Focused Cardiac Ultrasound at the Bedside

Focused cardiac ultrasound (FoCUS) is a readily accessible and widely used tool for the bedside diagnosis of basic cardiac pathology. Long championed by emergency room and critical care physicians, point-of-care ultrasound (POCUS) in general, including FoCUS, is increasingly utilized by a range of providers, including physicians and advanced practice providers in both inpatient and outpatient settings across many specialties. FoCUS is emerging as a fundamental clinical tool that is taught to many medical students across the country in their preclinical years, and it may eventually be considered a core competency for all physicians.

As technology has evolved, ultrasound machines have become more portable and affordable and offer improved image quality. Handheld devices are now financially attainable for many individuals or small provider groups. In addition to providing high-resolution images of cardiovascular structures, these devices are generally equipped with M-mode and color Doppler modalities. A range of products are available on the market, including wireless and smartphone-compatible devices and probes ( Fig. 11.1 ). Given the progressive miniaturization of ultrasound, it is conceivable that these same devices may eventually include spectral and tissue Doppler capabilities. With these increases in availability, portability, and quality, many medical providers now routinely use FoCUS in their daily practice. This chapter reviews the basics of performing a focused cardiac ultrasound examination, scope of practice and diagnostic targets of FoCUS, impact on patient outcomes, current training and certification practices, and quality assurance challenges.

Scope of Practice

Although cardiac ultrasound is a powerful tool for directly assessing anatomy and physiology at the point of care, its accuracy and utility are highly dependent on user skill. The safe and successful application of FoCUS depends on recognition by the user of both her or his personal limitations and the limitations of the technology. Given the expanding availability of portable ultrasound machines, it is important to define the purpose and scope of FoCUS. Multiple specialty, subspecialty, and imaging societies have published guidelines on the appropriate usage of FoCUS. Although these recommendations vary on specific details, there is overarching agreement on the general role and scope of FoCUS.

FoCUS is a targeted examination that is performed at the bedside by the primary care provider with the goal of answering a specific clinical question. FoCUS is primarily a qualitative examination and includes only basic semiquantitative assessments of cardiac structure and function. This is distinctly different from limited echocardiography, which involves a limited number of images but is still a comprehensive diagnostic test that is performed by a trained sonographer using a multimodality ultrasound machine and interpreted by an echocardiographer. Even in limited echocardiography, sonographers record additional views and data for full quantitative metrics as needed. Limited echocardiography studies must also be interpreted by a physician who is credentialed in echocardiography, typically a cardiologist. This limits its utility as the initial test in many critical care and emergency settings. As a problem-focused bedside examination performed by the primary care provider, FoCUS is well suited for use in clinically urgent cases in which there is an explicit diagnostic or management question that can be answered with ultrasound, and the findings can be immediately incorporated into patient management. Serial FoCUS examinations can also be performed to assess evolving clinical status, which is not practical for limited echocardiography.

Portable ultrasound machines are simpler to use and have a more focused suite of features compared with traditional echocardiogram machines. In the hands of expert users, these portable machines have the capacity to diagnose a wide range of cardiac pathologies ( Table 11.1 ). However, there is a clear gap between the diagnostic capacity of FoCUS in the hands of experts compared with less experienced users. Although the capacity of these machines is quite broad, it is important to consider what is appropriate and within the diagnostic scope for most users.

Table11.1

Diagnostic Capacity of Portable and Handheld Ultrasound Machines in the Hands of Experts.

Cardiovascular Anatomy	Assessment Method	Published Examples (References)
LV size	End-diastolic dimension	, , , , ,
LV hypertrophy	Interventricular septum and posterior wall diameter	, , , ,
Global LV function	Visual estimate	, , , , , , , ,
Left atrial enlargement	Parasternal long-axis dimension Visual estimate	,
RV size	Visual estimate	, , , ,
Global RV function	Visual estimate	, , , ,
Inferior vena cava size	Subcostal long-axis diameter	,
Pericardial effusion	Visually present vs. absent	, , , , ,

Echocardiography as an Adjunct to the Physical Examination

FoCUS has proved to be clearly superior to the physical examination for several cardiovascular findings when used by both cardiologists and noncardiologists ( Table 11.2 ). ^, Examples include left ventricular (LV) systolic dysfunction, increased LV filling pressures, and increased right atrial (RA) pressure. Compared to the traditional physical examination signs such as displaced cardiac point of maximal impulse, the presence of an S3 or S4 heart sound, and elevated jugular venous pressure, direct visualization of cardiac anatomy under ultrasound offers increased sensitivity for detection of these abnormalities. FoCUS is also more accurate than a physical examination at localizing the source of a murmur in patients with valvular pathology, although such findings are not necessarily clinically significant.

