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Chest Emergencies in Pregnant Patients
Key Points
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In pregnant patients presenting with signs of acute myocardial infarction with no known history of coronary artery disease, spontaneous coronary artery dissection should be suspected.
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Patients with preexisting vascular conditions, such as aortopathies and hereditary hemorrhagic telangiectasia, should be closely followed throughout pregnancy, as these conditions can exacerbate.
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In a pregnant patient with suspected pulmonary embolism, the fetal radiation dose does not significantly differ between a perfusion scan and computed tomography; however, the radiation dose to the breast is lower with a perfusion scan.
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Whenever possible, imaging that does not utilize ionizing radiation or gadolinium contrast agents should be used to minimize risk to the fetus.
Introduction
Pregnancy causes changes in the hemodynamics and hormones that can induce stress, unmask underlying preexisting conditions, or increase the risk of certain cardiothoracic conditions. Examples of such entities include cardiomyopathy, coronary artery dissection, and pulmonary embolism, among others. Maternal cardiovascular complications account for more than 25% of all pregnancy-related deaths in the United States. Imaging plays an essential role in both diagnosing these entities and guiding treatment throughout pregnancy and in the postpartum period.
Imaging Approach
Echocardiography is currently the first-line modality for evaluation of cardiac function, given its availability and lack of ionizing radiation. Echocardiography is able to assess biventricular systolic function, detect hemodynamic derangement and wall motion abnormalities, and identify complications such as thrombus. It may be limited by poor acoustic windows, especially in women in late pregnancy or in the immediate postpartum period.
Cardiac magnetic resonance (CMR) has become the gold standard examination for cardiac volumetric and flow quantification due to high soft tissue contrast resolution, high accuracy, and reproducibility. CMR is particularly useful for identifying masses, especially thrombus. Intravenous gadolinium contrast should not be administered, especially in the first trimester, as repeated doses of gadolinium have been shown to be teratogenic in animal studies. Gadolinium is considered safe for women who are breastfeeding. While there is no data to suggest fetal harm from magnetic resonance, there are theoretical concerns such as fetal acoustic damage and teratogenesis. Pregnant patients should undergo magnetic resonance imaging (MRI) in a 1.5-T scanner, as most of the data in the literature are derived from scanners with 1.5 T or less.
Whenever possible, imaging modalities that do not utilize ionizing radiation are preferred. Chest radiography is a quick and useful modality to assess for cardiac enlargement and pulmonary edema in patients presenting with dyspnea. With computed tomography (CT), the risk of radiation to the mother is similar to that of nonpregnant women, with the only exception being the breast tissue. Pregnant females have more sensitive breast tissue due to tissue proliferation. Radiation effects on the fetus depend on both the dose and the age of the fetus. The embryo is most sensitive during the first 2 weeks after conception, which usually results in failure of implantation. Most of the data regarding the effects on radiation on the fetus are extrapolated from exposure after the atomic bomb detonations of Hiroshima and Nagasaki. In general, a fetal absorbed dose of less than 50 mGy is considered safe with regards to teratogenic or abortive effects ; this dose is rarely exceeded with the advent of lower-dose protocols. Techniques such as decreasing the kilovoltage or tube current and reducing the exposure time, modulating the dose, adjusting the collimation and scan length, and increasing the pitch can be employed to lower radiation dose. For reference, a retrospective coronary CT is estimated to deliver a fetal dose of approximately 3 mGy. While iodinated contrast material can cross the placenta, it has no teratogenic effects.
Cardiac Complications
Heart Failure
There are two categories of heart failure: heart failure with reduced ejection fraction and heart failure with preserved ejection fraction. Pregnancy can result in exacerbation of maternal cardiovascular conditions, such as hypertension, or lead to the development of new conditions such as cardiomyopathy. These conditions may result in heart failure, which accounts for approximately 9% of hospitalized maternal-related deaths. Even though heart failure accounts for less than 2% of pregnancy-related hospitalization, more than 60% of pregnancy-related heart failure diagnoses occur in postpartum patients. Patients with preexisting comorbidities such as cardiomyopathy, valvular disease, diabetes, and hypertension are more likely to develop heart failure. Heart failure patients are also more likely to develop pregnancy-associated conditions, such as preeclampsia and diabetes.
