Cardiovascular Diseases and Pregnancy
WHEC Practice Bulletin and Clinical Management Guidelines for healthcare providers. Educational grant provided by Women's Health and Education Center (WHEC).
Cardiovascular adaptations to pregnancy are well tolerated by healthy young women. However, these adaptations are of such magnitude that they can significantly compromise women with abnormal or damaged heart. Heart diseases of varying severity complicate about 1% of pregnancies and it is the third leading cause of death in 25 to 44 year old women. In developing countries rheumatic heart disease still accounts for the majority of cases, while in industrialized countries because of better medical and surgical management has enabled more girls with congenital heart disease to reach childbearing age. Hypertensive heart disease frequently complicated by heart disease or obesity, has become a relatively common cause of postpartum heart failure. Other varieties are even less common and include coronary, thyroid, syphilitic, and kyphoscoliotic cardiac disease, as well as idiopathic cardiomyopathy, corpulmonale, constrictive pericarditis, various forms of heart block, and isolated myocarditis.
The purpose of this document is to review current guidelines to manage cardiovascular diseases affecting pregnancy, and preconception counseling. The new guidelines for antibiotic prophylaxis for infective endocarditis are also discussed. There is some controversy over the optimal approaches to clinical assessment and treatment of women with cardiac diseases. Management hinges on the severity of cardiac diseases, gestational age and evaluation of relative risks. Additional guidelines on the basis of consensus and expert opinion also are presented. Without accurate diagnosis and appropriate care, heart disease in pregnancy can be a significant cause of maternal mortality and morbidity.
Hemodynamic Changes in Normal Pregnancy:
Hemodynamic refers to the relationship between blood pressure, cardiac output, and vascular resistance. Blood pressure is measured by auscultation, use of an automated cuff, or directly with an intra-arterial catheter. Cardiac output is measured by dilutional techniques requiring central venous access, by Doppler or two-dimensional echocardiographic techniques, or by electrical impedance. Peripheral resistance is calculated using Ohm's law:
Total peripheral resistance (TPR) = Mean arterial pressure (MAP) x 80/Cardiac output (CO); where TPR is measured as dyne.sec.cm-5, MAP as millimeters of mercury (mm Hg), and CO as liter per minute (L/min). Cardiac output (CO) is the product of heart rate (HR) and stroke volume (SV). CO = HR x SV.
HR and SV increase as pregnancy progresses to the third trimester. After 32 weeks, SV falls, with the maintenance of CO becoming more and more dependent on HR. Vascular resistance falls in the first and early second trimesters. The magnitude of fall is sufficient to offset the rise in CO, resulting in a net decrease in blood pressure. Labor, delivery, and the postpartum period are times of acute hemodynamic changes that may result in maternal decompensation. Tachycardia is a normal response. Significant catecholamine release increases afterload. Each uterine contraction acutely redistributes 400 to 500 ml of blood from the uterus to the central circulation. During normal pregnancy, arterial blood pressure and vascular resistance decrease while blood volume, maternal weight, and basal metabolic rate increases (1). Cardiac output increases significantly and it continues to increase and remains elevated during the pregnancy. During the first stage of labor, cardiac output increases moderately, and during the second stage, with vigorous expulsive efforts, it is appreciably greater. After the substantively augmented cardiac output, in immediate postpartum most of the pregnancy-induced increase is lost very soon after delivery.
During pregnancy, some of the cardiac sounds may be altered (2).
Three key features of the maternal hemodynamic changes in pregnancy are particularly relevant to the management of women with cardiac disease:
In conditions such as mitral stenosis, in which CO is relatively fixed, the drive to achieve an elevated CO may result in pulmonary congestion. If a patient has an atrial septal defect, the incremental increase in systemic flow associated with pregnancy will be magnified in the pulmonary circulation to the extent that pulmonary flow exceeds systemic flow. If, for example, a shunt ratio of 3:1 is maintained in pregnancy, pulmonary flow may be as high as 20 L/min and may be associated with increasing dyspnea and potential desaturation. Many cardiac conditions are HR dependant. Tachycardia reduces left ventricular filling and CO. Coronary blood flow is also dependant on the length of diastole. The increasing HR in pregnancy may be associated with a worsening of tachyarrhythmias. Reduction in vascular resistance may be beneficial to some patients; afterload reduction reduces cardiac work.
