eMedicine Specialties > Clinical Procedures > Radiology

Bedside Ultrasonography, Cardiac Evaluation: Treatment & Medication

Author: Timothy Jang, MD, Assistant Professor of Medicine, Director of Emergency Ultrasound, David Geffen School of Medicine at UCLA, Olive View-UCLA Medical Center; Clinical Faculty, Washington University School of Medicine
Coauthor(s): Cori A Poffenberger, MD, Clinical Instructor, David Geffen School of Medicine, University of California at Los Angeles; Emergency Ultrasound Fellow, Department of Emergency Medicine, Harbor-UCLA Medical Center, Torrance
Contributor Information and Disclosures

Updated: Aug 11, 2009

Anesthesia

• Anesthesia is generally not necessary for the sonographic evaluation of the heart, great vessels, and pleural spaces.

Equipment

• Ultrasound machine
• Ultrasound-conducting gel

Positioning

• If possible, patients should be evaluated in the left lateral decubitus position, with the left arm raised up above the head. 
  • This position brings the heart out toward the chest wall, displaces the lingula of the left lung out of the way, and opens the intercostal space by spreading the ribs.
  • Male patients should have the entire left hemithorax exposed for the examination. Take care with female patients to minimize the exposure of sensitive areas.
• Patients who are sick, however, are often not able to comply with such positioning.
  • Patients in respiratory distress must often be scanned in an upright sitting position.
  • Patients with hemodynamic compromise must often be scanned supine and are unable to roll on to the left side.

Technique

Subxiphoid 4-chamber view

Place the transducer-probe in the subxiphoid area directed into the chest and toward the left shoulder, as shown in the image below.

The left lobe of the liver is used as an acoustic window to view the heart. This view can be difficult to obtain if the patient is obese or if intervening bowel gas is present. It often requires increasing the depth and pressing the probe into the abdomen and angling the probe so that it is nearly parallel to the skin. In such cases, the clinician can place his or her palm over the top of the probe with the thumb on the side of the probe.

The probe indicator should be pointed toward the patient's left hip (cardiology orientation) or right shoulder (abdominal orientation), as illustrated below.

Parasternal long-axis (PLA) view

The probe should be placed in the parasternal fourth or fifth intercostal space with the transducer indicator directed pointed to the patient’s right shoulder, as shown below.

This allows for typical identification of the right ventricle, left atrium, left ventricle, aortic valve, aortic root, aortic outflow tract, and surrounding pericardium, as shown below.

The right atrium is typically not visualized on the PLA view.

To see more of the base of the heart (ie, aortic root) try dragging the probe cephalad one intercostal space.

To see more of the apex, try dragging the probe laterally toward the midclavicular line.

Parasternal short-axis view

From the PLA position, rotate the probe clockwise 90° such that the probe indicator is pointed toward the patient’s left shoulder, as shown below.

This allows for identification of the left ventricle, right ventricle, and pericardium. In this view, the right ventricle is closer to the surface and appears crescent-shaped, while the left ventricle is deep to the right ventricle and appears circular. See the image below.

The parasternal short axis view has 4 levels: aortic valve, mitral valve, papillary muscles, and apex.

Sweep or fan the probe up toward the patient's right shoulder and down toward the patient's left hip to scan through all 4 levels. Each level provides unique information.

In terms of assessing global left ventricle function, the papillary muscle level typically is the most useful, as this is a midventricle view.

Apical 4-chamber view

If possible, have the patient raise the left arm up over his or her head to try and spread the ribs.

Palpate for the cardiac point of maximal impulse (PMI) and place the probe there with the indicator pointed toward the left axilla and the probe in a coronal plane relative to the heart, as shown below, aimed toward the base of the heart.

This allows for identification of the left ventricle, right ventricle, left atrium, right atrium, and pericardium.

Direct the transducer-probe up toward the base of the heart. If the probe is directed anteriorly, the left ventricular outflow tract and aortic valve can often be seen; this is known as an apical 5-chamber view, shown below.

Subxiphoid long-axis view of the inferior vena cava (IVC)

Place the transducer-probe in the subxiphoid area, in a sagittal or long axis plane as shown below, and directed somewhat cephalad.

Follow the IVC up until it is seen entering the right atrium.

To assess for central venous pressure (CVP) and volume status, determine the overall size of the IVC and the amount of change with respiration (known as the sniff test), as illustrated below.

An IVC smaller than 1.7 cm with 50% collapse on inspiration is considered normal. Dilatation of the IVC (or the hepatic veins) and decreased respiratory collapse are findings indicative of elevated CVP and possible fluid overload.