Table11.2

Cardiac Bedside Examination: Traditional Versus FoCUS Findings.

Adapted from Kimura B. Point-of-care cardiac ultrasound techniques in the physical examination: better at the bedside. Heart . 2017;103:987–994, Table 2 .

Entity	Physical Finding (SN%/SP%)	FoCUS Finding (SN%/SP%)	Notes
LVSD	S3 in ED (11–51/85–98) ; rales in ED (13/98) ⁵ Displaced apical impulse (5–66/93–99) ; 15% incidence in symptomatic HFrEF cohort	Subjective estimation of contraction and/or EPSS >1cm (69–94/88–94) ^, ^, ^,	US criteria vary among studies but are easily learned and are reproducible by noncardiologists. Prevalence of physical findings in LVSD is <20%, and even lower in asymptomatic LVSD.
Elevated LA filling pressures	S4 (35–71/50–70)	LAE (53–75/72–94) ^, ^, ^,	LAE is prognostic and not found by physical examination. US learned after brief training.
Pulmonary edema or interstitial disease	Rales (19–64/82–94) ; (62/68) in ED	B lines (85–98/83–93) ^, ^,	B lines are US artifacts and potentially vary among devices. US easily learned by novices. Prevalence of 13% in HFrEF cohort.
Pleural effusion	Dullness to percussion (73–89/81–91) ^,	Fluid in thorax (64–90/72–95) ^,	Studies of physical findings used chest radiography as gold standard, whereas US used computed tomography. Significant increase in SN with US, especially for small effusions.
RVE or pulmonary hypertension	Sustained left parasternal lift (71/80)	RV/LV > 1 (55/69)	Nonspecific finding of RVE is seen in RVMI, submassive pulmonary embolism, chronic cor pulmonale. Expert US practice needed to use spectral Doppler.
Elevated central venous pressures	JVP (47–92/93–96) ; (37/87) in ED ; 22% incidence in HFrEF cohort	IVC plethora (73/85)	FoCUS is advantageous in the supine ICU patient. FoCUS data include nonexpert users. JVP by US correlates with physical estimates but underestimates catheter-confirmed pressure.
Valve regurgitation	Murmur for mild-or-worse mitral regurgitation (56–75/89–93) or aortic insufficiency (54–87/75–98)	Color Doppler (82/93) for mild severity	Color Doppler jet area limitations apply. Expert practice likely necessary to quantify severity.
Severe aortic stenosis	Late-peaking murmur (83–90/72–88)	Restricted cusp mobility (85/89)	Expert auscultation coupled with FoCUS may be the best screening method.

ED , Emergency department; EPSS , E-point septal separation; FoCUS, focused cardiac ultrasound; HFrEF , heart failure with reduced ejection fraction; ICU , intensive care unit; IVC , inferior vena cava; JVP , jugular venous pulsations; LAE , left atrial enlargement; LVSD , left ventricular systolic dysfunction; POCUS , point-of-care ultrasound; RVE , right ventricular enlargement; RVMI , right ventricular myocardial infarction; S3 , third heart sound; S4 , fourth heart sound; SN% , percent sensitivity; SP% , percent specificity; US , ultrasound.

Diagnostic Targets of FoCUS

Beyond serving as an adjunct to the physical examination, FoCUS is a valuable diagnostic tool to further evaluate a number of specific clinical findings and diagnoses. The potential consequences of using FoCUS as a diagnostic test rather than just an extension of the physical examination have been detailed and debated in the literature and in clinical practice. ²⁵ Potential diagnostic targets for FoCUS include LV and right ventricular (RV) function, volume status, and pericardial effusion.

LV Size and Function

FoCUS allows reliable and accurate assessment of global LV systolic function, even for novice users with only basic training. ^, ^, ^, The LV has a relatively simple hemi-ellipsoid shape and can be imaged from multiple views. An assessment of global function is made based on the degree of myocardial motion and thickening through systole. End systolic chamber size is also observed because patients with septic shock typically have hyperdynamic LV function with a small LV chamber and near-obliteration of the LV cavity at end-systole. Such visual assessments are a reasonable approximation of quantitative measurements of ejection fraction by formal echocardiography. However, whereas quantitative estimates of LV function are possible with a complete echocardiographic study, with FoCUS, a qualitative approach is used to designate LV function as either normal or significantly abnormal. When image quality is poor or LV function is uncertain, a formal echocardiogram is recommended to determine appropriate clinical management.

