The Pregnant Patient With Cardiac Disease

Diagnosis Including Cardiovascular Imaging

The diagnosis of cardiovascular disease during pregnancy may be challenging because symptoms and physical signs often overlap with the physiologic changes of pregnancy. Pregnant women frequently complain of dyspnea and fatigue, and exercise tolerance is often decreased. Tachypnea, peripheral edema, and lower extremity venous stasis also may occur during pregnancy in women without cardiac disease. Even in women with known preexisting cardiovascular disease, it is important to differentiate expected pregnancy changes from pathologic exacerbations of underlying disease. The distinction is extremely important because it may trigger unnecessary modifications in management on the one hand or may lead to a failure to change management on the other.

A pregnant woman who presents with symptoms consistent with possible cardiovascular disease or exacerbation of known cardiovascular disease requires a careful medical history, family history, and physical examination ( Box 18.1 ) interpreted in the context of the physiologic changes of pregnancy. Many disorders such as cardiomyopathy, Marfan syndrome, CHD, or Brugada syndrome can be identified by taking a careful personal and family history. In women who are already in the second trimester, blood pressure should be measured either upright or in the left lateral position to prevent compression of the inferior vena cava and aorta. The pulse often has a rapid upstroke and collapse (a “bounding” character) because of the reduced systemic vascular resistance (SVR) and increased cardiac output. Resting heart rate is generally increased in pregnancy, but rates greater than 100 beats/min or bradycardia (heart rate <50 beats/min) require further evaluation for an underlying cause. Jugular venous pressure should be normal, so elevated jugular venous pressure and pulmonary rales are the most reliable signs of heart failure. A loud and widely split S ₁ heart sound caused by the early closure of the mitral valve and the presence of a third heart sound (S ₃ ) are normal in pregnancy. Soft ejection systolic murmurs are heard in more than 90% of pregnant women, usually over the left upper sternal border and the right side of the heart, because of increased cardiac output and increased flow through cardiac valves. These murmurs generally disappear by about 6 weeks postpartum. However, very loud murmurs or a palpable thrill suggest underlying pathology. Furthermore, diastolic murmurs are almost always caused by a pathologic process. The murmurs of aortic and mitral regurgitation commonly decrease during pregnancy because of the decrease in SVR, but the murmurs of mitral or aortic stenosis increase because of increased flow through the valves. Auscultation of new or changed murmurs is a reason for further investigation. Oximetry is an important diagnostic tool in patients with cyanotic CHD or patent shunt lesions. Many pregnant women show some degree of peripheral edema and lower extremity venous stasis because of uterine compression of the inferior vena cava impeding venous return. However, it should be symmetric and decrease with leg elevation and the left lateral decubitus position.

Box 18.1

Abnormal Physical Examination Findings During Pregnancy

• Heart rate >100 beats/min or <50 beats/min at rest

• Pulmonary rales

• Systolic murmur louder than 3/6, especially with palpable thrill

• Any diastolic murmur

• Murmur that persists beyond 6 weeks postpartum

• Asymmetric lower extremity edema

A woman with suspicious findings in the history and physical examination will often need cardiovascular testing during pregnancy. Additionally, pregnant women with known cardiac disease may need testing to judge how they are handling the added stress imposed by pregnancy. Pregnancy may impact the safety, application, and interpretation of several diagnostic cardiac procedures. Additionally, choosing the optimal diagnostic procedure requires consideration of safety for the mother and the fetus. Imaging modalities that do not use ionizing radiation are preferred as long as the required diagnostic information can be obtained. If the necessary information requires a study that uses ionizing radiation, the radiation dose to the fetus should be kept as low as possible.

The electrocardiogram (ECG) often changes during pregnancy. These changes may include a 15- to 20-degree left-axis deviation caused by diaphragmatic elevation, nonspecific ST-segment and T-wave changes (e.g., T-wave inversion in leads III and aVF and ST depression), supraventricular and ventricular ectopic beats, and the presence of small Q waves in lead aVF. If a pregnant woman has a suspected arrhythmia not captured on an ECG or in women with previous documented symptomatic arrhythmias and in women with palpitations, a Holter monitor is indicated because it is noninvasive and safe to use in pregnancy. It is important, however, to correlate symptoms with any abnormality and not treat asymptomatic arrhythmias during pregnancy because the treatments may be detrimental to the fetus. Exercise testing may be useful in the context of early pregnancy to establish functional capacity and assess heart rate, blood pressure, and ischemic changes to exercise. Exercise testing should be used with caution in women with an incompetent cervix, bulging membranes, recent vaginal bleeding, placenta previa or abruption, or preeclampsia. Women with symphyseal-pubic dysfunction, common during pregnancy, may be unable to perform the test because of limited movement. The procedure must be stopped if hypotension develops because this can lead to fetal distress. Performing submaximal exercise tests to reach 80% of predicted maximal heart rate in asymptomatic pregnant patients with suspected cardiac disease does not increase the risk of spontaneous abortion. Dobutamine stress tests should be avoided in pregnant women because there are limited data on their safety in pregnancy.