Diagnosis and Evaluation of Heart Disease:
Many women with heart disease have been diagnosed and treated before pregnancy. The structured questions for the review of cardiac symptoms are: "how many flights of stairs can you walk up with ease?" -- Two? One? None? "Can you walk a level block?" "Can you sleep flat in bed?" -- how many pillows? "Does your heart race?" "Do you have chest pain?" -- with exercise? -- when your heart races? Many of physiological changes of normal pregnancy tend to make the diagnosis of heart disease more difficult. Some clinical indicators of heart disease during pregnancy are: progressive dyspnea or orthopnea, nocturnal cough, hemoptysis, syncope, chest pain. Clinical findings suggestive of heart disease are: cyanosis, clubbing of fingers, persistent neck vein distention, systolic murmur grade 3/6 or greater, diastolic murmur, cardiomegaly, persistent arrhythmia, persistent split-second sound and signs of pulmonary hypertension may be present.
Most diagnostic studies are non-invasive and can be conducted safely in pregnant women. In most cases, conventional testing including electrocardiography, echocardiography, and chest radiography will provide necessary data. If indicated, right-heart catheterization can be performed with limited X-ray fluoroscopy. On rare occasion, it may be necessary to perform left-heart catheterization. Technetium99-labeled albumin or red cells are often used to evaluate ventricular function. The estimated fetal radiation exposure for a 20-m Ci dose study is 120 m rad, well below the accepted level for significant teratogenic or oncogenic effect. Thallium201 used to evaluate regional coronary perfusion, yields a fetal exposure of 300 to 1100 m rad, depending on the stage of gestation (2). In cases with clear indications, any minimal theoretical risk will be outweighed by maternal benefits.
Women with cardiac diseases may benefit from counseling before the decision to become pregnant. Maternal mortality generally varies directly with functional classification at pregnancy onset; however, this relationship may change as pregnancy progresses. The American College of Obstetricians and Gynecologists (ACOG) had adopted the three-tiered classification according to risks for death during pregnancy (4):
Women with significant heart disease should be counseled before pregnancy regarding the risk of pregnancy, interventions that may be required and potential risks to the fetus. However, women with significant uncorrected disease often present with an ongoing established pregnancy. In this situation, the risks and benefits of termination of pregnancy versus those of continuing a pregnancy should be addressed. The decision to become pregnant or carry a pregnancy in the context of maternal disease is a balance of two forces: 1) the objective medical risk, including the uncertainty of that estimate; and 2) the value of the birth of a child to an individual woman and the patient. The first goal of counseling is to educate the patient. Only a few cardiac diseases represent and overwhelming risk of maternal mortality: Eisenmenger's syndrome, pulmonary hypertension with right ventricular dysfunction, and Marfan's syndrome with significant aortic dilation and severe left ventricular dysfunction. Most other conditions require aggressive management and significant disruption in lifestyle.
Intercurrent events such as antepartum pneumonia or obstetric hemorrhage pose the greatest risk of initiating life-threatening events. Fastidious care can reduce but not eliminate the risk of these events. Maternal congenital heart disease increases the risk of congenital heart disease in the fetus from 1% to approximately 4-6% (6). Marfan's syndrome and some forms of hypertrophic cardiomyopathy are inherited as autosomal dominant conditions; the offsprings of these women carry a 50% chance of inheriting the disease. The second goal of counseling is to help each women integrate the medical information into her individual value system and her individual desire to become a mother. Many women with significant but manageable heart disease choose to carry a pregnancy. The basis of their decisions should be individualized.
Management of Classes I and II:
Most of the women in class I and II undergo pregnancy without morbidity; however, special attention should be directed toward both prevention and early recognition of heart failure. Infection has proved to be an important factor in precipitating cardiac failure. Each woman should receive instructions to avoid contact with persons who have respiratory infections, including common cold, and to report at once any evidence for infection. Bacterial endocarditis is a deadly complication of valvar heart disease. Pneumococcal and influenza vaccines are recommended. Cigarette smoking is prohibited, both because of its cardiac effects as well as the propensity to cause upper respiratory infections. The onset of congestive heart failure is generally gradual. The first warning sign is likely to be persistent basilar rales, frequently accompanied by a nocturnal cough. A sudden diminution in ability to carry out usual duties, increasing dyspnea on exertion, or attacks of smothering with cough is the symptoms of serious heart failure. Clinical findings may include hemoptysis, progressive edema, and tachycardia.
