Echocardiography

Echocardiography is a method of obtaining an image of the structure and movements of the heart using ultrasound (inaudible, high frequency sound waves).

Why is it done?

Echocardiography is a diagnostic technique that is used to detect structural, and some functional, abnormalities of the heart wall, heart chambers, heart valves, and large coronary arteries. The procedure is also used to diagnose congenital heart disease, heart valve disease, endocarditis, cardiomyopathy (heart muscle disorders), aneurysms (ballooning of the heart or blood vessel walls), pericarditis (inflammation of the membrane that surrounds the heart), and blood clots in the heart.

How is it done?

Echocardiography is harmless and causes no discomfort. A transducer (an instrument that sends out and receives sound signals) is placed on the patient’s chest, or an ultrasound probe is passed into the oesophagus using a flexible endoscope (viewing tube). Ultrasound waves are reflected differently by each part of the heart, resulting in a complex series of echoes. These are viewed on a screen and may be recorded, or the results can be printed out.

Developments

Developments such as multiple moving transducers and computer analysis have helped to provide clear anatomical pictures of the heart. Doppler echocardiography is used to measure the velocity (speed) of blood flow through the heart. It allows for the assessment of structural abnormalities such as a mitral valve prolapse and septal defects.

Echocardiography in detail - technical

Topics covered:

  • Essentials
  • History of echocardiography
  • Principles of echocardiography
  • Transthoracic echocardiography
  • Transoesophageal echocardiography
  • Stress echocardiography Intracardiac echocardiography
  • 3D echocardiography
  • Portable echocardiography
  • Further reading

Essentials

Ease of use, rapid data provision, portability, and safety mean that echocardiography has become the principal investigation for a variety of cardiac conditions. A modern, transthoracic echocardiography examination combines real-time two-dimensional imaging of the myocardium and valves with information about velocity and direction of blood flow obtained by Doppler and colour flow mapping. A complete examination can be performed in most patients in less than 30 min.

Valvular heart disease—echocardiography has revolutionized the diagnosis and follow-up of patients with these conditions. Serial cardiac catheterization to assess severity and progress of valvular stenosis has been almost completely superseded by Doppler echocardiography, and the role of invasive investigation is increasingly limited to the assessment of the coronary arteries prior to revascularization.

Transoesophageal echocardiography—this is now a routine investigation in many centres. Under sedation, an ultrasound probe is passed into the oesophagus to a position behind the heart, producing excellent resolution of cardiac structures. It is used diagnostically in many emergency situations, including aortic dissection and suspected prosthetic mechanical valve dysfunction, and as an additional method of monitoring cardiac performance during cardiac and noncardiac surgery.

Other technological developments—these include (1) stress echocardiography—used to detect occult coronary disease and predict cardiac risk; (2) use of contrast agents—these improve visualization of the endocardium in patients with poor acoustic windows and allow some estimation of myocardial perfusion; and (3) real-time three-dimensional imaging—this is available on most new machines and allows detailed assessment of myocardial and valvular function.

History of echocardiography

In 1842, Christian Doppler noted that the pitch of a sound wave varied if the source of sound was moving. His mathematical formulae are still in use today, and his discovery coined the name of the eponymous technique. Ultrasound was developed in 1880 by applying an electric charge to a crystal. In 1912, the British engineer Richardson identified that sound waves could be used to detect underwater objects, leading to the development of sonar. In 1929, the Soviet scientist Sergei Sokolov developed a technique using ultrasound to identify flaws in metal components of ships and tanks. This technology then remained of military interest until after the Second World War, when medical applications of ultrasound were discovered.

Carl Herz and Inge Edler from Sweden are credited with the origins of clinical echocardiography. Their development of the cardiac ‘supersonic reflectoscope’, in 1954, allowed the movements of the posterior heart wall to be seen for the first time. The A-mode and M-mode techniques were subsequently refined and used to detect mitral stenosis, pericardial effusions, left atrial tumours, and aortic stenosis. Meanwhile, a Japanese group started to use Doppler techniques to examine the functioning of the heart.

