Emergency echocardiography is a core application of emergency ultrasound and is a key element of the FAST examination.1,176,177 Although comprehending image orientation178 and acquiring images can be somewhat challenging, emergency echocardiography has had a major impact on emergency clinicians’ ability to detect cardiac abnormalities and on patient care and can be life-saving.179 (See Figure 20.) It provides emergency clinicians with time-sensitive anatomic and physiologic information in a variety of cardiac-related scenarios, including cardiac arrest, unexplained hypotension, syncope, shortness of breath, and chest pain.180-183 Emergency echocardiography can help risk-stratify patients in the ED and further guide resuscitative efforts.184,185 At times, the information and disorders noted on focused cardiac ultrasound are vast and may surpass what the emergency clinician is able to appreciate and integrate. As per the American Society of Echocardiography (ASE)/ACEP Consensus Statement, the ability to assess global left ventricular function and detect pericardial effusions and right heart dilatation (chamber sizes) are within the scope of emergency clinicians and can help answer critical patient management questions.186,187
Left Ventricular Function
Assessment of left ventricular function is a fundamental application of emergency echocardiography and helps predict clinical outcomes for a variety of disease states. The ability to assess a patient’s overall left ventricular function — from cardiac standstill to a hyperdynamic ejection fraction — allows emergency clinicians to better manage patients who present with chest pain, dyspnea, or unexplained hypotension or who are in cardiac arrest.188 Although regional wall motion abnormalities and quantitative measurements are beyond the scope of most emergency clinicians, the visual (qualitative) assessment of global left ventricular systolic function is not.187 With appropriate education and training, emergency clinicians can differentiate between normal and severely depressed left ventricular systolic function similar to cardiologists. Moore et al demonstrated that, with focused training, emergency physicians can accurately determine left ventricular function in hypotensive patients.188 Although this study showed good agreement between emergency physicians and cardiologists for patients with normal and severely depressed left ventricular function, emergency physicians had more trouble categorizing patients with moderately depressed left ventricular function. This underscores the need for emergency clinicians to recognize their limitations and to obtain consultative imaging studies when indicated.
Pericardial fluid typically appears as an anechoic space between the epicardium and the pericardium. (See Figure 21.) Ultrasound is an ideal modality to detect the presence of pericardial fluid and its impact on right heart filling.177,189,190 Although cardiac tamponade is largely a clinical diagnosis, emergency echocardiography may demonstrate findings consistent with impending tamponade prior to the development of physical examination findings and hemodynamic compromise.191-193 The amount of fluid required to impair filling and cause circulatory failure depends on the rate of accumulation. Pericardial effusions may be graded as small (less than 10 mm), moderate (10-15 mm), or large (greater than 15 mm).193-196
Numerous studies have demonstrated that emergency physician–performed emergency echocardiography has sensitivities approaching 100% for the detection of pericardial effusions.184,197,198 When compared with the expert over-read of images, emergency physician–performed emergency echocardiography for effusion has a sensitivity of 96% to 100%, a specificity of 98% to 100%, a positive predictive value of 93% to 100%, and a negative predictive value of 99% to 100%.1 The echocardiographic findings consistent with cardiac tamponade include the following: right ventricular (RV) free wall inversion during ventricular diastole (the hallmark finding), right atrial inversion during ventricular systole (more common and one of the earliest findings), increased respiratory variation of mitral or aortic inflow velocities (inspiratory decrease greater than 25%), and a dilated inferior vena cava with decreased inspiratory collapse.196
Right Heart Dilatation
Patients with right heart failure can be difficult to diagnose and manage. The thin-walled right ventricle (RV) is extremely sensitive to load, so small changes in pressure lead to large changes in volume. Right ventricular dilatation is the normal response to RV pressure or volume overload.195 Although assessing for RV systolic dysfunction and for paradoxical septal motion are beyond the scope of most emergency clinicians, assessing for RV dilatation (chamber size) may not be.187 Typically, the RV is smaller than the left ventricle (LV), with an RV-to-LV ratio of 0.6:1.0. When the RV is noted to be equal in size to the LV, the RV is moderately dilated. When the RV is larger than the LV, severe dilatation is present.201 The apical 4-chamber view is used to compare RV and LV size, and the relative sizes are compared at the tips of the atrioventricular valves. When RV dilatation is present, the RV apex is closer to – or even encompasses – the LV apex.196 In the appropriate clinical setting, RV dilatation can suggest RV outflow tract obstruction possibly due to pulmonary embolism; however, emergency echocardiography is not sensitive for pulmonary embolism. Patients with pulmonary embolism and evidence of right-heart dysfunction have increased morbidity and mortality, and emergency echocardiography can be used to riskstratify and to better manage these patients.201,202
Emergency echocardiography provides emergency clinicians with immediate structural and physiologic data that can be life-saving. The ability to assess patients for pericardial effusions, global left ventricular function, and right heart dilatation can provide answers to critical questions, risk-stratify patients in the ED, and further guide resuscitative efforts. Although there is literature to support the ability of emergency clinicians to detect pericardial effusions and to assess global left ventricular function, future studies should further investigate their ability to detect echocardiographic signs of tamponade and right heart dilatation.
James Q. Hwang; Heidi Harbison Kimberly; Andrew S. Liteplo; Dana Sajed
March 2, 2011