Labor and Delivery:
Management of cardiac disease in pregnancy is frequently complicated by unique social and psychological concerns. Women with rheumatic heart disease may have frequently lived outside the traditional medical care system owing to conditions of poverty, immigration, and cultural differences. Care must be exercised to facilitate their access to care and their comfort with the environment of care. Standard cardiac care for labor and delivery are (6):
In general, delivery should be accomplished vaginally unless there are obstetrical indications for cesarean delivery. Relief from pain and apprehension is especially important. While intravenous analgesics provide satisfactory pain relief for some women, continuous epidural analgesia is recommended for most situations. The major danger of conduction analgesia is maternal hypotension. This is dangerous in women with intracardiac shunts, in whom flow may be reversed with blood passing from the right-to-left within the heart or aorta, thereby by-passing the lungs. Hypotension can be hazardous with pulmonary hypertension or aortic stenosis because ventricular output is dependent upon adequate preload (9). In women with these conditions, narcotic conduction analgesia or general anesthesia may be preferable.
During labor, the mother with significant heart disease should be kept in a semi-recumbent position with lateral tilt. Vital signs should be taken frequently between contractions. Increases in pulse rate much above 100 per minute or in the respiratory rate above 24, particularly when associated with dyspnea, may suggest impending ventricular failure. With any evidence of cardiac decompensation, intensive medical management must be instituted immediately. It is essential to remember that delivery itself will not necessarily improve the maternal condition. Moreover, emergency operative delivery may be particularly hazardous. Clearly, both maternal and fetal conditions must be considered in the decision to hasten delivery under these circumstances. For cesarean delivery, epidural analgesia is preferred by most clinicians; spinal analgesia is contraindicated with some lesions and general endotracheal anesthesia with thiopental, succinylcholine nitrous oxide, and at least 30% oxygen has also proven satisfactory.
Intrapartum Heart Failure:
Unless the underlying pathophysiology is understood and the cause of the decompensation clears, empirical therapy is hazardous. Cardiovascular decompensation during labor may manifest as pulmonary edema and hypoxia, hypotension or both. The proper therapeutic approach will depend upon the specific hemodynamic status and the underlying cardiac lesion. For example, decompensated mitral stenosis with pulmonary edema due to absolute or relative fluid overload is often best approached with aggressive diuresis, or if precipitated by tachycardia, by heart rate control with beta-blocking agents (3,5). On the other hand, the same treatment in a woman suffering decompensation and hypotension due to aortic stenosis could prove fatal.
Women who have shown little or no evidence of cardiac distress during pregnancy, labor or delivery may still decompensate after delivery. Therefore, it is important that meticulous care be continued into the postpartum period. Postpartum hemorrhage, anemia, infection, and thromboembolism are much more serious complications with heart disease and may act as precipitating factors in heart failure. If tubal ligation is to be performed after vaginal delivery, it may be best to delay the procedure until it is obvious that the mother is afebrile, not anemic, and has demonstrated that she can ambulate without evidence of distress. Women who do not undergo tubal sterilization should be given detailed contraceptive advice.
Management of Classes III and IV:
These severe cases are uncommon today in industrialized countries. The important question in these women is whether pregnancy should be undertaken. If woman chooses to become pregnant, she must understand the risks and cooperate fully with planned care. If seen early enough, woman with some types of severe cardiac disease should consider pregnancy interruption. If pregnancy is continued, prolonged hospitalization or bed rest will often be necessary. As for less severe disease, epidural analgesia for labor and delivery is usually recommended. Vaginal delivery is preferred in most cases, and cesarean delivery is limited to obstetrical indications. The decision for cesarean delivery must take into account the specific cardiac lesion, overall maternal condition, availability and experience of anesthetic support, as well as physical facilities. These women often tolerate major surgical procedures poorly, and should be delivered in a facility which has experience with complicated cardiac disease.
Cardiac Surgery during Pregnancy:
Valve replacement during pregnancy: although usually postponed, valve replacement during pregnancy occasionally may be lifesaving. A number of reviews and small series all confirm that surgery on the heart or great vessels is associated with major maternal and fetal morbidity and mortality (7, 8). Valvar surgery is associated with about 9% maternal mortality and perinatal mortality about 30%. The fetal response to cardiopulmonary bypass pump during surgery is usually bradycardia, and high-flow normothermic perfusion is recommended.
