Echocardiography

What’s new?

C More accurate assessment of left ventricular function is feasible

with 3D-TTE.

C Guidance by 3D TOE is increasingly required for percutaneous

INVESTIGATIONS

EchocardiographyMatthias Paul

Lindsay Smith

Mark Monaghan

(non-coronary) cardiac interventions (e.g. PFO-/ASD-closure,

trans-catheter aortic valve implantation).

AbstractEchocardiography e the investigation of the heart with ultrasound e is

the most frequently used cardiac imaging modality. Transthoracic echo-

cardiography is a powerful tool to evaluate the structure and function of

the heart. Further evaluation is possible with transoesophageal echocar-

diography. However, its higher resolution and image quality are accom-

panied by a small risk of complications. Stress echocardiography allows

identification of patients with significant coronary artery disease with

high sensitivity and specificity. The aim of this article is to outline the

information that echocardiography can provide and the clinical situa-

tions where it is indicated. Further advanced applications such as

contrast and three-dimensional echocardiography will also be

discussed.

Keywords contrast echocardiography; coronary artery disease; Doppler;

echocardiography; heart valve diseases; stress; three-dimensional;

transoesophageal; ventricular function

Echocardiography provides a wealth of information, and impor-

tantly, is a non-invasive technique which does not involve

radiation and is readily available at the bedside.

Basic ultrasound physics

Ultrasound waves transmitted into the body travel with

a distinct velocity and are reflected at interfaces between tissues

of different density (e.g. blood and myocardium). The time

these echoes require to return to the transducer is analyzed and

a two- or even three-dimensional image of a cross-section of the

heart can be generated. Ultrasound waves reflected by moving

structures such as red blood cells and myocardium cause

a frequency shift of the ultrasound (¼Doppler effect). This is

the basis of Doppler-echocardiography (colour, continuous and

pulsed-wave Doppler), which enables accurate

measurements of blood flow and myocardial tissue velocities

(Figures 1e3).

Matthias Paul MD is a Clinical Fellow of Cardiology at King’s College

Hospital, London, UK. Competing interests: none.

Lindsay Smith MD MRCP is a Research Fellow in Cardiology, King’s

College Hospital, London, UK. Competing interests: none.

Mark Monaghan PhD FRCP(Hon) FACC FESC is Director of Non-Invasive

Cardiology at King’s College Hospital, London, UK. Competing

interests: none.

MEDICINE 38:7 371

Transthoracic echocardiography (TTE)

A transthoracic study is usually performed by an experienced

sonographer or a trained doctor and takes approximately 40 min

for a full study. Optimal positioning of the patient is important

since the bony thorax and the lungs represent obstacles to the

ultrasound. While the patient is resting comfortably on his left

side, a set of standard views is acquired from the left parasternal,

apical, subcostal and suprasternal positions. Rotation and

angulation of the transducer enable different planes of the heart

to be visualized from a single position.

Left ventricular function

The commonest reason for requesting a TTE is evaluation of left

ventricular function. By scanning the left ventricle from different

views global systolic function can be qualitatively described as

normal, mildly, moderately and severely impaired. In order to

assess systolic function quantitatively, left ventricular area is

measured in two planes at end-systole and end-diastole, and

volumes and ejection fraction derived by applying Simpson’s

method. However, absolute numbers must be used carefully, as

the method is based on a number of assumptions. 3D echocar-

diography is more accurate and reproducible1,2 and may be

considered in patients where serial comparison is necessary (e.g.

during potentially cardiotoxic chemotherapy or in patients where

Figure 1 Transthoracic apical four chamber 2D image shows all the four

chambers of the heart (RA ¼ right atrium, RV ¼ right ventricle, LA ¼ left

atrium, LV ¼ left ventricle) and is therefore called 4-chamber view. The

mitral valve appears thickened, the tricuspid valve looks normal.

Crown Copyright � 2010 Published by Elsevier Ltd. All rights reserved.

