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Bedside echocardiography 

Bedside echocardiography
Chapter:
Bedside echocardiography
Author(s):

Stephen Hickey

, Coralie Carle

, and Donna Greenhalgh

DOI:
10.1093/med/9780199692958.003.0032
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Introduction

Bedside echocardiography has developed into a valuable diagnostic and monitoring tool. Within the CICU it is used to assist the intensivist in making rapid diagnoses and initiating appropriate interventions.

Indications

  • Diagnosis of haemodynamic instability:

    • Cardiac failure

    • MI

    • PE

    • Pericardial effusions

    • Cardiac tamponade

    • Valvular problems

    • Cardiac arrest

  • Estimation of volume status

  • Monitoring the effects of interventions

  • LV assessment:

    • Size

    • Degree of filling

    • Contractility

    • Regional wall-motion abnormalities

  • RV assessment:

    • Size

    • Degree of filling

    • Contractility

  • Evaluation of pyrexia of unknown origin

  • Assessment of endocarditis

  • Assessment of failure to wean

  • Aid to placement of ECMO cannula/IABP.

Transthoracic or transoesophageal echocardiography?

Echocardiographic images of the heart can be obtained through the chest wall (transthoracic echocardiography (TTE)) or from the oesophagus (transoesophageal echocardiography (TOE)). TTE is a safe, non-invasive technique that can be rapidly performed in awake and sedated patients. It is the preferred technique in the critical care environment. However, if a TTE examination provides unsatisfactory views, it may be necessary to perform a TOE examination of the heart. TOE, a semi-invasive technique, is preferable to TTE in a number of specific situations: a detailed interrogation of the mitral valve (including prosthetic valves), assessment of the left atrial appendage for clot formation, assessment of vegetations associated with endocarditis, and suspected aortic dissection.

Use TTE for:

  • Assessment of pericardial effusions

  • Optimal views of the left ventricular apex

  • Optimal views of the left atrium

  • Assessment of volume status using the inferior vena cava and subhepatic veins

  • Optimal Doppler beam alignment in apical view for aortic, mitral, and tricuspid valves.

Use TOE for:

  • Inadequate TTE views (e.g. obesity, chest wall abnormalities, emphysema, IPPV with high levels of positive end expiratory pressure)

  • Assessment of structures close to the oesophagus (e.g. left atrial appendage, mitral valve)

  • Interrogation of prosthetic mitral valves

  • Assessment of vegetations

  • Suspected aortic dissection.

Transthoracic echocardiography

Understanding the image

The heart is situated in the anterior mediastinum, with its long axis lying along a line from the right shoulder to the left nipple. When viewed from the front the most anterior structures are the right atrium and right ventricle and the most posterior structure is the left atrium. The ultrasound transducer produces a thin fan-shaped beam that slices through the heart. The slice or image that is achieved depends on the position of the probe on the chest. TTE uses various standard positions (or windows) on the chest in order to assess cardiac structure and function. The images are displayed on a screen with the top of the screen representing the position of the transducer—structures closer to the transducer are seen nearer the top of the screen.

Echocardiography windows

There are three main echocardiography ‘windows’ in the chest and abdomen that allow ultrasound waves to be transmitted to and reflected from the heart. It is also possible to visualize the lungs (Fig. 32.1).

Figure 32.1 Location of the echocar-diography windows. 1: subcostal. 2: apical. 3: parasternal. 4: pleural. Image taken from FATE-card and reproduced with permission from Profes-sor Ph.D. MDSc Erik Sloth. <http://www.usabcd.org> (FATE-app available for free download at App Store and Android Market).

Figure 32.1 Location of the echocar-diography windows. 1: subcostal. 2: apical. 3: parasternal. 4: pleural. Image taken from FATE-card and reproduced with permission from Profes-sor Ph.D. MDSc Erik Sloth. <http://www.usabcd.org> (FATE-app available for free download at App Store and Android Market).

Subcostal window

  • Place the transducer parallel to the skin inferior to the right costal margin and direct the ultrasound beam upwards towards the heart.

Apical window

  • Place the transducer over the apex of the heart and direct the ultrasound beam parallel to the long axis of the heart—aim towards the sternum.

Parasternal window

  • Place the transducer adjacent to the left sternal margin in the 2nd–4th intercostal space.

Pleural window

  • Place the transducer on the lateral thoracic wall.

Preparing the patient

Optimizing the position of the patient will help improve the quality of the images you obtain. Subcostal images are best obtained with the patient lying flat on their back with a relaxed abdomen. For parasternal and apical images, tilting the patient to the left brings the heart closer to the chest wall and improves the images obtained. In addition, abduction of the patient’s left arm increases the gap between the ribs and widens the echocardiographic window. The view obtained will change throughout the respiratory cycle. It may be possible to ask spontaneously breathing cooperative patients to hold their breath when the image is at its best. In ventilated patients it may be possible to manipulate the ventilator briefly to obtain the necessary images.

Preparing yourself and the machine

Space is often limited in the critical care bed area, but it is important to position the machine and screen so that you are comfortable whilst scanning. Don’t forget to enter the patient’s details into the machine and attach ECG leads from the machine to the patient. Identify the ‘marker dot’ on the probe (this allows the probe to be correctly orientated). Ensure that you have a supply of ultrasound gel and paper towels to clean up the gel at the end. Dim the lights if possible.

With your dominant hand, hold the probe between your thumb and first and second fingers. Ensure there is sufficient ultrasound gel and then apply gentle pressure through the probe to obtain an image. When scanning rest your wrist on the chest wall to prevent the probe from slipping. It is important to learn how small movements of your wrist and probe can alter the image. The probe can rotate, tilt, and slide in order to achieve the desired image. Always scanning from the same position maximizes the benefits of these ‘learned movements’. Remember that the image quality may be improved by moving the position of the probe or the position of the patient.

