277CHAPTER 29 Echocardiographic Imaging rate corrected circumferential fiber shortening (Vcfc) and can help determine if an abnormality in wall motion is due to exces sive afterload or decreased contr[.]
CHAPTER 29 Echocardiographic Imaging A B EF (A4C) 277 46 % • Fig 29.11 Left ventricular ejection fraction (EF) as measured from apical four-chamber view The EF is calculated from the difference between diastolic volume (A) and systolic volume (B), divided by the diastolic volume rate-corrected circumferential fiber shortening (Vcfc) and can help determine if an abnormality in wall motion is due to excessive afterload or decreased contractility There is an inverse linear relationship between Vcfc and end-systolic wall stress.51 Although load independent, the calculation for Vcfc is based on the same measurement as FS; therefore, the calculation is accurate only for a normally shaped left ventricle Spectral Doppler and tissue Doppler imaging (TDI) can also be used to assess left ventricular systolic function When an adequate jet of mitral regurgitation is present, the mean change in left ventricular systolic pressure (LV dP/dt) can be obtained from measuring the acceleration time between m/s and m/s.45 A value of 1200 mm Hg/s or greater is considered normal This is a nongeometric measurement and has been shown to correlate with MRI-derived assessment of left ventricular systolic function in patients with Fontan physiology.52 LV dP/dt can be particularly useful when bandages or other causes of poor acoustic windows prohibit obtaining adequate 2D imaging for assessment of function TDI can be used to measure peak S9 wave from lateral or septal wall as an easy measure of left ventricular systolic function that can often be obtained in patients with suboptimal images for other measures of function.45 TDI can also be used to calculate the myocardial performance index (MPI; Fig 29.12).45 The MPI assesses elements of both systolic and diastolic function The normal left ventricle MPI value in children is 0.32 0.06.53 Right Ventricular Systolic Function The complex shape of the right ventricle makes calculation of right ventricular systolic function more difficult than that of the left ventricle Therefore, a qualitative assessment of right ventricular systolic function often is preferred Conversely, multiple quantitative measures can be assessed and both tricuspid annular plane • Fig 29.12 Tissue Doppler image obtained from apical four-chamber view showing peak septal S9 (arrow) and mitral valve closure to opening time (time A between yellow lines) and systolic ejection time (time B between gray lines) used to calculate myocardial performance index = (A – B)/B systolic excursion (TAPSE) and right ventricular fractional area change (FAC) are recommended for assessment of right ventricular systolic function.45 Perhaps the simplest measure of right ventricular systolic function is TAPSE, which is obtained by placing M-mode through the tricuspid valve from an apical view (Fig 29.13) Although validated for use in pediatrics,54 alterations to right ventricular geometry can affect its accuracy in measuring right ventricular function Right ventricle FAC is similar to left ventricular EF in that it is a volumetric assessment of right ventricle function, but it does not take into account the entire right ventricle volume and has suboptimal reproducibility.55 Similar to the left ventricle, TDI can be used to obtain S9 wave 278 S E C T I O N I V Pediatric Critical Care: Cardiovascular • Fig 29.13 Tricuspid annular plane systolic excursion obtained by M-mode from apical four-chamber imaging as measured by height of the blue line • Fig 29.14 Different types of cardiac strain: circumferential (red arrow), radial (green arrow), and longitudinal (yellow arrow) and MPI, with a normal right ventricle MPI value of 0.28 0.04.53 3D assessment of the right ventricle may be the most accurate measurement of right ventricular systolic function; it has good correlation to MRI findings in children after surgical repair of congenital heart disease.56 However, 3D assessment of the right ventricle is time-consuming and requires special software that is not readily available Systolic Function: Strain Measurement of cardiac strain is an advanced imaging technique for the assessment of cardiac (mainly ventricular) function Simply stated, strain is the change in the length of an object secondary to an applied stress and is expressed as a percentage change relative to the original length Therefore, if a segment of myocardium shortens during systole, strain is negative, while if a segment lengthens or expands, then strain is positive Strain can be measured in the longitudinal, circumferential, and radial directions (Fig 29.14) by TDI, speckle-tracking echocardiography (STE), or CMR techniques In contradiction to first reports, strain as measured by STE is load dependent and angle dependent, although less angle dependent than when measured by TDI.57 Inherent advantages include the ability to assess different segments of the myocardium individually, which avoids tethering and translational effects From a practical standpoint, longitudinal strain measured by STE represents almost the entirety of current clinical use There is a growing body of evidence that left ventricular global longitudinal strain is superior to left ventricular EF in detecting subclinical cardiac dysfunction or predicting clinical outcomes This includes adults