e4 Abstract Echocardiography is the use of ultrasound to image cardiovascular structures The echocardiography probe transmits sound waves through the body and receives the reflections of these sound w[.]
e4 Abstract: Echocardiography is the use of ultrasound to image cardiovascular structures The echocardiography probe transmits sound waves through the body and receives the reflections of these sound waves The processor then uses the data to generate an image Echocardiography arose as a widespread clinical diagnostic test in the 1970s and 1980s Previously, invasive angiography was the cardiac diagnostic test of choice Echocardiography supplanted invasive angiography because of its ability to obtain anatomic, hemodynamic, and functional data noninvasively Additional advantages of echocardiography include the absence of ionizing radiation, its portable nature, and the fact that most patients not require sedation/anesthesia Limitations include the long time it takes to perform a complete study, poor image quality in patients with greater mass, the fact that some hemodynamic and functional assessments are indirect measurements or calculations, and the need for a highly skilled operator These strengths and weaknesses highlight both the usefulness of echocardiography in the intensive care unit setting and the importance of interpreting results with the knowledge of its limitations Key words: echocardiography, transesophageal echocardiography, color Doppler, spectral Doppler, strain analysis 10 30 Chapter Title Diagnostic and Therapeutic Cardiac Catheterization CHAPTER AUTHOR REID C CHAMBERLAIN, KEVIN D HILL, AND GREGORY A FLEMING PEARLS • • To gain basic knowledge of the development of the eye To develop essential understanding how abnormalities at P Evarious A R L Sstages of development can arrest or hamper normal formation the ocular structures and can visual pathways • The cardiacofcatheterization laboratory play an important di • • agnostic and/or therapeutic role in the management of children in the pediatric intensive care unit For patients with cardiac disease whose critical care course is not progressing as expected, early exploration for diagnosis of unsuspected or residual defects or hemodynamic derangements by cardiac catheterization is sometimes warranted Cardiac catheterization provides an important diagnostic and therapeutic option to enhance the management of children in the critical care environment Since first used in the 1940s, the role of cardiac catheterization has continued to evolve.1 With improvements and better understanding of noninvasive imaging, cardiac catheterization is rarely used as the initial diagnostic modality for cardiac disease However, it continues to provide valuable diagnostic information in select clinical scenarios Moreover, an increasing repertoire of interventional approaches has expanded the potential therapeutic role of cardiac catheterization as a less invasive method for treating certain cardiac diseases in children As with all clinical studies or tests, it is important to understand and interpret catheterization results within the context of the study limitations and environment obtained Furthermore, to maximize therapeutic benefit from cardiac catheterization, the critical care team must understand appropriate timing, indications, and limitations of catheter-based interventions In the appropriate setting, comprehensive hemodynamic data, angiography, and therapeutic interventions from a catheterization can help the pediatric critical care team in managing complex patients with cardiac disease Catheterization Laboratory Environment Cardiac catheterization laboratories are often remote from the intensive care unit (ICU) and rarely configured to accommodate critical care personnel and equipment Safe and effective performance of a cardiac catheterization requires planning and multidisciplinary coordination between the ICU and catheterization lab staff, respiratory therapy, perfusion, and anesthesia Safety starts with transportation of the critically ill child from the ICU to the • • To acquire adequate information about normal anatomy of the eye and related structures and develop a strong foundation for the understanding of common ocular problems and their consequences To maximize the utility of catheterization, it is important to understand procedural benefits and limitations Effective communication between care teams is important to ensure safety and to maximize procedural benefits catheterization laboratory, a process that should be carefully planned in advance, particularly for patients requiring mechanical