Heart failure in the pregnant or postpartum patient can be a result of increased vascular resistance, decreased left ventricular function, or valvular dysfunction. Preeclampsia, hypertrophic cardiomyopathy, and pulmonary hypertension can be accentuated during pregnancy and lead to increased vascular resistance resulting in heart failure. Cardiomyopathies including peripartum cardiomyopathy (PPCM), inherited disorders, drug reactions, or ischemia can cause left ventricular dysfunction and heart failure. Valvular disease in the setting of endocarditis or rheumatic heart disease can also lead to heart failure.
Clinical Manifestations
Pregnant patients with heart failure usually develop symptoms related to right, left, or biventricular dysfunction. Changes related to pregnancy can have signs and symptoms that overlap with those of heart failure. For example, mildly elevated jugular pressure and lower extremity edema are findings that are not uncommonly encountered in pregnancy and occur due to physiologic changes. Additionally, pregnant women can experience dyspnea as a result of increased, progesterone-induced, respiratory drive. It is believed that this overventilation is a physiologic response to increase carbon dioxide excretion to create a higher gradient between the fetal and maternal circulation. Signs and symptoms that should prompt a workup for heart failure include orthopnea, paroxysmal nocturnal dyspnea, palpitations, and syncope. Worrisome findings on physical examination include cyanosis, resting tachycardia, collapsing pulse, hypo- or hypertension, pulsatile and elevated jugular pressures, auscultatory findings of pulmonary edema, and signs of respiratory distress.
Imaging Manifestations
Chest radiography is the first imaging modality in a pregnant patient presenting with dyspnea or lower extremity edema. In patients with left-sided heart failure, the chest radiograph will show interstitial signs of pulmonary edema and, in more severe forms of edema, perihilar airspace opacification. The cardiac silhouette is usually enlarged, and pleural effusions are usually present. Echocardiography has the same utility as in nonpregnant patients, offering evaluation for ventricular and valvular function. CT is not used in the evaluation of patients with heart failure, unless it is indicated to exclude other causes of dyspnea, such as pulmonary embolism.
CMR is useful for diagnosing the underlying etiology of the patient’s heart failure, as it allows for assessment of function, volume, morphology, and tissue characterization. In the postpartum patient, gadolinium should be used. Patterns of myocardial enhancement are particularly useful for characterization of myocardial processes such as subendocardial enhancement in the setting of ischemia or subepicardial and midmyocoardial enhancement in myocarditis. Patients with dilated cardiomyopathy will have a dilated poorly functioning left ventricle with midmyocardial enhancement. Other underlying etiologies may be suggested by function and morphology of the left ventricle alone, such as takotsubo, which manifests with characteristic apical ballooning.
Peripartum Cardiomyopathy
PPCM refers to left ventricular dysfunction and cardiac failure that occurs in the peripartum period. While relatively uncommon, the incidence is rising, with an incidence in the United States ranging from 1 in 1000 to 4000 live births. The rise in the number of cases may be due to increased awareness, workup, and diagnosis. Risk factors that are becoming more prevalent include age, where more than half of the cases occur in women over the age of 30 years, increased incidence of cardiovascular risk factors (i.e., diabetes, hypertension, and obesity), and increased multifetal pregnancies. Additionally, more than 40% of PPCM occurs in Black American women, who are three times more likely than White Americans to develop this condition.
