Identifying the cause of acute dyspnea in the emergency department is often challenging, even for the most experienced provider. A detailed history may not be obtainable because of extreme dyspnea, and management is often initiated before more standard testing (laboratory results and chest radiography) is available. Additionally, imaging with portable plain film radiographs has been shown to be inaccurate in the differentiation of ADHF (acute decompensated heart failure) from COPD (chronic obstructive pulmonary disease).¹

A focused bedside ultrasound in conjunction with the clinical exam can be the ideal tool for the emergency physician in the rapid evaluation of the undifferentiated dyspneic patient.^2-4

In isolation, focused echocardiography in the ED can determine gross cardiac function. Limited pulmonary ultrasound can determine the presence or absence of pulmonary edema. Inferior vena cava (IVC) collapsibility can be a rough marker for central venous pressure (CVP).

Using specific aspects of each of the previous focused ultrasounds allows the clinician to visualize the lack of forward cardiac flow and its effects on the lungs and the afferent venous vasculature, defining the process of ADHF.^2,4-6

A three-view bedside sonographic examination or “triple scan” (focused evaluation of the heart, lungs, and inferior vena cava) is an ideal adjunct in the clinical evaluation and management of the acutely dyspneic patient.

For the novice sonographer, the goal of the exam is not to rule out the various other processes that present as acute dyspnea in the emergency setting (pulmonary embolism, pneumonia, asthma, etc.), but rather to confirm the presence of ADHF and allow the clinician to execute appropriate initial therapies.

Poor systolic cardiac function, edema in the lungs, and congestion of the IVC can confirm clinical findings at the bedside and reduce clinical uncertainty.

Procedure

The evaluation of the acutely dyspneic patient can be performed with any standard portable ultrasound system. Either a curvilinear low-frequency transducer (5-2 MHz) or a phased-array transducer (5-1 MHz) can be used for various parts of the exam. The patient can remain sitting upright (often the most comfortable position for the acutely dyspneic patient).

Two-View Focused Echocardiography For the more novice sonographer, we recommend using the parasternal long (PSL) and parasternal short (PSS) views in succession to evaluate for gross cardiac function (exclusion of a pericardial effusion can also be performed in this view). Our explanation of the views is different from that of our cardiology colleagues as we consistently maintain probe marker position to the patient’s right on ultrasound exams in the ED.⁷ As with all ultrasound examinations, certain patients will be difficult to image, and other views (subxiphoid, etc.) that will not be discussed here may be useful.

To obtain the PSL view, place the probe adjacent to the sternum (at the level of the nipple) with the probe marker facing the patient’s right shoulder (Fig. 1). If the standard cardiac structures are not visualized, we recommend sliding the ultrasound probe in a cephalad or caudal direction, while continuing to point the probe marker toward the patient’s right shoulder (Fig. 1). When the heart is identified, rotate the axis of the ultrasound probe until a view of the right ventricle, mitral valve, left ventricle, and descending thoracic aorta is obtained (Fig. 2). The clinician can ensure the lack of a pericardial effusion in the dependent position between the descending thoracic aorta and myocardium (Fig. 3). The clinician should then grossly evaluate cardiac function by looking at the gross squeeze/movement of the left ventricle. Visually estimating mitral valve E-point septal separation (EPSS), the minimum distance between the anterior leaflet and the interventricular septum in the PSL axis, is an alternative method to assess left ventricular systolic function.5 An EPSS of more than 0.7 cm correlates with an ejection fraction (EF) under 30%; however, this may not be accurate in cases of aortic insufficiency or mitral stenosis. In cases of severe systolic cardiac dysfunction, a distance greater than 1 cm between the anterior mitral valve leaflet and interventricular septum is not uncommon (Fig. 4). Again, gross estimation in conjunction with evaluation of mitral valve movement will allow the clinician to note poor cardiac systolic function.

After obtaining the best PSL view, rotate the probe 90 degrees until the probe marker faces the patient’s right iliac crest (Fig. 5) to obtain the PSS view. When an image of the left and right ventricular chambers is obtained, slightly move the probe toward the apex of the heart in order to be lower than the mitral valve for gross cardiac function.

The goal of the focused echo for the triple scan is not to determine mild functional cardiac impairment. Patients who are experiencing ADHF have moderate to severe cardiac dysfunction, and the sonographer should focus on the evaluation of gross dysfunction.

