Focus On: Bedside Ultrasound Assessment of Left Ventricular Function

Contributors
Sebastian Siadecki MD; Turandot Saul MD, RDMS; Resa E Lewiss MD, RDMS

Disclosures
In accordance with the Accreditation Council for Continuing Medical Education (ACCME) Standards and American College of Emergency Physicians policy, all individuals in control of content must disclose to the program audience the existence of significant financial interests in or relationships with manufacturers of commercial products that might have a direct interest in the subject matter.

This activity has been planned and implemented in accordance with the Essential Areas and Policies of the Accreditation Council for Continuing Medical Education (ACCME). The American College of Emergency Physicians is accredited by the ACCME to provide continuing medical education for physicians.

The American College of Emergency Physicians designates this enduring material for a maximum of 1 AMA PRA Category 1 CreditTM. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

"ACEP Focus On: Bedside Ultrasound Assessment of Left Ventricular Function" is approved by the American College of Emergency Physicians for one ACEP Category I credit.

Disclaimer
ACEP makes every effort to ensure that contributors to College-sponsored programs are knowledgeable authorities in their fields. Participants are nevertheless advised that the statements and opinions expressed in this article are provided as guidelines and should not be construed as College policy. The material contained herein is not intended to establish policy, procedure, or a standard of care. The views expressed in this article are those of the contributors and not necessarily the opinion or recommendation of ACEP. The College disclaims any liability or responsibility for the consequences of any actions taken in reliance on those statements or opinions.

Questionnaire Is Available Online
This educational activity is designed for emergency physicians and should take approximately 1 hour to complete. Participants will need an Internet connection through Firefox,Safari or Internet Explorer 6.0 or above to complete this Web-based activity. The CME test and the evaluation form are located online at www.ACEP.org/focuson. 

The participant should, in order, review the learning objectives, read the article, and complete the CME post-test/evaluation form to receive up to 1 ACEP Category I credit and 1 AMA PRA Category 1 Credit^TM. You must score at least 70 percent to receive credit. You will be able to print your CME certificate immediately. 

This article was published online October 1, 2012. The credit for this CME activity expires September 30, 2015.

Please contact ACEP with any questions and read our privacy policy and copyright notice. 

Introduction
Emergency physicians must oftenmanage critically ill patients whose hemodynamic status is unclear,especially early in the course of their disease.

Correct and timely diagnosis of theprevailing hemodynamic process is of utmost importance, and thephysical exam and vital signs alone are often unreliable. Moreover, congestive heart failure isextremely prevalent in the emergency department population, andmore than half of patients with moderate to severe systolicdysfunction have never been diagnosed with heart failure.

Bedside echocardiography by theemergency physician offers a rapid, noninvasive, and inexpensivemethod to determine the role that the patient's systolic cardiacfunction may be playing in their disease process. Besides thediagnosis of heart failure, assessment of left ventricular (LV)function can help distinguish between cardiac and other etiologiesof undifferentiated hypotension or shock. Multiple studies havedemonstrated that emergency physicians with focused training intransthoracic echocardiography can accurately determine leftventricular ejection fraction (LVEF) in critically ill patients.

In combination with other commonemergency department ultrasound applications such as evaluation ofthe inferior vena cava (IVC) as a marker of intravascular volumestatus, and evaluation of the lungs and pleura, assessment of LVEFcan be a valuable tool in the management of critically illpatients.

Indications 

• Undifferentiated hypotension
• Chest pain
• Dyspnea
• Suspicion of cardiogenic shock

Performing theultrasound
Positioning and probe selection:

Place the patient in the supineposition with the head of the bed as flat as the patient cantolerate. A low-frequency probe (3.5-5 MHz), such as a phased arrayor curvilinear probe, should be selected.

Obtaining the cardiacwindows:
There are four primary cardiac views or "windows" that canbe used to obtain an adequate view of the left ventricle:subxiphoid 4-chamber, parasternal long axis, parasternal shortaxis, and apical 4-chamber. Of these, the parasternal views arepreferred for the assessment of LVEF by most users.

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 3^rd or 4^th 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 towards 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 the mitral valve.

Apical four chamber: Toobtain this view, the transducer should be placed at the apex ofthe heart, where the point of maximal impulse (PMI) may be felt, inthe midclavicular line, 5^th intercostal space or lower.The probe footprint should be angled towards the right shoulderwith the probe marker directed towards the patient's right. Somerotation or translation of the transducer may be required for allfour chambers to appear in the image. The left ventricle willappear 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.

