Transthoracic echocardiography (TTE) has major application in the intensive care unit (ICU). Proficiency in TTE allows the intensivist to determine the diagnosis of cardiopulmonary failure, develop management strategies, and follow the results of therapeutic interventions with serial examinations. By definition, critical care echocardiography (CCE) is performed by the intensivist in the ICU. The clinician personally acquires and interprets the image at the bedside and uses the information to immediately guide management. It follows that the intensivist must have a high level of skill in image acquisition that requires knowledge of ultrasound physics, machine controls, and transducer manipulation. This chapter reviews important elements of image acquisition with emphasis on transducer manipulation. The reader is referred to Chapters 2 and 3 for a comprehensive discussion of physics and machine controls.

Proficiency in CCE can be separated into basic and advanced levels. Basic CCE is performed as a goal-directed examination using a limited number of views (see Chapter 6 and Table 7-1). It is designed to answer specific clinical questions at the bedside. Proficiency in advanced CCE requires a high level of skill in all aspects of image interpretation and acquisition. Advanced CCE allows a comprehensive evaluation of cardiac anatomy and function using two-dimensional (2D) imaging and Doppler echocardiography. Both basic and advanced CCE require skill in image acquisition.

Technical Issues

The performance of TTE has challenges that relate to the fact that the heart is surrounded by lung and ribs, both of which block ultrasound transmission. Since ribs block ultrasound, cardiac transducers are designed with a small footprint to scan through the rib interspace. During scanning, left arm abduction may increase the size of the interspace. Aerated lung also blocks ultrasound, so that placing the patient in the left lateral decubitus position may be helpful. In this position, the heart is moved from behind the sternum and the left lung moves laterally, thus exposing more of the heart for examination. While the left lateral decubitus view improves visualization from the parasternal and apical views, the supine position is best for the subcostal examination.

The critically ill patient may be difficult to place in a favorable scanning position. Patients on ventilatory support, particularly when hyperinflated, may have poor parasternal and apical windows. Very often, the subcostal view yields the only acceptable image. TTE image quality may be poor in the edematous or muscular patient. Obesity presents a special challenge, as it attenuates the penetration of ultrasound. In addition, abdominal obesity elevates the diaphragm, particularly when the patient is supine and when passive on ventilatory support. The heart is then rotated into a more vertical position. This makes it difficult to obtain properly orientated parasternal views. The presence of chest dressings, wounds, or subcutaneous air also degrade TTE image quality. Transesophageal echocardiography (TEE) is an alternative in the patient who fails TTE. Artifacts in echocardiography relate, in part, to the fact that the heart is a highly mobile organ in constant motion within the thorax. Translational, torsional and rotational movement of the heart may be misinterpreted as reflecting actual cardiac contractile function.

In addition to these challenges, CCE is performed in a difficult operating environment. The patient is often surrounded by multiple ICU devices, so that positioning of the machine and operator may be difficult. The light level in the patient room is often too bright for optimal screen display. The echocardiographer is under pressure to complete the examination rapidly, because the patient is critically ill and other patients demand attention. The results of the study frequently require immediate response so that image acquisition and interpretation must be accurate. The intensivist should always attempt to obtain the best image quality. However, image quality may be limited in the critically ill and may be below the standards mandated by standard cardiology echocardiography practice.

Advanced CCE requires that the intensivist has proficiency in Doppler measurement. The physics of Doppler measurement are covered in detail in Chapter 2 and its clinical applications in other chapters of the book. The technical issues related to Doppler include the following:

1. 
   

   Doppler measurements are angle dependent; therefore, the best angle of Doppler interrogation may not be necessarily obtained from standard imaging orientation. The examiner should feel free to use nonstandard 2D image views if required for optimal Doppler measurement.

   
   
2. 
   

   A poor quality 2D image (e.g., related to obesity or edema) does not preclude good quality Doppler measurements. The examiner should always attempt standard Doppler analysis even if the 2D image is suboptimal.

   
   
3. 
   

