Pediatric Echocardiography - Research Paper Example

Abstract Pediatric echocardiography is one of the technologies that has gained momentum in the recent times. A few decades ago, evaluation and management of cardiac diseases in children was mainly based on clinical clues, ECG and Chest X-ray. Thereafter, 2D echocardiography dominated the scenario and became the main tool of evaluation of cardiac diseases in children. Due to the complexity in the mechanics, anatomy and physiology of the heart, exact diagnosis of the cardiac condition is critical for management of cardiac disease. In pediatric age group, the spectra of cardiac diseases are wide and also complex and hence arises the need for reliable investigating tool. Further advances in this technology a couple of decades ago have led to more reliable and accurate forms of echocardiography, the 3D imaging, Doppler echocardiography and tissue Doppler. These advances have posed a challenge to echocardiographers who need to be on their tiptoes in acquiring knowledge and also maintaining their skills by keep abreast with latest technology and changes. In this article, pediatric echocardiography will be discussed with references to its uses, limitations, impact on the professionals, impact on the patients, feasibility and accessibility. Introduction Creating images of the heart using ultrasonic waves is known as echocardiography. The images of the heart are created using 2-dimensional, 3-dimensional or doppler ultrasound. The test is routinely used in a clinical set up for screening, diagnosis and management of various diseases of the heart. In the current medical era, echocardiography has become the primary imaging tool for the evaluation, diagnosis, assessment and management of congenital and acquired cardiac disease in newborns, infants, children and adolescents. The most ideal tool for assessment of cardiac problems is transthoracic echocardiography (Mertens et al, 2008). The procedure is portable, efficacious and noninvasive and provides detailed overview of the various anatomical, physiologic, and hemodynamic information of the heart. The various types of echocardiogram currently used are 2D echocardiogram, pediatric transesophageal echocardiogram, fetal echocardiogram, stress echocardiogram and intraoperative transesophageal echocardiogram (Mertens et al, 2008). Pediatric echocardiography is unique when compared to adult echocardiography. There is a wide spectrum of diseases. Many of the cardiac conditions encountered are congenital. Certain additional views are added for better imaging like right parasternal view, subxiphoid view and suprasternal notch view. Distraction tools and sedation may be necessary for complete and proper evaluation. Over several decades pediatric echocardiography has evolved and advanced. Despite that, the technology has some limitations which also merits importance (Mertens et al, 2008). In this article, various attributes of pediatric echocardiography will be discussed. The impact of pediatric echocardiography on patient Until 4 decades ago, physicians could only vaguely ascertain the anatomy and function of heart based on clinical examination, auscultation, ECG and chest X-ray. Several revolutions in technology have changed the practice of pediatric cardiology, one of which is noninvasive imaging techniques. In 1980s, several advances in echocardiography, changed the face of pediatric cardiology (Mertens et al, 2008). Prior to that, cardiac catheterisation and angiography were the main techniques to evaluate the function of the heart. Calculation of intracardiac shunts and direct measurement of pressures was possible with the procedures. The main disadvantage with them was they were invasive procedures and associated with some risks. Another disadvantage with them was exposure to radiation. Cardiac ultrasound or pediatric echocardiography, on the other hand is a noninvasive technique that allows assessment of the anatomy, evaluation of the function of the valves, ventricular diastolic function and ventricular systolic function. Initially the 2D echocardiography was used which focused mainly on the cardiac anatomy. Based on this, several congenital lesions were defined in detail and this contributed to better diagnosis, treatment and eventually good outcome for the patients. Development of doppler techniques led to visualization and quantification of velocities of the blood pool inside the heart and this enhanced the accuracy of diagnosis of heart disease in children. Thus, pediatric echocardiography, replaced cardiac catheterisation to a large extent. Several congenital lesions in the heart like ventricular septal defects, atrial septal defects, Fallot's tetrology, transposition of great arteries and arterial trunks are made based on pediatric echocardiography (Mertens et al, 2008). In the neonatal intensive care unit, echocardiography has made striking impact in the management of babies even without congenital cardiac disease. Sick babies are evaluated for persistent pulmonary hypertension and patent ductus arteriosus