In the 1960s, multielement scanners allowed the development of two-dimensional (2D) echocardiography, and when it was realized in the 1970s that Doppler could be used to determine pressure gradients across valves, echocardiography took off as an important clinical investigation. Transoesophageal echocardiography and stress echocardiography were subsequently developed in the late 1970s.

Further refinement of these echocardiography techniques has occurred over the last 30 years. Miniaturization of the transducers now permits intracardiac and intracoronary ultrasound. Transpulmonary contrast agents are allowing myocardial perfusion to be examined. Tissue Doppler imaging, tissue tracking, and spectral Doppler are providing more detailed analysis of myocardial function. Real-time three-dimensional (3D) echocardiography is now becoming a standard feature on modern equipment, and echocardiography is now able to determine pressures in all cardiac chambers, precisely measure cardiac function, and accurately assess valvular disease, making the days of invasive assessment obsolete.

Principles of echocardiography

The transducer used for most echocardiographic examinations contains piezoelectric crystals that emit ultrasound frequencies of 2.5 to 5 MHz. Most of the sound energy is scattered or absorbed, but reflection occurs at interfaces between tissues of different acoustic impedance (e.g. between blood and muscle). The transducer collects these reflections and the time delay between emission and reception is calculated. This allows the depth of the reflection to be derived and its position to be displayed on a screen as a dot (pixel). The brightness of the dot is related to the magnitude of the reflected signal. In general, higher-frequency transducers allow better discrimination between structures, but the increased attenuation leads to reduced penetration.

There are three main echocardiographic techniques: 2D (cross-sectional), M-mode, and Doppler.

2D echocardiography (cross-sectional)

Cross-sectional images are constructed as the ultrasound beam sweeps across the heart in a sector. Between 50 and 100 cross-sections are presented each second, giving the impression of a moving picture. These images are readily interpretable by an observer with knowledge of cardiac anatomy, and this technique is the cornerstone of modern echocardiography.

M-mode echocardiography

M-mode echocardiography preceded modern 2D imaging. Unlike 2D imaging, which uses a series of sweeps across the heart, M-mode uses a single static beam of very frequent ultrasound pulses. The narrow beam is analogous to a vertical mineshaft passing through various layers of rock. Displayed in real time, this results in reflections from cardiac structures being displayed as horizontal lines, with superficial structures at the top of the screen and the deeper structures at the bottom. These data are interpretable when one knows which structure each line represents. The technique has excellent spatial resolution; hence, with the advent of 2D echocardiography and Doppler, M-mode is now principally used for measurement of cardiac chamber dimensions and observation of the relative movement of cardiac structures to each other, e.g. the relationship of the anterior leaflet of the mitral valve to the septum in hypertrophic cardiomyopathy.

Doppler echocardiography

The Doppler principle allows the velocity and direction of movement of an object (or moving blood in the case of cardiac ultrasonography) to be calculated from the shift in the frequency of a reflected waveform relative to the observer. Cardiac imaging employs pulsed-wave, continuous-wave, and colour-Doppler techniques. Pulsed-wave Doppler allows information about flow to be obtained from a particular point within the heart. The range of detectable velocities is limited, and the technique is used for sampling normal and low velocities, e.g. mitral valve flow. Continuous-wave Doppler identifies the peak velocity encountered along the ultrasound beam and is particularly valuable for measuring high-velocity jets, e.g. as seen in aortic valve disease. It is important to remember that failure to align the transducer exactly parallel to flow results in measurement of artefactually low velocities and potentially an underestimation of valvular stenosis.

Colour Doppler allows a dynamic representation of the direction and velocity of flow to be superimposed onto a 2D image of the heart. Velocities towards the transducer are usually coded in red and velocities away in blue. Turbulent and high-velocity flow produces variable velocities and results in a mosaic pattern that is ideal for characterization of regurgitant lesions. This technique is now so sensitive that it can detect trivial regurgitation during the closure of many normal heart valves.