Figure 2 Mitral regurgitation visualized with colour Doppler. The coloured

area represents the high velocity jet through the mitral valve moving

towards the roof of the enlarged left atrium.

INVESTIGATIONS

important clinical decisions are going to be based upon the

parameters). Furthermore, regional left ventricular wall motion

can be assessed and abnormalities suggesting ischaemic or

scarred myocardial tissue detected. Diastolic function can also be

determined helping to distinguish those patients with diastolic

heart failure. However, although TTE is extremely valuable in

patients with heart failure, a scan is not indicated if brain natri-

uretic peptide values are normal.3

Valve disease

TTE allows detailed evaluation of valvular anatomy and function

and is therefore invaluable in the assessment of valve disease.

Hence, one of the most frequent indications is a heart murmur.

However, in the absence of symptoms, an innocent murmur (i.e.

a soft ejection murmur and normal second heart sound) does not

justify an echocardiographic assessment. In a febrile patient

a systolic murmur can often be auscultated because the hyper-

dynamic physiology causes flow acceleration and turbulence. If

Figure 3 Continuous wave Doppler signal of severe aortic stenosis.

Velocity of blood flow ( y-axis) is recorded against time (x-axis). The peak

velocity of about 5 m/s is consistent with severe aortic stenosis.

MEDICINE 38:7 372

there is a clinical suspicion of endocarditis, TTE may identify

vegetations and is therefore indicated, but it is important to note

that a normal TTE does not completely exclude endocarditis.3 In

patients with proven valvular disease, progression is monitored

by TTE as indications for surgical intervention are mainly based

on echocardiographic criteria and symptoms.4

Cardiomyopathies

TTE is usually diagnostic for hypertrophic cardiomyopathy and

plays an important role in identifying patients with other types of

cardiomyopathies [i.e. dilated cardiomyopathy, arrhythmogenic

right ventricular cardiomyopathy (ARVC) and infiltrative disease

causing restrictive cardiomyopathy]. Further investigation with

cardiovascular magnetic resonance may be necessary, particu-

larly for ARVC and infiltrative disease.

Other indications

TTE also allows assessment of right ventricular function and

estimation of systolic pulmonary artery pressure. Pericardial

disease can be detected and the haemodynamic influence of

pericardial effusion evaluated. Atrial and ventricular septal

defects and other major congenital heart disease can be

excluded, although agitated saline (‘bubble’) contrast may be

needed for smaller atrial defects. And intracardiac masses

such as tumours and thrombi may be identified; the use of

a transpulmonary contrast agent may be helpful in these

circumstances.

A comprehensive but not exhaustive list of indications can be

found in Table 1.

In conclusion, TTE is a powerful tool to evaluate the structure

and function of the heart. As with other diagnostic tests it should

only be requested when the result will influence the management

of the patient. To get the most out of a study adequate clinical

information is vital and a specific question must be phrased. This

allows the echocardiographer to look carefully for specific abnor-

malities and to decide whether additional techniques such as

contrast echocardiography, or further investigations are indicated.

Transoesophageal echocardiography (TOE)

Insertion of the ultrasound transducer mounted on the tip of

a probe similar to a gastroscope into the oesophagus and

stomach enables the heart to be imaged from close proximity

without obstruction by the bones and lungs. This results in

higher resolution and better image quality and allows assessment

of structures not well visualized by the transthoracic approach.

However, the procedure is semi-invasive and therefore comes

with a small risk of complications and may be uncomfortable for

the patient. Serious complications, such as oesophageal perfo-

ration, laryngospasm, ventricular arrhythmia and severe

hypoxia, are rare (<0.1%) but fatal incidents have been reported

(<0.01%).7,8

Thus, a study should be performed only if:

� there are no contraindications (see Table 2);

� a transthoracic examination was inconclusive because of poor

image quality;

� further evaluation of pathologic findings is necessary; or

� assessment of structures not well seen by TTE (i.e. left atrial

appendage, descending aorta is required).