The preferred test during pregnancy to screen for structural cardiac abnormalities and to monitor ventricular and valvular functions and pulmonary pressures is transthoracic echocardiography (TTE). Many echocardiographic measurements require adjustment for pregnancy, including measurement of chamber dimensions, left ventricular (LV) mass, and in quantifying velocities across valves as these will all be increased in pregnancy. The use of transesophageal echocardiography (TEE) allows for more detailed examination but is more invasive than TTE and may be associated with pulmonary aspiration, which is a greater risk during pregnancy than in the nonpregnant state. TEE may still be indicated in the diagnosis of endocarditis, mechanical valve thrombosis, and complex CHD. However, the use of general anesthesia with tracheal intubation may be necessary to protect the airway.

Although it is preferable not to perform chest radiography during pregnancy because of the ionizing radiation risks, if other tests fail to diagnose the cause of dyspnea or cough, it may be necessary. The chest radiography findings in pregnancy may have a number of seemingly pathologic changes, including prominent vascular markings, a horizontal position of the heart, a flattened left heart border, and a raised diaphragm caused by the gravid uterus. Pulmonary edema, however, should not be seen.

In the setting of suspected acute pulmonary embolus, a computed tomography pulmonary angiogram should be performed because the risk to the fetus is outweighed by the danger of missed pulmonary emboli and can be minimized by lead shielding. Although echocardiography may aid in the diagnosis by identifying raised pulmonary artery pressures and impairment and dilatation of the right ventricle, it is less specific.

Cardiac magnetic resonance imaging (MRI) can provide information on cardiac anatomy and function without the use of ionizing radiation. However, it is generally only used if other investigations such as echocardiography cannot provide the relevant information because the safety of MRI in the early stages of pregnancy has not yet been determined. The safety of gadolinium during pregnancy has not been demonstrated and should be avoided if possible.

The use of cardiac catheterization for visualization of coronary arteries and measurement of intracardiac pressures gives high radiation exposure to the fetus and should only be used if absolutely clinically required. However, it is the diagnostic tool of choice in the management and treatment for ST-segment elevation myocardial infarction (MI) in pregnancy. To reduce fetal radiation exposure, catheterization via the radial artery is preferred to the femoral artery approach, and lead shielding of the uterus should be used. Although heparin is required for the procedure, an activated clotting time not exceeding 300 seconds is preferable to minimize risk of placental bleeding.

It is unclear what dose of radiation constitutes a danger to fetuses, but there is likely a very low risk of congenital malformations, neurobehavioral or intellectual abnormalities, fetal growth restriction, or pregnancy loss at doses of radiation less than 50 mGy (milligray) (10 mGy = 1 rad).

Cardiovascular Physiologic Changes of Pregnancy, Labor, and Delivery

Cardiovascular physiologic changes of pregnancy are summarized in Table 18.4 .

Coronary Artery Disease

The incidence of significant coronary artery disease (CAD) in pregnancy is not known, although the incidence of acute myocardial infarction (AMI) during pregnancy or the postpartum period is 3 to 6 per 100,000 deliveries, with a 5% to 37% mortality rate. Fetal death after maternal AMI is 12% to 34%.

Whereas myocardial oxygen demand is increased during pregnancy because of increases in heart rate and preload, myocardial oxygen supply is decreased secondary to a decrease in coronary perfusion pressure, dilutional anemia, and shortening of diastole. This will present a challenge to women with known or previously undiagnosed CAD. This challenge becomes greater during labor and delivery and especially immediately after delivery because of further increases in cardiac output. Although CAD in pregnancy is relatively uncommon, it has increased with the increasing maternal age and increased risk factors such as hypertension, diabetes, obesity, and smoking among women of reproductive age.

Pregnancy-related hypertensive diseases are also associated with an increased incidence of AMI. Additionally, the hypercoagulable state of pregnancy may lead to coronary thrombosis or embolism in women without underlying CAD. Severe postpartum hemorrhage may result in myocardial ischemia, and the use of methyl­ergonovine for postpartum bleeding can cause coronary vasospasm.

The diagnostic principles for myocardial ischemia during pregnancy are the same as for the nonpregnant patient and are based on angina symptoms, ECG changes, and increase in cardiac biomarkers (e.g., troponin). Creatine phosphokinase and its MB isoenzyme may not be helpful in the diagnosis of myocardial ischemia during pregnancy because these enzymes are often elevated during pregnancy, particularly during labor. The differential diagnosis of chest pain includes common pregnancy symptoms (e.g., gastroesophageal reflux disease, nausea and vomiting), musculoskeletal pain, aortic dissection, and preeclampsia.

