Cross-sectional echocardiography: Physical principles, anatomic planes, limitations and pitfalls

Although M mode echocardiography has achieved a prominent role in the diagnosis and management of patients with cardiovascular disease, the limited area of view afforded by M mode techniques has restricted the application of ultrasound in many areas. The development of two dimenslonal echocardiography has obviated many of the limitations inherent in the narrow view of the M mode technique. It has enabled imaging of the heart from additional transducer locations, permitted determination of shape and anatomy and provided the ability to determine motion along two axes. Several types of two dimensional echocardiographs have been developed, and each type offers both advantages and disadvantages. Although two dimensional echocardiography has provided a larger area of view with ultrasound, it has also introduced new limitations including a larger and bulkier transducer, a much reduced sampling rate and a difficult display medium (videotape). In addition, new considerations regarding ultrasonic resolution have been raised. Two dimensional techniques have resulted in new pitfalls in ultrasonic diagnosis related to instrument artifacts as well as to performance and interpretation of the examination. The spurious appearance of cardiac masses because of these ultrasonic artifacts represents a particularly prominent diagnostic pitfall that must be avoided in daily practice. It is anticipated that the new wider field of view provided by two dimensional echocardiography combined with a Standard high resolution capability of ultrasound (2 to 4 mm) will result in an increasingly large role for echocardiography in the management of patients with heart disease.     

Assessment of echocardiography in clinical practice

Echocardiography should be viewed as a technique that can be very useful in certain specific situations. It is important for the clinician to know which patients can profit most from this examination. Because the technique is apparently harmless, there will be an obvious tendency to use echocardiography to screen all patients with heart disease or suspected heart disease. Such an approach would be improper. The referring physician should have a specific reason for obtaining each examination. The cost of the test is not insignificant, and with the development of newer, more expensive echocardiographic equipment, future costs will probably be even higher. Thus, indiscriminate use of any diagnostic examination, including echocardiography, should be avoided.The echocardiographic examination should also be considered as evolving. Improvements are constantly being made, and the current examination is certainly not perfected. There are many technical details involved in doing this examination. This fact is the basis for the problem in training people to provide echocardiographic services. Although the examination may be reasonably harmless and painless for the patient, the technique is by no means simple. Because of the intricacies of the examination, the subtleties of the interpretation, and the knowledge explosion in the field, an increasing amount of training and experience is necessary to perform and interpret echocardiograms.Despite its many problems and limitations, the popularity of echocardiography testifies to the fact that this tool can be extremely helpful in many patients. This examination can provide information which is most difficult to obtain in any other manner. Unlike many other noninvasive cardiologic tests that provide graphic recordings of physical findings, echocardiography gives information that cannot be obtained at the bedside. In some respects, the use of ultrasound to examine the heart is more natural than any other imaging technique that relies on the interpretation of radiographic or isotopic shadows or silhouettes. Echocardiography is not dissimilar to sonar used by several animals, such as bats and dolphins. Anyone who has seen these animals use their sonar must be impressed with the fact that ultrasound can be very effective in sensing one's environment. Although we will probably never approach the skill with which these animals use ultrasound, there will undoubtedly be important improvements and advances in echocardiographic technology. Thus, from all indications, echocardiography should play an increasingly important role as a diagnostic tool in cardiology.     

Personalized echocardiography: clinical applications of advanced echocardiography and future directions

Future cardiology practice will be increasingly individualized, and thus to maintain its central role, echocardiography must keep pushing to expand the boundaries of real-time data acquisition from tissue and fluid motion, and yet still provide efficient and timely data analysis that leads to succinct, clear clinical recommendations tailored to each person in our care. In this article, recent efforts to expand echocardiography techniques into an era of increasingly personalized cardiology, including advances in color-coded tissue Doppler, 3D echocardiography and complex exercise stress echocardiography are described. The common metric for success in each of these efforts is the development of robust and institutionally supportable echocardiography protocols for specific cardiology disease populations that currently may be underdiagnosed and/or undertreated. The common result in each case should be the creation of new guidelines that can supplement the current standard protocols advocated by professional echocardiography organizations.     