   Continuous wave (CW) Doppler has range ambiguity but is able to measure high velocity of blood flow. Pulsed wave (PW) Doppler is able to measure blood flow velocity in a small sample area, but due to aliasing phenomena, it cannot measure high blood flow velocity.

   
   
4. 
   

   Color flow Doppler has specific pitfalls. It is gain sensitive such that over and under gaining will over or under estimate the severity of vascular regurgitation, respectively. It is subject to the aliasing phenomena. Color Doppler jets that are directed along the wall of the atrium systematically underestimate the severity of regurgitation.

Nomenclature

TTE examines the heart in tomographic planes obtained by positioning the transducer and “slicing” the heart through different planes. By obtaining multiple views of the heart, the examiner integrates the information to yield a comprehensive evaluation of cardiac anatomy and function. The addition of Doppler analysis gives important information related to cardiac pressures and flows. The American Society of Echocardiography (ASE) has defined the standard tomographic views of the heart.¹ The three standard image planes are as follows:

1. 
   

   The long-axis plane is parallel to the long axis of the left ventricle (LV). This is defined by a line that goes through the LV apex and the center of the base of the LV intersecting with the center of the aortic valve (AV).

   
   
2. 
   

   The short-axis plane is perpendicular to the long-axis plane.

   
   
3. 
   

   The four-chamber plane is perpendicular to both the short- and long-axis views. This is defined by a plane that goes through the LV apex and intersects the LV and right ventricle (RV) and atria.

The various tomographic planes of TTE are characterized by the position of the transducer required to obtain the image (the window) and the resulting image plane (the view). Transducer manipulation occurs as follows:

1. 
   

   Move: The transducer is shifted to a different position on the thorax.

   
   
2. 
   

   Tilt: The transducer is tilted or rocked along the same tomographic plane without moving it.

   
   
3. 
   

   Angle: Without moving the transducer, angulation is changed to obtain adjacent tomographic planes.

   
   
4. 
   

   Rotate: The transducer is rotated without moving, tilting, or angling it in order to obtain orthogonal tomographic planes.

Image orientation is standardized for adult TTE. The transducer position is projected at the top of the screen. The image orientation marker is set to the upper right of the screen. In the long-axis view, superior or cephalad cardiac structures project to the right of the screen. In the short-axis view, left-sided cardiac structures project to the right side of the screen. This is reverse to the orientation used for abdominal, thoracic, and vascular ultrasonography.

The basic or goal-directed CCE examination includes five views without Doppler analysis, while the advanced CCE examination includes a minimum of 14 views of the heart with comprehensive Doppler measurements. At each view, the examiner may choose to obtain one or more tomographic planes by tilting and angling the transducer. There is no officially sanctioned sequence for image acquisition. However, regardless of the sequence used; the intensivist should use a methodical approach to image acquisition for initial examination. The examination should be performed in standard sequence, as this reduces the likelihood that views will be omitted. Typically, CCE uses sequential follow-up examinations of the heart to check for response to therapy, progression or regression of disease, and new problems. Follow-up examinations may be very limited in scope. Certain situations do not permit any but the briefest examination. For example, echocardiography performed during cardiopulmonary arrest may include only several seconds of a subcostal view during a pulse check.

In the previous chapter, the authors reviewed the concept of basic critical care echocardiography (CCE). It is likely that most readers of this chapter will be interested in this important application of CCE, and they will not choose to develop competence in advanced CCE. The basic CCE examination is a mandatory part of training in general critical care ultrasonography, whereas advanced CCE is not.² The intensivist needs to decide what skill level in echocardiography is required for their practice. Therefore, this chapter is divided into two parts. The first part focuses on image acquisition needed for basic CCE, the second reviews the complex image set relevant to advanced CCE.

The basic CCE examination consists of the following views:³

1. 
   

   Parasternal long axis

   
   
2. 
   

   Parasternal short axis at the midventricular level

   
   
3. 
   

   Apical four-chamber view

   
   
4. 
   

