Heart disease complicates between 1-4% of all pregnancies in North America, with the majority of complications due to congenital heart disease. During pregnancy, the body undergoes physiological changes that can exacerbate or unmask existing heart disease.

These cardiovascular adaptations are evident by the 5^th to 8^th week of gestation and peak by the late second trimester. The preload is increased due to the associated rise in blood volume. The after load is also reduced due to the decline in systemic vascular resistance. The creation of a low-resistance circuit in the uteroplacental circulation and vasodilatation contribute to the decline in vascular resistance, although the exact mechanism is not completely understood. Overall, there’s a 30 to 50% rise in total cardiac output above the woman’s baseline leading to a benign flow systolic ejection murmur that’s early peaking, soft in over 90% of women. Jugular venous pressure (JVP) is often normal or mildly increased. Displaced apex, varicose veins and edema can all be normal during pregnancy. Signs of actual pathology include the presence of a fourth heart sound, fixed splitting of the second heart sound, diastolic or any loud murmur.

The normal physiological adaptations of pregnancy can have deleterious effects on the mother with pre-existing heart disease and on her developing fetus, because her cardiac reserve is reduced.

Risk factors for adverse outcomes of the pregnancy include NYHA class III or IV heart failure, cyanosis at the baseline prenatal visit, aortic stenosis (valve area less than 1.5 cm²), mitral stenosis (valve area less than 2.0 cm²), smoking, multiple gestations, and the use of anticoagulants throughout pregnancy. Regurgitant lesions tend to be well tolerated during pregnancy, but obstructive lesions like those listed above are predictors of adverse events. Other harbingers of trouble include a left ventricular outflow gradient higher than 30 mm Hg, left ventricular ejection fraction less than 40%, prior congestive heart failure, TIAs, stroke and any arrhythmias including atrial fibrillation.

Patients with severe pulmonary hypertension should avoid pregnancy altogether as they face 30% mortality. Marfan syndrome is an autosomal dominance genetic disorder that carries a 50% transmission rate to the baby and women with an aorta greater than 40 mm should avoid pregnancy to prevent dissection of the aorta.

When arrhythmias are infrequent and well tolerated, and when patients are minimally symptomatic, conservative management is advised. When arrhythmias cause intrusive symptoms or hemodynamic compromise, antiarrhythmic therapy is indicated. Digoxin, hydralazine, calcium blockers, metoprolol and labetalol are relatively safe during pregnancy. ACE and ARB therapies are contraindicated in pregnancy, with a 30% fetal morbidity when administered after 14 weeks of gestation, but they can be safely used during lactation.

Blood ties — so anticoagulate

Women with a pre-existing prosthetic valve typically tolerate pregnancy well if they’re hemodynamically stable. The main issue is the need for anticoagulation during the antepartum period. Warfarin is tetratogenic when given between weeks 6 and 12 of gestation. Warfarin embryopathy has an estimated incidence of 5-7%. Low molecular weight heparin (LMWH) or unfractionated heparin (UFH) is an alternative to oral anticoagulation, since it doesn’t cross the placenta, or carry the same tetratogenic risk as warfarin. But there’s limited data investigating the use of LMWH or UFH in pregnant women with prosthetic valves. An alternative strategy is to use warfarin from the beginning of the second trimester until 36 weeks gestation, maintaining an INR of 2.5 to 3.5. Then, switch to LMWH or UFH from 36 weeks until delivery. Given the lack of data in this area, there’s no consensus recommendation on an anticoagulation regimen.

The moment of truth

Women with an acquired cardiac disease, who are otherwise functionally normal, should be encouraged to undergo labour spontaneously. But induction should be considered if there’s concern regarding the cardiac functionality of the patient. Due to the increased risk associated with caesarean section, its use should be reserved for obstetrical indications. Intramuscular or intravenous opiates effectively relieve the pain of labour and can be safely used in women with cardiac disease. Epidural anesthesia should be used cautiously because of its effect on decreasing venous return, potentially leading to a significant drop in cardiac output, especially in women with particular heart diseases. Pulse oximetry and continuous ECG monitoring should be used to monitor the patient’s hemodynamic status during labour. Continuous fetal monitoring is also indicated, because a drop in maternal cardiac output may expose the fetus to decreased oxygenation and lead to fetal acidosis or death.

Antibiotic prophylaxis

The evidence points to a rate of pregnancy-related endocarditis of 0.5% among women with congenital heart disease. The 2007 American Heart Association (AHA) guidelines on the prevention of infective endocarditis don’t recommend routine antibiotic prophylaxis for either caesarean or vaginal delivery. But individual decisions must be made for women at the highest risk, including those with prosthetic cardiac valve, previous endocarditis, certain congenital defects, and cardiac transplantation recipients with valvular abnormalities.

After delivery, further hemodynamic changes occur, which can also threaten heart failure in women with a pre-existing cardiovascular condition. Such patients should be monitored for 12 to 24 hours postpartum to ensure hemodynamic stability.

Peripartum cardiomyopathy is newly diagnosed left ventricular dysfunction that tends to occur in the last trimester or more commonly in the 6 months postpartum. The incidence is in the order of one per 1,500 pregnancies. Half of these women will improve by 6 months. In North America, this is the number one cause of pregnancy-related death.

References

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