and administration of fluids and oxygen are adjusted according to this. The commonly used route for echocardiography is transthoracic echocardiography. Of recent interest is the transesophageal echocardiography which further enhances the diagnostic value of echocardiography and assists in monitoring various interventional and surgical techniques related to heart. Introduction of perioperative transesophageal echocardiography has improved surgical outcomes in congenital heart disease (Mertens et al, 2008). According to Randolph et al (2002), peri-operative transesophageal echocardiography increases surgical outcomes by atleast 14 percent. According to the authors, this technique can refine the preoperative diagnosis and evaluation of immediate results in the postoperative period after cardiopulmonary bypass can be done in the operating room itself before the patient is shifted to intensive care unit. This technique also has made it possible for device closure of ventricular septal defects and atrial septal defects in the "cath lab". One major limitation with transesophageal probes is that they are large in size and hence cannot be used in children less than 3 kg. This is an important limitation factor because more and more babies less than 3 kg are undergoing cardiac surgeries in the recent era due to early diagnosis and management. Indications for echocardiography in pediatric age group It is very important to possess the knowledge of indications for echocardiography for obtaining appropriate information necessary for the diagnosis and management of the pediatric patient. Children with established heart disease need frequent cardiac evaluation with the help of echocardiography in order to ascertain the progression or evolution of the disease and determine appropriate interventions in a timely manner. Serial studies may be recommended based on the cardiac problem, to evaluate and monitor the function of the valve, the growth of various cardiovascular structures, function of the ventricles and potential sequelae following medical or surgical intervention (Mertens et al, 2008). The patients may present with a wide range of clinical features like failure to thrive, cyanosis, exercise induced syncope or chest pain, congestive heart failure, murmurs or cardiomegaly. There are various categories into which children with cardiac anomalies can fall into. They include right-to-left shunts, left-to-right shunts, regurgitant lesions, obstructive lesions, conotruncal anomalies, etc. Cardiac disease may also be a part of syndrome like in Down's syndrome. Echocardiogram in children is also an essential tool for evaluation of acquired heart diseases like rheumatic fever, infective endocarditis, systemic lupus erythematosus, myocarditis and Kawasaki disease. Echocardiography is also recommended in newly diagnosed systemic hypertension and non-cardiac conditions like pulmonary hypertension, thromboembolic events, sepsis, indwelling catheters, sepsis and superior venacava syndrome. In children with arrhythmias, echocardiography is the best evaluation tool and has implications for patient management (Mertens et al, 2008). Instrumentation in pediatric echocardiography The ultrasound instrument must possess hardware and software suitable for pediatric imaging. The transducers must be able to scan through wide range of depths in children. Both high frequency and low frequency transducers must be available. Multifrequency transducers are now available (Mertens et al, 2008). Continuous wave doppler transducer is another requirement (Mertens et al, 2008). Along with these, the videoscreen and display of appropriate size suitable for observation must be available. The display must be such that it identifies the parent institution, has a patient identifier and also the date and time of study. The data must be recorded and stored in such a way that the moving images can be played again. It should not be stored only as static images. It is important to allow sufficient time for each study based on the type of procedure. For a transthoracic echocardiography, the approximate time required is 45- 60 minutes. In complicated cases, more time may be required. The study must be performed in a darkened room with the patient lying preferably in semireclined position (Mertens et al, 2008). The environment must be comfortable. Non-cooperative small children may be sedated. Privacy and comfort of the patient must be maintained. Before starting the procedure, the sonographic gel must be warmed to body temperature. While performing studies on preschool children appropriate distracting strategies must be taken like keeping toys in the room, games movies or television. Every child must be accompanied by a parent or a guardian except in issues related to privacy. Some children may need sedation and appropriate protocols for the same must be written. The protocols must include the type of sedatives, appropriate doses for age, weight and surface area and appropriate monitoring during and after the examination. Each laboratory must be prepared to handle medical emergencies in children. 