272 SECTION IV Pediatric Critical Care Cardiovascular Transesophageal Echocardiography Transesophageal echocardiography (TEE) involves placing a spe cialized TEE probe through the patient’s oropharynx[.]
272 S E C T I O N I V Pediatric Critical Care: Cardiovascular Transesophageal Echocardiography Transesophageal echocardiography (TEE) involves placing a specialized TEE probe through the patient’s oropharynx into the esophagus and stomach, allowing for superior visualization of intracardiac structures TEE is somewhat limited in the visualization of extracardiac structures such as the aortic arch, branch pulmonary arteries, and distal systemic and pulmonary veins TEE requires sedation Thus, when performed in the ICU, it requires assistance by the critical care or anesthesia team Sedation should be sufficient to provide appropriate analgesia and amnesia It should also keep the patient motionless for safety and better image quality Risks, in addition to sedation, include bleeding and injury to the oropharynx, teeth, esophagus, and stomach Common indications for a TEE in the ICU setting include poor transthoracic echocardiography image quality, endocarditis, and intracardiac thrombus in the setting of embolic phenomena or persistent atrial arrhythmias The identification of a vegetation on cardiac imaging is a major criterion in the modified Duke criteria for endocarditis.10 TEE is more sensitive than transthoracic echocardiography and is the gold standard for detecting vegetations.11,12 However, TEE can have limited sensitivity in some patients, necessitating additional imaging modalities.13 Periprocedural TEEs, such as those performed during congenital cardiac surgery, allow for procedural guidance and postoperative anatomic and functional assessment.14 In the pediatric cardiothoracic operating room, the postoperative TEE may be complemented by an epicardial echocardiogram This involves placing a transthoracic probe in a sterile sleeve that is then positioned directly onto the cardiac surface.15 Proper interpretation of periprocedural TEE and epicardial echocardiogram is critical to the postprocedural care of these patients Fetal Echocardiography Fetal echocardiography involves the evaluation of fetal cardiovascular anatomy and function These studies are performed by transabdominal imaging, although transvaginal studies can also be performed It would be unusual for a pediatric ICU patient to require a fetal echocardiogram, but the mother of a neonate in the pediatric ICU may have had a fetal echocardiogram during pregnancy (Fig 29.3) Therefore, the intensivist should be familiar with the interpretation of these results Currently, many patients with congenital heart disease have a prenatal diagnosis Fetal echocardiography has a 68% sensitivity for detecting congenital heart disease16; however, it has some limitations Standard postnatal congenital heart disease screening (physical examination and pulse oximeter) should be performed even in the patient with a normal fetal echocardiogram A prenatal diagnosis allows for proper planning leading up to the delivery and postnatal care Fetal echocardiography can also guide intrauterine therapies, such as transplacental pharmacologic treatment of fetal arrhythmias, fetal balloon atrial septostomy, and aortic balloon valvuloplasty.17–19 Fetal echocardiography has been shown to improve outcomes in some congenital heart disease populations.20 A proper fetal diagnosis can also alleviate unnecessary postnatal anxiety and inform decisions regarding safe maternal-infant bonding in the delivery room.21 Intracardiac Echocardiography Intracardiac echocardiography (ICE) involves the transvenous insertion of a specialized echocardiography probe into cardiac chambers This allows for detailed imaging with the probe in very close proximity to intracardiac structures The obvious risk of this approach is its invasive nature and need for transvenous access Because of this, ICE is predominantly performed in the cardiac catheterization laboratory where adequate transvenous access is already obtained In this setting, ICE can be used to guide the transvenous placement of intracardiac devices.22 ICE has limited application in the pediatric ICU setting; however, the intensivist caring for patients after cardiac catheterization should be familiar with this imaging modality and at least have a cursory understanding of its features Cross-Sectional Imaging Cross-sectional imaging modalities, such as cardiovascular magnetic resonance imaging (CMR) and cardiac computed tomography (CT), may be a useful adjunct to echocardiography in some pediatric ICU patients These modalities can provide important additional information, particularly when delineating extracardiac vascular structures Cardiac CT provides excellent spatial resolution, which is most useful in small patients and when imaging small structures, such as coronary arteries An additional advantage of cardiac CT is its short image acquisition (scanning) time Its disadvantages include lack of portability (stationary location), nephrotoxicity of intravenous iodinated contrast, and radiation exposure with subsequent increased malignancy risk.23 CMR offers the advantages of myocardial tissue characterization and is an excellent imaging modality in the evaluation of the pediatric patient with elevated troponins and possible myocarditis.24 CMR also allows for accurate quantification of ventricular volumes, which may be instrumental in the surgical planning of patients with hypoplastic ventricles25 or regurgitant valves.26 The use of CMR is limited by its long imaging time, need for sedation/anesthesia in younger patients, stationary location, limited use in patients with renal failure, and contraindications to metal support devices in the scanner Point-of-Care Ultrasound • Fig 29.3 Fetal echocardiogram of a fetus with a diagnosis of hypoplastic left heart syndrome RA, Right atrium; RV, right ventricle Point-of-care ultrasound (POCUS) represents a balance between quick access to simplified scanning technology involving the fewest people and the limitations imposed by potentially reduced machine functionality coupled with greater disease complexity Its CHAPTER 29 Echocardiographic Imaging applications range from assessment of cardiac function and intravascular volume status to evaluations of abdominal processes, pulmonary disease, bladder filling, and rapid trauma assessment Cardiac POCUS is now routinely used in critical care, emergency and hospital medicine, and veterinary practices along with the neonatal ICU environment, with the latter use often termed targeted neonatal echocardiography Training in cardiac POCUS has been advocated to begin in medical or allied health professions schools,27 with different approaches ranging from an extension of the physical examination to a limited diagnostic study in its own right Guidelines and standards for training and its use in adult patients have been published by echocardiography societies and other national organizations.28–30 The use of POCUS in children has paralleled its increased application in adults, including the recent publication of evidencebased guidelines for its use in critically ill children and infants.31 Several considerations are necessary for the expansion of cardiac POCUS use in pediatrics These include adapting scanning equipment designed primarily for adults to the different needs of children, such as higher-frequency transducers and more frequently displayed frame rates for faster heart rates, plus establishing additional training and appropriate usage criteria for children Not all accepted cardiac measurement techniques for adults have been fully validated in children or in the setting of congenital heart disease Consequently, the patient’s underlying status should drive the decision on whether the strengths of a fast cardiac POCUS assessment of ventricular function will benefit the patient (i.e., if the patient has a systemic left ventricle) or will be potentially confounded by abnormal anatomy and physiology (i.e., a patient with a single right ventricle and a Fontan, or cardiac malposition) Most importantly, any obtained images should be archived for comparison to guide future studies and for quality assurance Cardiac POCUS has been evaluated in the pediatric ICU and has been found to be sensitive for assessment of pericardial effusion and left ventricular size and function.32 However, benefits beyond these have not been proven Structural Congenital Heart Disease and Intracardiac Shunting Transthoracic echocardiography is the test of choice for accurately diagnosing most congenital heart disease in pediatric patients In the ICU setting, an initial limited echocardiographic evaluation can help guide therapy for new patients by showing obstruction to blood flow, assessing ventricular and valvar function, and demonstrating the source of both pulmonary and systemic blood flow This allows for a rapid assessment of the patient’s physiologic state and the need for therapies, such as a prostaglandin infusion for ductal patency or inotropic support After initial stabilization, performance of a complete echocardiogram is essential to evaluate the details of cardiovascular anatomy for surgical or other interventional planning The evaluation of cardiac shunting and blood flow is an essential component in the assessment of cardiovascular physiology At the atrial level, reversal of the normal left-to-right shunt is indicative of an elevation in right atrial pressure above left atrial pressure, which can be seen in situations such as tricuspid valve stenosis, right ventricular dysfunction, or pulmonary hypertension An elevation in the mean pressure gradient of an atrial shunt can be seen in single-ventricle patients with a restrictive atrial septum (Figs 29.4 and 29.5), hemodynamically significant mitral 273 • Fig 29.4 Color Doppler image of an atrial septal defect in a patient with hypoplastic