Echo modes

A variety of ultrasound techniques are employed in order to fully assess the heart’s structure and function. These include two-dimensional (2D), Motion or M-mode, and Doppler (continuous wave Doppler (CWD), pulsed wave Doppler (PWD), and colour flow mapping (CFM)).

2D Echo

  • A succession of slices taken over a cross-section of tissue. When displayed sequentially on a screen it provides ‘real-time’ imaging of the heart (Fig. 32.2).

  • Use to assess anatomy and movement of the ventricles and valves.

Motion or M-mode

  • Images of a single slice taken over time (Fig. 32.3). This allows highly accurate measurements of moving structures. The ultrasound beam should be perpendicular to the structure of interest. Computer software allows measurements to be made and stored.

  • Use for measurement of cardiac dimensions and timing of events (e.g. diastolic collapse).

Doppler Echo

Uses the Doppler principle to detect the velocity of red blood cells moving towards and away from the transducer.

Continuous wave Doppler

  • Measures the maximum blood velocity detected along the length of the ultrasound beam. Cannot therefore localize the exact position of the flow disturbance.

  • The calculated velocity is displayed on a velocity/time graph with blood flow towards the transducer displayed above the baseline and flow away displayed below the baseline (Fig. 32.4).

  • Can measure high velocities.

  • Use to assess valvular stenosis, valvular regurgitation, and the velocity of flow across intracardiac shunts.

Pulsed wave Doppler

  • Measures the blood velocity in a specific sample volume (e.g. in the left ventricular outflow tract (LVOT)). The position of the sample volume is selected by the operator.

  • The calculated velocity is displayed on a velocity/time graph with blood flow towards the transducer displayed above the baseline and flow away displayed below the baseline (Fig. 32.5).

  • Is only accurate below velocities of 2m/s.

  • Use for stroke volume and cardiac output calculations.

Colour flow mapping

  • Measures blood velocity and direction at several points within a set area.

  • The CFM is superimposed on the 2D image. Blood velocities away from the transducer are coloured blue and velocities towards the transducer coloured red (BART: Blue Away Red Towards) (Fig. 32.6). Higher velocities are represented by lighter shades of red or blue. If velocities exceed the processing ability of CFM colour reversal (aliasing) will occur.

  • Use for assessing regurgitation and shunts.

Abbreviated scanning protocols

A full standard TTE examination involves a series of images and measurements and may take up to 20 minutes. An abbreviated echocardiography examination performed by non-cardiologists has been shown to be both feasible in the critical care environment and contribute significantly to patient management. Whilst cardiologists provide an invaluable service for routine and comprehensive echocardiography, there is a need for a 24 hour a day service for critically ill, haemodynamically unstable patients. The ability to reassess the patient after an intervention is essential. There is therefore a need for an intensivist-led abbreviated echocardiography examination.

Focus-assessed transthoracic echocardiography (FATE)

Within the general intensive care population, TTE performed by trained intensivists, has been shown to provide diagnostic images in 91% of spontaneously breathing and 84% of mechanically ventilated patients and directly change management in >50% of studies.

One abbreviated echocardiographic examination is the FATE protocol. It has been shown to provide one or more useful images of the heart, allowing clinical decision-making, in 97% of patients.

The FATE assessment incorporates the following five views:

  • Parasternal long-axis (LAX) view

  • Parasternal short-axis (SAX) view

  • Apical view

  • Subcostal view

  • Pleural view.

The aims of the FATE protocol are to:

  • Exclude obvious pathology

  • Assess contractility

  • Assess wall thickness and dimensions of the chambers

  • Visualize the pleura on both sides

  • Relate the information to the clinical context.

The views incorporated into the FATE assessment will be discussed in detail over the following pages.

Further reading

Jensen MB, Sloth E, Larsen KM, Schmidt MB. Transthoracic echocardiography for cardiopulmonary monitoring in intensive care. Eur J Anaesthesiol 2004;21:700–7.Find this resource:

Orme RML’E, Oram MP, McKinstry CE. Impact of echocardiography on patient management in the intensive care unit: an audit of district general hospital practice. B J Anaesthes 2009;102(3):340–4.Find this resource:

Parasternal long axis

Obtaining the view

  • Patient tilted towards their left.

  • Marker dot orientated towards the patient’s right shoulder.

  • Place the transducer adjacent to the left sternal margin the 2nd–4th intercostal space.

  • The mitral and aortic valves should be in the middle of the image with the left ventricular walls lying horizontally across the screen.

Image explained (Fig. 32.7)

  • Right ventricle: chamber closest to the transducer at the top of the screen. Use M-mode to measure size.

  • Aortic valve: assess leaflet movement and use CFM to identify regurgitation.

  • Aortic root and ascending aorta: measure the dimensions of the LVOT, sinuses of Valsalva, sinotubular junction, and ascending aorta.

  • Mitral valve: anterior leaflet (closest to transducer) and posterior leaflets seen. assess leaflet movement and use CFM to identify regurgitation.

  • Left ventricle: septal and posterior walls. Use M-mode to measure size, function, and wall thickness.

  • Left atrium: use M-mode to measure size.

  • Descending aorta: circular structure posterior to the left atrium.

  • Pericardial effusions: may be identified in front of the right ventricle or behind the left ventricle. Measure using M-mode.

Figure 32.7 Parasternal long-axis view: image and line diagram. RV, right ventricle; LV, left ventricle; AO, ascending aorta; LA, left atrium.

Figure 32.7 Parasternal long-axis view: image and line diagram. RV, right ventricle; LV, left ventricle; AO, ascending aorta; LA, left atrium.