circulatory or ventilator support Once in the laboratory, space may be limited; therefore ergonomics should be considered in advance in case of emergencies that might require access to the patient Application of all invasive and noninvasive monitoring should occur prior to full sterile draping of the patient, sometimes even in the ICU prior to transport Adequate sedation and anesthesia during cardiac catheterization are essential to facilitate acquisition of meaningful hemodynamic data and to facilitate interventional procedures For many interventional procedures, sedation may be appropriate; however, for prolonged procedures or those with the potential for significant hemodynamic compromise, general anesthesia is preferable Ideally, for critically ill patients, a dedicated pediatric cardiac anesthesia team should manage sedation or anesthesia, mechanical ventilation, and medication administration during the procedure Communication between the anesthesia and cardiology teams is crucial to optimize procedural safety and to facilitate obtaining accurate hemodynamic data, as these data can be affected by changes in oxygenation, ventilation, and hemodynamic state Diagnostic Cardiac Catheterization Diagnostic cardiac catheterization assesses the blood flow, shunting, and resistance through the cardiac system, and can provide dynamic intracardiac and intravascular imaging In patients with complex cardiac anatomy, pulmonary hypertension, unexplained cardiac or pulmonary hemodynamic compromise, or with concerns for important residual or recurrent anatomic lesions after 289 290 S E C T I O N I V Pediatric Critical Care: Cardiovascular cardiac surgery, physiologic data from catheterization may provide important diagnostic information that cannot be assessed by less invasive means.2 However, it is necessary to understand the limitations and sources of error in the catheterization laboratory in order to appropriately interpret and apply the data obtained Cardiac catheterization provides a hemodynamic assessment at a moment in time, often under sedation, that may differ from the dynamic changes in a wakeful or agitated state The hemodynamics may change over time with disease progression or interventions Furthermore, errors can be introduced when hemodynamic parameters, such as blood flow, shunts, and resistance, are calculated.2 For these reasons, providers should interpret hemodynamic data with caution and with thoughtful consideration of the limitations 70% 70% 98% 70% 15-25/8-12 M = 10-18 70% 98% A = 4-12 V = 5-14 M = 3-10 70% Oxygen Saturation Differences in oxygen saturations across vascular beds are used to calculate blood flow and shunting in the cardiovascular system Saturations are typically obtained in the systemic veins, across the chambers of the right heart, and in the pulmonary arteries (PAs) Systemic saturations and, when accessible, pulmonary venous saturations, are also a standard part of a comprehensive diagnostic cardiac catheterization In patients with hemodynamically significant left-to-right shunting lesions (i.e., atrial or ventricular septal defects), shunting of oxygenated blood into the deoxygenated circuit will result in a step-up in saturations across the right side of the heart.3 Conversely, in patients with right-to-left shunts (e.g., tetralogy of Fallot) or complete mixing lesions (e.g., singleventricle heart defects), shunting will result in systemic desaturation When interpreting saturation data, it is important to recognize that there can be significant sampling variability For example, sampling in proximity to the low-extraction renal blood return will result in higher saturations than sampling in close proximity to the high-extraction hepatic or coronary sinus blood return Pressure Assessment A full pressure assessment of the right side of the heart consists of direct pressure measurements in the branch PAs, main PA, right ventricle, and right atrium Pressure assessment of the left side of the heart consists of direct pressure measurements in the left ventricle, ascending aorta, and descending aorta For patients with an atrial septal defect (ASD) or patent foramen ovale (PFO), a direct left atrial pressure may be obtained For patients with an intact atrial septum, direct left atrial pressure can be obtained only by performing a transseptal puncture; therefore it is typically estimated by obtaining a pulmonary capillary wedge pressure (PCWP) Fig 30.1 demonstrates normal intracardiac and PA pressures When stenosis is present, the degree of obstruction can be quantified by the pressure gradient across the lesion For ventricular