Cardiac Evaluation Using Bedside Ultrasonography

Updated: Nov 09, 2022
Author: Timothy Jang, MD; Chief Editor: Timothy Jang, MD 

Practice Essentials

Patients who present to the emergency department (ED) with chest pain, shortness of breath, or dyspnea on exertion are often tachycardic or even hypotensive. Unfortunately, history and physical examination alone often lack the sensitivity and specificity to accurately diagnose the underlying etiology. Ultrasonography is frequently used in the ED in diagnostic and therapeutic procedures and in evaluation of critically ill patients because of its bedside applicability, rapidness, and inexpensive cost. Focused cardiac ultrasonography performed by emergency physicians has been shown to be sufficient in terms of accuracy of findings and diagnosis.[1]  Focused bedside echocardiography (FBE) is a valuable and increasingly available imaging modality that can be used to better manage these patients.[2, 3, 4, 5]

When emergent interventions such as intubation, fluid resuscitation, or pressors are indicated, FBE should not delay the initiation of such treatment. While FBE can be difficult to perform in patients presenting in extremis or during ongoing resuscitations, the information obtained through FBE can be lifesaving. Anesthesia is generally not necessary for sonographic evaluation of the heart, great vessels, and pleural spaces.

Benefits of FBE include the following: 

  • Decreases time to diagnosis for pericardial effusions.[6, 7]

  • Helps diagnose pericardial effusions in cases of pulseless electrical activity.[8]

  • Helps assess left ventricular function, even with limited views[8, 9] or in the setting of hypotension.[10, 11]

  • Helps assess volume status and central venous pressure (CVP).[12]

  • Helps diagnose decompensated congestive heart failure. (FBE has been shown in some instances to be even more accurate than chest radiographs.[13] It can be used alone or in conjunction with N-terminal pro-brain-type natriuretic peptide [NT-ProBNP] levels to help differentiate between congestive heart failure [CHF] and chronic obstructive pulmonary disease [COPD] in patients with shortness of breath.[14] )

  • Helps diagnose deep vein thrombosis.(DVT)

  • While not sensitive for pulmonary embolism (PE), FBE findings can prompt pursuit of this diagnosis or risk-stratify those patients who are found to have PE.[15, 16, 17]

  • Can be learned and integrated into clinical practice with limited training.[13, 16, 18, 19, 20]

  • Can be performed at the bedside to avoid removing critically ill patients from the immediate clinical area.

Components of FBE include the following:

  1. Subxiphoid 4-chamber view

  2. Parasternal long-axis and short-axis views

  3. Apical 4-chamber view

  4. Subxiphoid long-axis view of the inferior vena cava (for assessment of CVP and volume status)

  5. Assessment of the internal jugular vein (for assessment of CVP and volume status)

  6. Examination of the femoral and popliteal veins (if DVT is suspected).

Indications for FBE include the following:

  • Any patient presenting with chest pain, shortness of breath, or dyspnea on exertion

  • Code or arrest situations such as pulseless electrical activity (PEA)

  • Suspected left- or right-sided heart failure

  • Suspected pulmonary embolism

  • Suspected cardiac tamponade

  • Unexplained hypotension

  • Assessment of central venous pressure and volume status

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, the transducer-probe should be used 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 while trying 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).

 

Technique

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 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.

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.

Probe position for subxiphoid view Probe position for subxiphoid view

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 while 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 image below shows the subxiphoid view.

Ultrasound image of subxiphoid 4-chamber view. Ultrasound image of subxiphoid 4-chamber view.

Parasternal long-axis (PLA) view

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

Probe position for parasternal long-axis view. Probe position for parasternal long-axis view.

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

Ultrasound clip of parasternal long-axis view. The aortic outflow tract is well visualized in this view. The patient has an enlarged right ventricle and a decreased left ventricular ejection fraction.

The right atrium typically is 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.

Probe position for parasternal short-axis view Probe position for parasternal short-axis view

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 and the clip below.

Ultrasound image of parasternal short-axis view. Ultrasound image of parasternal short-axis view.
Ultrasound clip of the parasternal short-axis view.

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 provides a midventricle view.

Apical 4-chamber view

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

Probe position for apical view Probe position for apical view

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 the aortic valve can often be seen; this is known as an apical 5-chamber view, as shown below.

Normal ultrasound image of apical 4-chamber view. Normal ultrasound image of apical 4-chamber view.

Subxiphoid 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.