RV Size and Function

The RV has a less axially symmetric geometry than the LV. The base of the RV (tricuspid annulus) is in the same plane as the mitral annulus, whereas the body of the RV wraps around the LV in a U shape and connects to the RV outflow tract, which lies anterior to the aortic valve. As a result, it is more difficult to systematically image and assess the RV than the LV. Despite this, FoCUS can be a valid tool to assess RV size and function in clinically urgent situations. ^, The RV is significantly enlarged if it is larger than the LV (RV:LV size ratio >1:1). Other signs of RV pressure or volume overload include interventricular septal bowing toward the LV. However, FoCUS users must recognize that these are not specific or sensitive findings and do not necessarily indicate acute pathology because the same signs are present in chronic RV dysfunction. RV function normally appears as dynamic as that of the LV; any reduction in the RV dynamic motion raises concern for RV systolic dysfunction.

Pericardial Effusion

FoCUS is highly sensitive and specific for the detection of pericardial effusion. ^, Fluid in the pericardial space appears as a dark space between the myocardium and pericardium. Identification of pericardial fluid does not require the same careful attention to image quality as does the assessment of biventricular function or volume status, making FoCUS an accurate assessment tool even for less experienced users. As with ventricular function, multiple views are obtained to ensure that focal or loculated pockets of fluid are not missed. Pericardial fluid must also be carefully differentiated from pleural fluid, especially in the parasternal views, where the descending aorta serves as a dividing marker between fluid in the pericardial. space (superficial to the aorta) and fluid in the pleural space (deep to the aorta).

Intravascular Volume Status

Although a variety of ultrasound parameters have been studied for the assessment of intravascular volume status, assessment of inferior vena cava (IVC) size and respiratory variation is the most appropriate technique for FoCUS users in the spontaneously breathing patient. The IVC should be visualized in the long axis as it crosses the diaphragm into the RA. As intrathoracic pressure drops with spontaneous inspiration, blood is drawn into the thoracic cavity and the diameter of the intraabdominal IVC decreases. RA pressure is estimated by measuring the maximal diameter of the IVC 2 to 3 cm before it passes through the diaphragm and calculating the percentage change with inspiration. M-mode can cause significant errors and should not be used to make IVC measurements because there is no way to visually ensure that the true long axis of the IVC is maintained throughout the respiratory cycle. In the spontaneously breathing patient, a dilated IVC with diminished inspiratory collapse indicates an elevated RA pressure. ^,

Notably, this method is not a reliable estimate of RA pressure in patients on positive-pressure ventilation because of alterations in intrathoracic pressure. Additional potential confounding factors include baseline RV dysfunction, significant tricuspid regurgitation, and cardiac arrhythmias such as heart block. Other ultrasound parameters of volume status, such as stroke volume variation and aortic flow velocities, are more technically difficult and require a level of quantitative assessment that is beyond the ability of most FoCUS users.

Limitations of FoCUS

More complex anatomic or physiologic abnormalities are typically beyond the scope of what FoCUS can reliably diagnose. FoCUS does not include quantitative assessment of blood flow or tissue velocities, so any diagnosis that relies on these metrics is outside the purview of FoCUS. This includes grading the severity of valvular abnormalities, determining the hemodynamic effects of a pericardial effusion, and diagnosing diastolic dysfunction. These limits should be especially respected in regard to valve assessment. Although obvious valve dysfunction may be observed, especially in extreme cases such as a severely calcified aortic valve or flail mitral valve leaflet, such findings should quickly be followed up with a formal echocardiogram.

Grading of valve dysfunction by ultrasound is a technically demanding task that incorporates complex quantitative assessments from multiple windows and is beyond the capacity of FoCUS. Despite this, FoCUS may be the only readily available tool in resource-limited areas and has been used as an effective screening tool for cardiac pathology, including valve disease, under these circumstances. Utilizing remote review by experts, nonphysicians working in a low-resource area and trained in FoCUS were able to follow a screening protocol that included valve assessment ( Fig. 11.2 ) to identify both mitral and aortic valve pathology ( Fig. 11.3 ); the results were confirmed by formal echocardiography in 79% of cases.

Fig. 11.2, FoCUS screening protocol used in a resource-limited area.