IVC Diameter

Open table in new window

Adapted from: Recommendations for Chamber Quantification: A Report from the American Society of Echocardiography’s Guidelines and Standards Committee and the Chamber Quantification Writing Group, developed in conjunction with the European Association of Echocardiography, a branch of the European Society of Cardiology, p 1458-9.

Assessment of the femoral and popliteal veins

See eMedicine article Bedside Ultrasonography, Deep Vein Thrombosis.

Pearls

• On average, most patients have at least one good or adequate view of the heart (subxiphoid, parasternal, or apical). If a given view is difficult to obtain, try dragging the probe cephalad or caudad one interspace or toward the sternum or midclavicular line.
• Patients with chronic obstructive pulmonary disease (COPD) tend to have poor parasternal views but good subxiphoid views, as their hyperexpanded lungs tend to push the heart inferiorly.
• Patients who are obese tend to have poorer subxiphoid views and better parasternal views.
• If the subxiphoid view is difficult to obtain because of bowel gas, use the transducer-probe to perform gentle, graded compression. This can often stimulate the bowel to peristalse out of the way. Another technique is to reattempt the view from a position just to the right of midline and try to use more of the liver as an acoustic window.
• The parasternal long-axis (PLA) view should visualize the aortic root. If the aortic root is absent, the image is most likely oblique. In this case, angle the transducer slightly in either direction to optimize the image.
• The parasternal short-axis view should be obtained with the image plane at the level of the papillary muscles. This ensures a true transverse cut through the left ventricle and allows for proper evaluation of left ventricle function.
• If the meniscus of the internal jugular (IJ) vein is not identifiable, try having the patient sit up (if central venous pressure [CVP] is high, the top of the IJ may be impossible to see unless the patient sits up) or lie down (if CVP is low, the top of the IJ may be impossible to see unless the patient lies down).

Complications

• Typically, no complications are associated with this imaging modality.

Additional Cardiac Ultrasound Indications

Cardiac ultrasonography for assessment of fluid status and intravascular volume

The inferior vena cava (IVC) is important to evaluate because it can provide an assessment of the patient’s fluid status and right atrial pressures.

• Measure the IVC diameter in both inspiration and expiration.
• The IVC should collapse with inspiration in the normal patient.
• The collapse index is obtained using the IVC diameter measurements in inspiration and expiration. Collapse index = ([Exp Diameter-Insp Diameter]/Exp Diameter) X 100%
  • A collapse index >50% suggests right atrial pressures <10 mm Hg, whereas a collapse index <50% suggests right atrial pressures >10 mm Hg.¹²
    • A low collapse index (and, thus, elevated right atrial pressures) correlates with potentially life-threatening pathology, such as decompensated left heart failure, tamponade, tension pneumothorax, and massive pulmonary embolism (PE) causing right heart failure.
    • Other possibilities include primary pulmonary hypertension, end-stage COPD and cor pulmonale, and pulmonary fibrosis.
  • Some clinicians consider the collapse index to be a bit cumbersome and prefer a more qualitative approach whereby the percent of collapse of the IVC with inspiration is indicative of a patient’s volume status.
    • A complete collapse of the IVC with inspiration is considered evidence of low CVP (<5 cm), a collapse of <50% is considered evidence of elevated CVP (>10 cm), and an increase in size of the IVC with inspiration is considered evidence of normal CVP (5-10 cm).
    • Using this method, emergency physicians have over 80% correlation with formal echocardiography among patients with fluid overload, which is especially important among patients in whom the cause of dyspnea may not be obvious (eg, patient with COPD and CHF).¹³
• For those clinicians who prefer a more quantitative approach to fluid assessment with IVC measurements, the IVC diameter/aorta diameter (ICV/Ao) index appears to be another option.
  • The aorta diameter correlates with body surface area (BSA), age, and sex, thus allowing for a more patient-specific assessment of fluid status.
  • Furthermore, this allows providers to use the maximal IVC diameter without having to particularly time measurements relative to the respiratory cycle, which can be difficult in patients with severe dyspnea.
  • An IVC/Ao index of 1.2 is normal. The index is lower in patients who are dehydrated and higher in patients with intravascular fluid overload.¹⁴

Cardiac ultrasonography for assessment of left ventricular function

Left ventricular function can be assessed in several ways.