Parasternal short axis (aortic)

Obtaining the view

  • Centre the parasternal long axis view on the aortic valve and rotate the transducer clockwise through 90° until the heart is seen in transverse section. By directing the ultrasound beam from the patient’s right shoulder to left flank, serial short-axis (transverse) slices through the heart from the base to apex can be obtained.

  • Marker dot now orientated towards the patient’s left shoulder.

  • The aortic valve should appear in the centre of the screen with all three of its cusps visible. The tricuspid and pulmonary valves are seen on the left and right of the screen respectively.

Image explained (Fig. 32.8)

  • Right ventricle: the most anterior chamber (nearest the transducer) that curves around the aortic valve.

  • Aortic valve: seen in the centre of the screen with a ‘Mercedes Benz logo’ appearance. Assess leaflet movement and use CFM to identify regurgitation.

  • Tricuspid valve: seen to the left of the screen. Assess leaflet movement and use CFM to identify regurgitation. Estimate pulmonary artery pressure using CWD.

  • Pulmonary valve: seen to the right of the screen. Assess leaflet movement and use CFM to identify regurgitation. Use CWD to identify outflow obstruction.

Figure 32.8 Parasternal short-axis (aortic) view: image and line diagram. RA, right atrium; RV, right ventricle; RVOT, right ventricular outflow tract; LA, left atrium; RCC, right coronary cusp; LCC, left coronary cusp; NCC, non-coronary cusp.

Figure 32.8 Parasternal short-axis (aortic) view: image and line diagram. RA, right atrium; RV, right ventricle; RVOT, right ventricular outflow tract; LA, left atrium; RCC, right coronary cusp; LCC, left coronary cusp; NCC, non-coronary cusp.

Parasternal short axis (mitral)

Obtaining the view

  • From the parasternal short-axis aortic view, tilt the transducer towards the apex of the heart/left flank. This is a very small movement.

  • The left ventricle should be round and symmetrical with the ‘fish mouth’ view of the mitral valve visible.

Image explained (Fig. 32.9)

  • Mitral valve: anterior (closest to the transducer) and posterior leaflets clearly seen. Assess leaflet movement. Assess stenosis by tracing the valve area (planimetry) and use CFM to identify regurgitation.

Figure 32.9 Parasternal short-axis (mitral) view: image and line diagram. RV, right ventricle; AMVL, anterior mitral valve leaflet; PMVL, posterior mitral valve leaflet.

Figure 32.9 Parasternal short-axis (mitral) view: image and line diagram. RV, right ventricle; AMVL, anterior mitral valve leaflet; PMVL, posterior mitral valve leaflet.

Parasternal short axis (mid-papillary)

Obtaining the view

  • From the parasternal short-axis mitral view, tilt the transducer a little more towards the apex of the heart (left flank) until the bodies of the papillary muscles come into view.

  • The left ventricle should be round and symmetrical and the bodies of both papillary muscles seen.

Image explained (Fig. 32.10)

  • Left ventricle: septal, anterior, lateral, and inferior walls seen. Use M-mode to measure size and wall thickness. Can assess global and regional LV function.

  • Right ventricle: use M-mode to measure size and look for any diastolic collapse.

Figure 32.10 Parasternal SAX view (mid papillary): image and line diagram. RV, right ventricle; LV, left ventricle.

Figure 32.10 Parasternal SAX view (mid papillary): image and line diagram. RV, right ventricle; LV, left ventricle.

Apical 4-chamber

Obtaining the view

  • Place the transducer over the apex of the heart and direct the ultrasound beam parallel to the long axis of the heart.

  • Marker dot orientated towards the patient’s left flank.

  • All four chambers and the mitral and tricuspid valves should be seen. The ventricular septum should lie vertically down the centre of the screen.

Image explained (Fig. 32.11)

Left-sided chambers are seen to the right of the screen.

  • Left ventricle: septal, apical, and lateral walls seen. Can assess global and regional LV function.

  • Right ventricle: assess size (compare with left) and function.

  • Atria: right and left atria and intra-atrial septum are seen. Can assess atrial volumes.

  • Mitral valve: anterior and posterior mitral valve leaflets seen. Assess leaflet movement. Assess stenosis by using CWD to calculate the pressure half time. Use CFM to identify regurgitation.

  • Tricuspid valve: lateral and septal leaflets seen. Assess leaflet movement and use CFM to identify regurgitation. Estimate pulmonary artery pressure using CWD.

Figure 32.11 Apical 4-chamber view: image and line diagram. RV, right ventricle; LV, left ventricle; RA, right atrium; LA left atrium.

Figure 32.11 Apical 4-chamber view: image and line diagram. RV, right ventricle; LV, left ventricle; RA, right atrium; LA left atrium.

Apical 5-chamber

Obtaining the view

  • From the apical 4-chamber view, angle the transducer anteriorly towards the chest wall until the ‘5th chamber’ (the LVOT) comes into view.

Image explained (Fig. 32.12)

  • Aortic valve: assess leaflet movement and use CFM to identify regurgitation. Assess stenosis by using CWD to determine the peak velocity/peak gradient.

  • LVOT: use PWD to calculate the velocity–time integral (VTI) of the LVOT, which can be used, along with the cross-sectional area of the LVOT, to calculate cardiac output.

Figure 32.12 Apical 5-chamber view: image and line diagram. RV, right ventricle; LV, left ventricle; RA, right atrium; LA, left atrium; LVOT, left ventricular outflow tract.

Figure 32.12 Apical 5-chamber view: image and line diagram. RV, right ventricle; LV, left ventricle; RA, right atrium; LA, left atrium; LVOT, left ventricular outflow tract.