3-D echocardiography Since the advent of imaging technology over 5 decades ago, drastic changes have been occurring in the technology every decade (Mertens et al, 2008). In 2D ultrasound technology alone, many improvements have occurred with reference to resolution, image quality, range of indications and availability. However, several limitations with 2D technology reduced the scope of its applications when compared to CT scanning and MR imaging. The most important limitation with 2D scanning is the dependence of the radiologist on non-continuous series of representative sections of the internal organs to depict the anatomy. Other limitations include fixed imaging plane, lack of quantitative documentation of spatial relationship and irrational volume measurements because of reliance on 2-dimensional geometrical model, rather than 3-dimensional model. These limitations are overcome by 3D scanning technology (Lazebnik and Desser, 2007). The conventional scanning method that is commonly used for medical and obstetric purposes is 2-D scanning in which the sound waves are sent straight down and the reflected sound waves are used for image construction (Lazebnik and Desser, 2007). In 3-D scanning, the sound waves are sent in different angles and a sophisticated computer program is used to reconstruct a 3-dimensional volume image using the reflected echoes, thus allowing one to gauge not only the height and width of the organs but also the depth. Thus 3D ultrasound is also known as volumetric ultrasound. However, no movement is shown in the images (Lazebnik and Desser, 2007). 3D technology has several advantages. The sonographer is able to scan the region of interest using volume transducer with a single sweep itself, unlike 2D ultrasound. The sonographer does not need to acquire series of multiple images and thus the scanning time is drastically reduced. Thus this technology is easily applied from cranial ultrasound of neonates because images can be taken in a sweep and the patient does not have to be sedated. The volumes of 3D ultrasound can be processed even after acquisition as in CT imaging to obtain different views and also to ascertain troubleshoots questions. Another major advantage of post processing is teleradiology, because the reader already has all the necessary information of the volume that is scanned and thus remote interpretation is possible. 3D technology allows quantification of the volume of the plaque and direct visualization of arterial atherosclerosis. According to a study by Landry, Spence and Fenster (2005), carotid plaque volume and characterization can be successfully quantified using 3D technology. Some studies have also used 3D technology for aortic artery plaque characterization. Addition of color doppler to 3D ultrasound helps in the evaluation and grading of stenotic lesions and flow dynamics. Since 3D technology allows reformation of volumetric data in order to visualize flow in a plane parallel to the vessel that is interrogated, the inter-observer variability is very low and it is a big advantage in the field of cardiovascular studies. Since the contraction motion of the heart is basically 3 dimensional, 3D imaging of heart has several advantages (Mertens, 2008). It is a well known fact that the anatomy of heart is a complex 3D structure and reconstruction with 2D images is actually difficult (Mertens et al, 2008). Hence it was logical to develop 3D imaging, although it was a difficult step. Initially, 3D reconstruction was done based on ECG-gated 2D images that were obtained after the probes were rotated on the chest of the patients. This procedure was not only time-consuming but also cumbersome. The probes were large and they could not be applied for small children. Real time 3D imaging with echocardiography became feasible technically only after the advent of matrix probes which have the ability to process ultrasound beams that is transmitted in different directions into the tissues. There are more than 2000 elements in these probes and hence scanning can occur at the same time in different planes (Mertens et al, 2008). These probes help in acquisition of full volumetric datasets which can be rotated and sliced rapidly in any direction needed for analysis and evaluation of cardiac anatomy. Since quantitative measurements are also possible, it is possible to measure volumes, surfaces, orifices and shapes. Such spacial information facilitates in the assessment of congenital heart disease. There is immense research in this regard for assessment of ventricular septal defects, atrial septal defects, atrioventricular septal defects. Mechanism of valvular regurgitation is being assessed with the help of 3D color doppler imaging and this had made it possible for detailed assessment in the preoperative stage. Recently, high frequency 3D transducers have been introduced which are useful in spacial resolution even in very small infants. Thus detailed 3D imaging can be done even in very small infants (Mertens, 2008). Tissue doppler