Transthoracic echocardiography

Imaging is usually performed with dedicated echocardiography equipment with the patient lying on their left hip in the left lateral position and with their left arm behind their head. Ultrasound cannot travel through bone and thus cardiac imaging is performed via intercostal spaces to the left of the sternum and at the apex of the heart in the axillary line. These ‘echo windows’ provide standard views described as the parasternal short and long axis and apical two-, four-, and five-chamber views. Useful additional views can also be obtained from the subcostal and suprasternal approach in some patients. A standard echocardiography examination involves 2D imaging from the parasternal, apical, and subcostal approaches supported by M-mode measurements, continuous, pulsed, and colour Doppler.

Valvular heart disease

Transthoracic echocardiography is the investigation of choice for patients with suspected valvular heart disease. All four cardiac valves can be visualized and interrogated by Doppler and 2D echocardiography. Concomitant abnormalities in ventricular performance can be assessed simultaneously.

Aortic stenosis

2D echocardiography can usually image the aortic valve cusps; if they are thin and freely mobile, it is unlikely that there is significant aortic stenosis. However, if the valve cusps are thickened and calcified, interrogation by continuous-wave Doppler is mandatory. The severity of aortic stenosis is usually expressed as the peak pressure difference (or gradient) across the valve, and is calculated from the maximum flow velocity (V) using the modified Bernoulli equation (pressure gradient = 4V2). In patients with normal left ventricular systolic function, a peak gradient measured by Doppler of over 65 mmHg or a mean gradient of over 40 mmHg suggests significant aortic stenosis.

When chronic critical outflow obstruction results in declining left ventricular function and reduced cardiac output, the gradient produced by any degree of valve obstruction also falls. Doubt about the severity of the stenosis can usually be resolved by calculating the valve area using the continuity equation, which uses data from Doppler and 2D echocardiography. In experienced hands this provides valuable additional information, but accurate measurement of the left ventricular outflow-tract diameter can be difficult and if the findings are not consistent with other data, the investigation should be either be repeated or the patient should be referred for cardiac catheterization. A valve area of less than 1 cm2 usually represents severe aortic stenosis.

Aortic regurgitation

Assessment of the mechanism and severity of aortic regurgitation requires a combination of all three echocardiography modalities. M-mode may demonstrate fluttering of the anterior leaflet of the mitral valve and, in the setting of acute, severe aortic regurgitation, may reveal premature closure of the mitral valve. 2D echocardiography will occasionally demonstrate prolapse of one more of the aortic cusps, but even severe aortic regurgitation can occur through an aortic valve that appears to be structurally normal.

The severity of aortic regurgitation can be estimated using continuous-wave and colour Doppler (see Chapter 16.14.1), although assessment can be difficult as it is influenced by left ventricular function. Doppler-derived pressure half-time and measurement of regurgitant fraction and/or flow convergence zone are valuable when there is uncertainty over lesion severity. M-mode and colour Doppler can be combined and, when the regurgitant jet fills more than 50% of the left ventricular outflow tract, the regurgitation is classified as severe.

In patients with severe asymptomatic aortic regurgitation, a serial increase in left ventricular dimensions or a progressive fall in ejection fraction are indications for surgery. However, any increase in ventricular dimension should be at least 0.5 cm before it is regarded as significant, given the limited reproducibility of echocardiographic parameters.

Mitral stenosis

Mitral valve stenosis is well visualized using either M-mode or cross-sectional echocardiography. Its severity can be determined by estimating the area of the valve orifice either by direct planimetry of the 2D short-axis image or from the Doppler pressure half-time (mitral valve area = 220/pressure half-time). A valve area of less than 1.0 cm2 usually indicates severe mitral stenosis. Transthoracic echocardiography is also used to assess the suitability of the mitral valve for balloon dilation, although transoesophageal imaging is necessary to exclude left atrial thrombus.

Mitral regurgitation

Transthoracic echocardiography will usually demonstrate the mechanism and severity of mitral regurgitation. 2D imaging identifies abnormalities of the valve leaflets and colour flow shows jet direction and area. Severe mitral regurgitation is suggested by increased left ventricular end-diastolic dimension and hyperdynamic wall motion due to volume overload. Precise quantification of the amount of regurgitation is demanding as it is influenced by left ventricular function, the direction of the jet, and left atrial size. Various algorithms have been devised to improve quantification of mitral regurgitation, including measurement of the flow convergence zone and the proximal isovelocity surface area (PISA) method, but most centres simply classify the extent of regurgitation as mild, moderate, or severe (Table 1).