Fig. 11.3, Prevalence of cardiac pathology diagnosed by remote expert review of FoCUS images.

Additionally, FoCUS is not sensitive enough to reliably diagnose regional wall motion abnormalities, aortic dissection, or LV thrombus. ^, If initial FoCUS findings suggest any of these diagnoses, additional studies are recommended to avoid diagnostic error. For example, image acquisition for regional wall motion assessment requires multiple apical views (4-chamber, 2-chamber, long-axis), with adequate endocardial definition to clearly see each of 17 wall segments. Contrast administration is often necessary for adequate visualization. Images that are off-axis or of insufficient quality can lead to misdiagnosis of regional myocardial dysfunction via both false-positive and false-negative findings. Identifying abnormal wall segment motion is also a high-level skill that requires extensive experience in echocardiographic interpretation and can be confounded by prior intrathoracic surgery, interventricular conduction delays, and ventricular interdependence.

Similarly, intimal flaps that might indicate aortic dissection can be confounded by image artifacts. This is not to say that such findings can never be captured by FoCUS; indeed, one small retrospective study indicated that patients with aortic dissection identified on initial FoCUS examination were ultimately diagnosed much faster and had higher survival rates than those who were not assessed with FoCUS. However, FoCUS is not a sufficient test in these cases, and suspicion for any of these more complex abnormalities should lead to formal echocardiography or other imaging for confirmation of the diagnosis.

Basic Approach to the FoCUS Examination

Under ideal circumstances, the mechanics of performing a FoCUS examination are similar to those of a sonographer performing standard echocardiography. However, it is often difficult to achieve optimal positioning and attain complete views in clinically urgent scenarios. This section presents a suggested approach to the FoCUS examination. A comprehensive curriculum is beyond the scope of this chapter, but numerous online resources are available for self-study ( Table 11.3 ). After a standard approach to the FoCUS examination is implemented, positioning and views can be adjusted as needed based on the clinical setting.

Table 11.3

Recommended Open-Access Online Resources for Learning FoCUS.

Publisher	Title of Online Course/Modules	Website at the Time of Publication
American Society of Echocardiography	Cardiovascular point-of-care imaging for the medical student and novice user	https://aselearninghub.org/topclass/topclass.do?expand-OfferingDetails-Offeringid=138217
American Society of Emergency Physicians	Echocardiography for emergency physicians	https://www.acep.org/sonoguide/cardiac.html
Stanford University	Focused bedside TTE and ultrasound	https://www.edx.org/course/focused-bedside-tte-and-ultrasound
University of Toronto	Virtual transthoracic echocardiography: Focused cardiac ultrasound	https://pie.med.utoronto.ca/TTE/TTE_content/focus.html
University of Utah	Perioperative echocardiography education (includes some noncardiac topics)	https://echo.anesthesia.med.utah.edu/tee/focus-content/

Views are obtained from one of three acoustic windows, areas where the heart can be visualized with minimal interference from the lungs or ribs. These are the parasternal, the apical, and the subcostal windows ( Fig. 11.4 ). There are standard starting points for each window that should be fairly consistent from patient to patient. From these standard locations, larger initial adjustments with the transducer are often needed to localize the anatomy because the orientation and position of the heart vary slightly for each patient. This may involve moving up or down between rib spaces as needed. Finer adjustments are then made with the transducer to achieve the desired view.

Fig. 11.4, Transthoracic echocardiographic windows.

Positioning

Parasternal and apical views are best obtained with the patient in the left lateral decubitus position. If possible, have the patient raise the left arm above the head. This will widen the intercostal spaces and create a larger ultrasound window. If the patient is unable to roll into a left lateral decubitus position, the parasternal views can be obtained from a supine position. However, quality apical views are often difficult to obtain in supine patients.

Subcostal views are best obtained with the patient supine. If necessary, have the patient bend the knees up to relax the abdominal wall and allow for more maneuverability of the probe.

Before beginning the examination, drape the patient’s chest with a towel. In female patients, the towel can be used to both cover and lift breast tissue when obtaining apical views.

Standard Views

There are five standard views for a FoCUS examination, and they are typically obtained in the following order: parasternal long-axis, parasternal short-axis at the mid-ventricle, apical 4-chamber, subcostal 4-chamber, and subcostal IVC views. For less experienced users, the parasternal and subcostal views are the easiest to obtain and are less susceptible to errors in acquisition that can lead to inaccurate interpretation. Additional views may be learned over time, but the five views described here form the basis of a standard examination.

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