Cardiac Disease in Pregnancy

After completing this article, readers should be able to: Pregnancy causes considerable physiologic change in women, particularly in their cardiovascular systems. Circulating blood volume increases dramatically, and cardiac output increases up to 50% by the end of pregnancy. Pregnant women who have cardiac disease must be able to accommodate these normal changes to have a successful pregnancy. Inability to do so can result in increased morbidity and mortality.Cardiac disease is an important cause of nonobstetric mortality during pregnancy and can result in significant morbidity. (1)(2) Approximately 10% of all maternal deaths in the United States can be attributed to cardiac disease, a number that has remained consistent for the last half century. (1) In one study of 1,000 pregnant women who had various types of cardiac disease and were followed by the same health-care team over a 10-year period, more than 75% of the women had no complications during pregnancy. (2) Among the remaining 25%, the following complications were seen most often: The overall maternal mortality rate in this group was 2.7%, and the stillbirth and spontaneous abortion rate was 7.7%.Cardiac disease covers a wide range of conditions, including congenital heart disease, acquired disease such as rheumatic valvular disease, and coronary disease. It is estimated that 1% to 3% of women either have cardiac disease entering pregnancy or are diagnosed with cardiac disease while they are pregnant. (1)(3) The frequency of specific types of cardiac disease seen in an individual medical center depends on the patient population and local conditions. Advances in the diagnosis and treatment of congenital heart disease have increased the survival rate of children affected with these disorders. As this population enters childbearing age, pregnancy counseling and management need to be addressed. Pregnant women who have congenital heart disease represent the largest number of patients seen at some referral centers, comprising as many as 70% to 80% of all the cardiac patients evaluated. (1)(4)(5) It is estimated that 1 in 10,000 pregnancies is associated with coronary heart disease, notably myocardial infarction. (6)The purpose of this article is to review the physiologic changes of pregnancy that affect cardiac disease, preconception counseling, general management throughout pregnancy, and neonatal implications.The cardiovascular changes that occur during pregnancy result in a high-flow, low-resistance state. Changes begin as early as 7 weeks’ gestation and persist until approximately 2 weeks postpartum. (7) Some of these alterations may be problematic for the woman who has cardiac disease.Blood volume increases approximately 1,600 mL in the singleton pregnancy and 2,000 mL in the twin pregnancy. Blood volume begins to increase as early as 7 weeks’ gestation and peaks at approximately 32 weeks’ gestation. In addition, by term, approximately 500 to 900 mEq of sodium and 6 to 8 L of total body water are accumulated. The composition of whole blood changes, with red blood cells increasing 20% and plasma volume increasing 45% to 50%. (7) The increase in plasma volume is responsible for the physiologic anemia of pregnancy, although the ability to carry oxygen actually increases (approximately 1,400 mL/min by term). (1) Blood flow to the uterus at the end of pregnancy increases greater than 50-fold when compared with the nonpregnant state. Uterine flow rates can be as high as 750 mL/min, consuming 10% to 15% of maternal cardiac output. (8) Cardiac output is a function of heart rate times stroke volume. During pregnancy, the maternal heart rate increases slightly, which, in addition to the markedly increased blood volume, results in an increase in cardiac output of up to 50% by term. (7)Extra blood volume can be problematic for women who have stenotic valves, dysfunction of the myocardial muscle, or ischemic heart disease. In these cases, the inability of the heart to accommodate the excess volume may lead to congestion in the heart and lungs or acceleration of ischemia. Areas of vascular weakness or defect, as seen with Marfan syndrome and aneurysms, respectively, may rupture or be weakened further under the pressure of extra blood flow. (9)(10)(11)(12)The previously noted changes account for the high-flow state of pregnancy. The low-resistance state results from a 25% decrease in SVR. Blood pressure drops in response to the decline in SVR, with the nadir occurring at 20 weeks’ gestation. As blood volume increases, blood pressure returns to early prenatal values during the third trimester. (7) Women who have left-to-right shunts are susceptible to shunt reversal if pulmonary hypertension is present or if SVR drops too low and particularly if these events occur simultaneously. Clinical signs of shunt reversal are hypoxemia and maternal and fetal decompensation. (9)(10)Labor marks a period of fluctuations in cardiac output. Uterine contraction can cause as much as 300 mL of blood to re-enter the central circulation, thereby increasing cardiac output. With the increase in cardiac output, blood volume to the placenta increases to approximately 750 mL/min. Because oxygen consumption can increase 300% during labor, the increased blood flow satisfies the demand for oxygen in the patient who has adequate blood