and arterial pressures, the peak systolic gradient typically estimates the degree of stenosis For venous pressures, or when measuring pressure gradients across the atrioventricular valve, the mean gradient is more commonly used to estimate stenosis.3 Flow Calculations The two most commonly used methods to estimate blood flow through the cardiovascular system are thermodilution and the Fick method In a structurally normal heart without significant valve regurgitation or intracardiac shunting, thermodilution can be used to assess the cardiac output The thermodilution catheter 70% A = 3-8 V = 3-7 M = 2-5 90-120/4-10 70% 15-25/2-8 98% 90-120/50-70 M = 60-80 • Fig 30.1 Normal cardiac pressures and saturations in pediatric and adolescent patients without cardiac disease A, Atrial; M, mean; V, ventricular has a proximal port that sits in the right atrium as well as a distal thermistor that is positioned in the PA and measures the change in blood temperature following a cold saline injection through the proximal port In a structurally normal heart, the estimated blood flow using thermodilution is equivalent to the cardiac output since the pulmonary (Qp) and systemic (Qs) blood flows are equal (Qp:Qs 1) Since most patients with congenital heart disease have some degree of intracardiac shunting lesion and/or valvar insufficiency, thermodilution cannot be used to measure cardiac output, and the Fick method is preferred Table 30.1 lists simplified equations for calculating flows, shunts, and resistance by the Fick method The Fick method estimates blood flow by measuring the change in oxygen content across a vascular bed relative to the rate of oxygen extraction or delivery quantified by the patient’s oxygen consumption (Vo2).3,4 The oxygen content of the blood is composed of oxygen bound to hemoglobin (represented by the oxygen saturation), and the concentration of dissolved oxygen (represented by the partial pressure of oxygen [Po2]) The dissolved oxygen content is low in patients breathing room air and can be omitted from the equation When supplemental oxygen is used, the dissolved oxygen concentration increases and must be accounted for in the calculation by adding 0.0032 Po2 to the denominator of the equation Estimating Shunts Estimating the ratio of blood flowing through the pulmonary vascular bed to blood flowing through the systemic vascular bed is important for many congenital heart lesions Commonly referred CHAPTER 30 Diagnostic and Therapeutic Cardiac Catheterization TABLE 30.1 Equations for Calculating Flows, Shunts, and Resistance by the Fick Method Indexed for Body Surface Area Cardiac output (Qs) (L/min/m2) Pulmonary blood flow (Qp) (L/min/m2) Hgb ( Ao sat MV sat ) 1.36 10 Indexed Vo2 Hgb (PV sat PA sat ) 1.36 10 ( AO sat MV sat ) (PV sat PA sat ) Systemic vascular resistance (WU m2) diagnostic tool in the pediatric catheterization laboratory to generate three-dimensional images that assist in identifying pathology, guiding interventions, and monitoring for complications.6 Indexed Vo2 Qp:Qs Pulmonary vascular resistance (WU m2) 291 Mean PA pressure mean PCWP Qp Mean Ao pressure mean RA pressure Qs Calculations assume an Fio2 content of 21% with concentration of dissolved O2 omitted Hgb measured in mg/dL Saturations measured as fractional saturation (i.e., 0.96 for a saturation of 96%) 1.36 is a constant derived from the O2 content/g Hb (1.36 mL O2/g Hb); multiplying by 10 converts Hgb from g/dL to g/L Ao, Aortic; Hgb, hemoglobin concentration; MV, mixed venous; PA, pulmonary artery; PCWP, pulmonary capillary wedge pressure; PV, pulmonary vein; RA, right atrial; Vo2, oxygen consumption (mL/min/m2); WU, Wood unit to as Qp:Qs, this ratio can be calculated by dividing the difference between the aortic and mixed venous saturations by the difference between the pulmonary vein and PA saturations (see Table 30.1; assuming that Fio2 21%) Quantifying the degree and direction of shunting through the cardiovascular system can help to inform clinical management decisions, including expected clinical course and/or need for surgical referral Resistance Calculations Based on the principle of Ohm’s law, the change in pressure through a system is equal to the flow of blood multiplied by the resistance to flow This equation is rearranged such that measured and estimated values obtained during the catheterization are used to determine vascular resistance (see Table 30.1) The equation uses the change in mean pressures across a vascular bed and assumes equal blood flow across all vascular beds For this reason, one cannot accurately calculate pulmonary vascular