• The simplest and probably most effective method is to visualize the endocardial border and estimate the ejection fraction (EF) based on the change in left ventricle size between diastole and systole. Operators can then characterize the EF as "normal" (>50% change) or "diminished" (decreased movement of the left ventricular walls and only a small change in left ventricle size between diastole and systole).
• While this method may seem too simple, some emergency physicians find it to be easier to perform with limited training, and it has been shown to be as good as more quantitative methods in the evaluation of patients in the emergency department (ED). In fact, several studies looking at emergency physicians’ sonography of left ventricular function relied only on a gross visual assessment of left ventricular function without making any quantitative measurements.¹⁵
• A more quantitative approach would be to obtain actual measurements of the left ventricle in both diastole and systole. Several methods for this approach have been suggested in the emergency medicine literature.
  • The Moore-Tayal-Rose protocol
    • The diameter of the left ventricle can be measured at the level of the tips of the mitral leaflets in the parasternal long and short axes, while the area of the left ventricle can be determined by manually tracing the area of the left ventricle in the apical 4-chamber or parasternal long views. The volume can then be estimated by multiplying the area by the length and comparing the volumes in diastole and systole.
    • In a study of 4 emergency physicians who completed 6 hours of videotape instruction on echocardiography, this method led to an 84% agreement rate with left ventricular function determined by cardiologists.¹⁶
    • This method was especially good at detecting severe left ventricular dysfunction in patients with decompensated congestive heart failure (CHF).
  • The Randazzo-Snoey protocol
    • Left ventricular cross-sectional measurements are obtained in diastole and systole in 2 planes, using the subcostal, parasternal short axis, parasternal long axis, or 4-chamber views. The EF is then calculated by dividing the systolic measurement by the diastolic measurement.
    • In a study of 8 clinicians who underwent 3 hours of training, this method had an overall agreement of 86% with echocardiography read by cardiologists¹³ and was especially good at identifying patients with normal left ventricular function, which would help differentiate patients with COPD from those with CHF.

Other cardiac pathologies

• Pericardial effusions
  • Pericardial effusions are characterized by an anechoic stripe between the epicardium and pericardium. A small effusion can be physiologic but must be differentiated from tamponade, which is a life-threatening cause of right heart failure that causes compression of the right heart. Sonographic signs of tamponade include diastolic collapse of the right heart (atrium or ventricle) and increased respiratory variation in mitral flow, which is known as "sonographic pulsus paradoxus." However, since many emergency physicians perform focused ultrasonography without Doppler flow capabilities, many do not even assess for a sonographic pulsus to make the diagnosis of tamponade. In general, tamponade is not a subtle finding and should be suspected by the presence of a moderate to large pericardial effusion and a wide pulse pressure or hemodynamic instability on clinical examination.
  • On the other hand, one must consider whether a small effusion is physiologic or pathologic, and that cannot be absolutely determined by a single echocardiogram. Therefore, the patient’s clinical history, risk factors, and particular differential diagnosis must also be considered. Be sure to arrange follow-up for repeat echocardiograms in all patients with an effusion identified by bedside echocardiography.
  • Physicians must also distinguish epicardial fat from a pericardial effusion, which is the most common cause of false positives among studies performed by emergency physicians. Differentiating between these conditions may be difficult, which is another reason that further evaluation is warranted in patients suspected of having a small effusion. Signs of epicardial fat include the presence of gray-scale echoes that move with the heart, anechoic stripes less than 1 cm thick, and the lack of an effect on myocardial function.
• Right ventricular abnormalities
  • Many chronic conditions (eg, pulmonary hypertension, cor pulmonale) may result in right ventricular dilatation and/or hypertrophy. However, sonographers need to be aware of the main signs of right ventricular strain, namely right ventricular dilation, right ventricular hypokinesis, abnormal septal motion, and tricuspid regurgitation. In particular, in the setting of an acute outflow obstruction (eg, in massive PE, the size of the right ventricle closely approximates that of the left ventricle and, potentially, exceeds it.
  • In the short-axis view, the right ventricle is normally crescent-shaped; if this is a rounded, dilated structure, it suggests elevated right-sided pressures, as seen with pulmonary emboli and severe pulmonary hypertension. A right ventricle larger than the left ventricle should always be considered pathologic and, in the setting of acute dyspnea or chest pain with hemodynamic instability, should be considered pathognomonic of a life-threatening PE; further evaluation and treatment should be done immediately. Likewise, in the apical 4-chamber view, if the right atrium and right ventricle appear rounded or rigid, suspect causes of elevated right-sided pressures such as PE and pulmonary hypertension.
• Aortic dilation
  • The aortic root should be visualized in the PLA view and measure less than 3.5-4 cm.
  • A dilated aortic root suggests either dissection or aneurysm in the appropriate clinical setting. Therefore, patients with aortic dilation should undergo further evaluation.

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