Chapter 95: Critical Care Echocardiography

Echocardiography has major applications in the intensive care unit (ICU) for rapid assessment of the patient with hemodynamic failure. Critical care echocardiography (CCE) is an essential skill for the frontline intensivist. This chapter will review key aspects of CCE with emphasis on the basic CCE examination.

The American College of Chest Physicians/Société de Réanimation de Langue Française (ACCP/SRLF) statement on competence in critical care ultrasonography divides CCE competency into basic and advanced levels.¹ Basic CCE requires competence in a limited number of transthoracic echocardiography (TTE) views with an option to use limited transesophageal echocardiography (TEE). Basic CCE is a fundamental skill for all intensivists, and requires a relatively short training period. Competence in advanced CCE requires the intensivist to have a skill level comparable to a cardiology trained echocardiographer in both TTE and TEE, and requires a long training period by comparison to basic TTE.^2,3 Only a small proportion of intensivists need this level of skill, so this chapter will focus on basic CCE. The Accreditation Council of Graduate Medical Education has recently established that knowledge of critical care ultrasonography is a mandatory component of critical care fellowship training in the United States.⁴ Within a few years, all graduating fellows will be competent in this essential skill; attending level intensivists will need to develop competence in basic CCE as well.

Competence in basic CCE requires training. Noncardiologists can become competent in basic CCE.⁵ Exact requirements for training methods have not been standardized, but a recent statement suggests that basic CCE training include at least 10 hours of course work (comprised of lectures, didactic cases, and image interpretation) and a minimum of 30 fully supervised TTE studies (image acquisition and interpretation).² While these numbers offer some guidance, they do not guarantee that the trainee is sufficiently trained. Competency based testing at the end of the training period provides assurance that the clinician has achieved the requisite skill. Competence in basic CCE includes the ability to acquire and interpret the necessary images, but also mastery of the cognitive elements of the field (Table 95–1). Key clinical syndromes and their associated CCE findings are summarized in Table 95–2.

The ACCP/SRLF Statement on Competence defines the basic CCE examination as including five standard views: parasternal long-axis (PSL) view, parasternal short-axis (PSS) midventricular view, apical four-chamber (AP4) view, subcostal long-axis (SCL) view, and inferior vena cava (IVC) longitudinal axis view. There are several methods described for the performance of a goal directed cardiac examination that have a variety of acronyms. They all have in common a limited number of views designed to rapidly assess cardiac anatomy and function in the patient with hemodynamic failure.

Acquiring adequate CCE views is often challenging due to the nature of ICU patients. Imaging conditions may not be optimal due to the presence of equipment at the bedside and poor lighting conditions. Electrodes and wires may need to be repositioned to allow for optimal placement of the probe. Ribs and aerated lungs do not allow the transmission of ultrasound, and thus can obscure TTE windows. Left-arm abduction may increase the size of the intercostal space, and placing the patient in the left lateral decubitus position may move the heart laterally from behind the sternum making image acquisition easier; however, this may be difficult in the critically ill patient. Image quality may be suboptimal in the obese, edematous, or muscular patient. Frequently, some views may not be obtainable, so every examination must include an attempt at all views. For this reason, the examiner should establish a set scanning routine that includes the same sequence in every patient, as well as a methodical approach to interpreting each image.

With modern-generation portable ultrasonography machines, most medical ICU patients will yield serviceable images. In some situations, image acquisition may not be successful, for example, in the patient who is morbidly obese or following cardiac surgery. In this case, TEE may be required.

A convex probe with a small footprint capable of imaging at frequencies between 2.5 and 5 MHz should be used. Harmonic imaging is a preferred feature, which enhances image resolution. The image orientation marker is set in the upper right of the screen.

Parasternal Long-Axis View

The transducer is placed in the left 3rd or 4th intercostal space adjacent to the sternum with the orientation marker pointing towards the patient’s right shoulder (Figure 95–1) (Table 95–3). The probe position is adjusted in order to line up the aortic valve (AV), mitral valve (MV), and the largest left ventricular (LV) areas (Figure 95–2).