• Move the transducer in acoordinated and systematic fashion, using the four main types ofmotions: 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 chestwall
• Hold the probe as close to thefootprint as possible and place the 5^th digit againstthe chest wall for stability
• Use an adequate amount ofconducting gel
• Optimize depth and gainsettings
• Moving the patient into a left lateral decubitus position can help bring mediastinal structures closer to the anterior chest wall

Evaluation / Interpretationof Left Ventricular Systolic Function
Many methods exist for echocardiographic assessment ofLVEF, ranging from simple visual estimation to complex methodsinvolving multiple measurements and biometric softwarecalculations.

The fastest and most practicalmethod for emergency physicians to estimate LVEF is a visualassessment. Typically, this assessment is separated into threecategories: hyperdynamic or normal (LVEF >50%), moderatedysfunction (LVEF 30-50%), and severe dysfunction (LVEF <30%). A subjective visual assessment should be madeof the degree of contraction between systole and diastole, with theheart evaluated in at least two views. All visualized walls of theventricle should move symmetrically and vigorously towards thecenter of the chamber during systole and the walls should thickenas the muscle contracts. This method is somewhatoperator-dependent; however, even with only several hours oftraining, emergency physicians have been shown to be able to makeassessments that correlate well with echocardiography performed bycardiologists. The best way to become more proficient is topractice at the bedside, especially in patients known to havenormal or depressed cardiac function.

There are several pitfalls of thismethod; asymmetric wall motion abnormalities may be difficult toevaluate, and LVEF may not be a good indicator of cardiac output incases of valvular disease such as aortic stenosis or mitralregurgitation. It is also unclear how many studies one mustperform to become proficient at this estimation.

Other methods of estimating LVEFrequire some measurements and may be more time consuming andrequire more practice to become comfortable with, but are stilluseful for emergency physicians to be aware of.

Mitral valve E-point septalseparation (EPSS) is a relatively simple measurement, the use ofwhich has also been studied in emergency physicians. EPSS ismeasured as the distance in millimeters between the anteriorleaflet of the mitral valve and the inter-ventricular septum in theparasternal long axis view during the early opening point of themitral valve in early diastole. Images are obtained in M-mode byplacing the white vertical line over this area. EPSS measurementsof 6 mm or less are seen in patients with normal LVEF and an EPSSmeasurement greater than 7mm indicates poor LV function. Thismethod can be particularly useful in patients with coronary arterydisease and resultant regional wall motion abnormalities, which canmake subjective visual estimation difficult.

The M-mode LV dimensional orTeichholtz method is also performed using the parasternal long axisview, with images obtained of the left ventricle in M-mode. Measurements are made of the right ventricle(RV) internal dimension, inter-ventricular septum thickness, LVinternal dimension and LV posterior wall thickness at end-diastoleand end-systole. These measurements are then analyzed by thebiostatistical software of the ultrasound machine, which calculatesthe LVEF. The Teichholtz method only uses a single diameter of theLV in the calculation and therefore its accuracy depends onsymmetric assumptions about the chamber. This method is far moretime-consuming and complex, thus making it less practical for quickassessments of LV function in critical patients.

The 2-dimensional Border Tracingmethod also depends on biostatistical calculations by theultrasound machine. An apical 4-chamber view is obtained, and animage is captured at end-systole and end-diastole. For each ofthese images, the inside border of the left ventricle is traced andthe software estimates the volume of the left ventricle,subsequently calculating the EF based on these estimates.

Use in combination with IVCevaluation
Sonographic estimation of LVEF can be even more clinicallyuseful in determining a patient's hemodynamic state when combinedwith evaluation of intravascular volume status using measurementsof the inferior vena cava. As discussed in a previous ACEP Focus On(June 2011), the degree of collapse of the IVC with respiratoryvariation can indicate whether the patient is intravascularlyvolume depleted or hypervolemic. Using these two sonographicassessments together can help to differentiate between cardiogenic,hypovolemic, and other forms of shock, and can help directresuscitation in cases where there may be multiple concurrentprocesses - for example, a patient with underlying congestive heartfailure who is acutely septic.

Pearls andpitfalls 

• Scan in a systematic fashion
• Improve the quality of the exam by appropriating depth andgain
• Bowel gas may impede the subxiphoid view; body habitus orhyperinflated lungs may impede the parasternal views
• Consider your sonographic findings within the clinical contextof the patient
• Qualitative and quantitative measurements of LVEF areoperator-dependent; the best way to obtain more accurate findingsis to practice