both preload and afterload. - Coronary perfusion is crucially dependent on the maintenance of diastolic pressure and time, and cardiac output is relatively fixed. Analgesia for labour is best provided by parenteral narcotics as well as by inhalation of nitrous oxide and oxygen. For the second stage of labour, pudendal nerve blockade can be used. Good analgesia has also been provided by intrathecal narcotics. General anaesthesia is the technique of choice for caesarean section.

Aortic Regurgitation
These patients tolerate the circulatory overload produced by pregnancy very well and most techniques of analgesia and anaesthesia have been used successfully. A decrease in left ventricular afterload (such as occurs with neuraxial blockade) can lead to an improvement in cardiac function by reduction of the regurgitant fraction.

Anaesthesia and Analgesia in Patients with Congenital Heart Disease:
Tetralogy of Fallot (Figure E.4)
This condition is the most common cyanotic heart condition observed in pregnant patients. Cyanosis is the result of a right-to-left shunt the degree of which is determined by the amount of obstruction to right ventricular outflow. One of the principal anaesthetic aims in managing these patients is to prevent an increase in this shunt. As with Eisenmenger's syndrome, the ratio of systemic to pulmonary vascular resistance is one determinant of the magnitude of the right-to-left shunt and the level of cyanosis is also affected by changes in cardiac output (mixed venous oxygen saturation effect).
All known techniques of analgesia and anaesthesia have been used with good results but major regional blocks have to be used with caution due to the risk of a severe decrease of systemic vascular resistance (2). For caesarean section both light and deep levels of general anaesthesia have been advocated (3). Tachycardia or infundibular spasm can be prevented by the administration of propranolol.

Eisenmenger Syndrome
These patients present with pulmonary hypertension with right-to-left or left-to-right shunt at aortopulmonary, ventricular or atrial level. A decrease in the ratio of systemic to pulmonary vascular resistance results in increasing cyanosis. In these patients pregnancy and delivery are associated with a high mortality rate (4). Epidural blockade using low concentrations of local anaesthetic has been used to produce satisfactory analgesia in labour (5, 6). For caesarean section the anaesthetic technique of choice is general anaesthesia using drugs that do not depress cardiovascular function.

Coarctation of the Aorta.
The main cardiovascular consequence of coarctation is a chronically-increased left ventricular afterload that causes hypertrophy of the left ventricle. Epidural blockade as well as intrathecal morphine have both been successfully used to provide analgesia in labour (7). General anaesthesia is preferred for caesarean section (3).

Patients with Cardiomyopathy:
On the basis of anatomical and functional features cardiomyopathies can be classified as either dilated or hypertrophic. There is little information regarding the anaesthetic management of patients with a cardiomyopathy in labour. In principle, depression of myocardial function should be avoided in those patients with a dilated cardiomyopathy, but mild afterload reduction may be of benefit. In those patients suffering from a hypertrophic cardiomyopathy, preload should be well-maintained (to avoid systolic cavity-obliteration) and beta-agonists (whether used for tocolysis or cardiovascular reasons) should be avoided. Peri-partum cardiomyopathy is discussed in Chapter 41.

References:
1. Walters WAW, McGregor WG. Cardiac Output at rest during pregnancy and puerperium. Clin Sc 30:1, 1966

2. Ostheimer GU, Alper MH. Intrapartum anaesthetic management of pregnant patient with heart disease. Clin Obstet Gynecol 18: 81, 1975

3. Mangano DT. Anesthesia for the pregnant cardiac patient. In: Anesthesia for obstetrics. S Shnider & G. Levinson eds. 345-381, William and Wilkins, Baltimore 1986

4. Gleicher N, Midwall J, Hockberger D, et al. Eisenmenger's syndrome in pregnancy. Obs Gynecol Surv 3:721, 1979

5. Crawford JS, Mills WG, Pentecost BL. A pregnant patient with Eisenmenger's syndrome. Br J Anaesth 43:1091, 1971

6. Midwall J, Jarfin H, et al. Shunt flow and pulmonary haemodynamics during labour and delivery in Eisenmenger syndrome. Anesth Analg 56: 543, 1977

7. Barnes CG. Medical Disorders in obstetric practice, 4 Edition, 72-79, Blackwell Scientific, Oxford 1974

8. Clark SL, Phelan JP, et al. Labour and delivery in presence of mitral stenosis: central haemodynamic observation. Am J Obstet Gynecol 152: 984, 1985

9. Moir DD, Willocks J. Epidural analgesia in British obstetrics. Br J Anaesth 40:129, 1968

10. Marx GF, Hodgkinson R. Special considerations in complications of pregnancy. In Marx GF; Bassel GM eds, 297-334, Elsevier 1980

11. Crawford JS. Principles and practice of obstetric anaesthesia. Blackwell Scientific, 1988

12. Ferguson JE, Wyner J, et al. Maternal Health complications. In Anaesthesia in obstetrics, G. Albright et al. eds. Butterwoths 1986