resistance in the setting of branch pulmonary stenosis or pulmonary vein stenosis without knowing the percentage of blood flow to each lung This can be accomplished with supplemental data from a lung perfusion scan or cardiac magnetic resonance imaging (MRI) but requires a more complicated equation for calculating resistance in a parallel system Angiography Imaging of the cardiovascular system in the catheterization laboratory is performed via fluoroscopy with timed injections of iodinated contrast to visualize the intraluminal surfaces of the heart and vessels in real time Catheterization laboratories specializing in congenital heart disease typically use biplane angiography systems, allowing for selection of a variety of imaging angles as well as simultaneous imaging in two planes.5 Over the last decade, rotational angiography has become a new Indications Due to advances in noninvasive imaging, cardiac catheterization is no longer the first-line diagnostic modality for congenital heart disease In fact, most patients with congenital cardiac defects not require a cardiac catheterization prior to surgical intervention, assuming an expected preoperative course However, there are numerous clinical scenarios in which a diagnostic catheterization is indicated to provide supplemental and/or definitive diagnostic data for the patient In 2011, Feltes et al published a scientific statement from the American Heart Association that summarizes indications for cardiac catheterization and intervention in pediatric cardiac disease.7 Table 30.2 summarizes indications for diagnostic catheterization Before proceeding with an invasive catheterization, it is recommended that a complete noninvasive imaging evaluation be completed.7 It is important to note that the guidelines not provide an exhaustive list of potential indications, and many are supported by expert consensus only Additionally, a cardiac catheterization is an invasive procedure with associated risks For these reasons, open communication between intensivists, interventionalists, and potentially surgeons is key to providing high-quality patient care that minimizes harm Pulmonary Vascular Resistance and Vasoreactivity Testing Patients with known or suspected pulmonary hypertension can benefit from catheterization to diagnose or rule out structural disease involving the PAs or pulmonary veins, as in cases of multiple thromboembolic disease or undiagnosed pulmonary vein stenosis Acute pulmonary vasoreactivity testing with pulmonary vasodilators, such as supplemental Fio2, inhaled nitric oxide, and/or intravenous sildenafil is often performed in patients with pulmonary hypertension due to increased pulmonary vascular resistance.8,9 Vasoreactivity response is important for prognostication and for planning longer-term management strategies for patients with pulmonary hypertension In the presence of structural heart disease with a left-to-right shunt and elevated pulmonary vascular resistance (PVR), pressure and saturation measurements are often repeated with pulmonary vasodilators to assess both the reactivity of the pulmonary vascular bed and any contribution of ventilation/ perfusion abnormalities to hypoxemia If breathing 100% oxygen and inhaled nitric oxide increases pulmonary blood flow and dramatically increases Qp:Qs (with a fall in PVR), then the PVR is considered reactive, indicating that pulmonary hypertension is potentially reversible and therefore more amenable to therapeutic intervention The patient with a high, unresponsive PVR and a small left-to-right shunt may have extensive pulmonary vascular damage from underlying lung injury or irreversible obstructive pulmonary vascular disease The reactivity of the pulmonary vascular bed and change in PVR are important components to the assessment of patients potentially undergoing cardiac surgery, including cardiac transplantation An elevated PVR or PA pressure is a risk factor for surgical intervention and/or cardiac transplantation.10 In patients with heart failure, left atrial hypertension can be a potent cause of secondarily elevated PVR If PVR decreases with 100% 292 S E C T I O N I V Pediatric Critical Care: Cardiovascular TABLE 30.2 Indications for Diagnostic Cardiac Catheterization Class I Indication (Procedure Is Beneficial, Useful, and Effective) Level of Evidence Class IIa Indication (Weight of Evidence Favors Usefulness) Level of Evidence To obtain hemodynamic and anatomic data at the time of interventional catheterization A To determine pulmonary pressures, resistance and transpulmonary gradient in palliated single-ventricle patients prior to