Echocardiography has been a component of emergency medicine practice for over 20 years, and serves as an integral diagnostic tool in the evaluation of patients with cardiac and noncardiac disorders. Echocardiography represents the only diagnostic modality capable of providing real-time bedside information for acutely ill patients in the emergency department (ED). In addition to cardiac anesthesiologists and cardiologists, trainees in U.S.-based emergency medicine residency and fellowship programs now often acquire specialized training in echocardiography.

Transthoracic echocardiography (TTE) has proven to have several applications in routine clinical practice including the detection of cardiac effusion and tamponade, estimating cardiac ejection fraction, and as an important adjunct during specialized procedures such as pericardiocentesis.1,2 Under certain circumstances, however, TTE may be impractical (ie, during active chest compressions in the arresting patient), impossible (ie, in the morbidly obese patient), or inadequate (ie, definitive imaging of the ascending aorta). In such cases, transesophageal echocardiography (TEE) may be a suitable alternative, and in some cases can be regarded as the first-line echocardiographic investigation. While TEE is still primarily under the purview of the cardiologist or cardiac anesthesiologist, suitably trained emergency medicine physicians have also begun to incorporate TEE into their practice. Regardless, physicians using TEE as a tool for clinical management need to be adequately trained in performance and interpretation, which has prompted the American Society of Echocardiography to publish a policy statement on echocardiography in the ED.3

• Guidelines for the clinical application of echocardiography in the ED. The ACC/AHA/ASE guidelines for the clinical application of echocardiography (2003) have established recommendations for the use of echocardiography in the critically ill or injured patient (Table 23–1), including that echocardiography is appropriate to use in patients with suspected aortic injury, hemodynamically unstable patients, patients with serious blunt or penetrating chest trauma, and suspected pre-existing valvular or myocardial disease in the trauma patient. Table 23–2 details the specific clinical conditions and diagnoses for which echocardiography can be a useful diagnostic tool in the ED.
  
• Transthoracic versus transesophageal echocardiography in the ED. The ACC/AHA/ASE guidelines for the clinical application of echocardiography (2003) have also delineated the conditions and settings in which TEE (as opposed to TTE) provides the most definitive diagnosis in critically ill or injured patients, including the hemodynamically unstable patient with suboptimal TTE images or those on ventilators; major trauma or postoperative patients; suspected aortic dissection or other aortic injury; and other conditions in which TEE is superior (ie, endocarditis and cardiac source of emboli).4

TEE has several general advantages that make it a reasonable and useful imaging modality in the ED. TEE is relatively noninvasive and, once placed within the esophagus posterior to the heart, is capable of transmitting real-time images even during active cardiopulmonary resuscitation (CPR), thus permitting cardiac functional information to be viewed by all providers within range of the display monitor. It has been demonstrated to be safe, with low complication rates when used by experienced operators,5 and may result in a management change in up to 80% of cases.6 However, one must exercise added caution when using TEE in the ED given the acuity of the patient population, and only adequately trained providers should perform and interpret studies. For example, one study examining the complication rate in 142 patients undergoing TEE in the ED found a 12.6% complication rate including respiratory issues (n = 7), hypotension (n = 3), emesis (n = 4), agitation (n = 2), cardiac dysrhythmia (n = 1), and death (n = 1),7 a higher complication rate than reported in other clinical situations.8 Other disadvantages of the use of TEE in the ED relate to problems with incomplete (or absent) historical details in ED patients about the last oral intake, which can result in a need for gastric aspiration and decompression; the unexpected encountering of contraindications to TEE probe placement (such as esophageal webs, strictures, or varices); or unstable/unconscious patients incapable of providing consent.

While most studies of echocardiography in the ED have employed TTE as the first-line study, in many clinical situations including obesity, mechanical ventilation, lung disease, and poor echocardiographic windows, TTE limits clinical evaluation. For example, in a study by Varriale and Maldonado,9 they employed TTE as first-line echocardiographic imaging while studying patients with cardiac arrest, but required subsequent TEE to obtain acceptable images in 20% of their patients. In other studies, the failure rate of the transthoracic approach in the ICU setting has been reported to be 10% to 40%.10–12 The critically ill patient in the ED is often managed by intubation and mechanical ventilation, and up to one-half of such patients cannot be adequately imaged by TTE.13 TTE can also be impeded by objects on the chest wall such as lines, catheters, and electrocardiographic (ECG) leads, and even if performed by an experienced technician, TTE requires frequent interruption of CPR for repeated, intermittent acquisition of images during resuscitation. This is particularly relevant given the emphasis on minimizing the interruption of chest compressions in ACLS guidelines. Recently, an algorithm has been proposed for the use of TTE in resuscitation, to be executed simultaneously during CPR cycles to reduce interruptions.14

With TEE, on the other hand, once the probe is placed, it serves as a continuous monitor as it can remain in the esophagus even during active chest compressions15 and is not affected by objects on the chest wall. Continuous monitoring permits images to be viewed by the entire resuscitation team if a display-ready monitor is available, and can allow confirmation of adequate chest compressions by observing appropriate changes in chamber size as the heart alternately fills and empties.