left heart syndrome There is aliasing of color indicative of restrictive left-to-right flow • Fig 29.5 Spectral Doppler image of an atrial septal defect in a patient with hypoplastic left heart syndrome indicating a mean left-to-right gradient of 15 mm Hg or tricuspid stenosis with inadequate forward flow, or in cardiomyopathy with significantly elevated ventricular filling pressures Ventricular shunt direction can be used to evaluate the difference in ventricular pressures In the setting of unrepaired tetralogy of Fallot, the reversal of normal left-to-right ventricular shunt can be seen in the setting of a hypercyanotic spell caused by right ventricular outflow tract obstruction In the absence of aortic obstruction, the left ventricular systolic blood pressure is the same as the systemic systolic blood pressure Therefore, a ventricular shunt gradient can be used to estimate the right ventricular systolic pressure In patients with aortic or pulmonary obstruction, the direction of shunt in the ductus arteriosus can give an important clue as to the hemodynamic significance of the stenosis If there is inadequate forward aortic or pulmonary flow, then ductal flow is in the direction to augment that flow In the absence of left or right ventricular outflow tract obstruction, the direction and velocity of shunting across a restrictive patent ductus arteriosus can provide an estimate of pulmonary artery pressures Valve Anatomy and Function Assessment of valve function is an important part of the evaluation of cardiovascular physiology in the ICU 2D imaging of valve structure provides information about valve anatomy that is 274 S E C T I O N I V Pediatric Critical Care: Cardiovascular • Fig 29.6 Two-dimensional image of a vegetation on the underside of the pulmonary valve • Fig 29.7 Spectral Doppler of a pulmonary regurgitation jet with a measurement of the end-diastolic gradient important in surgical planning, determining the mechanisms for valve dysfunction, and evaluating for acquired diseases such as endocarditis (Fig 29.6) Color flow Doppler can show the location and size of regurgitation jets and flow turbulence in areas of abnormal flow, such as valve stenosis Spectral Doppler tracings allow for quantification of valve stenosis by measurement of peak and mean gradients across valves For measurement of peak gradients, the simplified Bernoulli equation (provided earlier) is used to accurately estimate pressure The mean pressure gradient is calculated from a tracing of the spectral Doppler velocity curve Atrioventricular valve regurgitation and stenosis are important factors in ventricular filling and function The evaluation of regurgitation is difficult, as there are no reliable quantifying measures in the congenital cardiac population, in which the valve anatomy is often abnormal and there are frequently multiple regurgitant jets Assessment of atrioventricular valve regurgitation is aided by looking at secondary changes, such as atrial enlargement and pulmonary or systemic vein flow reversal with ventricular systole Therefore, the best assessment of atrioventricular valve regurgitation is by the subjective judgment of a trained observer who can take into account all of these factors The peak atrioventricular valve spectral Doppler gradient is used to estimate systolic ventricular pressure by adding it to the directly measured or assumed associated atrial pressure This is used for the assessment of pulmonary ventricular or pulmonary artery hypertension The peak gradient of systemic atrioventricular valve regurgitation can also be used to estimate systemic ventricular pressure The mean gradient across an atrioventricular valve correlates well with direct measurements by cardiac catheterization, whereas the peak gradient is much less useful.33 Secondary findings with significant atrioventricular valve stenosis include atrial enlargement and systemic or pulmonary vein flow reversal with atrial systole Semilunar valve function directly affects the effective cardiac output to the pulmonary and systemic circulations Both semilunar valve stenosis and regurgitation affect myocardial oxygen demand by increasing the pressure and volume load, respectively, on the associated ventricle Regurgitation is best quantified by the width of the regurgitant jet, as the length of the jet and deceleration slope are affected by the pressure gradient across the valve and ventricular filling pressures In the setting of more severe regurgitation, secondary flow reversal is seen in the pulmonary arteries and descending or abdominal aorta The pulmonary regurgitation jet can be especially useful in the setting of pulmonary hypertension, as it allows measurement of the pulmonary artery end-diastolic • Fig 29.8 Spectral Doppler gradient of a left ventricular outflow tract with elevated velocity and peak and mean gradients pressure (Fig 29.7) The peak spectral Doppler gradient across the pulmonary valve correlates best with a direct