Subcostal

Obtaining the view

  • Increase the depth of the image.

  • Patient lying flat on their back, abdomen relaxed, and knees bent.

  • Hold the probe in the palm of your hand. Place the transducer parallel to the skin inferior to the right costal margin and direct the ultrasound beam under the ribs, towards the heart. Gentle downwards pressure may be needed.

  • Marker dot orientated towards the patient’s left shoulder.

  • All four chambers and the mitral and tricuspid valves should be seen. The septa should lie horizontally across the screen.

Image explained (Fig. 32.13)

Good view to assess right-sided chambers (as they lie closest to the transducer) and pericardial effusions. This is an alternative view if unable to obtain parasternal views.

  • Liver: top left of the image. Freely transmits ultrasound waves.

  • Diaphragm: hyperechoic linear structure between the liver and the right heart that moves with respiration.

  • Right ventricle: adjacent to the diaphragm. Free wall and septum seen. Compare size with left and assess function. Use M-mode to measure size and wall thickness. Assess intra-ventricular septum for defects using CFM.

  • Right atrium: assess intra-atrial septum for defects using CFM. Use M-mode to measure size.

  • Tricuspid valve: assess leaflet movement and use CFM to identify regurgitation.

  • Left ventricle: septal and lateral walls seen.

  • Left atrium: use M-mode to measure size.

  • Mitral valve: assess leaflet movement.

  • Pericardium: assess size and depth of any effusions.

Figure 32.13 Subcostal view: image and line diagram. RV, right ventricle; LV, left ventricle; RA, right atrium; LA, left atrium.

Figure 32.13 Subcostal view: image and line diagram. RV, right ventricle; LV, left ventricle; RA, right atrium; LA, left atrium.

Inferior vena cava

Obtaining the view

  • From the subcostal view rotate the transducer anticlockwise whilst keeping the right atrium in view.

  • The inferior vena cava (IVC) appears as a tubular structure that empties into the right atrium.

Image explained (Figs 32.14 and 32.15)

  • IVC: measure the diameter and any changes associated with respiration in order to estimate right atrial pressure (Table 32.1).

Table 32.1 Right atrial pressure (mmHg)

0–5

5–10

10–15

15–20

>20

  • IVC

  • Size (cm)

  • Respiratory/sniff variation

  • <1.5

  • Collapse

  • 1.5–2.5

  • ↓>50%

  • 1.5–2.5

  • ↓<50%

  • >2.5

  • ↓<50%

  • >2.5

  • No change

  • Other

  • RA size

Normal

Normal

↑↑

↑↑

IVC, inferior vena cava; RA, right atrium.

Reproduced from the Journal of the American Society of Endocardiography, Lang, M., et al, ‘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’, Vol. 18, Issue 12, pp. 1440-1463, Copyright 2005, with permissions from Elsevier Ltd.

Figure 32.14 IVC view: image and line diagram. RA, right atrium.

Figure 32.14 IVC view: image and line diagram. RA, right atrium.

Figure 32.15 Example of change in IVC diameter with ‘sniffing’: image and line diagram.

Figure 32.15 Example of change in IVC diameter with ‘sniffing’: image and line diagram.

Pleural

Obtaining the view

  • Place the transducer on the lateral thoracic wall in the mid axillary line.

  • Marker dot orientated towards the patient’s axilla.

  • Caudal structures seen to the left of the screen. Identify the diagram, liver, and lung tissue.

Image explained (Fig. 32.16)

  • Diaphragm: a bright line that curves across the image and moves with respiration.

  • Liver/spleen: seen on the left of the image adjacent to the diaphragm.

  • Lung tissue: seen on the right of the image.

  • Pleural effusion: appears as a hypoechoic (dark) area.

Figure 32.16 Pleural view with effusion: image and line diagram.

Figure 32.16 Pleural view with effusion: image and line diagram.

Investigating hypotension

Unexplained hypotension in the CICU is usually secondary to hypovolaemia, vasodilatation, or cardiac failure. Bedside echocardiography can be used to help differentiate between these possible causes.

Hypovolaemia or vasodilatation?

Hypovolaemia

Hypovolaemia results in reduced left ventricular filling. The volume/area/diameter (surrogates for left ventricular filling) of the left ventricle at end diastole and end systole will therefore be noticeably reduced. Starting from smaller than normal at end diastole, the left ventricle contracts until the papillary muscles are close to meeting—kissing papillary muscles.

Vasodilatation

Vasodilatation results in ↓ peripheral vascular resistance and therefore ↑ stroke volumes. End-diastolic left ventricular volume remains constant but end systolic volumes are reduced. Starting from normal size at end diastole, the left ventricle contracts until the papillary muscles are close to meeting.

  • Obtain short-axis images of the left ventricle (parasternal SAX view).

  • Measure the internal diameter (LVID)/trace the internal circumference of the left ventricle in end diastole (LVIDd) and end systole (LVIDs) (Figs 32.17, 32.18, 32.19, and 32.20).

Figure 32.17 Parasternal SAX view.
End diastole. LVIDd = 2.66cm.

Figure 32.17 Parasternal SAX view.

End diastole. LVIDd = 2.66cm.

Figure 32.18 Parasternal SAX view.
End diastole. LVIDd = 3.89cm.

Figure 32.18 Parasternal SAX view.

End diastole. LVIDd = 3.89cm.

Figure 32.19 Parasternal SAX view.
End systole LVIDs = 1.61cm.

Figure 32.19 Parasternal SAX view.

End systole LVIDs = 1.61cm.

Figure 32.20 Parasternal SAX view.
End systole LVIDs = 1.46cm.

Figure 32.20 Parasternal SAX view.

End systole LVIDs = 1.46cm.