volume, appropriate hemoglobin levels, and a healthy cardiovascular system. On delivery of the fetus and placenta, it is estimated that 1,000 mL of blood can be displaced from the uterus and lower extremities back into the maternal circulation. (7)(8)(13) Pulmonary hypertension and certain valvular lesions require a consistent amount of volume or preload to maintain cardiac output. Fluctuations in volume delivered to the right side of the heart during labor and at the time of delivery can result in a decline in cardiac output. (9)(10)Pregnancy is a hypercoagulable state. An increase in certain clotting factors in conjunction with depression of the fibrinolytic system places the pregnant woman at increased risk for thrombus formation. This is particularly problematic with certain types of atrial fibrillation and mechanical heart valves. The need for anticoagulation to prevent thrombus formation can place the patient at risk for postpartum hemorrhage. (9)Many of the normal symptoms of pregnancy, such as fatigue, dyspnea, orthopnea, and palpitations, can mimic symptoms of cardiac disease. (14)(15) Careful examination for abnormal cardiovascular signs and symptoms is an important part of prenatal care because cardiac disease may be unmasked by physiologic changes of pregnancy (Table 1).It is mandatory that women who have chronic cardiac disease undergo a complete evaluation before attempting pregnancy. The basic evaluation should include: complete cardiovascular history and physical examination, 12-lead electrocardiography, transthoracic echocardiography, and possibly pulse oximetry or arterial blood gas determination. (4) Transthoracic echocardiography confirms the lesion and determines severity. An ejection fraction of less than 55% is associated with an increased risk of heart failure during pregnancy. (16)(17) An exercise stress test mimics changes seen during pregnancy, such as elevation in heart rate, and can assist the clinician in estimating cardiac response. (14) Doppler flow studies are useful in measuring the size of the affected valve(s), which then helps to determine the risk of complications during pregnancy. (16)Determining the woman’s ability to function within the constraints of her cardiac disease is an important baseline and ongoing assessment. The New York Heart Association (NYHA) Functional Classification is used to determine the woman’s baseline functional status and to monitor how functional status changes in response to the changes of pregnancy (Table 2). (1)In general, if the patient has a symptomatic lesion that can be corrected, this should be undertaken before pregnancy. (4)(14) In two studies comparing women who had cyanotic lesions that were corrected prior to pregnancy with women who did not have corrective surgery, the women who had the corrective surgery had fewer early pregnancy losses and small-for-gestational age infants. (14)(18)(19) Women who have stenotic valves that are classified as severe also should be considered for palliative treatment before pregnancy. (17)Different types of cardiac disease have been grouped into risk categories to estimate maternal risk. The risk assigned to each group is based on treatment given by a multidisciplinary health-care team experienced in caring for pregnant women who have cardiac disease (Table 3).Although useful, assigning of risk categories should be accompanied by a thorough review of the literature for the woman’s specific lesion that takes into consideration outcomes associated with new treatments and therapies. (9) Because pregnancy is a dynamic state, the woman’s functional classification may change during the course of the pregnancy. A woman who has mitral stenosis functional class I may be NYHA functional class III or IV at the time of delivery. (20)Anticoagulation therapy is required for some cardiac disease, most notably valvular lesions complicated by atrial fibrillation and mechanical valves. Controversy exists as to the best medication and regimen to achieve adequate anticoagulation. When used for anticoagulation for mechanical valves, warfarin is believed to provide better protection against thrombus formation than heparin. Because warfarin may be teratogenic during organogenesis, its use during early pregnancy is not recommended. Fetal/neonatal complications reported when warfarin was administered during organogenesis include nasal hypoplasia, optic atrophy, abnormalities of the digits, changes in the epithelium, mental impairment, and chondroplasia punctata. (17) In addition, because warfarin crosses the placental barrier, it must be discontinued late in the pregnancy to reduce the risk of intracranial hemorrhage in the fetus during the delivery process. (1)(4)(17)(21)To achieve therapeutic heparin levels to prevent thrombus formation, the partial thromboplastin time must be approximately twice that of normal. However, it can be difficult to achieve a consistent level of therapeutic anticoagulation with unfractionated subcutaneous heparin. (1) The ability of low-molecular weight heparin to provide adequate anticoagulation with mechanical valves remains uncertain. (22) The optimal choice for anticoagulation (warfarin, heparin, or a combination of both) in pregnancy in the setting of a mechanical heart valve is controversial, and close collaboration between specialists in obstetrics, cardiology, and anesthesia