Mitral valvotomy during pregnancy: this operation is less common because the incidence of rheumatic mitral stenosis has declined. Within the past 20 years, percutaneous trans-catheter balloon dilatation of the mitral valve has largely replaced surgical valvoplasty during pregnancy. The normal mitral valve surface area is 4.0 cm2. When stenosis narrows this to less than 2.5 cm2, symptoms usually develop. The most prominent complaint is dyspnea due to pulmonary venous hypertension and pulmonary edema. Other common symptoms are fatigue, palpitation, cough, and hemoptysis. Coexisting atrial fibrillation is especially ominous and commonly is associated with heart failure, thromboembolic disease and death.
Antibiotic Prophylaxis for Infective Endocarditis:
The recommendations for endocarditis prophylaxis from the American Heart Association (11) have changed for three main reasons:
The specific changes pertinent to the obstetricians and gynecologists are discussed as follows.
Delivery: Infective endocarditis prophylaxis is no longer recommended for vaginal or cesarean delivery in the absence of infection, regardless of the type of maternal cardiac lesion. Mitral valve prolapse is no longer considered a lesion that ever needs infective endocarditis prophylaxis. Only cardiac conditions associated with the highest risk of adverse outcome from endocarditis are appropriate for any infective endocarditis prophylaxis. In patients with one of these conditions and who have an established infection that could cause bacteremia, such as chorioamnionitis or pyelonephritis, the underlying infection should be treated in the usual fashion and the treatment should include a regimen effective for infective endocarditis prophylaxis. Prophylaxis should be given intravenously.
Dental: The American Heart Association recommends that only those women with cardiac conditions associated with the highest risk of adverse outcome from endocarditis receive infective endocarditis prophylaxis for certain dental procedures. Specifically, prophylaxis should be provided for all dental procedures that include manipulation of the gingival tissue or periapical region of the teeth or oral mucosa. Prophylaxis is not required in the following circumstances: injecting anesthetic into non-infective tissue, general dental cleaning, cavity filling, performing radiography, placing or adjusting orthodontic appliances, or when there is bleeding from trauma to lips and oral mucosa.
Antibiotic Prophylaxis Appropriate for Infective Endocarditis (12):
Cardiac Conditions for which Prophylaxis for Deliveries Associated with Infection, or Certain Dental Procedures, is Reasonable:
Critical Care -- Hemodynamic Monitoring:
Acute indications for invasive hemodynamic monitoring are broadly categorized below. Severe preeclampsia, sepsis, adult respiration distress syndrome (ARDS), pneumonia, previously undiagnosed heart disease, and fluid management after resuscitation from obstetric hemorrhage are the most common conditions that require hemodynamic monitoring. Certain conditions, particularly maternal heart disease as discussed earlier, require a planned, prospective decision for invasive monitoring. In these cases, the therapeutic window for hemodynamic management is narrow and knowledge of the patient's baseline, compensated hemodynamic status can serve as a goal for intrapartum management. In many cases, initial therapy can and should made empirically based on an understanding of the patient's specific data, obtained from hemodynamic monitoring, may be required. Understanding principles of management is particularly important for obstetricians who do not necessarily anticipate critically ill patients in their practice.
