Mitral regurgitation

Mitral regurgitation is usually tolerated well during pregnancy. The marked decrease in systemic vascular resistance that occurs during pregnancy alleviates the abnormal physiologic stress imposed by this lesion. Rarely, reactive pulmonary hypertension and severe right heart failure may ensue.

There are no specific recommendations for the management of mitral regurgitation during labour and delivery. Prior to labour symptoms may be managed with diuretics and vasodilators. During labour, regional anaesthesia is usually well tolerated. However, in complicated NYHA class 3-4 cases, general anaesthesia may be required.

Aortic stenosis

In general the symptoms of aortic stenosis are masked by progressive left ventricular hypertrophy and are thus easily missed. Overall, patients who were asymptomatic prior to pregnancy usually tolerate pregnancy relatively uneventfully.

Echocardiographic determination of valve area is the best guide to severity of aortic stenosis. The hyperdynamic circulation of pregnancy frequently leads to overestimation of the degree of stenosis.

These patients tolerate tachycardia, hypovolaemia and systemic vasodilatation poorly, since coronary perfusion is critically dependent upon maintaining aortic diastolic pressure. General anaesthesia and caesarean section, with the aid of invasive haemodynamic monitoring, appears to be the safest means of successful delivery. Aggressive maintenance of systemic blood pressure with vasopressors (e.g. phenylephrine), is paramount to the avoidance of severe hypotension, acute left ventricular failure and cardiac arrest.

Spinal anaesthesia is generally contraindicated in these patients. There are reports of the successful management of vaginal delivery under carefully introduced and limited epidural analgesia, but this should be restricted to very experienced hands.

Aortic regurgitation

Aortic regurgitation reduces both cardiac output and coronary blood flow. The principles of management are: a reduction in afterload (to improve forward flow) and maintenance of a relatively high heart rate (to reduce the regurgitant fraction). In patients with aortic regurgitation there is reduced coronary flow in diastole; coronary flow has been documented to reverse in patients with severe aortic regurgitation. It is thus important to maintain systolic blood pressure within 15% of baseline levels in these patients. Many patients with aortic regurgitation improve symptomatically during pregnancy. During labour, epidural analgesia improves forward flow, and is therefore the anaesthetic of choice in patient's requiring an operative delivery.

Pulmonary stenosis

Pulmonary stenosis increases right ventricular work and can dramatically impair left ventricular output (due to reductions in forward flow). It is important to maintain preload and optimise ventricular contractility, whilst bearing in mind that excess fluid may precipitate acute right heart failure. Atrial fibrillation is also a potential complication of fluid overload.

The goals of haemodynamic management include maintenance of right ventricular preload, left ventricular afterload and right ventricular contractility. In general hypothermia, hypercarbia, acidosis, hypoxia and high ventilatory pressures should be avoided. Aorto-caval compression may result in profound hypotension as a result of acute reductions in right ventricular preload. Most reports recommend vaginal delivery under epidural anaesthesia, as operative delivery is associated with increased maternal mortality.⁸

Spinal anaesthesia may be associated with an uncontrolled reduction in right ventricular preload and should therefore be avoided in severe cases.

Managing valvular heart disease in pregnancy

Although most pregnant patients with valvular heart disease may be managed medically during pregnancy, it is occasionally necessary to consider valve replacement. This may become a necessity in the patient with severe valvular disease (particularly stenosis), where termination of pregnancy is not considered to be an option. Severe symptomatic disease, threatening maternal or fetal well-being is an accepted indication for either balloon- valvuloplasty or valve replacement.¹⁵

When needed, valve replacement is best undertaken during the second trimester. Cardiopulmonary bypass and hypothermia carry substantial risk for the fetus. Fetal bradycardia and death are not uncommon.¹⁵ Meticulous care should be given to the maintenance of blood pressure during bypass and fetal well- being should be monitored continuously with a cardiotocograph.

Bacterial endocarditis prophylaxis

Pregnancy carries no additional risk for bacterial endocarditis. The Committee on Rheumatic Fever, Endocarditis and Kawasaki Disease (American Heart Association), do not recommend routine antibiotic prophylaxis in patients with valvular heart disease undergoing uncomplicated vaginal delivery or caesarean section (unless infection is suspected). Antibiotic prophylaxis as practiced for the prevention of wound sepsis is more than adequate.

Antibiotics are optional for high-risk patients with prosthetic heart valves, a previous history of endocarditis, complex congenital heart disease or a surgically constructed systemic- pulmonary conduit.¹⁶

Pregnant patients with valvular heart disease should receive prophylactic antimicrobial therapy for invasive urinary tract or gastrointestinal procedures.¹⁷ Intravenous ampicillin and gentamicin, or oral amoxycillin should be used in the non- penicillin allergic patient. Vancomycin and gentamicin are used in the patient with penicillin allergy.¹⁶

Anticoagulant therapy in patients with prosthetic valves

Although it is undeniably important to provide ongoing anticoagulation to the pregnant patient with a prosthetic valve, there is debate regarding the optimal agent. Unfortunately there are no randomised trials providing guidance in this area.¹⁸ The use of warfarin and other coumadin derivatives carries a well- established risk of embryopathy, whilst the use of subcutaneous unfractionated heparin has been reported to be ineffective. Low molecular weight heparins have been considered as an alternative but data is limited to trials and reports of only 25 patients, with a treatment failure rate of 20%.¹⁹ Data suggests that the low molecular weight heparins are neither safe, nor effective, in preventing thromboembolic complications in patients with prosthetic heart valves (whether pregnant or not).²⁰

Traditional teaching is that patients should be anti-coagulated with heparin in the first trimester of pregnancy and then converted to warfarin for the remainder of the pregnancy. Warfarin should then be stopped just prior to delivery.

Fetal, but not maternal outcome has been reported to be better where bioprosthetic valves are used instead of mechanical prostheses (in both aortic and mitral positions).²¹

Conclusion

As a rule, regurgitant valvular lesions are far better tolerated in pregnancy than are stenotic lesions. Patients who are asymptomatic, or only have minimal symptoms before falling pregnant, tend to tolerate pregnancy well. Patients with severe symptomatic valvular heart disease should ideally be counselled against pregnancy. In the event of pregnancy, early consultation between obstetrician and anaesthesiologist allows for planning with regards to both the timing of delivery and optimal analgesia/ anaesthesia.

The main principles of management with regard to valvular heart disease in pregnancy are as follows:

• Early identification of the disease, and the assessment of the severity of the lesion(s).
• The appreciation of the severity of risk incurred by both mother and fetus.
• High-risk lesions, for either mother or fetus, should be managed in a high care environment where invasive monitoring is possible, both pre- and post delivery.
• Regional anaesthesia techniques in labour are an attractive option, and may be employed with good outcomes in many patients.
• Carefully titrated epidural anaesthesia for labour is associated with less sympathetic blockade than spinal or epidural anaesthesia for caesarean delivery. Thus, the effective use of regional anaesthesia for labour does not necessarily predict that this method will be safe for caesarean delivery in severe cases.
• Severe mitral or aortic stenosis, or any valvular heart condition associated with pulmonary oedema or heart failure, are contraindications to regional anaesthesia, (except in rare circumstances).

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