This view allows for assessment for pericardial effusion, LV/RV size and function, septal kinetics, and valve anatomy. Pitfalls inherent to this view include underestimation of RV size, inaccurate assessment of LV size and function with off-axis views (false end-systolic effacement), and underestimation of regurgitant jets with color Doppler.

Parasternal Short-Axis at the Mid-Ventricular Level

From the parasternal long-axis view, the transducer is rotated 90° clockwise without angulation or tilting (Figure 95–3), resulting in a cross-sectional view of the heart at the midventricular/papillary muscle level with the orientation marker pointing towards the patient’s left shoulder (Figure 95–4).

This view allows for assessment for pericardial effusion, LV/RV size and function, and septal kinetics. Pitfalls inherent to this view include inaccurate assessment of the LV if off-axis views are obtained (ie, imaging the apex of the LV can create false end-systolic effacement and overrotation of the transducer may result in septal flattening).

Apical Four-Chamber View

The transducer is placed on the lower lateral chest with the orientation marker pointed towards the patient’s left shoulder and the tomographic plane adjusted to bisect the anatomic apex of the LV and the two atria (Figures 95–5 and 95–6). This view is best achieved with the patient in the left lateral decubitus position.

This view allows for assessment of LV/RV size and function, particularly identifying RV enlargement by the RV/LV ratio, and for assessment for pericardial effusion. Pitfalls inherent to this view include difficulty obtaining an on-axis image, which can result in inaccurate assessment of LV/RV size and function and an incorrect RV/LV ratio.

Subcostal Long-Axis View

The transducer is placed just below the xiphoid process with the orientation marker pointing towards the 3 to 4 o’clock position and the tomographic plane adjusted to bisect the LV and left atrium (LA). The transducer must be held at the top of its surface in order to allow it to lay as flat as possible on the patient’s abdomen (Figures 95–7 and 95–8).

This is often the best view on a mechanically ventilated patient as the liver serves as an acoustic window to the heart and the ultrasound is not blocked by an aerated lung. This view allows for assessment for pericardial effusion, LV/RV size and function, and the RV/LV ratio. This view is the best for a rapid assessment of cardiac function during pulse checks when performing cardiopulmonary resuscitation. Pitfalls include inaccurate assessment of cardiac structures when the view is off-axis.

Inferior Vena Cava Longitudinal View

From the SCL view, the transducer is rotated counterclockwise 90°, tilted inferiorly, and angled laterally to visualize the IVC in the longitudinal axis (Figures 95–9 and 95–10).

This view allows for assessment of preload sensitivity in a hypotensive patient and when assessing a patient for the presence of pericardial tamponade. Pitfalls inherent to this view include the misidentification of the aorta for the IVC, off-axis view of the IVC, and translational artifact mimicking respiratory variation of the IVC.

CCE differs from standard cardiology style echocardiography in that the intensivist personally performs and interprets the examination at point of care and integrates the results into the overall clinical assessment and management plan. The examination is limited in scope and may be repeated as often as needed to track response to therapy and the evolution of illness. This avoids the problems inherent to standard cardiology style echocardiography in the ICU: the delay between ordering and obtaining the study, the time gap before the image is interpreted, the clinical dissociation between the image interpreter from the clinical reality at the bedside, the perception that a full study is required in all circumstances, and the resistance to the performance of repeated study in close succession while the patient is in the ICU.

The basic CCE examination, being performed by the clinician in charge of the case, is always combined with the history, the physical examination, other imaging studies, and laboratory analyses. It is not performed in vacuo. When combined with other elements of critical care ultrasonography, Volpicelli et al achieved near perfect concordance with final diagnosis of the cause for shock using an approach that included basic CCE.⁶ Laursen et al report similar results with focused ultrasonography diagnosing previously missed life-threatening conditions.⁷ The basic CCE examination may be performed in two to three minutes. When combined with other aspects of critical care ultrasonography, Volpicelli required on average 4.9 minutes to perform an ultrasonography examination, which included basic CCE. Given its ease of use and demonstrated diagnostic utility, the basic CCE examination should be a standard part of the evaluation of every patient with hemodynamic failure. It can be productively combined with other aspects of critical care ultrasonography.