There are several specific situations in the ED for which TEE is an important diagnostic tool for clinical care and may be considered the first-line echocardiographic investigation, including assessment of patients presenting with cardiac arrest to identify reversible causes; evaluation of patients with chest pain to rule out acute aortic dissection; evaluation of the patient with chest trauma; and evaluation of the patient with unexplained hypotension. Examples of such situations are reviewed in a case-based format below.

A 52-year-old male with a history of coronary artery disease, hypertension, and Type 2 diabetes mellitus arrives via local emergency medical service transport. Approximately 20 minutes prior, the patient had reportedly become short of breath with associated chest pressure and nausea. Thereafter, he became unresponsive. Upon arrival at the home, EMS personnel found him prone on the floor, pulseless and apneic. Standard advanced cardiac life support (ACLS) protocol was initiated; organized electrical activity was present on the monitor, and hence the patient appeared to be in pulseless electrical activity (PEA) arrest. After transport to the ED, CPR was continued. Transthoracic echocardiography was attempted but the cardiac windows were inadequate due to the large body habitus of the patient and the resuscitation paraphernalia.

After several rounds of ACLS, discussion to end the resuscitation was initiated. Simultaneously, a TEE probe was inserted and a midesophageal four-chamber view revealed coordinated myocardial contraction but with severe left ventricular dysfunction and an estimated ejection fraction of 10% to 15% (Figure 23–1). Inotropic support with dobutamine and dopamine was initiated. Two days later, the patient recovered neurologically intact.

Despite resources allocated to such initiatives as 911 emergency services, broad distribution of automated electronic defibrillators (AEDs), national campaigns to promote bystander CPR, and standardized ACLS guidelines and training, the most recent data suggest that less than 5% of patients suffering an out-of-hospital cardiac arrest survive to discharge.16 The presence of comorbidities contributes to worse outcomes after presenting with cardiac arrest.17,18 In an effort to improve this dismal survival rate, several studies have detailed theoretical and actual benefits of ultrasound in the setting of cardiac arrest, and some have even lobbied for echocardiography to be incorporated into resuscitation protocols for PEA and asystole.19 Although currently there are no guidelines or recommendations for the use of echocardiography in cardiac arrest, it is thought that a protocol inclusive of echocardiography could lead to a decrease in time between onset of arrest and administration of appropriate therapies.

Role of TEE in the Arresting Patient in the ED

The definitive role of TEE during resuscitation of the arresting patient in the ED and its impact on mortality and morbidity remains to be established. However, a limited number of studies that may be generalizable to this patient population have been suggestive. For example, one small study of in-hospital cardiopulmonary resuscitation using echocardiography found that asystole was initially observed in 90% of patients during CPR; the return of ventricular contractions in four patients prompted positive inotropic therapy. Ventricular wall motion was detected in two patients with bradyarrhythmia (pseudo-electromechanical disassociation) and the causes of cardiac arrest were identified as massive pulmonary embolism and hypovolemia, respectively.9 In another study specifically evaluating TEE, van der Wouw15 performed TEE on 48 patients who arrested in either the in- or out-of-hospital setting. Patients underwent resuscitation and TEE anywhere in the hospital (including the ED but excluding the intensive care unit [ICU]). The underlying pathologic process was elucidated in 31 of 48 (64%) patients with 27 of 31 having the diagnosis confirmed by other studies (angiography or postmortem). Based on these results, TEE had a sensitivity of 93% and specificity of 50% with a positive predictive value (PPV) of 87%. Most importantly, in 31% of all cases (15 of 41), the treatment was changed after the TEE established a diagnosis.15 Memtsoudis et al20 reported a case series of TEE performed on 22 patients who had an unexpected arrest during noncardiac operative procedures. A suspected primary diagnosis was established with TEE on 19 of 22 patients, including acute myocardial infarction, thromboembolism, pericardial tamponade, and hypovolemia. The authors state that TEE aided further management in 18 patients.

