Functional echocardiography fECHO refers to a bedside, limited assessment of the ductus arteriosus, myocardial performance and pulmonary or systemic haemodynamics that is brief in nature and addresses a specific clinical question or management dilemma. This point-of-care ultrasonography is increasingly used internationally and locally among neonatal units to assist with management of neonatal haemodynamic conditions. This article intends to explain the modality, its indications, interpretation and implications for management, and how it impacts long-term outcomes, particularly in chronic lung disease for premature infants born before 32 weeks of gestation. This review will focus on fECHO as a clinical tool to assess the haemodynamics of sick neonates and how it assists in the logical choice for cardiovascular support. Training should be approached as a combined effort between the paediatric cardiology service and neonatology service. Functional echocardiography fECHO refers to a bedside, limited assessment of the ductus arteriosus DA , myocardial performance, and pulmonary or systemic haemodynamics; it is brief in nature and addresses a specific clinical question or management dilemma.
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The aim of this introductory review is to discuss four key elements of NPE. Indications for scanning are summarized to give the neonatologist with echocardiography skills a clear scope of practice. The fundamental physics of ultrasound are explained to allow for image optimization and avoid erroneous conclusions from artifacts.
To ensure patient safety during echocardiography recommendations are given to prevent cardiorespiratory instability, hypothermia, infection, and skin lesions. A structured approach to echocardiography, with the same standard views acquired in the same sequence at each scan, is suggested in order to ensure that the neonatologist confirms normal structural anatomy or acquires the necessary images for a pediatric cardiologist to do so when reviewing the scan.
Clinicians have been utilizing echocardiographic techniques in the neonatal intensive care unit NICU since the s 1 and there has been a significant increase in the application of this technology in the last decade. Indications for scanning : These have been suggested in a number of different consensus statements, 4 , 5 , 6 and will be reviewed here to provide an introduction to the judicious application of NPE.
Physics of ultrasound : An awareness of ultrasound physics is essential to understand the limitations of the technique and to avoid being misled by common image artifacts. Patient safety during echocardiography : An area that, particularly when considering cardiorespiratory stability and infection control, cannot be taken lightly.
Routine echocardiographic views : These views form the basis for both confirming normal structural anatomy and assessing hemodynamic status. The principal indications for NPE are discussed below.
Any child in whom structural congenital heart disease is suspected should have appropriate referrals made and appropriate therapy initiated, as would be the case based on clinical suspicion alone. As the level of experience of the neonatologist performing the scan, and the availability of a pediatric cardiologist will be variable, different centers will adopt different approaches to confirm normal structural anatomy.
In this review we focus on the acquisition of routine standard echocardiographic views to support an approach for the clinicians performing NPE to confirm normal structural anatomy, with timely review of the study by a pediatric cardiologist. Having accepted the need for confirmation of normal structural anatomy with the first assessments, the most common indications for NPE are discussed below.
There is general consensus that treatment should be based on an estimate of the hemodynamic significance of the patent ductus. Differentiating persistent pulmonary hypertension PPHN from cyanotic congenital heart disease is clinically challenging, and an early echocardiogram to confirm the diagnosis allows the clinical team to focus entirely on optimal PPHN management without retaining doubts over a structural lesion. NPE may have a role in confirming correct positioning of both umbilical and peripherally inserted central lines in the newborn.
Some centers also opt to use NPE to identify line-associated thrombus. This rare, but potentially catastrophic, complication is often associated with intracardiac placement of an indwelling line. Rapid identification of pericardial effusion in an acutely unwell newborn can allow therapeutic pericardiocentesis, which again can be guided by ultrasound. In our experience novice scanners are often intimidated by the need to understand the principles of physics when learning ultrasound.
However, it is vital that the user of the ultrasound machine understands the basics of how images are obtained and reconstructed so as to appreciate the limitations of the technology and understand common artifacts. In this section, we provide an overview of imaging physics and refer the reader to more comprehensive texts for additional detail.
Velocity in turn depends on the physical characteristics of the medium and can be calculated by applying the following formula:. In the imaging setting, ultrasound waves are generated by transducers equipped with piezoelectric crystals.
These crystals change shape when electric currents are applied through them, and similarly, they generate electric signals upon mechanical compression. Applying rapid alternating current to the crystals generates vibration and ultrasound emission. The combined durations of the transmission and receiver phases is the pulse repetition period; a shallower depth allows for a shortened receiver phase and therefore a shorter pulse repetition period and a higher frame rate Fig.
Pulse duration and pulse repetition period. Adapted from Rovner A. The principle of ultrasound—ECHOpedia Ultrasound probes are available in a variety of types of array. In echocardiography, a phased array transducer is generally used because of its small footprint, allowing imaging through small intercostal windows. Phased array probes can be steered and focused to further optimize imaging.
Some vascular applications favor a linear array for maximal spatial resolution. Interactions between emitted ultrasound waves and tissues are what produce the images. These interactions may be of different types, an awareness of which is key to understanding common image artifacts Fig.
Ultrasound and tissue interactions. The amount of reflection depends on the difference in the acoustic properties of the two tissues, specifically the acoustic impedance, which is mainly a product of tissue density. It is the significant difference between density of soft tissue and air that prevents ultrasound being able to image through overlying lung or pneumothorax. The magnitude of returning reflection is also influenced by the angle between the tissue border and the ultrasound beam.