Table 1 Classification of mitral regurgitation
  Mild Severe
Specific signs of severity
Vena contracta <0.3 cm >0.7 cm
Jet size <4 cm2 or <20% left atrium >40% left atrium
  Small and central Large and central or wall-impinging and swirling
PISA radius None/minimal (<0.4 cm) Large (>1 cm)
Pulmonary vein flow   Systolic reversal
Valve structure   Flail or rupture
Supportive signs of severity
Pulmonary vein flow Systolic dominant  
Mitral inflow A-wave dominant E-wave dominant (>1.2 m/s)
CW trace Soft and parabolic Dense and triangular
LV and LA Normal size LV if chronic MR Enlarged LV and LA if no other cause

CW, continuous wave; LA, left atrium; LV, left ventricle; PISA, proximal isovelocity surface area.

Pulmonary and tricuspid valve disease

In adults, 2D imaging of the pulmonary valve may be difficult, particularly if there is lung disease. Despite this, accurate Doppler information is usually obtainable. Tricuspid stenosis is very uncommon, but some degree of tricuspid regurgitation is detectable even in healthy individuals. Measurement of the peak velocity of tricuspid regurgitation (V) is valuable as, in the absence of pulmonary valve disease, it can be used to estimate pulmonary artery (PA) systolic pressure.

Prosthetic valves

Transthoracic echocardiography is commonly performed as part of the routine follow-up of prosthetic valves. It is usually able to assess biological valves accurately, but for mechanical mitral valve prostheses in particular, attenuation artefact produced by the metal may be problematic. Transoesophageal imaging is recommended when transthoracic imaging is suboptimal or if improved resolution is required, for example, in patients with suspected prosthetic valve endocarditis.

Abnormal left ventricular function

In most patients, a full transthoracic echocardiography study will confirm or refute a clinical suspicion of left ventricular dysfunction and identify the likely aetiology of any abnormality. Systolic and diastolic left ventricular function can be assessed and a variety of methods can be used to derive an estimate of left ventricular ejection fraction. In patients with ischaemic heart disease, assessment of regional wall motion is valuable and may occasionally demonstrate evidence of aneurysm formation. Left ventricular hypertrophy is detected by echocardiography and a measurement of left ventricular mass can also be derived. Echocardiography is recommended in suspected heart failure as patients can have a combination of impaired systolic and diastolic dysfunction. Transthoracic echocardiography may also detect intracardiac thrombus, particularly in patients with impaired systolic ventricular function.

Left ventricular hypertrophy

Minor concentric left ventricular hypertrophy is common in patients with hypertension. In hypertrophic cardiomyopathy, 2D imaging may demonstrate asymmetrical septal hypertrophy with disproportionate thickening of the interventricular septum compared with the left ventricular free wall, or dramatic concentric hypertrophy with left ventricular cavity obliteration. Other characteristic features of hypertrophic cardiomyopathy include systolic anterior motion of the mitral valve and partial midsystolic closure of the aortic valve, which usually correlates with the presence of outflow tract obstruction. In the absence of conditions that may induce ventricular hypertrophy, for example, aortic stenosis, these findings are diagnostic of hypertrophic cardiomyopathy. Colour Doppler can demonstrate turbulence in the outflow tract and continuous-wave Doppler may detect characteristic ‘dynamic’ gradients that increase in severity as systole progresses. Other associated echocardiographic abnormalities in hypertrophic cardiomyopathy include mitral regurgitation and severe diastolic dysfunction.

Atrial fibrillation

Most patients with atrial fibrillation should undergo echocardiography as it excludes a structural cause for atrial fibrillation (e.g. mitral stenosis) and facilitates thromboembolic risk stratification. It also allows measurement of left atrial dimensions, which is valuable as cardioversion is less likely to be successful when this is large. Identification of left ventricular hypertrophy can guide the choice of antiarrhythmic drug therapy. Transoesophageal echocardiography can be useful to facilitate cardioversion in patients with atrial fibrillation of unknown duration by excluding intracardiac thrombus, particularly in the left atrial appendage.