peak-to-peak measurement by cardiac catheterization33 while the mean spectral Doppler gradient has a better correlation for the aortic valve (Fig 29.8).34 Ventricular Function Assessing Volume Status Any assessment of cardiac function must include an assessment of the loading conditions under which the heart is working Most simply, these are preload (the filling status of the heart) and afterload (the resistance against which the heart pumps) With almost no exception, every measurement of cardiac systolic or diastolic function is affected by one or the other (or both) of these loading conditions within the range of expected human physiology.35 Much has been written about the noninvasive assessment of volume status given the significance of right atrial pressures for right-sided hemodynamics and outcomes, and to guide decisions on fluid management.36 For instance, a child with a hypertrophied right ventricle that is stiff from cardiopulmonary bypass immediately after repair of tetralogy of Fallot may exhibit higher right atrial pressures with the amount of fluid needed to maintain right ventricular preload and cardiac output than a child with a CHAPTER 29 Echocardiographic Imaging surgically enlarged right atrium after heart transplantation performed with a biatrial anastomosis Knowing when preload and fluid state are excessive and diuretics are required is similarly useful, as in the setting of pulmonary hypertension For adult patients, several guidelines and recommendations are available that reasonably predict right atrial pressure from noninvasive measurements, particularly involving inferior vena caval size and changes with respiratory maneuvers.37–39 Other measurements have included spectral Doppler inflow velocities and patterns,38 tissue Doppler measurements,40,41 speckle tracking strain rates,41 and both 2D and 3D measurements of right atrial size.36 However, many of these measurements fail to achieve clinical utility when applied to critically ill adults with considerable overlap between fluid-responsive and non–fluid-responsive groups and poor interrater reliability This creates a clinical “gray zone” in which measurements are helpful at the extremes but not helpful to guide more nuanced management.39 All of these problems are exacerbated in the acute postcardiothoracic surgery setting40 and lose correlation in the setting of positive-pressure ventilation.42 The application of these techniques to children is even more problematic, especially in a critical care setting Confounders can range from the simple, such as how to standardize a “sniff” in a child to assess inferior vena cava collapsibility, to the more complex, such as the physiologic impact of one patient with an intracardiac shunt compared with a second child without any shunt Not surprisingly, conflicting data are reported in the literature These likely reflect the differences in compliance of varying structures such as the right atrium, liver/inferior vena cava, abdomen, and chest in the pediatric patient compared with the adult,43 among other reasons However, research in this area continues, with pediatric systemic venous and right atrial normograms now published,44 and simultaneous catheter-echo studies reported on the utility of advanced imaging techniques such as diastolic strain rate and the utility of the systolic:diastolic ratio.41 Assessing Diastolic Function The assessment of diastolic function is a natural extension of the assessment of volume status, as it incorporates the ventricular response to preload and filling, and atrial pressure reflects ventricular diastolic pressure This is a topic of great interest in adult and pediatric cardiology—in particular for the systemic ventricle (typically, the left ventricle)—both due to its greater challenge in measurement and the significant impact that abnormalities in left ventricular diastolic function may have on clinical outcomes.4,45 Right atrial pressure can be directly measured with relative ease through the placement of a central venous catheter In contrast, left atrial pressure can only be indirectly measured via a pulmonary capillary wedge pressure, which involves increased risk to the patient, or directly via transseptal puncture and placement of a catheter into the left atrium (a higher-risk procedure both in placement and opportunity for systemic embolization of air or thrombus) Direct measurement of the left ventricular diastolic pressure is even more complicated, requiring either prograde passage of a transseptal catheter across the mitral valve or retrograde passage of a catheter across the aortic valve All of these challenges make the noninvasive assessment of diastolic function more enticing and important In general, diastolic function can be affected by three different variables: impaired relaxation (early diastole), reduced restoring forces (recoil and untwisting), and decreased compliance/ increased chamber stiffness (late diastole) These are assessed using 275 