presenting with acute heart failure symptoms, adults who have received cardiotoxic chemotherapy, and adults with sepsis.58,59 Multiple other studies have demonstrated the utility of measuring strain for both the left and right ventricles in children60–62 (the latter also in adults), fetuses, and patients with and without congenital heart disease, although the wide-scale adoption of strain as a routine measurement in children has not yet occurred As an advanced technique, one must exercise care to maximize image quality and machine settings, use standardized views and frame rates, perform appropriate gating with simultaneous ECG leads, and visually review automated tracings to determine whether tracking adjustments are needed Different vendor algorithms have also prompted the recommendation for left ventricular global longitudinal strain to be calculated using a “length of line” technique with the caveat that serial studies should still be performed with the same vendor’s machine to minimize intervendor variability.63 Beyond an assessment of systolic function, strain as measured by STE can provide important information about ventricular dyssynchrony (i.e., the coordination of contraction between different myocardial segments) As shown in Fig 29.15, strain may be reduced (decreased contractility), uniformly reversed (consistent with infarcted myocardium), or dyssynchronous (contracting later than opposing segments) Knowing the nature of myocardial dysfunction can lead to better therapeutic decisions,64 such as the use of cardiac resynchronization therapy65 versus transplantation Pulmonary Hypertension Pulmonary hypertension is a commonly encountered problem in the pediatric ICU (see Chapter 53) Pulmonary hypertension in pediatric patients can be primary (idiopathic) or, more commonly, secondary related to lung disease (acute infection, pleural effusions, chronic lung disease/bronchopulmonary dysplasia), airway obstruction, gastroesophageal reflux, rheumatologic conditions, connective tissue disease, thromboembolism, or cardiac disease (left-to-right shunts, left atrial hypertension, pulmonary vein stenosis).66 Cardiac catheterization is the gold standard for diagnosis and quantification of pulmonary hypertension.67 However, its associated risks in an acutely ill pediatric patient can be significant Echocardiography is a noninvasive modality for diagnosing and quantifying pulmonary hypertension and can also identify cardiac causes of secondary pulmonary hypertension.66,68 Measuring the tricuspid regurgitation velocity with spectral Doppler can allow for calculation, via the modified Bernoulli equation, of the right ventricle to right atrial gradient (Fig 29.16) Adding a directly measured or assumed normal right atrial pressure of to 10 mm Hg to this gradient allows for an estimation of right ventricular systolic pressure and, in the absence of right ventricular outflow tract obstruction, pulmonary artery systolic pressure.69,70 A pulmonary regurgitation velocity can also be measured by spectral Doppler and an end-diastolic gradient can be calculated between the pulmonary artery and right ventricle end diastolic pressure The peak diastolic gradient can also be measured and has been shown to correlate with mean pulmonary artery pressures measured by cardiac catheterization.71 Mean CHAPTER 29 Echocardiographic Imaging A C 279 B D • Fig 29.15 Different longitudinal strain patterns (A) Normal longitudinal strain, peak strain approximately 219% (B) Uniformly decreased contractility, peak strain approximately 29% (C) Holosystolic stretch of two segments consistent with nonviable myocardium (white arrow) (D) Dyssynchronous activation pattern with opposing early (yellow arrows) and late (red arrows) stretching and contracting segments AVC, Aortic valve closure • Fig 29.16 Spectral Doppler image illustrating an elevated tricuspid valve • Fig 29.17 Apical four-chamber view of a patient with pulmonary hyperten- regurgitation velocity and gradient sion revealing a dilated and hypertrophied right ventricle LV, Left ventricle; RA, right atrium; RV, right ventricle pulmonary artery pressure greater than 25 mm Hg in children older than months of age is diagnostic of pulmonary hypertension.67 These measurements of right ventricular and pulmonary artery pressures must be interpreted in the setting of the systemic blood pressure, as the pulmonary artery pressures will change proportionally with systemic pressures Spectral Doppler measurements of right ventricular and pulmonary artery pressures can be problematic These measurements require a sufficient amount of regurgitation for measurements and, even in the setting of pulmonary hypertension, this is sometimes not the case.72 The spectral Doppler vector must be aligned with the regurgitation jet; an increasing angle of malalignment can lead to underestimates of right ventricular systolic pressures There are also indirect indicators of elevated right ventricular and pulmonary artery pressure on echocardiography Right ventricular changes, such as hypertrophy and decreased systolic function, can be indicators of pulmonary hypertension (Fig 29.17) Right ventricular functional assessment and quantification by echocardiography is difficult and, subsequently, often subjective One quantitative echocardiographic measure of right ventricular function is TAPSE, which is an M-mode measure of base-to-apex movement of the right ventricular myocardial wall (see Fig 