Following an embolic event or stroke

Echocardiography is the investigation of choice when a cardiac source of an embolus is suspected. It should be considered in all patients presenting with embolic occlusion of a peripheral artery, or thromboembolic episodes in more than one vascular territory. Echocardiography should not, however, be performed in circumstances when the result is unlikely to influence patient management. In patients with ischaemic stroke and a low likelihood of atheromatous arterial disease, an echocardiogram can be considered as, occasionally, it will detect occult abnormalities such as a cardiac thrombus or atrial myxoma. Contrast studies with Valsalva manoeuvre should be considered to exclude paradoxical embolism through a cardiac shunt from the right heart. In patients with a high clinical suspicion of a cardiac source of embolus, in whom transthoracic echocardiography is normal, transoesophageal echocardiography is recommended.

Pericardial disease

Echocardiography is not routinely indicated in patients with uncomplicated pericarditis. It can, however, diagnose the presence of pericardial fluid and is useful when a pericardial effusion is suspected and percutaneous drainage is being considered. Echocardiographic signs of pericardial tamponade include exaggerated respiratory variation in the mitral valve Doppler, presystolic closure of the aortic valve, and (particularly) right atrial and right ventricular diastolic collapse. Constrictive pericarditis is a difficult diagnosis to make using standard echocardiographic techniques. Patients may complain of episodic breathlessness and fluid retention, have characteristic abnormalities of the venous pressure, and have subtle abnormalities on mitral and tricuspid valve inflow Doppler patterns.

Pulmonary embolism

Echocardiography can be useful in patients with pulmonary embolism as it can demonstrate right ventricular dilation and/or impaired right ventricular systolic function. Tricuspid regurgitant velocity can be used to estimate pulmonary artery systolic pressure, although it is unusual for this to be more than 70 mmHg acutely. Exceptionally, 2D imaging may show a thrombus within the right heart or the proximal pulmonary arteries. Although echocardiography is diagnostically useful when it demonstrates features consistent with pulmonary embolism, it cannot exclude the diagnosis.

Infective endocarditis

Echocardiography cannot be used to exclude endocarditis but is valuable when endocarditis is suspected clinically while there is insufficient data to make a formal diagnosis. Under these circumstances, a typical vegetation detected by an experienced observer is regarded as a major criterion in the Duke diagnostic classification, and this may facilitate appropriate management. Transoesophageal echocardiography should be performed when there is a suspicion of aortic root abscess, if prosthetic endocarditis is suspected, or occasionally, in cases where there is persistent diagnostic doubt and the additional sensitivity and spatial resolution of echocardiography might be valuable.

Congenital heart disease

Echocardiography is the diagnostic modality of choice for patients with suspected congenital heart disease. Detailed transthoracic cardiac imaging is possible in cooperative infants and children, but occasionally sedation or a short anaesthetic may be required. Rates of cardiac catheterization have been reduced by miniaturization of transoesophageal probes that facilitate diagnosis and follow-up of complex congenital heart disease. Fetal echocardiography is performed when surveillance obstetric ultrasound is abnormal or in cases where previous history suggests a possible cardiac problem.

Transoesophageal echocardiography

Transoesophageal echocardiography is now available in many centres. The ultrasound probe is similar to the endoscope used for upper gastrointestinal investigation, except that there are no optical fibres. Transoesophageal echocardiography is an invasive procedure for which the patient’s written consent is (usually) required. After fasting for a minimum of 4 h, a local anaesthetic spray (10% lidocaine) is applied to the upper pharynx and the patient is usually sedated, typically with a short-acting intravenous benzodiazepine (e.g. midazolam 2 mg). The probe is manipulated into the oesophagus where its position behind the heart produces excellent resolution, particularly of posterior cardiac structures. Blood pressure and oxygen saturation are monitored throughout, and both resuscitation equipment and the benzodiazepine antagonist flumazenil should be readily available.