Clinical situations where transthoracic echocardiography (TTE) is appropriate5,6

- Valve disease

- suspected valve disease (i.e. pathologic) murmur

- follow-up of known native valve disease:

- if change in clinical status

- in asymptomatic patients with severe valve disease

- in pregnancy

- follow-up of prosthetic valves:

- baseline assessment following operation

- if change in clinical status

- if clinical suspicion of dysfunction (TOE indicated if TTE negative)

- periodic assessment of bioprosthetic valve (after 7 years for aortic and 5 years for mitral bioprosthesis)

- suspected endocarditis (consider TOE if TTE negative and high clinical suspicion)

- Ischaemic heart disease (known or suspected):

- chest pain with haemodynamic instability

- murmur following acute or recent myocardial infarction

- assessment of infarct size, presence of complications and baseline LV function following MI (consider contrast echo)

- evaluation of LV function with regard to ICDa or CRTb implantation

- Heart failure and cardiomyopathy:

- clinical cardiomegaly, clinical or radiographic signs of heart failure

- persistent hypotension of unknown cause

- suspected cardiomyopathy based on physical examination, ECG findings or family history

- baseline left ventricular function and follow-up when using cardiotoxic drugs, e.g. herceptin (consider 3D-TTE if available)

- Pericardial disease:

- pericarditis only if associated myocarditis suspected

- assessment of haemodynamic significance of pericardial effusion (note, pericardial tamponade remains clinical diagnosis!)

- Stroke, transient ischaemic attack, suspected cardiac masses:

- unexplained stroke or TIA (bubble contrast study only if closure of PFO-closure is considered)

- clinical, haemodynamic or auscultatory findings suggesting intracardiac mass

- Arrhythmia, palpitations and syncope:

- clinical suspicion of structural heart disease in proven arrhythmia

- syncope in a patient with suspected heart disease, exertional syncope

- Pulmonary disease:

- pulmonary hypertension and cor pulmonale

- in established pulmonary embolism (not for diagnosis!) to guide therapy (i.e. thrombolysis, thrombectomy)

- Hypertension:

- suspected left ventricular dysfunction

- suspected aortic coarctation

- Aortic disease:

- suspected aortic dissection (initial evaluation, TOE or CT angiography necessary for detailed assessment)

Note: this is a comprehensive but not exhaustive list.a ICD, implantable cardioverter-defibrillator;b CRT, cardiac resynchronization therapy; TOE, transoesophageal echocardiography

Table 1

INVESTIGATIONS

Informed consent must be obtained and the patient should be

fasted for at least 4 h prior to the procedure. To facilitate probe

insertion, the throat is locally anaesthetized and intravenous

sedation given as required. Monitoring of the ECG, oxygen

saturation and blood pressure is required throughout the proce-

dure and beyond that if sedation has been administered.

MEDICINE 38:7 373

Indications for TOE are listed in Table 3. TOE is frequently

required to exclude a cardiac source of embolism or endocarditis.

The left atrial appendage and left atrium are common sites of

thrombi, particularly with mitral stenosis and atrial fibrillation,

and are well visualized by TOE. In patients with a high clinical

suspicion of endocarditis and negative transthoracic study, TOE


Contraindications for transoesophageal echocardiography

Absolute Oesophageal or pharyngeal obstruction or trauma

Gastrointestinal bleeding

Instability of cervical vertebrae

Uncooperative patient

Relative Oesophageal varices or diverticula

Cervical arthritis

Oropharyngeal distortion

Bleeding diathesis or overanticoagulation

Table 2

INVESTIGATIONS

allows smaller vegetations (1e2 mm) to be seen. TOE also has an

important role in assessing mitral valve disease to guide inter-

vention (valvuloplasty) and surgery (mitral valve repair versus

replacement). Finally, it allows assessment of the ascending

aorta, arch and descending aorta in cases of suspected dissection

and aneurysm.