Placement of probe for a transverse view of the IV Placement of probe for a transverse view of the IVC.
Ultrasound image of transverse inferior vena cava Ultrasound image of transverse inferior vena cava (IVC) view.

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.

Placement of probe for longitudinal inferior vena Placement of probe for longitudinal inferior vena cava (IVC) view.
Ultrasound clip of longitudinal inferior vena cava. The inferior vena cava empties into the heart, which can be seen beating at the left side of the screen.

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.

Table. IVC Diameter* (Open Table in a new window)

IVC Size

Percent Collapse

RA Pressure, mm Hg

< 1.7 cm

>50%

0-5

>1.7 cm

>50%

6-10

>1.7 cm

< 50%

10-15

>1.7 cm

No collapse

>15

*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.

 

 

Pearls

Of note is the utility of cardiac ultrasonography in predicting worse survival outcomes in patients with cardiac standstill (ie, no cardiac activity witnessed with ultrasound). Unfortunately, despite increasing evidence surrounding use of ultrasound in arrest, bedside ultrasonography is still largely underutilized during the resuscitation process.[1]

Luong and associates have noted that as use of focused cardiac ultrasonography continues to expand, careful consideration is required regarding training, scope of practice, impact on patient outcomes, and medicolegal implications.[21]

Injuries from nail guns are a unique type of penetrating trauma seen in EDs. These life-threatening injuries require rapid diagnosis to help guide management. In one cases, bedside ultrasound revealed a metallic foreign body tracking through the right ventricle, with associated pericardial fluid and pericardial clot. This rapid diagnosis helped facilitate timely transport to the operating room for median sternotomy, foreign body removal, and pledgeted cardiac repair, emphasizing the diagnostic capabilities of bedside ultrasound for such case.[22]

Studies have shown promise in establishing best practices for evaluation of heart, lung, abdomen, and deep vessels. Bedside ultrasound is widely used; it does not replace the consultant but reduces inappropriate consultations, yielding cost savings for hospitals.[23]

 

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.[24, 25, 26]  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 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.[27]  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 shown over 80% correlation with formal echocardiography in patients with fluid overload, which is especially important in patients for whom the cause of dyspnea may not be obvious (eg, patient with COPD and CHF).[28]

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 to do 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.[24]

Respiratory muscle ultrasound is used to evaluate anatomy and function of the respiratory muscle pump. This safe, repeatable, accurate, noninvasive bedside technique can be successfully applied in different settings, including general intensive care and the ED. Mastery of this technique allows the intensivist to rapidly diagnose and assess respiratory muscle dysfunction in critically ill patients and in patients with unexplained dyspnea. Furthermore, this technique can be used to assess patient-ventilator interaction and weaning failure in critically ill patients.[29]

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 easier to perform with limited training, and it has been shown to be as good as more quantitative methods in evaluation of patients in the 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.[30]

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.

In 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 videotaped instruction on echocardiography, this method led to an 84% agreement rate with left ventricular function as determined by cardiologists.[31]  This method was especially good in detecting severe left ventricular dysfunction in patients with decompensated congestive heart failure (CHF).

In the Randazzo-Snoey protocol, left ventricular cross-sectional measurements are obtained in diastole and systole in 2 planes, using 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 overall agreement of 86% with echocardiography read by cardiologists[28] and was especially good for identifying patients with normal left ventricular function, which would help differentiate patients with COPD from those with CHF.

Pericardial effusions

Pericardial effusions are characterized by an anechoic stripe between the epicardium and the 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 wide pulse pressure or hemodynamic instability on clinical examination.[32]

On the other hand, one must consider whether a small effusion is physiologic or pathologic, and this 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 why 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 lack of an effect on myocardial function. The incidence of pericardial effusion is low in neonates, but early diagnosis is fundamental because of high morbidity and mortality, especially in cases of abrupt onset. Bedside ultrasonography have shown importance in screening of these cases.[33]

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 may be larger.

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, it 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 the right ventricle appear rounded or rigid, one should suspect causes of elevated right-sided pressures such as PE and pulmonary hypertension. Bedside ultrasound can assist in evaluation of suspected PE by assessing for acute right ventricular strain.[34]

Aortic dilation

The aortic root should be visualized in the PLA view and measures less than 3.5-4 cm.[35]

A dilated aortic root suggests either dissection or aneurysm in the appropriate clinical setting. Therefore, patients with aortic dilation should undergo further evaluation.