Although these results suggest the utility of TEE as an adjunctive diagnostic tool for in- or out-of-hospital arrest, they are confounded by the lack of a “gold standard” for comparison and lack of a control comparison group. For example, intracardiac thrombi identified may not represent causal factors in the cardiac arrest, but may just be a side effect of low flow states after cardiac arrest. Further, the diagnostic utility of TEE in myocardial infarction (MI) is limited in differentiation of acute wall motion abnormalities versus old MI, and is contingent upon an organized rhythm, which may be absent during cardiac arrest. Comparative effectiveness analyses are necessary comparing TEE to other diagnostic modalities during cardiac arrest before definitive statements about routine use of echocardiography in cardiac arrest management can be made.

TEE in Patients Presenting with Pulseless Electrical Activity

Often, cardiac arrest is due to pulseless electrical activity (PEA), also known as electromechanical dissociation (EMD). Upon echocardiographic evaluation, many of these cases are actually found to have some degree of cardiac activity, hence representing “pseudo-EMD.” Establishment of this condition has important diagnostic and prognostic implications, as patients who do have residual cardiac function (ie, those with severe left ventricular dysfunction like our case example) have a better prognosis than those patients with true EMD.21 In one study of echocardiography in 169 cardiac arrest victims, cardiac standstill was visualized in 139 patients; of these, none with echocardiographically identified cardiac standstill survived to leave the ED regardless of the initial electrical rhythm.21 Echocardiography can also be used to confirm asystole and ventricular fibrillation in those patients in whom the rhythm is unclear from the cardiac monitor.

In addition to helping to differentiate the underlying rhythm, echocardiography in cardiac arrest due to PEA or asystole can play an integral and comprehensive role in diagnosing the underlying primary cause (and hence the appropriate treatment), including cardiac effusion with tamponade, pulmonary embolus,22,23 severe hypovolemia,24–27 myocardial infarction,28 myocardial rupture, cardiogenic shock, mitral valve failure or papillary muscle rupture,29,30 and even tension pneumothorax. Unlike ventricular fibrillation and pulseless ventricular tachycardia, identification of the underlying cause is a key focus of treatment for PEA, and hence echocardiography can play a significant role in patient management.

TEE-Aided Diagnosis of the Underlying Cause in PEA Arrest

Pericardial Effusion

Pericardial effusion is usually easily detected by several routine TEE views, including the transgastric short-axis view and midesophageal four-chamber view (Figure 23–2). One must take care, however, to distinguish pericardial from pleural effusions. In the standard TTE parasternal long-axis view, for example, pericardial effusions normally lie anterior to the aorta, whereas pleural effusions lie posterior to the aorta (Figure 23–3). While visualization of an effusion is relatively straightforward, the diagnosis of pericardial tamponade is more difficult given that traditional echocardiographic evaluations such as mitral inflow respiratory flow variation, absent inferior vena caval inspiratory collapse, and presence of right ventricular diastolic collapse may be very difficult if not impossible in the patient with cardiac arrest. Hence one is reliant upon the physical examination and history to establish a diagnosis of pericardial tamponade. Visualization of a “swinging heart” may also help in diagnosing pericardial tamponade. Pericardial tamponade can be caused by trauma, aortic dissection, infection, neoplasm, congestive heart failure, uremia, autoimmune diseases, and radiation therapy.

Hypovolemia

Hypovolemia can be diagnosed on TTE and TEE by the presence of a small, flattened left ventricle in the four-chamber view. Further interrogation of the left ventricular outflow tract with Doppler echocardiography can help establish whether dynamic outflow obstruction related to the hypovolemia is present. In one study, left ventricular end-diastolic volume was found to correlate well with the presence of blood loss.31

Pulmonary Embolism

Pulmonary embolism is typically manifest as right ventricular hypokinesis and/or enlargement, and has been shown to be the cause of almost 5% of cardiac arrests, with PEA being the initial rhythm in 63%.32 Further details of the echocardiographic evaluation of pulmonary embolism are provided in Case 4.

Primary Cardiac Pathology

Echocardiography can be a very useful adjunct diagnostic tool for primary cardiac pathologies leading to cardiac arrest, including cardiogenic shock, myocardial infarction28 (diagnosed by findings of wall motion abnormalities in the proper clinical context), and complications of myocardial infarction including myocardial rupture, ventricular septal defect (VSD), mitral valve failure, and/or papillary muscle rupture.29,30 In an international registry from 19 medical centers of 251 patients after myocardial infarction, the cause of cardiogenic shock was severe left ventricular failure in 85%, mechanical complications in 5%, right ventricular infarct in 2%, and other comorbid conditions in 5%.33 Cardiac free wall rupture is usually a fatal complication of acute myocardial infarction. Echocardiographic diagnosis requires a careful search for the site of rupture and should be suspected if a region of thin myocardium or a small amount of pericardial effusion is present, particularly if a loculated effusion or clot is detected. Detection of a free wall rupture in such patients can lead to surgical repair with a subsequent survival rate of greater than 50%.34 In some cases, a pseudoaneurysm that forms after a free wall rupture is contained within a limited portion of the pericardial space. This occurs most frequently in the inferolateral wall, and is characterized by a small neck communication between the left ventricle and the aneurysmal cavity, with to-and-fro blood flow through the rupture site seen on Doppler and color-flow imaging.34 Mitral regurgitation often occurs in the setting of myocardial infarction, can be severe leading to hemodynamic compromise, and can be due to left ventricular dilatation leading to mitral annular dilatation, papillary muscle dysfunction, or papillary muscle rupture (Figure 23–4). Differentiating these causes of mitral regurgitation is important, as papillary muscle rupture is a serious complication that mandates urgent surgical repair.34