   Subcostal four-chamber view

   
   
5. 
   

   Inferior vena cava (IVC) view

What follows is a description of transducer use required to obtain the standard views of the basic CCE examinations. The discussion does not include a detailed review of Doppler measurements, beyond the use of color Doppler for screening purposes, as these are not part of the basic CCE.

Parasternal Long-Axis View

The transducer is placed in the left 3rd, 4th, or 5th intercostal space adjacent to the sternum and held perpendicular to the skin surface, with the transducer index mark pointing to the patient’s right shoulder (Figure 7-1 and Case 7-1). Movement of the transducer in either caudal or cephalad direction brings the parasternal long axis into view. The transducer should be moved in small increments to obtain the best tomographic view. With minor movement and angulation, the examiner seeks a view that bisects the mitral valve (MV), the AV and that includes the LV cavity in its longest axis. The LV apex is not visible in the parasternal long-axis view. The image should be orientated so that the ascending aorta is displayed on the right, with the LV cavity on the left of the screen. The right ventricular outflow tract (RVOT) and chest wall appear at the top of the screen. Posterior structures, such as the left atrium (LA), the pericardium, and descending aorta, appear at the bottom of the screen. While the perfect long-axis view displays the heart horizontally on the screen, technical limitations such as patient positioning, body habitus, mechanical ventilation, and examiner inexperience may yield a more vertical view of the heart.

Echocardiographic findings

Qualitative assessment of ejection fraction (EF); RVOT/LV wall thickness, size and function; LV segmental wall function; septal kinetics; LA chamber size; and evaluation of AV/MV anatomy with screening color Doppler analysis, descending aorta, and pericardial space.

Pitfalls of the parasternal long-axis view

For the basic CCE echocardiographer, the pitfalls of this view include the following:

1. 
   

   Inaccurate assessment of RV size: This is because the parasternal long-axis view affords a view of the RVOT and so cannot be used to determine RV size. The apical four-chamber and subcostal views are used for assessment of RV size.

   
   
2. 
   

   Inaccurate assessment of LV size and function: Off-axis views of the LV due to rotation or angulation may lead to erroneous assessment of LV size and function. In particular, the LV may appear to be hyperdynamic with end-systolic effacement; if the transducer is not orientated to identify the largest LV cavity and aligned through the midpoint of the AV and MV.

   
   
3. 
   

   Inaccurate assessment of MV and AV function: The MV and AV may appear to be anatomically normal on 2D view, but can have substantial degrees of regurgitation discernible only with color or spectral Doppler analysis. Proficiency in basic CCE does not allow the examiner to reliably exclude severe valvular regurgitation. Color Doppler has limitations not intuitively obvious to the inexperienced examiner. These include gain settings (“dial a jet”), wall jet effect (Coanda effect), angle effect (both of transducer and by Doppler interrogation angle relative to the jet), and shadowing by surrounding structures such as a prosthetic valve apparatus or a calcified annulus.

   
   
4. 
   

   Inaccurate assessment of pericardial and pleural effusion: Identification of a pleural effusion requires that the depth setting on the ultrasound machine be increased such that the structures posterior to the heart are visualized. A pleural effusion will be seen as a relatively hypoechoic space posterior to the LV and posterior to the descending aorta. A pericardial effusion will track anterior to the descending aorta.

Parasternal Short-Axis Midventricular View

From the parasternal long-axis view, the transducer is rotated 90° clockwise without angulation or tilting. This results in cross-sectional views of the heart. A good short-axis view follows from a good long-axis view. Rotation of the transducer may be achieved using a two-handed approach, keeping the transducer hand steady while rotating with the other hand will give the best results. The transducer is rotated until the short axis of the heart is obtained with the transducer index mark pointing towards the left shoulder. By angling the transducer along a right-shoulder-to-left-hip axis, multiple tomographic views of the heart may be obtained. For the basic CCE examination, the only view that is required is the midventricular tomographic plane (papillary muscle level) (Figure 7-2 and Case 7-2).