29.13) TAPSE has been shown to correlate with right ventricular EF and FAC in adults73,74 and predicts poor outcomes in neonates with pulmonary hypertension.75 The direction of shunting at atrial and ventricular septal defects and at a patent ductus arteriosus can 280 S E C T I O N I V Pediatric Critical Care: Cardiovascular • Fig 29.18 Parasternal short-axis image of a patient with pulmonary hypertension revealing systolic flattening of the interventricular septum and calculation of eccentricity index (EI D2/D1) D1, Diameter 1; D2, diameter 2; IVS, interventricular septum; LV, left ventricle; RV, right ventricle offer indications of pulmonary hypertension Right to left shunting at the ventricular and ductal levels indicates right ventricular and pulmonary artery pressures, respectively, that are greater than systemic Right-to-left atrial shunting indicates that the right atrial and ventricular end-diastolic pressures, in the absence of tricuspid valve stenosis, are greater than the left atrial pressure This is a finding of poor right ventricular compliance and can be seen with right ventricular hypertrophy and dysfunction caused by pulmonary hypertension Ventricular septal geometry can also indicate elevated right ventricular systolic pressures.76,77 The ventricular septum is normally convex in systole because left ventricular systolic pressure is significantly higher than that in the right ventricle As right ventricular systolic pressure increases in relation to left ventricular systolic pressure, the ventricular septum will begin to flatten and eventually become concave when right ventricular systolic pressure exceeds that in the left ventricle (Fig 29.18) This finding can be quantified using the eccentricity index and has been found to correlate with pulmonary hypertension in low-birth-weight infants.78 Assessment of right ventricular systolic pressures by ventricular septal wall geometry can be confounded by prior ventricular septal defect patches, bundle branch blocks, and ventricular pacing Comprehensive scoring systems incorporating these indirect echocardiographic measures have shown good inter- and intrarater agreement for the diagnosis of pulmonary hypertension in premature infants.78 Pericardial Effusion Pericardial effusion can be present in pediatric ICU patients due to a variety of etiologies, including postoperative bleeding or swelling, postpericardiotomy syndrome, trauma, underlying neoplastic disorder, infection, collagen vascular disease, or renal disease.79 Echocardiography is very sensitive for detecting even a small pericardial effusion Pericardial fluid is seen as an area of decreased acoustic density around the heart (Fig 29.19) but must be differentiated from pleural effusion and ascites, which can also appear in close proximity to the heart Pericardial effusions typically are not seen anterior to great arteries; the pulmonary and systemic venous connections to the posterior aspect of the heart usually keep pericardial effusions from extending behind the left atrium The presence or absence of fluid in these spaces can aid in • Fig 29.19 Apical four-chamber view showing a large circumferential effusion seen as the dark space (arrows) distinguishing pericardial from pleural effusion, as pleural effusions can occupy these areas Visualization of the diaphragm can help distinguish inferior pericardial effusions from ascites Pericardial effusions can be classified based on diastolic dimension of the effusion with small effusion being ,10 mm, moderate effusion being 10 to 20 mm, and large effusion being 20 mm.80 This classification is based on adults, and there are no specific dimensional criteria for classification in children In children, assessment of size of the effusion is typically subjective As the fluid often is circumferential and moves with changes in patient position, description of location and measurement of size allow for the best serial evaluation of a pericardial effusion in children In addition, one should note whether the effusion is global, localized, or loculated In addition to describing the appearance of the effusion, echocardiography plays a key role in the assessment of hemodynamic compromise from the effusion Pericardial effusions can lead to decreased cardiac output by limiting cardiac filling The likelihood of cardiac compromise from a pericardial effusion is dependent on both the size of the effusion and the rate of accumulation A very large, slowly accumulating effusion may allow for the pericardium to stretch, resulting in normal cardiac function despite the large volume of fluid around the heart Conversely, a rapidly accumulating effusion may compromise ventricular filling early, despite its small size Thus, the size of the pericardial effusion does not always correlate to its clinical significance Although there are echocardiographic findings to suggest the presence of cardiac tamponade, it remains a clinical diagnosis Patients in tamponade will have tachypnea, tachycardia, and hypotension due to compromised cardiac output Pulsus paradoxus is the classic physical finding in cardiac tamponade, showing an exaggerated variation in systolic blood pressure with respiration Detection of pulsus paradoxus requires an arterial line or manual blood pressure measurement with a stethoscope, as automated blood pressure recorders cannot detect the effect of respiratory variation in blood pressure Nonetheless, echocardiography remains the main diagnostic