Clinical Presentation
While most cases occur in the week after delivery, PCCM can also less commonly occur in the second or third trimesters. Current international guidelines define PCCM as symptomatic left ventricular dysfunction, with or without ventricular dilation, with an ejection fraction of less than 45% occurring from the last month of pregnancy to up to 5 months after delivery. This definition can help distinguish PCCM from an unmasked preexisting cardiomyopathy due to pregnancy, which usually occurs earlier, in the late second trimester. The exact pathophysiology of the disease remains unknown, with many proposed etiologies, including viral, nutritional, autoimmune, genetic, and hormonal causes, among others. Some postulate that the physiologic stress of pregnancy may expose an underlying genetic susceptibility or cardiovascular disease. Clinically, these patients present with signs of heart failure, including orthopnea and paroxysmal nocturnal dyspnea. During late pregnancy, it may be difficult to distinguish the PCCM from normal physiologic changes. Physical examination signs of PCCM include tachycardia, lower extremity edema, pulmonary rales, and elevated jugular venous pressure. Life-threatening presentation can occur with acute respiratory distress from low cardiac output heart failure, requiring emergent medical and mechanical support.
Imaging Manifestations
Echocardiography can help distinguish PPCM from other pregnancy-related cardiac diseases. Findings of PPCM include reduced systolic and diastolic left ventricular function ( Fig. 4.1 ); left ventricular dilation is not always necessarily present and therefore not included in the major criteria for diagnosis of this entity. CMR can be utilized for more accurate assessment of left ventricular function and volumes, as well as to evaluate for the potential complication of cardiac thrombus. Thrombus will typically appear as a mass within the ventricle that does not enhance on postcontrast imaging. High inversion times of 450 to 600 ms will show the thrombus to be of homogeneously low signal intensity compared with the surrounding blood pool.
Aortic Dissection and Aortopathies
While aortic dissection rarely occurs in women of child-bearing age, approximately half of all cases of dissection in women under the age of 40 years occur in pregnant patients. Patients with conditions that increase the risk for developing dissection, such as Marfan syndrome and bicuspid aortic valve, may undergo prophylactic prepartum surgery to mitigate, but are usually followed more closely with imaging. High-risk patients in which the aorta rapidly dilates to greater than 5 cm during pregnancy rarely require surgical repair while pregnant.
Clinical Manifestations
Aneurysmal aortic dilatation usually does not result in symptoms, unless there is direct compression of adjacent structures or resultant dissection or rupture. Rarely, dilatation of the descending aorta can cause compression of the recurrent laryngeal nerve, which results in hoarseness, or compression of the esophagus resulting in dysphagia. Aortic root dilation can also result in symptoms of heart failure from lack of aortic valve coaptation. Symptoms of dissection include sudden-onset chest pain that may radiate to the back and abdomen. The most critical complication of an aneurysm is rupture, usually presenting with severe chest pain, hypotension, and shock from either hemorrhagic or hemopericardium, resulting in tamponade. Patients with rupture may have diminished or absent lower extremity pulses.
Imaging
Surveillance imaging is required in high-risk patients. Echocardiography can be used to visualize the aortic root and the ascending aorta. MRI can provide a comprehensive analysis of the aorta, as the aortic arch and descending aorta can be well visualized without ionizing radiation. MRI can also visualize a dissection flap, if present, and establish the extent of the dissection, as the entire thoracic abdominal aorta can be imaged ( Fig. 4.2 ). On black blood spin echo sequences, the false lumen may be hyperintense due to slow flow and turbulence that leads to loss of a normal flow void. On bright blood sequences, the hypointense dissection flap can be seen surrounded by increased signal in both the true and false lumen. CT is often utilized in the emergency setting, as it offers faster image acquisition and great spatial resolution for vascular structures. Any stranding or hemorrhage in the mediastinum should raise suspicion for rupture. Noncontrast CT is useful for detection of intramural hematoma, which will appear as a hyperattenuating crescent in the aortic wall. Postcontrast images will show the dissection flap when surrounded by contrast in both the false and true lumen ( Fig. 4.3 ).
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