Exercise echocardiography: a clinically practical addition in the evaluation of coronary artery disease

There has been only modest clinical interest in exercise echocardiography because of the technical limitations of the procedure. Recognizing that there have been recent technical advances in the echocardiographic instruments and that echocardiography should, in theory, be an ideal technique for evaluating exercise-induced wall motion abnormalities, a clinically practical method of performing exercise echocardiograms was developed. By obtaining the echocardiograms immediately after treadmill exercise, with the patient sitting at the treadmill, a high percent of studies adequate for interpretation was obtained (92%). The addition of echocardiography to the treadmill exercise test significantly enhanced the diagnostic yield. In addition, in cases of one and three vessel disease, exercise echocardiography identified stenosis in specific coronary arteries. In patients with two vessel disease and left circumflex obstruction, specific vessel identification was less reliable. A high percent of patients with multivessel disease developed wall motion abnormalities with exercise that persisted for at least 30 minutes. It is concluded that echocardiography performed immediately after exercise with the new generation of echocardiographs can be a practical and useful clinical tool.     

Real-time three-dimensional echocardiography for improved evaluation of diastolic function using volume-time curves

BACKGROUND: Accurate assessment of left ventricular function is of the greatest importance in clinical cardiology for decision making. Diastolic dysfunction is getting more concern as a cause of heart failure while, currently used non-invasive modalities for diagnosing diastolic abnormalities have significant limitations. Dynamic left ventricular volume change was applied for the evaluation of diastolic function by various techniques that have been demonstrated to be of diagnostic value. However, it has not been accepted into clinical practice because existing techniques are either invasive, inaccurate, expensive or time consuming. REAL-TIME THREE-DIMENSIONAL ECHOCARDIOGRAPHY: Real-time three-dimensional (3-D) echocardiography is a new ultrasound technique that provides transthoracic volumetric images of the heart in real time. Thereby, the acquired images are ideally suited for the assessment of dynamic left ventricular volume change. Generation and analysis of left ventricular volume-time curves by real-time 3-D echocardiography has been demonstrated to be feasible in normal subjects and patients and accuracy of volume-time curves was good compared to magnetic resonance imaging. We compare the new real-time 3-D echo approach with the advantages and limitations of existing noninvasive and invasive techniques.     

The hand-carried echocardiographic device as an aid to the physical examination

Physical examination skills have been declining over the past several decades while technology has made diagnostic testing increasingly sophisticated. For patients with cardiovascular disease, the best approach to bedside diagnosis would be one that combines both physical examination and ready access to technology at the time of the patient encounter. Most cardiac testing is not performed at the bedside due to equipment size and time limitations for these tests. Small hand-carried echocardiographic devices are now available for rapid bedside examination. These devices compare well to full-featured systems when used in cardiology outpatient settings and in hospitalized patients who are not critically ill. Compared with physical examination by board certified cardiologists, these devices decrease diagnostic error. Early use of hand-carried echocardiographic devices after physical examination has been demonstrated to impact patient triage and treatment as well as uncover otherwise undetected cardiac disease. The degree of training required for responsible use of these devices is as yet unclear. However, organized training sessions have resulted in modest agreement with standard echocardiography and point-of-care echocardiography performed by expert echocardiographers. It is conceivable that the hand-carried echocardiographic devices will be used in medical school curriculum to enhance medical student education in the future.     

Pulmonary venous flow as assessed by Doppler echocardiography: potential clinical applications

During the past few years Doppler assessment of pulmonary venous flow has gained increasing interest. The growing experience with the use of transesophageal echocardiography, the approach that nearly always yields registrations adequate for quantitative analysis, has markedly contributed in this respect. The Doppler-derived pulmonary venous flow pattern can be regarded as a measure of left atrial inflow and it augments the clinical significance of Doppler transmitral flow in the evaluation of diastolic left ventricular function. This article summarizes physiological background, possible applications, and limitations of Doppler echocardiography of pulmonary venous flow in clinical cardiology.     

Bringing the heart into focus: a perspective on non-invasive cardiac imaging

Non-invasive cardiac imaging is already a cornerstone of cardiac diagnostics and will play an increasingly important role also in preventive and therapeutic cardiology. Several modalities can be used (echocardiography, nuclear, CT, CMR) and there is a need to study the respective role of these techniques in clinical practice and to anticipate on developments in the near future.     

Stress echocardiography: an overview.