The hemodynamic goals with an acute coronary syndrome during pregnancy are to prevent further ischemia by avoiding increases in myocardial oxygen demand or decreases in supply. Medical management is similar to nonpregnancy, with medical therapy consisting of β-blockers for tight heart rate control and low-dose aspirin, both of which have been found safe and effective in pregnancy. However, angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), and statins are known teratogens and should be avoided in pregnancy. The preferred approach for women with either acute ST-segment elevation MI (STEMI) or non–ST segment elevation MI (NSTEMI) with risk factors is percutaneous coronary angiography with intervention and reperfusion through stenting if needed. The radiation exposure to the fetus when shielding is used is minimal, and the benefits outweigh the risks. Clopidogrel should only be used for the shortest duration as possible because of the risk of placental bleeding during pregnancy and postpartum, and thus the use of bare-metal stents is preferred over drug-eluting stents. If clopidogrel is still being used at the time of vaginal or cesarean section delivery, the possibility of increased postpartum bleeding must be anticipated. The use of coronary artery bypass grafting is rarely needed during pregnancy and is associated with high fetal mortality rate. In women with NSTEMI without risk factors, conservative management with medical therapy and watchful waiting can be applied. Women with CAD should have the early institution of neuraxial anesthesia during labor to prevent pain and the increase myocardial oxygen demand that accompanies it. In the case of an AMI, labor and delivery should be delayed for at least 2 weeks if possible because maternal mortality rates are significantly increased during this time.

Valvular Heart Disease

The most common causes of valvular heart disease (VHD) in women of childbearing age are rheumatic heart disease and CHD (e.g., bicuspid aortic valve), with mitral stenosis the most common lesion encountered. VHD is a significant cause of maternal cardiac disease because rheumatic heart disease accounts for more than 90% of maternal cardiac disease cases worldwide. Pregnant women with VHD have an increased incidence of adverse maternal and fetal outcomes, with severe mitral stenosis forming a particularly high-risk group, with a reported maternal mortality rate of greater than 10% and a cardiac event rate of 67%. The most commonly encountered maternal cardiac complications are congestive heart failure and arrhythmias, and the most common fetal complications are prematurity and intrauterine growth retardation.

Women with known VHD before pregnancy should undergo preconception counseling. Women with moderate or severe mitral stenosis unless corrected before pregnancy or with moderate or severe aortic stenosis who are symptomatic or have LV dysfunction should be advised against pregnancy. Women at high risk who have a desire to pursue pregnancy should be managed by a multidisciplinary team in centers with expertise in the management of these patients. The hemodynamic changes of pregnancy can exacerbate mild symptoms. Symptoms tend to worsen with increasing gestational age. The severity of VHD and the prepregnancy NYHA functional class are the main predictors of adverse maternal and fetal outcomes. Many women with VHD are first diagnosed during pregnancy when the hemodynamic changes of pregnancy precipitate symptoms.

In general, regurgitant lesions are much better tolerated in pregnancy than stenotic ones because the decrease in SVR favors forward flow. In the absence of LV dysfunction, these lesions pose only a minor threat. Symptomatic patients may be treated with diuretics and afterload reduction with close monitoring for uteroplacental insufficiency. Afterload reduction should be provided with nitrates and hydralazine because ACE inhibitors and ARBs are contraindicated in pregnancy. However, the increases in preload, cardiac output, and heart rate during pregnancy cause a significant increase in the transvalvular gradient produced by stenotic lesions. In the case of mitral stenosis, it also compromises LV filling and increases left atrial pressure, which is then transmitted to the pulmonary veins. The decrease in LV filling and the increase in pressure in the pulmonary veins lead to deterioration in functional class with increased dyspnea, decreased exercise tolerance, and possibly pulmonary edema. Atrial arrhythmias (e.g., atrial fibrillation) associated with ventricular rate acceleration are a common cause of worsening symptoms and must be treated aggressively with rate control and possibly cardioversion.

In general, mitral stenosis is more of a management challenge than aortic stenosis because in aortic stenosis the increase in pressure is reflected initially to the hypertrophied left ventricle rather than the pulmonary veins as in mitral stenosis. Women with mild or moderate aortic stenosis generally tolerate pregnancy well. Medical therapy for stenotic lesions in symptomatic women consists of heart rate control with β-blockers and restriction of physical activity and preload reduction with diuretics. Metoprolol is the preferred β-blocker because atenolol has been linked to adverse fetal outcomes, including intrauterine growth retardation and preterm delivery. Heart rate control leads to improved LV filling and lower left atrial pressure. Diuretic use, in particular, must be accompanied by monitoring for signs of uteroplacental insufficiency. Patients with mitral or aortic stenosis who are refractory to medical therapy may be candidates for percutaneous balloon valvuloplasty, which should be done with abdominal shielding and delayed until after the first trimester if possible to minimize the radiation risks to the fetus.

Women with valve replacements, particularly mechanical prostheses, are at an increased risk for pregnancy complications and pose a particular challenge because of the risk of valve thrombosis and anticoagulation management. The presence of a mechanical prosthesis, particularly in the mitral position, is a contraindication to pregnancy. Warfarin should be continued until 36 weeks’ gestational age with the possible exception of weeks 6 to 12 because it is teratogenic, when a changeover to either unfractionated or low-molecular-weight heparin (LMWH) may be recommended, particularly if the dose of warfarin is greater than 5 mg/day. After 36 weeks, a changeover to heparin is recommended. Alternatively, these women can be switched from warfarin to LMWH from the beginning of pregnancy. These women require weekly monitoring of a postdose anti-Xa level.