Echocardiography in Emergency Clinical Presentation
- J. Todd Belcik, RCS, RDCS
- Jonathan R. Lindner, MD
Comprehensive two-dimensional and Doppler echocardiography, contrast echocardiography, and brief handheld echocardiographic imaging are all playing an increasing role in the management of patients presenting to the emergency department (ED). Two major assets of echocardiography have led to its increased use in the ED. First is that echocardiography can be performed portably at the patient bedside and provides immediate results on life-threatening conditions. Second is that echocardiography provides high-quality images on cardiovascular structure, function, and perfusion. This chapter reviews the major applications of echocardiography in patients presenting to the ED with acute illness. These applications can be broadly categorized as (1) diagnosis and prognosis of acute coronary syndrome (ACS) and (2) evaluation of patients with hypotension, dyspnea, and/or chest pain from causes other than ischemia alone.
Diagnosis and prognosis in acute coronary syndrome
Diagnostic Algorithms for Acute Coronary Syndrome
In the United States, more than 6 million patients present annually to the ED with chest pain (CP). A minority of these patients (10% to 30%) are ultimately diagnosed with either acute myocardial infarction (MI) or other forms of ACS. , In these patients, the correct diagnosis is often delayed or even missed in up to 5% of cases because of limitations in the accuracy and time required for standard diagnostic algorithms. , These standard practices include patient history, physical examination, 12-lead electrocardiogram (ECG), and circulating biomarkers for myocardial cell injury or loss. Although the ECG is generally useful for rapidly identifying patients with ST-elevation MI (STEMI), provided that there is not a left bundle branch block or ventricular paced rhythm, its accuracy in other forms of ACS is relatively low, correctly identifying ACS in approximately 30% to 50% of cases. Cardiac-specific serum troponin assays have markedly improved the diagnosis of ACS but are often negative, especially on the initial blood draw or if the degree of necrosis is small. The specificity of troponins also is problematic because they can be falsely elevated in myocarditis, stress cardiomyopathy, pericarditis, or other comorbid conditions such as severe renal insufficiency.
To address these limitations, noninvasive bedside echocardiography has been applied in order to more rapidly diagnose ACS, to identify those who have high-risk features of their ACS, and to reduce health care costs by confidently excluding ischemia in those whose symptoms are not from ACS.
Evaluation for Wall Motion Abnormalities
Assessment of regional wall motion by echocardiography in the acute setting can provide useful prognostic information in patients with CP. , This approach is particularly useful in those without prior MI who do not have preexisting wall motion abnormalities. In those with preexisting dysfunction, the appearance of new wall motion abnormalities can also be helpful. When patients are evaluated during symptoms or within a short period of resolution, the sensitivity of echocardiography for detecting regional wall motion abnormalities can be greater than 90%, whereas ECG does not provide definitive diagnosis in the majority. The notion that echocardiographic evidence of wall motion provides earlier diagnosis than positive troponins has been shown in several studies. , In particular, echocardiography has been shown to be useful in rapid diagnosis of ACS due to left circumflex disease, which is often “silent” on the standard 12-lead ECG. There is also evidence that the presence of a definitive wall motion abnormality in those with ACS increases likelihood of related late adverse events approximately fourfold.
Perhaps more important is that the negative predictive value of echocardiography is high. The presence of completely normal wall motion is able to exclude ischemia with a negative predictive value greater than 95%, provided that imaging is performed early in the course of symptoms. It should be cautioned that echocardiography may be falsely negative in situations where imaging is performed late after resolution of symptoms or if there is incomplete or inadequate visualization of all myocardial segments. Moreover, the dyssynergy caused by left bundle branch block or ventricular pacing can present problems with accurate evaluation of septal wall motion.
Although the presence of a new wall motion abnormality is a strong indicator of ACS in the setting of high pretest suspicion, many other conditions can lead to segmental wall motion abnormality ( Box 188.1 ). In particular, stress cardiomyopathy may present with segmental ventricular dysfunction, chest pain, positive troponin, and ECG changes that resemble STEMI or ACS. In the absence of angiography, the only reliable features that may suggest stress cardiomyopathy are a segmental pattern of dysfunction that is inconsistent with coronary artery disease and a clinical history of predisposing stress (e.g., severe emotional stress, intracerebral hemorrhage).
Stress cardiomyopathy (takotsubo myopathy)
Sarcoidosis
Focal myocarditis
Cardiac complications of severe allergic reactions
Chagas myocarditis
Pseudo–wall motion abnormality from posterior compression (hiatal hernia)
Illicit drug use
Myocardial Contrast Echocardiography for Left Ventricular Opacification
Despite advances in imaging technology, adequate evaluation of the endocardial border is still not possible in 10% to 15% of patients. Encapsulated microbubble ultrasound contrast agents that are stable after intravenous injection improve endocardial border delineation of the left ventricle in otherwise technically suboptimal studies. This issue is of particular importance in the evaluation of patients in whom ACS is suspected because (1) every segment needs to be visualized, (2) a high level of reader confidence is needed, and (3) the imaging environment in the ED is often suboptimal.
Clinical studies have demonstrated that ultrasound contrast agents substantially increase the number of interpretable segments, decrease interobserver variability, and increase reader confidence. The evaluation of regional wall motion with contrast echocardiography specifically for ED patients with chest pain has been demonstrated to provide incremental value to clinical information, the ECG, and initial troponin. , It also provides prognostic information with regard to likelihood of late adverse cardiovascular events and mortality. Left ventricular opacification with contrast echocardiography in those with already-recognized ACS can also reveal the presence of ventricular pseudoaneurysms or ventricular thrombus ( Fig. 188.1 ).
Myocardial contrast echocardiography perfusion imaging
The ability to rapidly assess myocardial perfusion at the patient bedside is a major asset for using myocardial contrast echocardiography (MCE) in the ED. Perfusion imaging techniques have been described in other chapters and, at the current time, are off-label applications for ultrasound contrast agents. MCE imaging performed without destructive pulse sequences provides information on microvascular blood volume that alone can be useful in patients presenting with chest pain by detecting severe resting ischemia or infarction ( Fig. 188.2 ). Imaging blood volume alone in this manner should be used with caution because attenuation artifacts can appear identical to blood volume abnormalities and because not all perfusion abnormalities can be detected by reduced microvascular blood volume.
