Cardiovascular disease in pregnancy: What ob/gyns need to know

Dr Hameed is Professor of Clinical Obstetrics & Gynecology, Professor of Clinical Cardiology, Medical Director, Obstetrics, Director, Quality and Safety at University of California, Irvine.

Dr Steller is a third-year resident in the Department of Obstetrics and Gynecology, University of California, Irvine.

Neither author has a conflict of interest to report in respect to the content of this article.

Cardiovascular disease (CVD) complicates 1% of all pregnancies.¹ It has surpassed hemorrhage, hypertensive disorders, and embolism to become the leading cause of indirect maternal death in pregnancy, accounting for approximately 26.4% of pregnancy-related deaths.^2,3 In the future, the number of pregnant women with CVD is likely to rise as advances in healthcare are simultaneously allowing children with congenital heart disease (CHD) to reach reproductive age and enabling women of advanced maternal age with CVD risk factors to become pregnant.⁴ Confronting CVD challenges and their associated morbidity and/or mortality requires:

·      Foundational knowledge of cardiac physiology and the hemodynamic changes of pregnancy, which can reveal or overwhelm a previously well-compensated defect

·      Early identification of cardiac disease regardless of the timing or the manner of presentation

·      Early involvement of a multidisciplinary cardiac care team including maternal fetal medicine, cardiology, and anesthesia

Cardiovascular physiology

Cardiac output is the product of the volume of blood pumped from the left ventricle with each heart beat (stroke volume) and the heart rate. Three major factors that affect stroke volume include:

·      Preload: the degree to which the ventricles are stretched prior to contracting; determined primarily by the volume and speed of venous return.

·      Contractility: largely affected by sympathetic and parasympathetic interplay.

·      Afterload: the aortic pressure during systole (systolic blood pressure); governed by vascular resistance.

Notably, ejection fraction is the fraction of outbound blood pumped from the left ventricle per beat, which is calculated by dividing stroke volume by end-diastolic left ventricular volume.

During pregnancy, the cardiac output increases by 43%. This increase is driven in the first trimester primarily by decreased vascular resistance (-21%), and later in pregnancy by increased plasma volume (+40%–50%) and heart rate (+17%).^5,6

Clinical implications during labor and delivery: Hemodynamic changes during Stage I of labor are induced by pain, anxiety, and contractions-all of which increase heart rate, stroke volume, and cardiac output by a further 50%. On the other hand, supine positioning may decrease cardiac output by decreasing preload due to compression of the inferior vena cava. Valsalva during Stage II adds large fluctuations in central venous pressure by increasing preload followed by decreased preload and increased systemic vascular resistance after each push. These fluctuations may effectively be attenuated by adequate pain control, minimization/avoidance of Valsalva, and assisted delivery. Stage III may be complicated by decreased preload secondary to blood loss and/or increased preload by the auto-transfusion of ~500 cc of blood that returns to systemic circulation following delivery of the placenta.⁵ Therefore, labor, delivery, and early postpartum are vulnerable periods in which decompensations or hemodynamic instability may occur in a patient with significant CVD.

Preconception care

Pre-pregnancy evaluation offers several advantages including an opportunity to review the risks of pregnancy for both the mother and fetus. Mothers with CHD have a 3%–15% risk of transmitting CHD to the fetus.⁷ In addition, risk of adverse perinatal outcomes, including miscarriage, preterm delivery, fetal growth restriction, and even death, approaches 30%.^8-12

Maternal risk assessment is disease-specific. It may range from negligible risk (WHO class I) to a very high risk of maternal morbidity and mortality (WHO class IV). Pregnancy is contraindicated in certain maternal conditions such as pulmonary hypertension, severe left ventricular dysfunction (ejection fraction <30%), history of peripartum cardiomyopathy, severe left ventricular outflow tract obstruction, and Marfan syndrome with dilated aorta (Table 1).¹³ In general, among patients with valvular heart disease, regurgitant valve lesions are better tolerated than valve stenosis in pregnancy.¹⁴ The risk of maternal and/or fetal complications is primarily based on the underlying cardiac lesion and functional capacity. Commonly used risk assessment models from CARPREG¹⁵ and ZAHARA^16,17 investigators may assist providers in not only counseling patients but also dictating which patients should receive a higher level of care, the frequency of antepartum/postpartum follow-ups, and timing/location of delivery (Table 2).

For most cardiac patients, an electrocardiogram, echocardiogram, and B type natriuretic peptide (BNP)^18,19 levels provide baseline assessment tools. All patients should receive maternal-fetal medicine, cardiology, and/or genetics consultations. Trending BNP levels at intervals through pregnancy and the postpartum period may be valuable in management of this high-risk group of women.

It is critical that maternal cardiac status be optimized prior to anticipated pregnancy; therefore a discussion regarding contraception and timing of pregnancy is of paramount importance. The use of long-acting reversible contraceptives (LARCs) is considered relatively safe in women with CVD.^20,21 A subset of cardiac patients may be on anticoagulation prior to pregnancy (ie, those with atrial fibrillation or prosthetic heart valves). The preconception period is an ideal time to review anticoagulation options and consider switching from warfarin to heparin due to the known teratogenic risk associated with use of warfarin during the first trimester.¹³

Evaluation of a patient with cardiac symptoms

Most patients with known or unknown heart disease may not present to their ob/gyn until after pregnancy is established. A thorough history and physical examination is likely to uncover most cardiac diagnoses. Risk factors such as African-American race, obesity, smoking, illicit drug use, high cholesterol, diabetes, and hypertension should also be reviewed.