Cardiac failure

Hypotension may be due to the:

  • Left ventricle:

    • Global dysfunction

    • Regional dysfunction

    • LV outflow obstruction (systolic anterior motion of the mitral valve)

  • Right ventricle:

    • Systolic dysfunction

    • RV outflow tract obstruction (PE)

  • Pericardium:

    • Fluid (tamponade)

    • Thickening (constrictive pericarditis).

Assessment of the left ventricle

  • Eye ball test

  • Dimensions and fractional shortening/ejection fraction

  • Measurement of CO.

Eyeball test

Use the parasternal short axis mid papillary view to obtain an overall picture of the heart’s function. Standardize the depth of the image to facilitate comparison and pattern recognition. See Fig. 32.21.

Figure 32.21 Parasternal short axis diagram illustrating coronary territories. RV, right ventricle; LV, left ventricle; ALPM, anterolateral papillary muscle; PMPM, posteromedial papillary muscle; RCA, right coronary artery; LCX, left circumflex artery; LAD, left anterior descending. Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 17.7, p. 288, Copyright the authors.

Figure 32.21 Parasternal short axis diagram illustrating coronary territories. RV, right ventricle; LV, left ventricle; ALPM, anterolateral papillary muscle; PMPM, posteromedial papillary muscle; RCA, right coronary artery; LCX, left circumflex artery; LAD, left anterior descending. Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 17.7, p. 288, Copyright the authors.

Is the heart empty or full?

  • Do the papillary muscles touch at end systole in the parasternal SAX view?

  • Assess the IVC in the subcostal view.

  • Assess RA size.

Is the heart contracting well?

  • Does it appear to move in a smooth or jerky manner?

Is there a regional wall-motion abnormality?

  • Look at each segment in turn. Placing a finger in the centre of the image may help identify an abnormally contracting segment.

  • Segments may be normal, hypokinetic, akinetic, or move paradoxically (dyskinetic).

Calculating fractional shortening and ejection fraction

M-mode

Use M-mode through the base of the heart (tips of the mitral valve leaflets) in the parasternal LAX view (Figs 32.22 and 32.23). Measure the left ventricular size at end diastole (timed with the R wave on the ECG) and at end systole (timed with the T wave on the ECG). The inbuilt software on the machine will then estimate the fractional shortening and ejection fraction.

Figure 32.22 Example of calculation of fractional shortening and ejection fraction using M-mode (parasternal LAX view).

Figure 32.22 Example of calculation of fractional shortening and ejection fraction using M-mode (parasternal LAX view).

Figure 32.23 Line diagram of parasternal long-axis M-mode. Image taken from FATE-card and reproduced with permission from Professor Ph.D. MDSc Erik Sloth. <http://www.usabcd.org> (FATE-app available for free download at App Store and Android Market).

Figure 32.23 Line diagram of parasternal long-axis M-mode. Image taken from FATE-card and reproduced with permission from Professor Ph.D. MDSc Erik Sloth. <http://www.usabcd.org> (FATE-app available for free download at App Store and Android Market).

Simpson’s method

Simpson’s method divides the left ventricle into a series of discs providing a 3D estimation of LV volume (Fig. 32.24). Using the inbuilt software, estimation of end-diastolic and end-systolic LV volumes facilitates estimation of the LV ejection fraction. This method can be made more accurate by repeating the process in another plane (apical 2-chamber) and taking the average of the values obtained.

Figure 32.24 Simpson’s method for estimation of ejection fraction. Obtain an apical 4-chamber view. Ensure that the endocardial border of the LV is clearly defined and that the ventricle is not foreshortened (ensure the apex is identified: it is fixed and doesn’t move towards the base during systole). Zoom in on the left ventricle and then record a loop. At end diastole (R wave on ECG), trace the endocardial border and note the calculated end diastolic volume (EDV). Scroll to end systole (T wave on ECG), trace the endocardial border and note the end systolic volume (ESV). The ejection fraction can then be calculated:




Ejectionfraction(
%
)=

EDV-ESV


EDV


×100

Figure 32.24 Simpson’s method for estimation of ejection fraction. Obtain an apical 4-chamber view. Ensure that the endocardial border of the LV is clearly defined and that the ventricle is not foreshortened (ensure the apex is identified: it is fixed and doesn’t move towards the base during systole). Zoom in on the left ventricle and then record a loop. At end diastole (R wave on ECG), trace the endocardial border and note the calculated end diastolic volume (EDV). Scroll to end systole (T wave on ECG), trace the endocardial border and note the end systolic volume (ESV). The ejection fraction can then be calculated:

Ejectionfraction( % )= EDV-ESV EDV ×100

Measuring cardiac output

Consider the flow in the LVOT. The volume of blood flowing through the LVOT over a given time period is the product of the cross-sectional area of the LVOT and the VTI:

Stoke volume LVOT = cross-sectional area LVOT × VTI LVOT

Cross-sectional area of the LVOT

  • Area of a circle = π × radius2.

  • Measure the diameter of the LVOT in the parasternal LAX view (radius=½ diameter). Ensure this is accurate as the value (and therefore any error) is being squared.

Velocity time integral of LVOT

  • Apical 5-chamber view.

  • Use PWD with the sample chamber situated in the LVOT.

  • On the resulting velocity–time graph, trace the outline of the velocity to calculate the VTI.

The volume through the LVOT can be used to calculate cardiac output:

cardiac output = volume LVOT × heart rate

See Fig. 32.25 and Table 32.2.

Figure 32.25 PWD with sample chamber in LVOT. VTI calculated.

Figure 32.25 PWD with sample chamber in LVOT. VTI calculated.