multiple 2D, spectral Doppler, and tissue Doppler measurements Common measurements include the mitral valve E/A wave Doppler ratio, E/e9 ratio, E wave deceleration time, left atrial size, mitral valve A wave duration, and pulmonary vein atrial systolic (Ar) wave reversal duration.4 Diastolic function grades, in both normal and diseased states, have been published for use in adults4 and are commonly employed in adult echo labs worldwide However, as for volume status, these measurements are affected by cardiac rhythm, heart rate (which may fuse inflow Doppler waves), atrial anatomy, and need for precise positioning of the pulsed wave sample volume for spectral Doppler measurements The use of multiple measurements is specifically recommended over use of a single measurement, as is inclusion of the standard vital signs, 2D imaging data, and clinical context.4 The most recent guidelines state that these measurements “are not necessarily applicable to children or the perioperative setting.”4 This explicit caution about directly extrapolating adult diastolic guidelines to pediatrics has been proven reasonable in several publications One of the first, in 2013, applied published adult diastolic guidelines to children with varying forms of cardiomyopathy, all of whom would be reasonably expected to have abnormal diastolic function Use of the guidelines, however, failed to reliably distinguish diastolic function abnormalities between groups and demonstrated additionally poor interobserver agreement.46 Subsequent studies for the right ventricle and left ventricle have further demonstrated that, as compared with adults, children may not progress through the same stages of diastolic dysfunction and that early (impaired relaxation) and late (decreased compliance) abnormalities may overlap considerably in the same patient.41,47 Challenges in connecting abnormal diastolic measurements to outcomes are also present in the setting of congenital heart disease, particularly in Fontan patients.48,49 Reasons for this problematic extrapolation of adult guidelines to children are several, including maturational changes in the myocardium (age), loading conditions (affected by the variables discussed earlier under assessing volume status), ventricular geometry, atrioventricular valve function, and ventricular-ventricular interactions in addition to the standard confounders of heart rate and rhythm.47 Of these, maturational changes may be easily overlooked until one considers the fetus, which has classic evidence of diastolic dysfunction even in the healthy state due to the differences in loading conditions, pulmonary physiology, decreased compliance produced by the fluid-filled intrauterine environment, and a myocardium that is stiffer with fewer contractile elements Active research continues in this area despite these challenges and with the understanding that novel approaches may be needed These include investigation into systolic/diastolic coupling and twist/untwist relationships, use of advanced imaging techniques such as diastolic strain rate measurements, or consideration of focused assessment on atrial mechanics, and its reservoir, conduit, and contractile functional components.36,41 These investigations may occur separately or in parallel to adult investigations, with the crucial understanding that careful validation is necessary before any clinical extrapolation is made between the two groups Assessing Systolic Function Assessment of systolic ventricular function is one of the most common reasons for obtaining an echocardiogram in the ICU setting It is also important to remember that ventricular function S E C T I O N I V Pediatric Critical Care: Cardiovascular – LVPWs – LVIDs – IVSs – LVPWd – LVIDd – IVSd Stroke volume 276 1.068 cm 4.380 cm 0.905 cm 0.760 cm 6.027 cm 0.615 cm EDV (MM-Teich) 182 ml IVS/LVPW (MM) 0.809 LV Mass (Cubed) 156 g LV Mass Index (Cubed) 99.4 g/m2 IVS % (MM) 47.2 % FS (MM-Teich) 27.3 % ESV (MM-Teich) 86.8 ml EF (MM-Teich) 52.3 % LVPW % (MM) 40.5 % Wall Stress 80.4 g/cm2 LVIDs Preload • Fig 29.9 Relationship between preload and stroke volume with increase in cardiac output through the preload-dependent stage with variation between normal state (blue line) and increased stroke volume in reduced afterload or increased inotropic effect (yellow line) and decreased stroke volume with increased afterload or decreased inotropic effect (purple line) is dependent on contractility, or ability to generate force at the level of the myocyte, as well as by pump function, or the deformation of the chamber leading to cardiac output Ventricular function is affected by loading conditions, such as volume status, valve function and blood pressure, and by inotropic support (Fig 29.9) At times, wall motion may appear decreased despite normal contractility Conversely, wall function can appear to be normal despite decreased contractility, such as in a patient with decreased function but that responds to inotropic support and