Focused Lung Ultrasound

The lung exam, as part of the triple scan protocol, evaluates the anterior and lateral chest. The anterior exam is most revealing for pneumothorax and alveolar interstitial syndrome (pulmonary edema) as identified by B-line artifacts arising from the pleura. The lateral exam, from the diaphragm to axilla, is best for detecting dependent pleural effusions.⁸ Position the probe longitudinally between two rib spaces starting at the mid-clavicular line (just below the clavicle) and scan caudally by slowly sliding the probe to the most dependent lung field (Fig. 6). Ensure the depth on the ultrasound screen is greater than 13 cm and increase the gain. The anterior lung exam answers two questions: the presence or absence of pneumothorax by assessing pleural sliding, and the presence of B-lines or A-lines from the pleura. We recommend scanning three or more ultrasound lung fields to determine the presence or absence of lung sliding (Fig. 6). Since the patient will often be sitting up, the exam will not be able to completely rule out the presence of a small apical pneumothorax (rarely if ever the cause of severe acute dyspnea in an ED patient). A-lines are hyperechoic, horizontal reverberation artifacts parallel to the pleura that represent normal or pathologically hyperaereted lungs. A-lines are commonly seen in patients with COPD and/or asthma (Fig. 7).³ B-lines are vertical reverberation artifacts arising from the pleura that are caused by thickened interlobular septa representing alveolar interstitial syndrome (AIS) (Fig. 7).⁹ Three or more B-lines visualized between a rib interspace are called “lung rockets” and indicate a positive scan for AIS. Their presence bilaterally defines pulmonary edema.³ The absence of B-lines in the anterior lung zones essentially rules out ADHF. The presence of poor systolic ejection fraction and bilateral B-lines in an acutely dyspneic ED patient indicates a high likelihood of the presence of ADHF.

IVC: Subxyphoid/Lateral Approach

The last part of the triple scan assesses IVC size and collapsibility. For the subxyphoid approach, the probe is positioned longitudinally just to the right of midline and rocked caudally to visualize the right atria if possible (Fig. 8). We recommend fanning the probe to the patient’s left to identify the aorta, and then back to the patient’s right to confirm the IVC. The IVC is differentiated from the aorta by observing its confluence with the hepatic vein and the right atrium. Once the IVC is identified, the provider assesses the collapsibility during inspiration, focusing approximately 2-3 cm caudal to the confluence of the hepatic vein. The IVC is categorized as plethoric (less than 15% collapse with inspiration), normal respiratory variability, or flat. We do not recommend measuring the IVC, but instead recommend looking for gross variability during respiration. A large, noncollapsible IVC suggests high right-sided pressures consistent with ADHF, but may also be present in cases of chronic pulmonary hypertension, large pulmonary embolus, valvular disorders such as pulmonary stenosis and mitral regurgitation, cardiac tamponade, and right-sided myocardial infarction.6 Fortunately, with the additional information obtained from both the focused echo and lung examination, the clinician is able to reduce diagnostic uncertainty.

Diastolic Dysfunction

Since diastolic dysfunction is a common cause of ADHF, can the triple scan be useful in this patient population?

Yes. In cases of ADHF from diastolic dysfunction, the process is still the same. Lack of forward cardiac flow secondary to poor cardiac relaxation (unlike systolic dysfunction where the problem is dysfunctional contraction) occurs classically in the elderly, long-term hypertensive patient with an acute elevation of blood pressure. Often, patients will have a mixture of both, and the benefit of the triple scan is that it allows the clinician to visualize this often-complex physiologic principle. In the classic case, the triple scan will show a thickened myocardium (with or without poor systolic cardiac function), B-lines in bilateral lung fields, and a plethoric IVC.

Summary and Conclusion

Evaluation of the acutely dyspneic patient in the ED is often challenging. A focused ultrasound examination consisting of bedside echocardiography, limited lung examination, and views of the IVC is a powerful tool that can visually represent the disease pathology. In the case of ADHF, the lack of forward blood flow and its resultant pulmonary congestion can be rapidly defined at the bedside, allowing for initiation of directed therapy and reducing clinical uncertainty. Focused echocardiography will indicate gross poor systolic function. The limited ultrasound exam of the anterior lungs will demonstrate bilateral B-lines/AIS. A patient with ADHF will have poor respirophasic IVC variability. The triple scan in conjunction with a clinical exam can be an ideal tool to rule in or rule out the diagnosis of ADHF.

References

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8. Lichtenstein DA. Ultrasound in the management of thoracic disease. Crit. Care Med. 2007;35(5 Suppl):S250-61.
9. Lichtenstein D, Mezière G. A lung ultrasound sign allowing bedside distinction between pulmonary edema and COPD: The comet-tail artifact. Intensive Care Med. 1998;24:1331-4.

Dr. Mantuani and Dr. Bailey are attending physicians at Alameda County Medical Center/Highland General Hospital, Oakland, Calif. Dr. Nagdev is Director of Emergency Ultrasound at Alameda County Medical Center/Highland General Hospital. The authors thank their patient-model Dr. Brad Ching (resident physician, Alameda County Medical Center/Highland General Hospital).