echocardiography Tissue doppler echocardiography is one of the recent developments in pediatric echocardiography. At any given point of time during the contractile cycle, the myocardium is moving and through this technique, myocardial velocities at any given point of time can be recorded. This makes it possible to assess regional myocardial function. This technique can be applied in different congenital lesions and it has been possible to evaluate systolic and diastolic function better. Normal values of these functions have been established even in pediatric age group and these values change with age (Mertens, 2008). In hypertrophic cardiomyopathy, which is common in children born to mothers with gestational diabetes, tissue doppler echocardiography is useful to prognosticate. These patients have decreased velocities of systolic and diastolic myocardium. One important aspect to note at this juncture is that velocity of any myocardial segment is influenced by global cardiac motion within the thorax and is influenced by the pulling and tethering by surrounding segments. Hence, the usefulness of regional myocardial velocities is limited. This limitation can be overcome by using measurement of regional deformation with the help of imaging of strain and strain rate. Quantification of deformation of regional myocardium using these techniques is possible by looking into velocity gradients within the myocardium. While strain rate "measures the rate of deformation of a myocardial segment", strain measures the local percentage of deformation within the same segment. With the help of this technology, quantification of regional myocardial function has been possible in different pediatric age groups. Thus, it has been possible to quantify function of the right ventricle in babies with tetralogy of fallot and also after the Senning procedure. In those receiving anthracyclines, in those with Duchenne muscular dystrophy and in hypertrophic cardiomyopathy, this technique helps in detecting myocardial dysfunction at subclinical levels also. Further research is needed to establish a relationship between geometry, loading and deformation. For this to happen, a combination of myocardial imaging, 3D technology and computational modelling of the mechanics of the heart is necessary (Mertens, 2008). Limitations The past 50 years have seen tremendous improvements in the technology of echocardiography and despite that, new challenges keep posing every now and then. One such challenges is using 2D ECHO to evaluate structures which are moving in 3-dimension. It is very difficult for the echocardiographer to reconstruct the different anatomic structures of the heart in 3D view. Lots of training and expertise is needed in this regard. Thus came up the need for real-time 3D echocardiography. Another limitation is that most of the studies with respect to echocardiography have been done with reference to adult hearts, especially the left ventricular function evaluation and hence this cannot be applied to the complex physiology of congenital heart disease. Assessment of systolic and diastolic functions in children is further difficult and complex because of complex geometrical equations and variable volume and pressure loading conditions. Infact, in many situations, evaluation of cardiac function is done by "eyeballing" technique that is subjective. Another major disadvantage with echocardiography is that is became difficult to evaluate extracardiac structures like peripheral and central pulmonary arteries, aortic arch with cervical vessels, systemic veins and pulmonary veins (Zoghbi, 2003).. These structures can be imaged using computed tomography or magnetic resonance imaging. Several new developments in echocardiography have occurred which are attempting to address these issues. These include 3D echocardiography, intracardiac echocardiography and tissue doppler echocardiography. Another limitation that merits importance at this juncture is that echocardiography is mainly a technique that is dependent on the operator and extensive training is mandatory for good outcomes. Despite introduction of high frequency 3D transducer beams, due to which spacial resolution is possible even in small babies, time resolution continues to be poor and there is scope for further improvement in the handling of volumetric datasets. 