an afterload-reducing agent Additionally, congenital heart defects may distort the normal ventricular anatomy, which may affect accuracy of some of the standard methods of assessing ventricular function A simple assessment of wall motion does not provide a complete picture of ventricular function Left Ventricular Systolic Function Left ventricular systolic function is traditionally assessed from Mmode or 2D measurements The simplest form of measurement is fractional shortening (FS) This can be performed by M-mode or 2D imaging45 by determining the change in left ventricular internal diameter taken during systole (LVIDs) or diastole (LVIDd) during a single beat (Fig 29.10): FS (LVIDd – LVIDs)/LVIDd Normal values are 28% to 45%, with lower values indicating decreased systolic function and higher numbers indicating hyperdynamic function FS has the advantage of being very quickly obtainable, but the measurement looks at left ventricular function across a single plane only Thus, it is not an assessment of global function and will not detect regional wall motion abnormalities 2D imaging can also be used to calculate the left ventricular ejection fraction (EF) In this calculation, assumptions are made about the left ventricular geometry in order to calculate diastolic and systolic volumes from 2D imaging The EF is then determined by calculating the percentage of volume ejected during a single heart cycle derived from the diastolic volume (Vd) and systolic volume (Vs) using the following equation: EF (Vd –Vs)/Vd 2D measurements of left ventricular EF can be obtained by Simpson’s biplane method using apical 4-chamber and apical LVIDd • Fig 29.10 M-mode assessment for left ventricular (LV) fractional short- ening (FS) from parasternal short-axis view Wall motion relative to chest wall and changes in wall thickness represented on the y-axis and changes in time on the x-axis FS is calculated as difference in LV diastolic (LVIDd) and systolic (LVIDs) dimensions divided by LVIDd 2-chamber views or from the area-length method using a combination of subcostal coronal or apical 4-chamber view with subcostal sagittal or parasternal short-axis view45 (Fig 29.11) A normal EF is 55% or above, with values of 45% to 50% indicating mild dysfunction, 35% to 45% indicating moderate dysfunction, and measures below 35% representing severe left ventricular systolic dysfunction The left ventricular volumes are based on assumptions of a conal shape and that spinning the left ventricle along its long axis will yield an accurate estimation of left ventricular size This assumption becomes less accurate in a dilated left ventricle in which the left ventricle is more spherical or in certain congenital heart diseases that may alter left ventricular geometry Accuracy of the calculation will be affected by any regional wall motion as can be seen with volume or pressure load on the right ventricle affecting septal wall motion, and with ischemia or conduction abnormalities that can affect various walls 3D imaging can also be used to calculate an EF (see Fig 29.2).45 3D EF allows for better detection of abnormalities in function due to regional wall motion abnormalities and correlates well with magnetic resonance imaging (MRI) findings of left ventricular function in children and adults with congenital heart disease.50 A limitation of left ventricular functional assessment by 3D imaging is artifact related to respiration and longer imaging times Additionally, the image must be of high enough quality to allow for clear delineation of the endocardium along the entire left ventricle in order to permit accurate tracing of the left ventricular chamber A large body habitus, lung interference, or bandages can make obtaining adequate images difficult Use of ultrasonic-enhancing contrast agents can produce a clearer delineation of the endocardial border However, these agents are contraindicated in the presence of a right-to-left shunt, which limits its use in congenital heart disease These measurements are all dependent on loading conditions In the setting of high afterload, the wall motion (FS and EF) may be severely decreased despite preserved contractility The stressvelocity index attempts to account for the loading condition by assessing wall stress, which takes into account wall thickness and pressure generation, against wall motion as measured by ... ventricular and valvar function, and demonstrating the source of both pulmonary and systemic blood flow This allows for a rapid assessment of the patient’s physiologic state and the need for therapies,... ventricular pressure by adding it to the directly measured or assumed associated atrial pressure This is used for the assessment of pulmonary ventricular or pulmonary artery hypertension The peak... systolic or diastolic function is affected by one or the other (or both) of these loading conditions within the range of expected human physiology.35 Much has been written about the noninvasive assessment