Stress echocardiography

Stress echocardiography allows identification of patients with

significant coronary artery disease with high sensitivity and

specificity. Diagnostic accuracy is higher compared to conven-

tional exercise stress testing and similar to radionuclide stress

perfusion imaging.9 Stress can be achieved either by physical

exercise (treadmill or bicycle) or pharmacologically with dobut-

amine. Regional wall motion (thickening and excursion) is

assessed at rest and during stress. New regional wall motion

abnormalities or worsening of pre-existing ones suggest revers-

ible ischaemia indicating flow-limiting narrowing of coronary

Clinical situations where transoesophageal echocardi-ography is most appropriate (in general only after priortransthoracic echocardiography)6

Cardiac source of embolism (thrombus, tumour, PFO)

Infective endocarditis

C small vegetations (1e2 mm)

C complications (abscess, valve perforation)

Aortic pathology (dissection, aneurysm, atheroma)

Mitral valve disease

C to determine suitability for balloon valvuloplasty in mitral

stenosis or repair in regurgitation

Prosthetic valve evaluation (particularly mitral valve prosthesis)

Septal defects (particularly ASD and PFO)

Intra- and perioperative monitoring

Congenital heart disease

Guidance of percutaneous (non-coronary) cardiac interventions

Note: this is a comprehensive but not exhaustive list. PFO, patent foramen

ovale; ASD, atrial septal defect.

Table 3

MEDICINE 38:7 374

arteries. Thus, stress echocardiography not only reveals signifi-

cant coronary artery disease but can also identify the affected

coronary territory and guide intervention.

As inotropic stress is required for both exercise and dobut-

amine stress echo, beta-blockers must be omitted 48e72 h before

the stress test in order to achieve significant stress and to

improve sensitivity.

Furthermore, stress echocardiography is used to determine if

there is viable myocardium after myocardial infarction, which

would potentially benefit from revascularization.

Contrast echocardiography

Use of contrast in echocardiography can improve image quality

markedly and allow detection of concealed abnormalities.

The simplest form of contrast can be produced manually by

agitating saline between two syringes connected to a three-way

tap. The air bubbles produced opacify the right side of the

heart but are too large to pass through the pulmonary capillaries.

Thus, any bubbles appearing on the left side of the heart indicate

a shunt, usually an atrial septal defect (ASD) or a patent foramen

ovale (PFO). Bubble contrast TTE is frequently used after

a stroke or transient ischaemic attack (TIA) since a PFO may

represent a gateway for emboli from the venous system to the

brain. However, this test should only be requested if PFO closure

is to be considered (Figure 4).

Commercially produced contrast agents are available and

consist of high-molecular weight gas filled microbubbles

approximately the size of red blood cells which are therefore able

to cross the pulmonary capillaries. These enhance endocardial

border definition of both ventricles and can reveal intraventric-

ular thrombus and apical hypertrophy. Furthermore, trans-

pulmonary contrast agents are widely used in stress

echocardiography when image quality is suboptimal or to assess

myocardial perfusion.10e12

Figure 4 Bubble contrast echo showing a patent foramen ovale. The

presence of bubbles in the left side of the heart is indicative of a right-left

shunt.


Figure 5 3D transoesophageal echocardiography image of a mechanical mitral valve prosthesis. Clearly visible is the ring of the prosthesis and the two

tilting disks in the middle (arrow). The * indicates a thrombus which prevents one disk from closing completely.

INVESTIGATIONS

Three-dimensional echocardiography

Real-time three-dimensional echocardiography has evolved

markedly over the last few years and is used increasingly in daily

clinical practice. It is of particular benefit in the assessment of left

ventricular global and regional function and is helpful in deter-

mining aetiology of valvular disease (especially of the complex

mitral valve) (Figure 5).13,14 With the advent of new trans-

catheter-based interventions, such as percutaneous ASD-/PFO-

closure and percutaneous valve procedures, 3D TOE guidance is

increasingly required.15 Further applications (e.g. 3D stress

echocardiography, right ventricular and atrial assessment) are

still used predominantly for research only but with further

technological advances they may soon find their way into clinical

practice. A

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