Table 32.2 Left ventricular dimensions and function

Normal

Mild

Moderate

Severe

LV wall thickness

IVSd/PWd (cm)

0.6–1.2

1.3–1.5

1.6–1.9

≥2

LV dimensions, women

LVIDd (cm)

3.9–5.3

5.4–5.7

5.8–6.1

≥6.2

LVIDd/BSA (cm/m2)

2.4–3.2

3.3–3.4

3.5–3.7

≥3.8

LV dimensions, men

LVIDd (cm)

4.2–5.9

6.0–6.3

6.4–6.8

≥6.9

LVIDd/BSA (cm/m2)

2.2–3.1

3.2–3.4

3.5–3.6

≥3.7

LV volume, women

LV diastolic volume (mL)

56–104

105–117

118–130

≥131

LV systolic volume (mL)

19–49

50–59

60–69

≥70

LV volume, men

LV diastolic volume (mL)

67–155

156–178

179–201

≥202

LV systolic volume (mL)

22–58

59–70

71–82

≥83

LV volume index

LV diastolic volume/BSA (mL/m2)

35–75

76–86

87–96

≥97

LV systolic volume/BSA (mL/m2)

12–30

31–36

37–42

≥43

LV function

Fractional shortening (%)

25–43

20–24

15–19

<15

EF (Simpson’s method) (%)

≥55

45–54

36–44

≤35

LA size, women

LA diameter (cm)

2.7–3.8

3.9–4.2

4.3–4.6

≥4.7

LA volume (mL)

22–52

53–62

63–72

≥73

LA size, men

LA diameter (cm)

3.0–4.0

4.1–4.6

4.7–5.2

≥5.3

LA volume (mL)

18–58

59–68

69–78

≥79

LA size, index

LA diameter (cm/m2)

1.5–2.3

2.4–2.6

2.7–2.9

≥3.0

LA volume (mL/m2)

16–28

29–33

34–39

≥40

BSA, body surface area; EF, ejection fraction; IVSd, intraventricular septum diameter; LA, left atrium; LV, left ventricle; PWd, posterior wall diameter; LVIDd, left ventricular internal diameter diastole. Reproduced from the Journal of the American Society of Echocardiography, 18, 12, Lang, M., et al. 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, pp. 1440–1463, Copyright 2005, with permission from American Society of Echocardiography and Elsevier.

Assessment of the right ventricle

  • Eye ball test

  • Dimensions and fractional area change

  • Estimating pulmonary artery pressure.

See Table 32.3.

Table 32.3 Right ventricular dimensions and function

Normal

Mild

Moderate

Severe

RV dimensions (apical 4 chamber)

Basal RV diameter (cm)

2.0–2.8

2.9–3.3

3.4–3.8

≥3.9

Base to apex length (cm)

7.1–7.9

8.0–8.5

8.6–9.1

≥9.2

PA diameter (parasternal SAX)

Main PA (cm)

1.5–2.1

2.2–2.5

2.6–2.9

≥3.0

RV area

RV diastolic area (cm2)

11–28

29–32

33–37

≥38

RV systolic area (cm2)

7.5–16

17–19

20–22

≥23

RV function

Fractional area change (%)

32–60

25–31

18–24

≤17

RV, right ventricle; PA pulmonary artery. Reproduced from the Journal of the American Society of Echocardiography, 18, 12, Lang, M., et al. 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, pp. 1440–1463, Copyright 2005, with permission from American Society of Echocardiography and Elsevier.

Eyeball test

In the apical 4-chamber view compare the right ventricle with the left ventricle.

  • The right ventricular area should be smaller than (usually 2/3) the area of the left ventricle and the cardiac apex formed solely by the left ventricle.

  • Equally sized ventricles suggest a moderately dilated right ventricle.

  • If the right is larger than the left and forms the cardiac apex, then the right ventricle is severely dilated.

Right ventricular dimensions

Figure 32.26 Basal diameter RV. Apical 4-chamber view. Normal diameter 2–2.8 cm

Figure 32.26 Basal diameter RV. Apical 4-chamber view. Normal diameter 2–2.8 cm

Figure 32.27 RV length. Apical 4-chamber view. Normal length 7.1–7.9cm.

Figure 32.27 RV length. Apical 4-chamber view. Normal length 7.1–7.9cm.

Figure 32.28 RV area. Apical 4-chamber view. Estimate RV function by measuring area in systole and diastole to calculate fractional area change.

Figure 32.28 RV area. Apical 4-chamber view. Estimate RV function by measuring area in systole and diastole to calculate fractional area change.

Estimating pulmonary artery pressure

  • Use an apical 4-chamber or parasternal SAX view with a visible jet of tricuspid regurgitation.

  • Align CWD through the tricuspid valve regurgitation.

  • Measure the peak velocity.

  • The tricuspid pressure gradient is calculated from the peak velocity using a modified Bernoulli equation:

    Pressure gradient = 4 × peak velocity 2

  • The RV systolic pressure, which is equivalent to pulmonary artery systolic pressure in the absence of pulmonary stenosis, is equal to the sum of the tricuspid pressure gradient and right atrial pressure (CVP).

Normal values

Normal values can be found in the Recommendations for chamber quantification: a report from the American Society of Echocardiography’s Guidelines and Standards Committee and the Chamber Quantification Writing Group (see Bedside echocardiography Further reading, p. 361).

There is also an iPhone application named EchoCalc created by the British Society of Echocardiography.

For some examples of important pathologies see Fig. 32.29.

Figure 32.29 Important pathology examples. Image taken from FATE-card and reproduced with permission from Professor Ph.D. MDSc Erik Sloth. <http://www.usabcd.org> (FATE-app available for free download at App Store and Android Market).