Even though transoesophageal echocardiography is commonly performed in high-risk, haemodynamically unstable patients, the rate of serious complications (aspiration and oesophageal rupture/tears) is less than 1%. Absolute contraindications to transoesophageal echocardiography include oesophageal tumours, strictures, diverticulae, and varices.

Who should have a transoesophageal echocardiogram?

The principal indications for transoesophageal echocardiography are listed in Bullet list 1. The principal advantages over transthoracic imaging are improved spatial resolution and the ability to image posterior structures such as the left atrium and descending aorta. It is valuable in a number of emergency situations, including suspected aortic dissection, prosthetic mechanical valve failure, and possible endocarditis. Transoesophageal echocardiography may be used to image the heart in patients in whom data from transthoracic imaging is unsatisfactory due to obesity, lung disease, or chest deformity. Other indications include screening for left atrial thrombus before cardioversion of atrial fibrillation, and monitoring cardiac performance during cardiac and some noncardiac surgery.

Bullet list 1 Principal indications for transoesophageal echocardiography

Valve disease
  • Mitral stenosis—to assess suitability for percutaneous balloon commisurotomy and exclude left atrial thrombus
  • Mitral regurgitation—to assess anatomy, severity and suitability for surgical repair
  • Prosthetic valves—particularly to assess prosthetic mitral regurgitation
Infective endocarditis
  • Possible aortic root abscess
  • Failure to respond to antibiotics, or recurrent fever in a patient with endocarditis
  • High clinical suspicion of endocarditis with no diagnostic abnormality on transthoracic imaging
  • Possible prosthetic valve endocarditis
Aortic disease
  • Possible acute aortic dissection
  • Follow-up of patients with known aortic pathology
  • Imaging aortic atheroma before surgery or patients with possible cholesterol embolization
Potential cardiac source of embolism
  • Before elective cardioversion of atrial fibrillation
  • Patients with valvular heart disease and a definite embolic episode despite anticoagulation
  • Patients with a definite embolic episode and a ‘normal heart’ on transthoracic imaging
Incomplete or impractical transthoracic imaging
  • Chest deformity or pulmonary disease
  • Patients undergoing mechanical ventilation
  • Congenital heart disease
  • Perioperative imaging of cardiac function and surgical procedures

Valve disease

Patients with mitral stenosis are at particular risk of thromboembolism, and transthoracic echocardiography has limited sensitivity for the detection of left atrial thrombus. Transoesophageal echocardiography is recommended in those patients with mitral stenosis if embolic events occur despite therapeutic anticoagulation, and may demonstrate spontaneous echocardiography contrast (smoke-like echoes produced by the interaction of erythrocytes and plasma proteins under conditions of stasis). This is an independent predictor of left atrial thrombus and cardiac thromboembolic events. Transoesophageal echocardiography is also used to assess anatomy and exclude left atrial thrombus before balloon valvuloplasty in patients with mitral stenosis and to assess anatomy, severity, and suitability for surgical repair in patients with mitral regurgitation. In patients with mitral prostheses, reverberation artefact overlying the left atrium limits the ability of transthoracic imaging to detect paraprosthetic regurgitation. Transoesophageal imaging provides excellent visualization of the left atrium and is particularly recommended under these circumstances.

Endocarditis

Characteristic vegetations or evidence of abscess formation identified by echocardiography are increasingly used as diagnostic criteria in patients with possible endocarditis. The excellent spatial resolution (<1 mm) of transoesophageal echocardiography makes it superior to transthoracic imaging for the detection of vegetations and its sensitivity may exceed 90%. Transoesophageal echocardiography should be considered when there is a high clinical suspicion of endocarditis but blood cultures are sterile and transthoracic imaging is not diagnostic, or under circumstances when the sensitivity of transthoracic imaging is particularly poor, for example prosthetic valves or calcific valvular disease. Transoesophageal echocardiography is also recommended if there is a possibility of aortic root abscess formation as this complication is not easily identified using transthoracic imaging and surgery may be required.