TEE during Cardiopulmonary Resuscitation

In addition to diagnostic utility, TEE can play a role in directing resuscitation efforts and minimizing CPR interruptions by virtue of allowing more rapid assessment of “pulse” following interventions such as defibrillation or epinephrine administration. Survival with shockable rhythms is better with shorter times to defibrillation, and patients who present with a non-shockable rhythm but convert to a shockable one in the ED have better outcomes if the latter is recognized and the appropriate intervention occurs.35 In this regard, TEE may be the most expedient way to detect such rhythms, particularly during an evolving code where a switch to a different part of the ACLS algorithm may be warranted. Since TEE can differentiate among low ejection fraction, electromechanical dissociation, and asystole, TEE can aid in the decision to cease resuscitative efforts since cardiac standstill (asystole) predicts negative outcome in the ED.36

A 68-year-old male presents to a community hospital with severe central substernal chest pain radiating to his neck, jaw, and back. Upon arrival to the ED, he is diaphoretic and complaining of weakness with a blood pressure of 203/99. An ECG performed on arrival reveals anterior ST segment elevation. The nearest cardiac center with catheterization capability is at least 1 hour away, and therefore the decision is made to initiate the thrombolytic protocol established at the hospital.

A portable chest x-ray is completed. The film is difficult to interpret given the patient’s body habitus, but a wide mediastinum cannot be excluded. Unequal blood pressures are noted in the arms, being approximately 20 mm Hg less in the left side. Given this physical exam finding and concern for aortic dissection, a TEE probe is placed. The image in Figure 23–5 is obtained, confirming an ascending aortic dissection extending into the left anterior descending artery. Thrombolytic therapy is deferred, and the patient’s blood pressure is controlled to 160 mm Hg with esmolol. An emergency consultation with thoracic surgery is obtained, and the patient is taken to the operating room (OR) for primary repair.

Aortic pathology constitutes a subset of cardiovascular disease with high morbidity and mortality; this is compounded by presentation that frequently mimics more common disease processes. ED physicians must maintain a high level of suspicion for aortic disease, as failure to consider it as part of the differential diagnosis can result in delivery of a contraindicated treatment (such as administering thrombolytic therapy in the patient thought to have an ST elevation MI) or a delay in recognition, which could jeopardize outcomes.

Acute aortic dissection occurs with an incidence of 2.9 per 100,000 per year.37 Any portion of the aorta can dissect. Aortic dissection typically begins with a tear from the lumen of the aorta through the intima into the medial layer. Subsequent propagation extends the intimal dissection away from the media. In addition to the classic aortic dissection instigated by a tear in the lumen of the aorta, spontaneous intramural hematoma is also a cause of aortic dissection. In this case, hemorrhage into the medial layer then dissects without rupture into the lumen. Intramural hematoma is more common in the descending aorta and arch, but can occur at any point along the aorta.

Classification of Aortic Dissections

Aortic dissections are classified by their location, with the most important factor being whether or not involvement of the ascending aorta is present. For example, the Stanford criteria differentiate aortic dissections by whether there is involvement of the ascending aorta, with such involvement classified as Stanford A (regardless of involvement of the descending aorta), and isolated descending aortic dissection classified as Stanford B. In the DeBakey classification, patients with both ascending and descending aortic involvement are classified as DeBakey I; isolated ascending aortic involvement DeBakey II; and isolated descending aortic involvement as DeBakey III. Additionally, isolated aortic arch dissections can occur. Patients with involvement of the ascending aorta have a higher risk of subsequent adverse outcomes, including pericardial effusion/ tamponade, rupture, dissection into the coronary arteries, and aortic insufficiency. It should be noted that most dissections will have multiple communication points between the true and false lumens, which may be important for surgical repair.38

More recent studies have suggested that intramural hematomas, intramural hemorrhage, and aortic ulcers may represent evolving aortic dissection or dissection subtypes. Therefore, a new classification scheme has been proposed (Table 23–3).39