is critical. (4)(17)(21)Of all cardiac diseases, the types associated with the highest risk for maternal mortality are Marfan syndrome with valve involvement, dilated cardiomyopathy, uncorrectable NYHA class III or IV lesion resistant to medical treatment, and pulmonary hypertension with either systolic pulmonary pressure greater than 50 mm Hg or with Eisenmenger syndrome. In these cases, a thorough discussion with the woman regarding pregnancy termination is mandatory. (1)(23)Preconception counseling should include a review of the patient’s disease and current functional status as well as a discussion of the anticipated risks to her of pregnancy. The possibility of preconception corrective surgery or therapy should be addressed. Management during pregnancy, the effect pregnancy might have on maternal life expectancy, and the ability of the patient to care for her child all are important issues to address during counseling. Patients should be made aware of any risks of fetal damage as a result of treatment during pregnancy as well as the increased risk of cardiac disease in the fetus/neonate. (4)(24)If the woman who has cardiac disease did not have the benefit of preconception counseling before pregnancy, testing and counseling as described previously should be undertaken as soon as possible. Women who have symptomatic valvular disease may be candidates for valve replacement or palliative therapy during pregnancy. The optimal time for the procedure may be during the second trimester to avoid organogenesis in the first trimester as well as the increased risk of preterm labor or decreased placental perfusion in the third trimester. (4)(16)(17)A multidisciplinary team should be assembled early in the pregnancy that includes obstetrics, cardiology, anesthesia, neonatology, and nursing. The purpose of the team is to review specific information about the woman’s cardiac disease, anticipate potential system problems or problems the woman may encounter during pregnancy, and develop a written plan of care that is available to all departments. (4)(24) The plan should include optimal gestational age for delivery, best location for labor and delivery, and specific plans for delivery, such as the need for invasive monitoring or subacute bacterial endocarditis prophylaxis. (4)At each prenatal visit, the functional status of the woman should be reassessed. Evaluation for abnormal cardiovascular signs and symptoms listed in Table 1 may warn of complications. Complications specific to pregnancy, such as preeclampsia, anemia, infection, and hyperthyroidism, are treated aggressively if found. (4)In a review of 276 pregnancies in 221 women who had cardiac disease, predictors of cardiac complications during pregnancy included history of a prior cardiac event or arrhythmia, NYHA functional class III or IV on entry to prenatal care, left heart obstruction (presence of a mitral valve or aortic valve lesion or both), and myocardial dysfunction. (25) Prior cardiac events were defined as heart failure, stroke, and transient ischemic attack. Arrhythmias were either bradyarrhythmias or tachyarrhythmias that were symptomatic or required treatment. A complication was reported in 18% of the 276 pregnancies. Among those who experienced a complication, 89% of the complications occurred in the antepartum period and were due to either heart failure or arrhythmia. (25)As stated earlier, labor and delivery involves substantial hemodynamic fluctuations. Uterine contractions during labor result in a rise in blood pressure, heart rate, cardiac output, and oxygen consumption. Relief of the discomfort of contractions can lessen the rise in blood pressure and heart rate, but it has less effect on cardiac output. (17) During the late second stage of labor, cardiac output can increase as much as 45%, and each contraction can increase the value an additional 15%. (13)(17)The timing, management, and route of delivery in a woman who has cardiac disease are dependent on her functional status late in pregnancy and her particular cardiac disease. Timing of delivery is based on functional status in response to the cardiovascular changes in late pregnancy, trends in functional status, the status of the fetus based on antenatal testing and growth measurements, and the possibility of further treatments that could relieve signs of decompensation to allow the pregnancy to continue. (1)For women who have cardiac disease, delivery is planned best at a time when all team members are available. This is especially true for women who have NYHA functional class III or IV disease and a risk classification of intermediate/moderate or high/major. (1) The optimal mode of delivery must be individualized. Vaginal delivery is reasonable for most women and is associated with less risk of hemorrhage, infection, and pulmonary edema as well as an easier postpartum recovery compared with cesarean delivery. Women who have suspected aortic dissection, a dilated aortic root, or severe valvular disease requiring urgent repair probably are delivered best via cesarean section. (1)(4)(14)The level of monitoring during labor is dependent on functional status and risk classification. Functional classification should be reassessed regularly during labor and delivery and specifically for a persistent heart rate greater than 100 beats/min at rest. If allowed to persist, such