Aortic disease

Transthoracic imaging of the aorta is limited to the proximal aortic root and the arch in most patients. Using transoesophageal imaging, most of the ascending and the entire descending thoracic aorta can be visualized and image quality is improved. This is particularly useful in patients with suspected acute aortic dissection and, in many cases, it is the only imaging necessary before emergency surgery (see Chapter 16.14.1). Large, mobile, or pedunculated aortic atheromas in the descending aorta which can be associated with ischaemic stroke may be detected by transoesophageal echocardiography. Transoesophageal imaging of the aorta has also been recommended in suspected cases of cholesterol embolization and to assess thromboembolic risk prior to cardiac intervention or surgery.

Thromboembolism

In patients with thromboembolism, there has been extensive debate over the value of imaging with transoesophageal echocardiography. Clinical examination, electrocardiography, and transthoracic echocardiography provide sufficient information to determine optimal management in the majority. However, transoesophageal echocardiography is indicated when embolic events occur in anticoagulated patients with native or prosthetic valvular heart disease, especially if endocarditis is suspected, or when transthoracic images are inconclusive. In patients with unexplained or cryptogenic ischaemic stroke, wider use of transoesophageal echo has been advocated. Transthoracic echocardiography and exclusion of alternative pathologies such as thrombophilia and carotid stenoses should precede the transoesophageal examination, but under these circumstances minor cardiac structural abnormalities are more likely to be clinically relevant.

Transoesophageal echocardiography is superior to the transthoracic approach for imaging the interatrial septum for atrial septal aneurysm (a redundant bulge in the area of the fossa ovale, with respiratory movement >10 mm) and assessing patency of the foramen ovale. However, the clinical relevance of such atrial septal abnormalities can be questionable as the relationship to the thromboembolic event is commonly speculative. Currently, anticoagulation is the usual management following an otherwise unexplained, single, embolic event, but occasionally a percutaneous or surgical correction of the defect is recommended.

Stress echocardiography

Diagnosis of reversible ischaemic myocardial dysfunction is now possible using echocardiography. Imaging can be performed either during or immediately after exercise, but more commonly an intravenous infusion of dobutamine is used to mimic the cardiac response to exercise. Development of reversible systolic regional wall-motion abnormalities suggests coronary artery disease. Stress echocardiography also has an increasing role in risk stratification before general surgical procedures and in assessing myocardial viability before revascularization. The use of transpulmonary contrast agents reduces the number of inconclusive scans, allows more accurate assessment of left ventricular function, and allows some measure of myocardial perfusion to be made.

Intracardiac echocardiography

Miniaturization of echocardiography probes has led to the development of echocardiography from within the heart. Small, flexible catheters with ultrasound transducers can be manoeuvred within the heart to provide very-high-resolution images of intracardiac structures. This has been particularly useful during percutaneous closure of atrial septal defects and during radiofrequency ablation procedures.

3D echocardiography 

Real-time, 3D image acquisitions are now available on most high-end echocardiography machines. Some systems acquire a series of gated images to reconstruct the entire heart during a cardiac cycle. This image can then be manoeuvred and slices cut away to visualize the area of interest. Regional wall tracking can also allow a 3D model of left ventricular function to be acquired and provides an accurate assessment of left ventricular function as well as identifying areas of left ventricular dysynchrony.

Portable echocardiography

Echocardiography equipment increases in sophistication but also continues to miniaturize, and now there are several small portable machines available. These are increasingly available in emergency and intensive care departments. A hand-held ‘screening echocardiogram’ can be performed in a matter of seconds to exclude pericardial effusion, recognize left ventricular dysfunction, and diagnose most valvular abnormalities. This is proving extremely useful in the management of the critically ill. A more detailed echocardiogram examination can be performed if the screening scan is abnormal or inconclusive.

Further reading

 
 
Cheitlin MD, et al. (2003). ACC/AHA/ASE guideline update for the clinical application of echocardiography: summary article. Circulation, 108, 1146.
 
Feigenbaum H (2004). Feigenbaum’s echocardiography. Lea & Febiger, Philadephia.
 
Flachskampf FA, et al. (2001). Recommendations for performing transesophageal echocardiography. Euro J Echocardiol, 2, 8.
 
Leeson P, Becher H, Mitchell ARJ (2007). Echocardiography (Oxford specialist handbooks in cardiology). Oxford University Press, Oxford.

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