In performing the basic CCE examination, the intensivist needs to consider the following questions:

1. Is there an imminently life-threatening cause for the shock such as cardiac tamponade, marked hypovolemia with an empty ventricle, massive valvular failure, or acute right heart failure?

2. What is the category of shock? Is it hypovolemic, obstructive, cardiogenic (valvular or pump failure), or vasoplegic?

3. What is the best initial management strategy? Does the patient need fluids, inotropes, vasopressors, mechanical assist, thrombolytics, surgery, or another intervention?

4. Is there more than one cause for the shock state or a coexisting condition that will complicate management of the primary cause such as sepsis with aortic stenosis, preexisting LV failure, or pulmonary arterial hypertension with a myocardial infarction?

5. What are the results of repeated CCE studies during the course of treatment? For example, is there improvement in global LV systolic function with treatment of a sepsis induced cardiomyopathy or unloading of the RV with decreasing levels of positive-end expiratory pressure as a patient’s acute respiratory distress syndrome improves?

Global LV Systolic Function

The intensivist who performs basic CCE needs to assess global LV systolic function. Systolic function can be characterized qualitatively as: severely reduced, moderately reduced, normal, or hyperdynamic.⁸ Qualitative assessment of LV function is useful for determining a management strategy for the patient with shock, that is, to guide the use of inotropes and/or volume resuscitation. Useful examples of video clips demonstrating degrees of LV dysfunction can be found at www.critcaresono.com. For the purposes of managing an unstable patient in shock, hyperdynamic is defined by end-systolic effacement of the LV cavity. Reduced diastolic excursion of the anterior leaflet of the MV is associated with severely decreased LV function. LV function is best assessed with the PSL view and its orthogonal view, the PSS view at the papillary muscle level. Detailed segmental wall motion analysis is beyond the scope of basic CCE.

Acute Right Heart Failure

There are two findings with basic CCE, which support the diagnosis of right heart failure.⁹ Flattening of the interventricular septum during systole is characteristic of RV pressure overload. This is best identified in the PSS view and results in a D-shaped LV (Figure 95–11). Dilatation of the RV is characteristic of RV diastolic overload. This is best identified by comparing the size of the RV and LV at end diastole in the AP4 or SCL views. An RV/LV ratio < 0.6 is normal, between 0.6 and 1 is moderate dilatation, and ≥ 1 is severe RV dilatation (Figure 95–12). Qualitative visual assessment of the ratio is as accurate as quantitative planimetry measurement.¹⁰ Normal RV free wall thickness is 3.3 mm ± 0.6 mm. Dilatation of the RV in the setting of normal RV free wall thickness supports an acute process, whereas a thickened RV free wall is likely secondary to a subacute or chronic process.

Pericardial Tamponade

Pericardial tamponade remains a clinical diagnosis and the echocardiographic features associated with it support the diagnosis in the appropriate clinical setting. A pericardial effusion is identified as an echo-free space surrounding the heart. Care must be taken to distinguish a pleural effusion from a pericardial effusion. A pericardial effusion is located anterior to the descending thoracic aorta compared to a pleural effusion which is located posterior to the descending thoracic aorta. Figure 95–13 demonstrates a PSL view of a patient with both a pericardial and pleural effusion.

Pericardial tamponade is associated with a dilated IVC without size variation in the respiratory cycle; swinging of the heart within the large pericardial effusion is characteristic as well. Early diastolic right atrial (RA) collapse has a sensitivity and specificity for tamponade of 92% and 100%, respectively, and occurs earlier than RV diastolic collapse, which carries a sensitivity of 64% and specificity of 100%.¹¹