a heart rate can result in decompensation with some forms of cardiac disease. Pulse oximetry (with the use of oxygen to maintain saturation at pre-established baseline levels), auscultation of the lungs, strict intake and output, and continuous fetal heart rate monitoring are basic monitoring components. (1)(9) The lateral recumbent position most often is the position of choice during labor because it maintains adequate venous return. (4)(14)(17)(26)Invasive hemodynamic monitoring should be considered for women who have NYHA functional class III or IV disease, pulmonary hypertension, impaired left ventricular function, severe aortic stenosis, or recent myocardial infarction. (1)(4)(14) Invasive hemodynamic monitoring may be contraindicated if the woman has had corrective heart surgery that involved placement of shunts or other devices. (1)Pain control is a key part of the labor and delivery management plan. Epidural anesthesia is the preferred method of pain control because it can decrease workload on the heart, provide consistent pain relief, and minimize the release of catecholamines in response to pain and stress. Early consultation with anesthesia ensures that the anesthesiologist has adequate time and information to determine the best method of maintaining adequate preload with epidural administration or, if epidural administration is contraindicated, the best method of managing the woman’s pain control needs. (1)(4)(6) Shortening the end of the second stage of labor with low outlet forceps or vacuum, thereby avoiding the Valsalva maneuver, prevents further hemodynamic changes that may affect cardiac function. (4)(14)During delivery, patients may be exposed to a period of bacteremia. The exact incidence is not known, and the duration of exposure is believed to be brief, but in certain women who have cardiac disease, the duration may be sufficient to result in the development of endocarditis. According to the American College of Obstetricians and Gynecologists, the American Heart Association, and the American College of Cardiology, women who have cardiac disease can be placed into three categories for risk of development of bacterial endocarditis during labor and delivery: negligible risk, moderate risk, and high risk (Table 4).(27)(28)(29)Antibiotic prophylaxis is initiated approximately 30 minutes before delivery and administered only for a total of 6 to 8 hours. The antibiotics used most commonly are ampicillin (2 g either intramuscularly or intravenously) plus intravenous gentamicin (1.5 mg/kg, not to exceed 120 mg). Six hours later, 1 g of either ampicillin or amoxicillin is administered by the appropriate route. Vancomycin is substituted for women who are allergic to penicillin. Women in the negligible-risk category do not require prophylaxis for an uncomplicated delivery or if bacteremia (eg, intra-amniotic infection) is suspected at the time of delivery. Women in the moderate-risk category should receive prophylaxis if bacteremia is suspected, but it is not recommended for an uncomplicated delivery. If infection is suspected in women who fall in the high-risk category, prophylaxis should be but it is if the delivery is The this to most is the inability to which be some prophylaxis to all women in the high-risk with warfarin should be discontinued at 2 weeks before delivery is anticipated and subcutaneous heparin therapy with heparin should be discontinued prior to The for heparin, should be available for delivery if therapy can be postpartum 6 to hours delivery. level of and is in the first postpartum because a significant number of deaths occur during this (1) Cardiac output may increase as much as delivery. (17) The risks postpartum are hemorrhage and pulmonary blood is treated with and replacement of blood and plasma as Pulmonary edema may be seen up to postpartum or on the specific cardiac disease and complications during pregnancy. The risk of pulmonary edema may increase postpartum as is into the vascular (1) The number of of close of the woman depends on the of cardiac disease. is exposed not only to the risks associated with maternal cardiac disease in pregnancy, but also to the increased risk of of a cardiac In the general the risk of congenital heart disease is less than When either is affected with congenital heart disease, the risk to the fetus increases counseling and fetal echocardiography are recommended in these to pregnant women who have cardiac disease are at risk for neonatal and cardiac complications. In one pregnant women who had heart disease were followed during and the frequency of maternal cardiovascular and neonatal complications was compared with a group of women who did not have heart disease and who experienced a total of pregnancies. such as hemorrhage, preterm delivery at less than weeks’ and occurred in of the group who had heart disease compared with in the control a significant between maternal heart disease and neonatal complications is believed to be by maternal low maternal oxygen and can be to maternal NYHA functional classification and left heart In the setting of maternal cardiac disease, especially functional class III and fetal with and antepartum testing is care of pregnant women who have cardiac disease is counseling is critical. of a multidisciplinary with close throughout pregnancy, is to achieve the best for the woman and her