Stress echocardiography has come a long way in the past ten to twelve years since it first began. There have been many procedural and technical advances. The results being obtained by those laboratories with active programs are very gratifying. Stress echocardiography is proving to be particularly valuable in women and in evaluating coronary angioplasty. Although the comparison between stress echocardiography and stress nuclear cardiology is actively being debated, the available data would suggest that the results are grossly comparable. There are certain subsets of patients which may be identified where one technique might excel over the other. The most important factor is undoubtedly the competence of the laboratory performing the test. A high quality nuclear study is clearly going to be better than a poor quality echocardiogram and vice versa. However, assuming a high degree of competence in either technique, stress echocardiography has many obvious practical advantages. There is no reperfusion necessary so that the patient does not have to return in four hours. There is no radiation involved. And the results are available immediately after the examination. For all of these reasons it is not surprising that stress echocardiography is gaining in popularity and should play an increasingly important role in the management of patients with coronary artery disease.     

Regional strain and strain rate measurements by cardiac ultrasound: principles, implementation and limitations.

The non-invasive quantification of regional myocardial function is an important goal in clinical cardiology. Myocardial thickening/thinning indices is one method of attempting to define regional myocardial function. A new ultrasonic method of quantifying regional deformation has been introduced based on the principles of 'strain' and 'strain rate' imaging. These new imaging modes introduce concepts derived from mechanical engineering which most echocardiographers are not familiar with. In order to maximally exploit these new techniques, an understanding of what they measure is indispensable. This paper will define each of these modalities in terms of physical principles and will give an introduction to the principles of data acquisition and processing required to implement ultrasonic strain and strain rate imaging. In addition, the current status of development of the technique and its limitations will be discussed, together with examples of potential clinical applications.     

Tricuspid regurgitation: noninvasive techniques for determining causes and severity

Tricuspid regurgitation is often not apparent on physical examination and several methods are now available to aid in this difficult assessment. Cardiac catheterization using right ventriculography, previously considered the diagnostic standard, has several limitations. Currently available noninvasive tools such as M-mode and two-dimensional echocardiography (with or without contrast), Doppler techniques and even radionuclide cardiologic imaging have added significantly to the precise assessment of the presence and severity of tricuspid regurgitation. This review examines the comparative use and limitations of these various techniques.     

State of the art: new developments in cardiac imaging

Cardiac imaging continues to reveal new anatomical and functional insights into heart disease. In echocardiography, both transesophageal and transthoracic three-dimensional imaging have been fully developed and optimized, and the value of the techniques that have increased our understanding of cardiac mechanics and ventricular function is well established. At the same time, the healthcare industry has released new devices onto the market which, although they are easier to use, have limitations that restrict their use for routine assessment. Tomography's diagnostic and prognostic value in coronary artery disease continues to increase while radiation exposure becomes progressively lower. With cardiac magnetic resonance imaging, myocardial injury and recovery in ischemic heart disease and following acute coronary syndrome can be monitored in exquisite detail. The emergence of new combined tomographic and gamma camera techniques, exclusively developed for nuclear cardiology, have improved the quality of investigations and reduced radiation exposure. The hybrid or fusion images produced by combining different techniques, such as nuclear cardiology techniques and tomography, promise an exciting future.     

A case of congenital cardiomyopathy with acute heart failure

A 45-year-old woman was admitted to our cardiology department for palpitations and dyspnoea. She had previously been investigated by echocardiography several times, resulting in a diagnosis of hypertrophic cardiomyopathy. However, a congenitally corrected transposition of the great arteries was diagnosed by our echocardiographic examination. The patient underwent electrophysiological evaluation and the accessory pathway was successfully ablated by applying radiofrequency pulses. This case report identifies that in patients with congenitally corrected transposition of the great arteries the primary diagnosis by echocardiography can sometimes be missed and that these patients are increasingly liable to develop Congestive Heart Failure with advancing age. In order to avoid diagnostic mistakes, more widespread dissemination of information about this congenital heart defect is essential.     

Comparison of exercise echocardiography with myocardial perfusion scintigraphy for the diagnosis of coronary artery disease.