Indications for hemodynamic monitoring:
The objective of hemodynamic monitoring is to provide continuous assessment of systemic and intracardiac pressures and to provide the means to determine CO, and therefore, to calculate systemic and pulmonary resistances. An arterial catheter is usually placed in the radial artery to measure systemic pressure. The diastolic pressure obtained usually correlates well with noninvasive measurements. The arterial catheter permits easy access to arterial blood sampling and relieves the patient from the discomfort of frequent blood draws. Measurements of intracardiac pressures and CO are obtained through the insertion of a catheter into the central venous circulation and advancement into and through the right side of heart. Venous access is most commonly obtained through the right internal jugular vein; a subclavian approach may also be employed. Once central venous access has been obtained and confirmed, a pulmonary artery catheter can be "floated" into the right side of the heart and pulmonary artery. If the patient has significant pulmonary hypertension, difficulty may be encountered maintaining placement in the pulmonary artery. CO is measured by thermodilution. A bolus of cold fluid is injected into the right atrium, and a curve of temperature change over time is recorded as the bolus passes through the pulmonary artery. From the shape of the curve, CO can be calculated; when the CO is higher, the dilutional curve is shorter in time and greater in maximum temperature change. More recently, catheters have been equipped with a heating element in the right atrial segment so that continuous measurement of CO can be performed. Summarized below are formulas used to calculate hemodynamic parameters (6),(8):
Calculated hemodynamic variables:
Strategies of hemodynamic therapy that may be applicable to a variety of clinical circumstances are as follows. The use of hemodynamic monitoring should be directed at answering specific questions of maternal pathophysiology. The table below summarizes the most common goals of therapy (5, 7, 8). To achieve each goal, a number of physiologic interventions are possible. Each of these interventions will precipitate a secondary or compensatory response. The secondary response if excessive, may adversely affect the patient. The choice of intervention from available options will often be determined by the potential for and magnitude of adverse effect. Hemodynamic monitoring permits the physician to choose and intervention and subsequently assess the positive and negative effect.
The use of pulse oximetry facilitates the early detection of maternal desaturation. Oxygen supplementation improves maternal saturation but does not correct the underlying cause. If desaturation is progressive, further intervention will be required. In a normal heart, diuresis to reduce preload works to decrease alveolar water in patients with elevated pulmonary artery wedge pressure (PAWP) and in patients with capillary leak. A reduction in capillary pressure from high normal to low normal will reduce the egress of water across damaged membranes. In many circumstances these interventions empirically based on a diagnosis and an understanding of maternal physiology. For example, tocolysis with β-mimetic agents can induce pulmonary edema. Timely diagnosis, discontinuation of the offending agent, oxygen supplementation, and a single diuretic dose will usually be sufficient therapy. If desaturation continues despite hemodynamic management, intubation may be required (10). Positive end-expiratory pressure (PEEP) can be used to increase intra-alveolar spaces. PEEP may impede venous return and decrease CO due to the effects of the associated increase in extracardiac intrathoracic pressure. PAWP in excess of PEEP is required for adequate ventricular filling. Only in the sickest of pregnant women with PEEP have a clinically significant impact on CO.
Disorders of blood pressure and perfusion can be managed with the knowledge of maternal hemodynamics. The antecedents and epidemiology of heart failure in young adults are poorly understood. Incident heart failure before 50 years of age is substantially more common among blacks than among whites. Hypertension, obesity, and systolic dysfunction that are present before a person is 35 years of age are important antecedents that may be targets for the prevention of heart failure (13).
Hemodynamic changes in pregnancy may adversely affect maternal cardiac performance. Intercurrent events such as infection during pregnancy are usually the cause of decompensation. Women with heart disease in pregnancy frequently have unique psychological needs. Labor, delivery, and postpartum are periods of hemodynamic instability. Invasive hemodynamic monitoring should be used to address specific clinical questions. Many maternal heart conditions can be medically managed during pregnancy. A few conditions such as Eisenmenger's syndrome are associated with a very high risk of maternal mortality. Many women with congenital heart disease can successfully complete a pregnancy. Preconceptual counseling is based on achieving a balance between medical information and the patient's value system.
Ideally, the patient with known heart disease should consult her physician before becoming pregnant in order to determine the advisability and optimum timing for pregnancy, the need for and timing of diagnostic procedures, the prospects for corrective or palliative cardiac surgery, the type of prosthetic valve to be used, and the need for discontinuing certain drugs during pregnancy. If a woman with heart disease presents for medical care after she has become pregnant, the obstetrician must be able to recognize the presence of preexisting cardiac disease, assess the degree of disability, and understand the impact of the added hemodynamic changes of pregnancy. Prepregnancy planning might include performance of an exercise tolerance test to determine if the woman with severe heart disease can tolerate the added hemodynamic burden of pregnancy. The obstetrician must also be able to anticipate, prevent, diagnose, and treat complications such as arrhythmia or congestive heart failure when they arise and advise the patient regarding discontinuation or continuation of the pregnancy and the risk of future pregnancies. Management of an obstetric patient with heart disease should be carried out by a team consisting of the obstetrician and obstetric nurse or midwife, as well as the cardiologist, anesthesiologist and neonatologist, at the time of labor.