Setting up the machine

The echocardiography machine should be positioned toward the head of the bed on either the right (for right-handed scanners) or the left side of the patient. A three-lead ECG should be placed on the patient, and lead II should be monitored. The ECG should have a positive R wave of sufficient amplitude to facilitate timing and capture of echocardiography loops. Patient details should be entered into the machine, and the storage media should be checked to ensure there is sufficient disc space to record the study.

Image display

TTE images are displayed in a standardized way. The transducer position is at the top of the screen at the apex of the sector scan. Thus, structures near the transducer are displayed at the top of the screen and more distant structures are displayed lower on the screen. One-centimeter markers shown along the lateral edge of the sector scan indicate distance from the transducer.

The orientation marker, which refers to the notch on the transducer, is shown on the right of the screen. With correct positioning of the transducer on the chest, in a short-axis view lateral cardiac structures are displayed on the right of the screen and medial structures are on the left of the screen. In a long-axis view, superior (i.e., toward the patient’s head) structures are displayed on the right of the screen and inferior structures (i.e., toward the patient’s feet) are displayed on the left of the screen. The term short axis refers to an image plane perpendicular to the structure of interest; the term long axis refers to an image plane parallel to the length of the structure of interest.

Transducers

TTE images are obtained with a phased array transducer capable of all imaging modalities. Phased array transducers have a small footprint to enable the transducer to be placed within the intercostal spaces and use electronic steering to create a fan-shaped ultrasound beam. Phased array transducers used for TTE operate over a range of frequencies (broadband), typically 1 to 5 MHz, which maximizes image resolution and depth penetration. Broadband transducers are particularly advantageous for adult transthoracic imaging, as there is an important trade-off between tissue penetration (low frequency is best) and image resolution (high frequency is best) (see Chapter 1 ).

Scanning windows and movements of the transducer

To ensure the optimal transfer of ultrasound energy from the transducer into the chest cavity, it is important apply adequate pressure and sufficient ultrasound transmission gel to the transducer footprint. TTE is performed through four acoustic windows ( Figure 17-1 ):

• •
  

  Left parasternal, in the third intercostal space just to the left of the sternum

  
  
• •
  

  Apical, overlying the apex beat

  
  
• •
  

  Subcostal, below the xiphoid process

  
  
• •
  

  Suprasternal, in the sternal notch

Acoustic windows used for TTE.

Within each scanning window, further manipulation of the transducer is required to obtain specific views. This is achieved by the following actions:

• •
  

  Angling the transducer from side to side

  
  
• •
  

  Turning (or rotating) the transducer, such that the orientation marker points in a different direction

  
  
• •
  

  Tilting the transducer toward structure of interest

Positioning the patient

Correct patient positioning improves image quality by bringing the heart closer to the chest wall, eliminating the lungs from the field of view, and opening up the acoustic window. Three patient positions are used for TTE:

• •
  

  Left lateral decubitus. The patient lies on his or her left side. Elevation of the left arm above the shoulder helps to open up the intercostal spaces. This is the best position when imaging from the left parasternal and apical windows.

  
  
• •
  

  Supine. The patient lies in a supine position with his or her knees raised. This is the best position when imaging from the subcostal windows.

  
  
• •
  

  Suprasternal supine. The patient lies in a supine position with his or her shoulders elevated and neck extended. This is the best position when imaging from the suprasternal notch.

Breathing manipulation

Since the lungs surround the heart, respiration can interfere with ultrasound transmission, especially during inspiration when the inflated lungs obscure the heart. Three breathing techniques are used to improve image quality:

• •
  

  Held expiration. The patient is asked to suspend breathing at end expiration. This technique is useful when imaging from the parasternal and apical windows.

  
  
• •
  

  Held inspiration. The patient is asked to suspend breathing at end inspiration. This technique may be useful when imaging from the apical two-chamber view.

  
  
• •
  

  Exaggerated inspiration. The patient is asked to breathe in deeply and hold his or her breath at maximal end inspiration. This technique is useful when imaging from the subcostal window.