Figure 32.29 Important pathology examples. Image taken from FATE-card and reproduced with permission from Professor Ph.D. MDSc Erik Sloth. <http://www.usabcd.org> (FATE-app available for free download at App Store and Android Market).

Further reading

Lang RM, Bierig M, Devereux RB, Flachskampf FA, Foster E, Pellikka PA, et al. 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. J Am Soc Echocardiogr 2005;18:1140–63.Find this resource:

Transoesophageal echocardiography

Introduction

This section will provide an overview of the information that can be obtained using TOE in the setting of the CICU. The majority of any echocardiographic examination involves the interpretation of moving images. There are many examples of these available via the Internet which are recommended to the reader.

Risks and precautions

TOE is described as an ‘invasive, non-invasive’ investigation since there is morbidity and indeed mortality described from its use. As such, safety is of extreme importance and the sonographer must review the patient’s history to exclude any contraindication to TOE before undertaking the study. The practice guidelines for perioperative TOE recommend ‘that TOE may be used for patients with oral, oesophageal or gastric disease, if the expected benefit outweighs the potential risk, provided the appropriate precautions are applied’. The precautions include considering other imaging techniques (e.g. TTE), asking for an upper GI opinion and perhaps endoscopy, using the smallest available probe, limiting the examination and avoiding unnecessary probe manipulation, and using the most experienced operator.

Prior to the examination consideration must be given to analgesia and sedation, and the monitoring of the patient’s vital signs must be delegated to another individual, or the monitors positioned such that the sonographer has a clear view of them during the procedure. This is of particular importance since in the majority of cases TOE is being performed to determine the cause of postoperative haemodynamic instability.

Specific indications for TOE in ICU.

  • Mitral valve assessment

  • Endocarditis

  • Embolism of unknown origin

  • Unexplained hypoxemia

  • Pulmonary thromboembolism

  • Aortic dissection.

The standard views

The ASE/SCA practice guidelines suggest 20 standard views to be obtained during a comprehensive TOE exam. There is no generally accepted order in which these views are obtained. Fig. 32.30 shows the views which most commonly provide relevant information in the CICU, and the abnormalities which may be detected.

Figure 32.30 The standard views of a comprehensive TOE examination. Reproduced from Shanewise et al. ASE/SCA Guidelines for Performing a Comprehensive Intraoperative Multiplane Transesophageal Echocardiography Examination: Recommendations of the American Society of Echocardiography Council for Intraoperative Echocardiography and the Society of Cardiovascular Anesthesiologists Task Force for Certification in Perioperative Transesophageal Echocardiography. Anesthesia & Analgesia, 89, 4, p. 870, copyright 1999, with permission from International Anesthesia Research Society and Wolters Kluwer.

Figure 32.30 The standard views of a comprehensive TOE examination. Reproduced from Shanewise et al. ASE/SCA Guidelines for Performing a Comprehensive Intraoperative Multiplane Transesophageal Echocardiography Examination: Recommendations of the American Society of Echocardiography Council for Intraoperative Echocardiography and the Society of Cardiovascular Anesthesiologists Task Force for Certification in Perioperative Transesophageal Echocardiography. Anesthesia & Analgesia, 89, 4, p. 870, copyright 1999, with permission from International Anesthesia Research Society and Wolters Kluwer.

Mitral valve assessment

The mitral valve is immediately close to the oesophagus and TOE provides excellent quality images for the assessment of the mitral valve. This may be essential for determination of the mitral valve morphology and diagnosis of mechanisms of mitral regurgitation. TOE is also invaluable for the assessment of the prosthetic mitral valve or mitral valve repair. The best views are shown in Figs 32.31, 32.32, and 32.33.

Figure 32.31 Mid oesophageal 4-chamber view (MO 4-chamber). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.11, p. 40, Copyright the authors.

Figure 32.31 Mid oesophageal 4-chamber view (MO 4-chamber). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.11, p. 40, Copyright the authors.

Figure 32.32 Mid oesophageal mitral commissural view (MO mitral commissural) (P3 on left of display, P1 on right, A2 in centre). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.13, p. 41, Copyright the authors.

Figure 32.32 Mid oesophageal mitral commissural view (MO mitral commissural) (P3 on left of display, P1 on right, A2 in centre). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.13, p. 41, Copyright the authors.

Figure 32.33 Mid oesophageal aortic valve long axis view (MO AV LAX).This view may reveal dynamic LVOT obstruction secondary to systolic anterior motion of the mitral valve (SAM). This uncommon but extremely important cause of hypotension following cardiac surgery is characterized by the anterior leaflet of the mitral valve prolapsing into the LVOT and perhaps even coapting with the interventricular septum which is usually hypertrophied. There is often associated mitral regurgitation and the velocity of this regurgitant jet may reveal that the pressure inside the left ventricle during systole is higher than the systemic blood pressure. Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.5, p. 37, Copyright the authors.

Figure 32.33 Mid oesophageal aortic valve long axis view (MO AV LAX).This view may reveal dynamic LVOT obstruction secondary to systolic anterior motion of the mitral valve (SAM). This uncommon but extremely important cause of hypotension following cardiac surgery is characterized by the anterior leaflet of the mitral valve prolapsing into the LVOT and perhaps even coapting with the interventricular septum which is usually hypertrophied. There is often associated mitral regurgitation and the velocity of this regurgitant jet may reveal that the pressure inside the left ventricle during systole is higher than the systemic blood pressure. Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.5, p. 37, Copyright the authors.

Possible findings in endocarditis

  • Vegetations on valves

  • Aortic root abscess

  • Perforated or destroyed leaflets of any valve

  • Dehisced mechanical valve

  • Mechanical or bioprosthetic valve dysfunction

  • Fistula between chambers.