3D ultrasound is also associated with several limitations. Fundamentally, it is not different from 2D ultrasound. Since acoustic impedance differences, the actual source of contrast is identical, contrast limitations still apply. The user interfaces of 3D ultrasound are complex and infact quite challenging to master. It is also difficult to determine image orientation because of lack of standardized display convention. Interpretation of common artifacts is difficult and at the same time, 3D scanning introduces new artifacts because of lack of standardized view (Lazebnik and Desser, 2007). Transducers of ultrasound are mobile and small when compared to those of computed tomography and magnetic resonance imaging. It is because of these properties that ultrasound can be used for viewing any part of the body in every position. However, one major limitation in this application is the small field of view, especially when high resolution linear arrays are used. the field of view excludes many identifiable landmarks. This limitation makes ultrasound a much inferior technology when compared to CT Scan or MRI. Impact of pediatric echocardiography on the profession Echocardiography of acquired and congenital pediatric cardiac disease is dependent on the operator and requires high levels of interpretive and technical skills. The echocardiographer needs to undergo specialized training for the assessment of various cardiovascular malformations so as to determine and recommend various treatment options and also to assess possible outcomes after interventions. Training and maintenance of competence after training is a challenge in pediatric cardiology. There are few established training programs in this field and the size of the programs is also small (Zoghbi, 2003).. Echocardiography is very useful to evaluate the condition of the heart and understand the various dynamics and mechanics of the disease. One good example is valvular regurgitation. Echocardiography helps in the evaluation of various valvular structures of the heart and also the impact of volume overload on different chambers of the heart (Zoghbi, 2003). It is possible to readily assess vegetations, calcifications, tethering and flail motion of the various chambers of the heart which in turn give indirect information about the severity of regurgitation. It is important to note that vegetations, calcifications and prolapse do not necessarily mean that the patient has regurgitation. But a flail leaflet is a definite indicator of regurgitation. In this regard, there is evidence that transesophageal echocardiography improves visualization of the structure of the valves and causes delineation of the severity and mechanism of regurgitation. Regurgitation leads to certain changes in the chambers and this depends on the duration and severity of the regurgitation. While chronic regurgitation is associated with hypertrophy of the chambers of the heart and increase in the size of the heart, these changes are not seen in acute causes of regurgitation like endocarditis. Progression of the impact of regurgitation on the mechanics of the heart can be evaluated serially by echocardiography (Zoghbi, 2003). When doppler echocardiography is used for evaluation of regurgitation, certain indices can be used to ascertain the severity of regurgitation. Color doppler helps in the visualization of the origin of the jet of regurgitaion, the width of the jet, spacial orientation of the jet and flow convergence. These components help in enhancing the accuracy of evaluation of regurgitation. The temporal resolution and size of the jet are basically influenced by the frequency of the transducer and the settings of the instrument like output power, gain, size of the image sector and its depth. Thus, it is very important for the echocardiographer to possess full knowledge of these aspects during interpretation of the mechanics and dynamics of the heart for accurate image interpretation and optimal image acquisition (Zoghbi, 2003). Conclusion Pediatric echocardiography is an important tool in the evaluation, monitoring and management of cardiac diseases in children. The technology is gaining momentum and evolving every decade. The latest is 3D imaging with color and tissue Doppler. The complexity of imaging and evolving technology makes is crucial for the echocardiographer to be well trained and be abreast with latest knowledge. Though is it the hallmark tool for cardiac evaluation in children it is fraught with several limitations and more research is warranted in this regard. References Lai, W.W., Geva, T., Shirali, G.S., et al. (2006). Guidelines and standards for performance of pediatric echocardiogram: a report from the taskforce of the pediatric council of the American Society of Echocardiography. J Am Sov Echocardiogr, 19, 1413- 1430. Landry, A., Spence, J.D., Fenster, A. (2005). Quantification of carotid plaque volume measurements using 3D ultrasound imaging. Ultrasound Med Biol., 31(6), 751-762 Lazebnik, R.S., and Desser, T.S. (2007). Clinical 3D ultrasound imaging: beyond obstetrical applications. Diagnostic Imaging: Continuing Medical Education, 1-6. Mertens, L., Ganame, J., Eyskens, B. (2008). What is new in pediatric cardiac imaging? Eur J Pediatr. 2008 January; 167(1): 1–8. Randolph GR, Hagler DJ, Connolly HM, Dearani JA, Puga FJ, Danielson GK, Abel MD, Pankratz VS, O’Leary PW (2002) Intraoperative transesophageal echocardiography during surgery for congenital heart defects. J Thorac Cardiovasc Surg., 124, 1176–1182 Zoghbi, WA, Enriquenz, SE, Foster, A.et al. (2003). American Society of Echocardiography: recommendations for evaluation of the severity of native valvular regurgitation with two-dimensional and Doppler echocardiography. European Society of Cardiology, 4(4), 237- 261 Read More