Standard transthoracic views and systematic examination

If possible, a full transthoracic imaging protocol should be performed ( Table 17-1 ). A complete study allows structures to be evaluated in several views, which improves diagnosis and eliminates errors due to artifacts. However, in the ICU, it is sometimes appropriate to perform a targeted study, for instance, when assessing the cause of hemodynamic instability (see Chapter 18 ) or looking for a thrombus in the LA appendage before electrical cardioversion. To avoid confusion and misinterpretation, it is important to restrict imaging to the standard views and to use certain landmarks within the heart, such as the ventricular septum, the RV moderator band, and the ventricular apex, for orientation.

Reference values for M-mode and 2-D transthoracic imaging are provided in Table 17-2 .

TABLE 17-2

Normal Echocardiographic Values

	Women				Men
	Reference range	Mildly abnormal	Moderately abnormal	Severely abnormal	Reference range	Mildly abnormal	Moderately abnormal	Severely abnormal
M-Mode Measurements
LV diastolic diameter (cm)	3.9–5.3	5.4–5.7	5.8–6.1	≥6.2	4.2–5.9	6.0–6.3	6.4–6.8	≥6.9
LV diastolic diameter/ BSA (cm/m 2 )	2.4–3.2	3.3–3.4	3.5–3.7	≥3.8	2.2–3.1	3.2–3.4	3.5–3.6	≥3.7
LV diastolic diameter/ height (cm/m)	2.5–3.2	3.3–3.4	3.5–3.6	≥3.7	2.4–3.3	3.4–3.5	3.6–3.7	≥3.8
LV septal thickness (cm)	0.6–0.9	1.0–1.2	1.3–1.5	≥1.6	0.6–1.0	1.1–1.3	1.4–1.6	≥1.7
LV posterior wall thickness (cm)	0.6–0.9	1.0–1.2	1.3–1.5	≥1.6	0.6–1.0	1.1–1.3	1.4–1.6	≥1.7
LA diameter (cm)	2.7–3.8	3.9–4.2	4.3–4.6	≥4.7	3.0–4.0	4.1–4.6	4.7–5.2	≥5.2
LA diameter/BSA (cm/m 2 )	1.5–2.3	2.4–2.6	2.7–2.9	≥3.0	1.5–2.3	2.4–2.6	2.7–2.9	≥3.0
LV fractional shortening (%)	27–45	22–26	17–21	≤16	25–43	20–24	15–19	≤14
Aortic root (cm)	2.0–3.6	—	—	—	2.0–3.7	—	—	—
Aortic root/BSA (cm/m 2 )	1.2–2.2	—	—	—	1.2–2.2	—	—	—
2-D Measurements
LV diastolic volume (mL)	56–104	105–117	118–130	≥131	67–155	156–178	179–201	≥201
LV diastolic volume/BSA (mL/m 2 )	35–75	76–86	87–96	≥97	35–75	76–86	87–96	≥97
LV systolic volume (mL)	19–49	50–59	60–69	≥70	22–58	59–70	71–82	≥83
LV systolic volume/BSA (mL/m 2 )	12–30	31–36	37–42	≥43	12–30	31–36	37–42	≥43
LV ejection fraction (%)	≥55	45–54	30–44	<30	≥55	45–54	30–44	<30
Main PA diameter (cm)	1.5–2.1	2.2–2.5	2.6–2.9	≥3.0	1.5–2.1	2.2–2.5	2.6–2.9	≥3.0
RV basal diameter (cm)	2.0–2.8	2.9–3.3	3.4–3.8	≥3.9	2.0–2.8	2.9–3.3	3.4–3.8	≥3.9
RV mid-diameter (cm)	2.7–3.3	3.4–3.7	3.8–4.1	≥4.2	2.7–3.3	3.4–3.7	3.8–4.1	≥4.2
IVC diameter (cm)	<1.7	—	—	—	<1.7	—	—	—
LA area (cm 2 )	≥20	20–30	30–40	>40	≥20	20–30	30–40	>40
LA volume (mL)	22–52	53–62	63–72	≥73	18–58	59–68	69–78	≥79
LA volume/BSA (mL/m 2 )	22 ± 6	29–33	34–39	≥40	22 ± 6	29–33	34–39	≥40

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