Embolism of unknown origin

TOE is superior to TTE in the examination of the left atrium and particularly the examination of the left atrial appendage which is a common source of arterial embolism. This is best seen in the MO 2-chamber view. Alternative embolic sources can be seen such as left-sided valve vegetations or intracardiac clot or tumour (LV or LA).

Figure 32.34 Mid oesophageal 2-chamber view (MO 2-chamber). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.14, p. 41, Copyright the authors.

Figure 32.34 Mid oesophageal 2-chamber view (MO 2-chamber). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.14, p. 41, Copyright the authors.

Unexplained hypoxaemia

Shunt at the intra-atrial level may be revealed either as a result of a patent foramen ovale or an atrial septal defect. Bubble contrast test (injection of agitated saline into the central line) and CFM can help determine the position and direction of any septal defect (Fig. 32.35). This important test to can help to exclude a cardiac cause of hypoxia post cardiac surgery.

Figure 32.35 Mid oesophageal bicaval view (MO bicaval). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.9, p. 38, Copyright the authors.

Figure 32.35 Mid oesophageal bicaval view (MO bicaval). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.9, p. 38, Copyright the authors.

Clot compression of the atria may be revealed in this view. Withdrawal of the central line should be considered if examination reveals the tip to be within the right atrium.

Pulmonary thromboembolism

Clot may be seen in the main pulmonary artery in massive pulmonary embolism. This is best seen in the MO ascending aorta SAX view (Fig. 32.36); however, the right main bronchus often partially obscures this view.

Figure 32.36 Mid oesophageal ascending aortic short-axis view (MO asc. aortic SAX). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.6, p. 37, Copyright the authors.

Figure 32.36 Mid oesophageal ascending aortic short-axis view (MO asc. aortic SAX). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.6, p. 37, Copyright the authors.

Aortic dissection

The assessment of aortic dissection is best done with TOE rather than TTE. Often the patient will have already had a contrast CT scan. A full assessment of the ascending arch and descending aorta should be performed. Classically an endothelial flap will be revealed in the ascending aorta in type 1 dissection. In addition, aortic regurgitation and pericardial haemopericardium may be revealed. In case of dissection into a coronary artery, evidence of a wall-motion abnormality will be present.

In addition to the mid oesophageal aortic valve long-axis view (MO AV LAX) seen earlier (Fig. 32.33) the views in Figs 32.37, 32.38, and 32.39 may be useful.

Figure 32.37 Mid oesophageal aortic valve short-axis view (MO AV SAX). The MO AV SAX view is a good starting point since the aortic valve is often easily identified by the Mercedes Benz sign when in the closed position. The left atrium lies closest to the probe and is displayed at the top of the screen. This view offers clear images of the left and right atria and the aortic valve. The RVOT is often less well seen since it is more distant from the transducer and any calcification in the aortic valve will cause ultrasound drop out. Compression of the left or right atria by blood clot which is often enough to lead to post cardiotomy tamponade may be seen in this view. The morphology of the aortic valve is seen. Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.4, p. 37, Copyright the authors.

Figure 32.37 Mid oesophageal aortic valve short-axis view (MO AV SAX). The MO AV SAX view is a good starting point since the aortic valve is often easily identified by the Mercedes Benz sign when in the closed position. The left atrium lies closest to the probe and is displayed at the top of the screen. This view offers clear images of the left and right atria and the aortic valve. The RVOT is often less well seen since it is more distant from the transducer and any calcification in the aortic valve will cause ultrasound drop out. Compression of the left or right atria by blood clot which is often enough to lead to post cardiotomy tamponade may be seen in this view. The morphology of the aortic valve is seen. Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.4, p. 37, Copyright the authors.

Figure 32.38 Mid oesophageal ascending aortic long-axis view (MO asc. aortic LAX). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.7, p. 36, Copyright the authors.

Figure 32.38 Mid oesophageal ascending aortic long-axis view (MO asc. aortic LAX). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.7, p. 36, Copyright the authors.

Figure 32.39 Transgastric mid papillary short axis view (TG mid SAX). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.18, p. 44, Copyright the authors.

Figure 32.39 Transgastric mid papillary short axis view (TG mid SAX). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.18, p. 44, Copyright the authors.

Assessment of ventricular function with TOE

Left ventricle

The transgastric mid SAX view is a useful view for the assessment of the LV function. Myocardium supplied by all three main coronary arteries are seen. The view is commonly referred to as the bouncing doughnut view (Fig. 32.39)!

Right ventricle

Right ventricular systolic function and dimensions can be assessed in this view (Fig. 32.40). Dilatation of the right ventricle is often associated with tricuspid regurgitation and determination of the peak velocity of the regurgitant jet across the tricuspid valve will provide the right ventricular and therefore the pulmonary artery systolic pressure. (RV systolic pressure = 4 × V max2 + CVP.) Clot compression of the RV may be seen but it is important to remember that the classic signs of tamponade (associated with pericardial effusion) are often absent in the post cardiac surgery setting with ‘regional tamponade’ or localized clot collection a common finding.

Figure 32.40 Mid oesophageal right ventricular inflow outflow view (MO RV inflow-outflow). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.8, p. 38, Copyright the authors.

Figure 32.40 Mid oesophageal right ventricular inflow outflow view (MO RV inflow-outflow). Reproduced with kind permission from Practical Perioperative Transoesophageal Echocardiography, David Sidebotham, Alan Merry, Malcolm Legget, 2003, Figure 3.8, p. 38, Copyright the authors.

Clot compression of the RV may be seen but it is important to remember that the classic signs of tamponade (associated with pericardial effusion) are often absent in the post cardiac surgery setting with ‘regional tamponade’ or localized clot collection a common finding.