Assessment of Preload Responsiveness

Inferior vena cava size and its respiratory variation may predict fluid responsiveness in the patient with shock. Acquiring a longitudinal view of the IVC and placing an M-mode scan line through it allows the examiner to measure the size of the IVC during inspiration and expiration (Figure 95–14). Using the IVC size and its respiratory variation to assess fluid responsiveness in passively breathing mechanically ventilated patients is well established.^12,13,14 Respiratory variation cutoff values of 12% (by using max – min/mean) and 18% (by using max – min/min) separates fluid responders from nonresponders. Data for assessing preload responsiveness in the spontaneously breathing patient are less robust. Expert opinion suggests that if the IVC diameter is < 1 cm, there is a high likelihood of fluid responsiveness; and if the diameter is > 2.5 cm, there is a low probability of fluid responsiveness.¹⁵

Valve Function and Pathology

Basic CCE allows the intensivist to identify major valve abnormalities that are visible on 2D imaging such as papillary muscle or chordal ruptures, severe aortic stenosis, or large valvular vegetations. Skill at color Doppler analysis of valve function is within the scope of basic CCE; however, more sophisticated Doppler analysis is not. If the clinician suspects significant valve pathology, an advanced CCE examination may be required.

1. Competence in basic CCE requires adequate training. The results of basic CCE may have major implications for the diagnosis and management of the critically ill patient, so it is incumbent upon the intensivist to have a high level of skill. To some trainees, skill at basic CCE appears easy to acquire. This is not the case. The training sequence should include multiple studies initially on normal subjects and then progressing to patients. Recent technological advances now allow trainees to learn on high fidelity TTE and TEE simulators which have the advantage of being able to demonstrate numerous pathologies for the trainee to experience.^16,17,18 The trainee should have access to a comprehensive image set that features multiple variations of normal and abnormal findings. The trainee must also master the cognitive base of the field, now widely available in articles, textbooks, and internet based resources. In order to assure proficiency, the training sequence should also include formal competency based testing.

2. By definition the basic CCE examination is limited in scope. It does not include a comprehensive image set, nor does it include Doppler measurements. The intensivist performing basic CCE must understand and accept this limitation and know when to call for a more comprehensive study. Inherent to ICU based echocardiography are the problems related to obtaining high quality images in the critically ill. Often the images of both basic and advanced CCE would be considered inadequate in quality by cardiology standards. Despite this, the critical care clinician needs to be able to interpret and apply the results at the bedside.

3. Documentation for CCE remains a challenge. Ideally, the entire CCE examination image set should be recorded and stored in a durable and accessible format for later review, and a formal report should be entered into the patient’s medical record for every study. This requires a well-designed picture archiving and communication system which is fully integrated into the portable ultrasonography machines. To compound the problem, in a busy ICU, the team may perform multiple examinations in rapid sequence in emergency situations, where documentation cannot take precedence over patient care. If the infrastructure to fully integrate CCE studies into the medical record does not yet exist at an institution, at a minimum, a short report should be entered into the medical record documenting the findings of the exam.

A common indication for TEE in the ICU is when TTE imaging fails due to poor image quality. This may occur due to reasons of body habitus, where TTE images are simply not adequate for interpretation. TEE is also useful in the cardiothoracic ICU, where dressings, wires, and tubes block TTE studies. Depending on the clinical circumstance, the TEE examination may be a comprehensive study; alternatively, a goal directed examination with a limited number of views may suffice.¹⁹

Advanced CCE requires the intensivist to achieve competence in all aspects of echocardiography that are standard to cardiology-type echocardiography, in addition to mastering elements of echocardiography that are particular to critical care medicine.^20,21,22 Competence in advanced CCE requires a long training period similar to the cardiologist who is trained in echocardiography. This includes training in TEE. The majority of intensivists do not have need for advanced level of training; as competence in basic CCE is sufficient for their clinical function. Although it is not known what proportion of intensivists should acquire skill at advanced CCE, one approach for the large ICU operation is for several team members to have advanced CCE training, whereas all other team members have basic CCE skill.

Competence in advanced CCE includes mastery of image acquisition and image interpretation of all standard echocardiography views and Doppler measurements.^23,24 Use of Doppler allows the intensivist to determine hemodynamic function through a wide variety of pressure and flow measurements. This permits the quantitative measurement of stroke volume, cardiac output, intracardiac pressures, preload sensitivity, and valve function.