Emergency physicians must often manage critically ill patients whose hemodynamic status is unclear, especially early in the course of their disease. Correct and timely diagnosis of the prevailing hemodynamic process is of utmost importance, and the physical exam and vital signs alone are often unreliable.¹ Moreover, congestive heart failure is extremely prevalent in the emergency department population, and more than half of patients with moderate to severe systolic dysfunction have never been diagnosed with heart failure.²

Bedside echocardiography by the emergency physician offers a rapid, noninvasive, and inexpensive method to determine the role that the patient’s systolic cardiac function may be playing in the disease process. Besides the diagnosis of heart failure, assessment of left ventricular (LV) function can help distinguish between cardiac and other etiologies of the undifferentiated hypotension or shock state. Multiple studies have demonstrated that emergency physicians with focused training in transthoracic echocardiography can accurately determine left ventricular ejection fraction (LVEF) in critically ill patients.³

In combination with other common emergency department ultrasound applications, such as evaluation of the inferior vena cava (IVC) as a marker of intravascular volume status, and evaluation of the lungs and pleura, assessment of LVEF can be a valuable tool in the management of critically ill patients.

Performing the Ultrasound

Place the patient in the supine position with the head of the bed as flat as the patient can tolerate. A low-frequency probe (3.5-5 MHz), such as a phased array or curvilinear probe, should be selected.

Obtaining the Cardiac Windows

There are four primary cardiac views or “windows” that can be used to obtain an adequate view of the left ventricle: subxiphoid four-chamber, parasternal long axis, parasternal short axis, and apical four-chamber. Of these, the parasternal views are preferred for the assessment of LVEF by most users.³

Subxiphoid

This view is perhaps the most familiar to emergency physicians as it is the view most often used in the focused assessment with sonography for trauma (FAST) exam. To obtain this view, the transducer is placed on the abdomen just inferior to the xiphoid process, held at a shallow, 15-degree angle to the surface of the abdomen, with the probe footprint angled toward the left shoulder. The probe marker is directed to the patient’s right. The depth should then be adjusted to include the posterior surface of the pericardium in the inferior portion of the image. In this view, the left ventricle is the larger, thicker-walled chamber in the right lower part of the image.

Parasternal Long Axis

In this view, the transducer is placed perpendicular to the chest wall at the third or fourth intercostal space just to the left of the sternal border, with the probe marker directed to the patient’s left hip. The left ventricle will be seen as the thick-walled, oval-shaped chamber in the left lower part of the resulting image.

Parasternal Short Axis

Once the parasternal long axis view is obtained, the short axis view can be visualized by rotating the probe 90 degrees clockwise, directing the probe marker toward the patient’s right hip. The left ventricle will appear in cross section as a thick-walled, roughly circular structure on the right side of the image. By sweeping the transducer from base to apex, several different short axis views may be obtained, including at the level of the papillary muscles, chodae tendinae, and mitral valve.

Apical Four Chamber

To obtain this view, the transducer should be placed at the apex of the heart, where the point of maximal impulse (PMI) may be felt, in the midclavicular line, fifth intercostal space or lower. The probe footprint should be angled toward the right shoulder with the probe marker directed toward the patient’s right. Some rotation or translation of the transducer may be required for all four chambers to appear in the image. The left ventricle will appear as the chamber in the upper right of the image.

Maximizing Image Quality

Because of the complex shape and motion of the heart, the number of structures to be identified, and patient factors such as body habitus, adequate cardiac views can sometimes be difficult to obtain. The following techniques can be used to improve the quality of the images obtained:

PIMove the transducer in a coordinated and systematic fashion, using the four main types of motions: sliding side to side in the direction of the probe marker, fanning in the short axis of the transducer, twisting or rotating, and angling the probe in relation to the surface of the chest wall.

• Hold the probe as close to the footprint as possible and place the fifth digit against the chest wall for stability.
• Use an adequate amount of conducting gel.
• Optimize depth and gain settings.
• Moving the patient into a left lateral decubitus position can help bring mediastinal structures closer to the anterior chest wall.

Evaluation and Interpretation of Left Ventricular Systolic Function Many methods exist for echocardiographic assessment of LVEF, ranging from simple visual estimation to complex methods involving multiple measurements and biometric software calculations.