Maximal reflection is obtained when tissue border is orthogonal to the ultrasound beam. A clear demonstration of this property is in imaging the membranous intraventricular septum from the four-chamber view see below when the false impression of a septal defect can be made since there is so little reflection from a structure that is almost in line with the ultrasound beam.
Hence, the ventricular septum should be interrogated from a subcostal or parasternal view, where the septum is orthogonal to the beam. Scattering : When an ultrasound beam meets a boundary consisting of small structures smaller than the wavelength of the sound , the ultrasound beam is scattered. This results in reflection of the beam to all directions and a disorganized returning signal. Most of the signal is lost due to the scattering in multiple directions.
Nonetheless, backscattering plays an important role in generating the eventual two-dimensional 2D image and most organs have a characteristic scatter signature owing to their specific structures.
Hyperechoic bright regions within an organ usually represent increased scattering. Refraction : Refraction refers to the bending of the ultrasound beam when it enters a medium where its propagation speed is different as is seen when looking at an object below the surface of water.
The degree of bending depends on the angle between the beam and the surface angle of insonation , and the degree of difference in propagation speeds between tissues. Refraction artifact may cause objects to appear in altered locations.
Attenuation : As ultrasound travels within tissues, part of the energy is lost to absorption and scattering. This results in weaker signal intensity from structures that are farther from the probe. The higher the frequency, the greater the attenuation, and therefore the lower the penetration. Absorption and cavitation : Absorption of ultrasound by human tissues is the process of energy loss by conversion to heat.
Cavitation occurs when microbubbles are formed due to high-energy ultrasound interaction. All clinical ultrasound systems work within carefully controlled energy settings, such as those set by the US Food and Drugs Administration, 19 and ultrasound imaging is not considered to have any biologic ill effects.
Since all imaging introduces energy into the body, imaging power and duration of scans should be kept to a minimum. In B mode Brightness mode a 2D image is produced which is a representation of an anatomic slice of tissue. In M mode Motion mode , one dedicated scan line is used to detect rapidly moving structures. This form of imaging provides the highest temporal and spatial resolution.
Harmonic imaging is applied in echocardiography to resolve the potential influence of tissue resonance on image quality. An ultrasound wave that penetrates the body will lead to resonance of tissue. The frequency of this resonance is characteristically a multiple of the initial transmitted frequency.
Since these harmonic frequencies are also being reflected in tissue, they contribute to the creation of the two-dimensional picture.
In harmonic imaging, all harmonic frequencies are filtered, except for the second harmonic component of the original signal, resulting in a higher resolution and fewer artifacts.
Harmonic imaging is widely used in adult echocardiography, as it results in better signal-to-noise ratio. As it has poorer axial resolution, it is not widely applied in newborns.
Resolution of ultrasound imaging includes both spatial and temporal resolution. Spatial resolution is further divided into axial, lateral, and elevational resolution. Axial resolution is the ability to differentiate structures that are aligned along the imaging beam Fig. Axial resolution is determined by spatial pulse length SPL , which is the product of wavelength and the number of cycles in one pulse. The lower the SPL, the higher the resolution.
Increasing the frequency decreases the wavelength, therefore yielding better resolution. Typical axial resolution is 0. Axial left panel and lateral right panel resolution. See text for details. Lateral resolution is the ability to discriminate objects located in an axis perpendicular to the ultrasound beam Fig. The major determinant of lateral resolution is beam width. Focusing the transmitted beam by applying the electric current to the individual piezoelectric crystals with time delay decreases the width of the beam at the focal point, thereby improving lateral resolution.
The focus position can be set by the operator and is one of the key steps in image optimization. Multiple focal points yield more homogenously distributed lateral resolution in the 2D image, but comes at the expense of a decrease in frame rate. Lateral resolution is best at shallow depths and narrow beams and worse with deeper imaging and wide beams. Frame rate depends on the time taken to create a single image line, and the number of lines that form each image. Frame rate can therefore be improved by decreasing the imaging depth, narrowing the image sector width, zooming into an area of interest, reducing the number of focus points, or decreasing the line density of the sector.
In pursuit of an accurate representation of anatomy, the ultrasound machine makes a number of assumptions about sound propagation in tissue. Artifacts are errors in image production and are normally caused by physical processes that affect the ultrasound beam. Recognizing imaging artifacts is of great importance to prevent misinterpretation of echocardiograms. A key principle of all imaging is a constant awareness of the possibility of image artifacts.
Artifacts can often be recognized by altering the image plane, depth, or frequency. Any unusual object should be viewed from multiple directions to ensure that it is anatomic rather than artifactual.
Reverberation artifacts are generated by strong reflectors, such as the ribs or pericardium, when waves do not travel directly to and from a tissue but have additional reflections within the tissue Fig.
Introduction to neonatologist-performed echocardiography
The use of echocardiography for the evaluation of the cardiovascular well-being of term and preterm infants is gaining significant interest. The aim of echocardiography in this setting is to provide hemodynamic information in real time in order to support bedside clinical decision making 1 , 2 , 3. This approach is perceived to enhance clinical judgment, provide a better understanding of active physiological processes, and monitor the response to treatment. Combination of clinical examination and bedside echocardiography has been shown to facilitate clinical decision making 4.
Echocardiography for the Neonatologist
Metrics details. Neonatologist performed echocardiography NPE has increasingly been used to assess the hemodynamic status in neonates. We conducted an on-line survey from June to September Structural echocardiography is frequently performed by neonatologists. Institutional protocols for NPE are lacking. There is an urgent need of a formal training process and accreditation to standardize the use of NPE.