tool in assessment of pericardial effusions.81 The echocardiographic findings suggestive of tamponade are based on Doppler flow patterns and 2D imaging of the right heart When the pressure within the pericardial space exceeds intracavitary pressure, there will be collapse of the chamber wall (Fig 29.20) Right atrial collapse begins in late ventricular diastole and can last into ventricular systole, with increased duration CHAPTER 29 Echocardiographic Imaging 281 Ao D A B • Fig 29.20 Parasternal long-axis view with pericardial effusion anterior to heart The arrow indicates area of right ventricular collapse in diastole indicative of cardiac tamponade Ao, Aorta; D, diastole increasing the sensitivity and specificity of this finding for presence of tamponade physiology.82 Similarly, expiratory collapse of the right ventricular free wall in late ventricular diastole is associated with tamponade, and the duration of collapse correlates with severity.83 The presence or absence of chamber collapse can be influenced by other hemodynamic factors, such as hypovolemia causing collapse in the absence of tamponade or increased right heart pressures preventing development of collapse There is better correlation between absence of collapse and absence of tamponade than there is for presence of tamponade in presence of collapse.84 Another common, but less specific, finding for cardiac tamponade is the septal bounce in which the interventricular septum moves toward the left ventricle in late diastole In adults, the inferior vena cava will become dilated and lose respiratory variation in size in tamponade, but this finding has not been validated in children Doppler findings can also indicate the presence of cardiac tamponade based on increase in the normal variation in cardiac output seen with respiration.81 A decrease in the mitral valve peak E wave velocity of more than 25% during inspiration, decrease in tricuspid valve peak E wave velocity of more than 40% during expiration, decrease in aortic valve peak velocity of more than 10% during inspiration, or increase in pulmonary valve peak velocity of more than 10% during inspiration suggests the presence of tamponade In large effusions, the heart often “swings” within the pericardial fluid, which can lead to changes in Doppler velocity that are unrelated to respiration and not indicative of tamponade Use of respirometer and care to ensure proper Doppler alignment can help avoid false-positive findings When tamponade is present, the pericardial space needs to be decompressed emergently Patients with large effusion but not meeting diagnostic criteria for cardiac tamponade often demonstrate a decrease in heart rate and improvement in blood pressure after pericardiocentesis Echocardiographic guidance can improve the ease and safety of pericardiocentesis The optimal site for needle insertion is typically just below the xiphoid process At times, however, other locations—such as apical, parasternal, anterior, or superior—may be preferable Echocardiography should be used to determine the window with access to the largest portion of the effusion, the absence of intervening lung or liver tissue, and the shortest distance between skin and the pericardial space Once the best location for approach is identified, echocardiography can be used to help guide passage of the needle into the pericardial space, reducing risk of penetrating the heart or injuring the coronary arteries When the effusion is bloody, visualization of the needle within the pericardial space can be very reassuring; location of the needle in the pericardium can also be confirmed by injection of agitated saline (Fig 29.21C) After proper location of the needle in the pericardial space is verified, a pericardiocentesis catheter can be inserted with use of a guidewire and dilator (Seldinger technique) A decrease in effusion size will be seen as fluid is removed (Fig 29.21D) Pericardiocentesis typically is performed at the bedside under echocardiographic guidance or in the cardiac catheterization laboratory Choice of location is determined by patient stability, resource availability, and physician preference The decision regarding whether to leave a pericardiocentesis drain in place at the end of the procedure depends on multiple clinical factors but is often left in place Intracardiac Vegetations and Thrombi Echocardiography may be used in the ICU setting to evaluate intracardiac masses, such as vegetations in infective endocarditis or intracardiac thrombus Endocarditis remains a clinical diagnosis guided by the modified Duke criteria,85 but echocardiography plays a key role in establishing the diagnosis The majority of children who develop endocarditis have underlying congenital heart disease, but endocarditis can also occur in the absence of structural heart disease or other risk factors In young children, ... left ventricular EF in detecting subclinical cardiac dysfunction or predicting clinical outcomes This includes adults presenting with acute heart failure symptoms, adults who have received cardiotoxic... pediatric ICU (see Chapter 53) Pulmonary hypertension in pediatric patients can be primary (idiopathic) or, more commonly, secondary related to lung disease (acute infection, pleural effusions,... (Fig 29.16) Adding a directly measured or assumed normal right atrial pressure of to 10 mm Hg to this gradient allows for an estimation of right ventricular systolic pressure and, in the absence