The fastest and most practical method for emergency physicians to estimate LVEF is a visual assessment. Typically, this assessment is separated into three categories: hyperdynamic or normal (LVEF greater than 50%), moderate dysfunction (LVEF 30%-50%), and severe dysfunction (LVEF less than 30%).⁴ A subjective visual assessment should be made of the degree of contraction between systole and diastole, with the heart evaluated in at least two views. All visualized walls of the ventricle should move symmetrically and vigorously toward the center of the chamber during systole, and the walls should thicken as the muscle contracts. This method is somewhat operator-dependent; however, even with only several hours of training, emergency physicians have been shown to be able to make assessments that correlate well with echocardiography performed by cardiologists. The best way to become more proficient is to practice at the bedside, especially in patients known to have normal or depressed cardiac function.

There are several pitfalls of this method; asymmetric wall motion abnormalities may be difficult to evaluate, and LVEF may not be a good indicator of cardiac output in cases of valvular disease such as aortic stenosis or mitral regurgitation.2 It is also unclear how many studies one must perform to become proficient at this estimation.

Other methods of estimating LVEF require some measurements and may be more time consuming and require more practice to become comfortable with, but they are still useful for emergency physicians.

Mitral valve E-point septal separation (EPSS) is a relatively simple measurement, the use of which by emergency physicians has also been studied. EPSS is measured as the distance in millimeters between the anterior leaflet of the mitral valve and the interventricular septum in the parasternal long axis view during the early opening point of the mitral valve in early diastole. Images are obtained in M-mode by placing the white vertical line over this area. EPSS measurements of 6 mm or less are seen in patients with normal LVEF; an EPSS measurement greater than 7 mm indicates poor LV function. This method can be particularly useful in patients with coronary artery disease and resultant regional wall motion abnormalities, which can make subjective visual estimation difficult.⁵

The M-mode LV dimensional or Teichholtz method is also performed using the parasternal long axis view, with images obtained of the left ventricle in M-mode.⁶ Measurements are made of the right ventricle (RV) internal dimension, inter-ventricular septal thickness, LV internal dimension, and LV posterior wall thickness at end-diastole and end-systole. These measurements are then analyzed by the biostatistical software of the ultrasound machine, which calculates the LVEF. The Teichholtz method uses only a single diameter of the LV in the calculation, and therefore its accuracy depends on assumptions about chamber symmetry. This method is far more time consuming and complex, making it less practical for quick assessments of LV function in critical patients.

The two-dimensional border tracing method also depends on biostatistical calculations by the ultrasound machine. An apical four-chamber view is obtained, and an image is captured at end-systole and end-diastole. For each of these images, the inside border of the left ventricle is traced and the software estimates the volume of the left ventricle, subsequently calculating the EF based on these estimates.

Use in Combination with IVC Evaluation

Sonographic estimation of LVEF can be even more clinically useful in determining a patient’s hemodynamic state when combined with evaluation of intravascular volume status using measurements of the inferior vena cava. As noted in a previous Focus On (ACEP News, June 2011), the degree of collapse of the IVC with respiratory variation can indicate whether the patient is intravascularly volume depleted or hyper- volemic. Using these two sonographic assessments together can help to differentiate among cardiogenic, hypovolemic, and other forms of shock and can help direct resuscitation in cases where there may be multiple concurrent processes – for example, a patient with underlying heart failure who is acutely septic.

References

1. Randazzo MR, Snoey ER, Levitt MA, Binder K. Accuracy of emergency physician assessment of left ventricular ejection fraction and central venous pressure using echocardiography. Acad. Emerg. Med. 2003;10:973-7.
2. Ma OJ, Mateer JR, Blaivas M. Emergency Ultrasound. The McGraw Hill Companies, Inc.; 2008.
3. Mark DG, Ku BS, Carr BG, et al. Directed bedside transthoracic echocardiography: Preferred cardiac window for left ventricular ejection fraction estimation in critically ill patients. Am. J. Emerg. Med. 2007;25:894-900.
4. Moore CL, Rose GA, Tayal VS, et al. Determination of left ventricular function by emergency physician echocardiography of hypotensive patients. Acad. Emerg. Med. 2002;9:186-93.
5. Secko MA, Lazar JM, Salciccioli LA, Stone MB. Can junior emergency physicians use E-point septal separation to accurately estimate left ventricular function in acutely dyspneic patients? Acad. Emerg. Med. 2011;18:1223-6.
6. John G, Peter JV, Pichamuthu K, Chacko B. Tutorial 5 – Assessment of LV systolic function. ICU Sonography (www.criticalecho.com/content/tutorial-5-assessment-lv-systolic-function; accessed June 7, 2012).