Pregnancy is a state of circulatory volume overload and roughly equates to a state of low-level continuous exercise. Minor symptoms of shortness of breath, tiredness, and swelling are commonly encountered in otherwise healthy pregnant women. These symptoms clearly overlap with those seen in various cardiac conditions. The biggest challenge for the ob/gyn is to differentiate between these physiologic symptoms and those related to cardiac disease. Symptoms should be evaluated in context of severity, risk factors, abnormal physical examination findings, and vital sign abnormalities. It is important to note that symptoms of progressive or severe shortness of breath, orthopnea, persistent/nocturnal cough, wheezing, chest pain, palpitations, or dizziness should be taken seriously because they may represent an underlying cardiac condition and/or impending decompensation. Likewise, abnormal physical examination findings such as murmurs, wheezing, crackles, etc. warrant timely appropriate work-up, referrals and follow-up as indicated.³Presence of cardiac risk factors, symptoms, and/or physical examination findings in combination should alert the ob/gyn to pursue the differential diagnosis of cardiac disease.

Overview of cardiac care during pregnancy

Considerations for prenatal care: A multidisciplinary approach is critically important for care of a pregnant woman with heart disease. A close collaboration between an obstetrician, maternal-fetal medicine specialist, cardiologist, anesthesiologist +/- cardiothoracic surgeon and neonatologist is required to optimize maternal and fetal outcomes. Patients should be evaluated at frequent intervals to assess functional status and/or development of new symptoms. Consideration should be given to transfer to a higher-level institution in selected cases. Pregnant women with CHD should receive care at an institution with expertise in CHD.^4,13

Considerations for anesthesia: Most patients with CVD will benefit from neuraxial anesthesia with a few important considerations. Individuals with pulmonary arterial hypertension or aortic stenosis are highly dependent on adequate preload to maintain cardiac output and hypotension from sympathetic blockade may lead to life-threatening consequences. In addition, in patients with intracardiac left-to-right shunts, hypotension may trigger a reversal in flow across the shunt, resulting in deoxygenated blood travelling from the right heart directly into systemic circulation without going through the lungs.¹³

Route of delivery: Vaginal delivery affords several advantages in a patient with CVD, including lower blood loss compared to cesarean delivery, less hemodynamic fluctuations (in the absence of Valsalva), and shorter recovery time. Patients are generally able to ambulate the same day without significant pain issues. Only a handful of cardiac diagnoses merit a cesarean delivery (Table 3).¹

General considerations for labor and delivery:

1)    Keep laboring patients in a semi-recumbent position with a lateral tilt to maximize cardiac output

2)    Institute venous thromboembolism prophylaxis

3)    Apply continuous pulse oximetry and use oxygen to keep oxygen saturation >95%

4)    Maintain a strict log of fluid intake and output

5)    Provide adequate analgesia

6)    Allow patients to labor down or have assisted second stage of labor

7)    Do not provide prophylaxis for bacterial endocarditis to a woman who is having a vaginal or cesarean delivery unless she is diagnosed with chorioamnionitis. Very few cardiac diagnoses require bacterial endocarditis prophylaxis^22,23

8)    For the first 24 hours after delivery, closely monitor patients for development of heart failure or arrhythmias

Postpartum and interconception care

The first 24 hours after delivery entail significant fluid shifts, which may result in decompensation of a previously stable patient. Selected patients may be candidates for continuous maternal heart rhythm monitoring in addition to close monitoring of vital signs and fluid status. Cardiac patients should be continued on most of their currently prescribed medications as dictated by their underlying diagnosis. In addition, medications such as angiotensin-converting enzyme inhibitors/angiotensin receptor blockers that were withheld during pregnancy may safely be reinstituted in the postpartum period. The discharge plan should clearly outline early follow-up appointments with the obstetrician, cardiologist, and primary care provider. Future pregnancy plans and contraceptive options should also be reviewed at time of discharge.

Considerations in the postpartum period: It is important to retain an index of suspicion for cardiac disease not only during pregnancy but also in the postpartum period. It is not uncommon for women to present after the customary 4– to 8-week postpartum period with new or worsening symptoms that may be representative of pregnancy-related cardiomyopathy (ie, peripartum cardiomyopathy). Peripartum cardiomyopathy is defined as left ventricular systolic dysfunction (with an ejection fraction <45%) that is diagnosed during the last month of pregnancy or within 5 months postpartum without any identifiable cause of heart failure.²⁴ Other diagnostic echocardiographic findings include a left ventricular end-diastolic dimension >2.7 cm/m² or fractional shortening of <30% by M-mode echocardiography.²⁵ These women typically present with symptoms that are often dismissed. Delays in diagnosis and appropriate treatment may result in devastating consequences.³

Summary

Pregnancy mimics heart disease. Normal physiologic complaints of pregnancy overlap with cardiac-related symptoms. In order to improve outcomes in mothers with preexisting or newly diagnosed cardiac conditions, it is imperative for ob/gyns, primary care physicians, and emergency room physicians to keep cardiac disease in the differential diagnosis of any pregnant or postpartum woman who has delivered within the previous year. Presence of cardiac symptoms should prompt further testing, appropriate referrals, and follow up.

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