The rationale of exercise echocardiography for the diagnosis of coronary artery disease is based on the detection of exercise-induced wall motion abnormalities by ultrasound. Some of the problems that had previously limited the widespread application of the test have been solved by the development of digital recording and side by side cine loop display of two-dimensional echocardiograms: thus, respiratory artifacts can be eliminated, the examination is faster, and the comparison between rest and stress images has become practical and reliable improving sensitivity. The sensitivity and specificity of exercise echocardiography vary from 70 to 100%, according to patient selection, the protocol, and the gold standard used. Few studies studied the value of exercise echocardiography as compared to the more established nuclear cardiology imaging. Data from these comparative evaluations show a strong correlation between the two techniques for identifying and localizing myocardial ischemia. With good equipment and after proper training, exercise echocardiography can provide both diagnostic and prognostic information for routine clinical care.     

Perioperative ultrasonic imaging in cardiac surgery

The use of ultrasonic imaging in patients undergoing cardiac surgery continues to grow. Recent data have substantiated the utility of intraoperative transesophageal echocardiography in the patient with mitral valve disease. This technique has become the procedure of choice for the on-line assessment of the degree of mitral regurgitation before and after cardiopulmonary bypass. Transesophageal echocardiography is being more widely used for the detection of regional wall motion abnormalities intraoperatively because recent data suggest that hemodynamic parameters may be insensitive for the detection of ischemic events. In the evaluation of patients with congenital heart disease and suspected aortic dissection, transesophageal echocardiography is becoming increasingly important. Newer applications of ultrasonic techniques include contrast echocardiography for evaluating myocardial perfusion and intraoperative evaluation of the ascending aorta for detecting atherosclerosis, which may be a source of atheroembolism. Ultrasonic imaging has become invaluable in the treatment of patients undergoing cardiac surgery.     

The value of contrast in stress echocardiography

Stress echocardiography is a well validated method of diagnosing myocardial ischaemia and viability. Its limitations are also well known, related to a subjective interpretation and lack of reproducibility. One of the solutions suggested to improve its diagnostic performance is the use of ultrasonic contrast agents which presents many advantages. In difficult patients, the left ventricular chamber may be opacified, both at rest and at peak effort with a significant improvement in the detection of the endocardial contour and in the reproducibility of the interpretation of the images. The diagnostic performance of stress echocardiography with contrast is less dependent on the conditions of observation. In addition, recent technical advances enable the same ultrasonic contrast agents to be used for the study of myocardial perfusion. The first clinical studies using these techniques report the feasibility of simultaneous analysis of wall motion abnormalities and myocardial perfusion on exercise. Further progress is expected to facilitate the interpretation and quantification of these investigations which should further increase the diagnostic value of stress echocardiography.     

Prediction of Intracardiac Pressures and Assessment of Ventricular Function with Doppler Echocardiography

Doppler echocardiography has had a profound influence on the clinical practice of cardiology. With the use of the modified Bernoulli equation, Doppler echocardiography provides a noninvasive technique for calculating intracardiac pressures. Compared to invasive measurements, the Doppler estimates of intracardiac pressures are accurate and reproducible. By the evaluation of intracardiac blood flow, Doppler echocardiography provides a technique for the evaluation of ventricular performance that is independent of ventricular geometry. This application of the Doppler technique is in its infancy and much investigative work is needed to correlate the invasive and noninvasive measurements of ventricular function and to determine the effect of factors such as heart rate, loading conditions, and cardiac drugs on the Doppler indexes of function. In the future, it is very likely that Doppler color flow mapping techniques will provide additional information on ventricular emptying and filling patterns that will be important in the noninvasive assessment of cardiac function.     

Situación actual: lo nuevo en técnicas de imagen cardiaca

Cardiac imaging continues to reveal new anatomical and functional insights into heart disease. In echocardiography, both transesophageal and transthoracic three-dimensional imaging have been fully developed and optimized, and the value of the techniques that have increased our understanding of cardiac mechanics and ventricular function is well established. At the same time, the healthcare industry has released new devices onto the market which, although they are easier to use, have limitations that restrict their use for routine assessment. Tomography's diagnostic and prognostic value in coronary artery disease continues to increase while radiation exposure becomes progressively lower. With cardiac magnetic resonance imaging, myocardial injury and recovery in ischemic heart disease and following acute coronary syndrome can be monitored in exquisite detail. The emergence of new combined tomographic and gamma camera techniques, exclusively developed for nuclear cardiology, have improved the quality of investigations and reduced radiation exposure. The hybrid or fusion images produced by combining different techniques, such as nuclear cardiology techniques and tomography, promise an exciting future.