Fontan B To assess pulmonary resistance and reversibility of pulmonary hypertension in patients with primary pulmonary hypertension or CHD when the assessment is needed to make surgical and medical decisions B To assess coronary circulation in suspected coronary artery anomalies or some cases of suspected or poorly delineated coronary involvement in Kawasaki disease B To characterize lung segmental pulmonary vascular supply in patients with complex pulmonary atresia B To assess for cardiomyopathy or myocarditis B To determine coronary circulation in pulmonary atresia with intact septum B To assess anatomy and hemodynamic parameters in postoperative cardiac patients when the early postoperative course is unexpectedly complicated and noninvasive imaging fails to yield a clear explanation C To assess for graft vasculopathy after cardiac transplantation B To clarify CHD diagnosis when noninvasive imaging and testing yields incomplete information C To assess for candidacy for cardiac transplantation (unless risk of catheterization outweighs benefit) C Level of evidence A: Data derived from multiple randomized clinical trials or meta-analysis Level of evidence B: Data derived from a single randomized trial or nonrandomized studies Level of evidence C: Only consensus opinion of experts, case studies, or standard of care CHD, Congenital heart disease Data from Feltes et al Indications for cardiac catheterization and intervention in pediatric cardiac disease: a scientific statement from the American Heart Association Circulation 2011;123(22):2607–2652 Fio2/inhaled nitric oxide during pretransplant catheterization, they still may be suitable candidates for cardiac transplantation and pulmonary vasodilators should be considered in the postoperative setting However, in patients such as these with elevated PVR in the context of downstream obstruction (i.e., from left atrial hypertension), pulmonary vasodilators should be used cautiously prior to heart transplantation, as fixed downstream obstruction can lead to pulmonary edema with excessive pulmonary vasodilation Similarly, for patients with simple left-toright shunts (ASD, ventricular septal defect [VSD], patent ductus arteriosus [PDA]) and elevated PVR more than Wood units m2, pulmonary vasoreactivity testing can be used to determine operative candidacy and need for postoperative pulmonary vasodilator therapy.9 Therapeutic Cardiac Catheterization Since William Rashkind ushered in the era of therapeutic cardiac catheterization in 1966 with the performance of the first balloon atrial septostomy, there have been significant advances in transcatheter interventions for patients with congenital heart disease In the current era of imaging, therapeutic interventional catheterizations are more common than diagnostic catheterizations The following section provides a brief overview of some of the interventional procedures performed in critically ill infants, children, and adolescents, including indications, procedural considerations, and safety concerns We will also briefly discuss some of the novel transcatheter therapies that often require recovery and postprocedural management in the ICU Pericardiocentesis While pericardiocentesis and pericardial drain placement can occur at the bedside, cardiologists may also perform this procedure in the catheterization laboratory.11 The catheterization laboratory provides an environment with access to invasive monitoring, multimodality imaging, and anesthesia support Slight variations in accepted indications for pericardiocentesis exist but generally depend on hemodynamic stability, effusion size, and diagnostic assistance.11,12 In patients with cardiac tamponade and hemodynamic instability, pericardiocentesis is indicated regardless of the size of the pericardial effusion, presuming that the fluid collection can be safely accessed via a percutaneous approach Clinically, patients with tamponade physiology may have distant heart sounds, hypotension, and elevated central venous pressure with jugular venous distension, also known as the Beck triad Additionally, patients may have tachycardia and tachypnea, narrow pulse pressure, and pulsus paradoxus (decrease in systolic blood pressure of 10 mm Hg with inspiration) In hemodynamically stable patients, pericardiocentesis may be indicated for the following: large pericardial effusion; concern for a purulent effusion; or diagnostic uncertainty, particularly in patients with underlying immunodeficiency or malignancy.12 For pericardiocentesis, echocardiographic guidance is commonly used to minimize the risk of complications.13 Fluoroscopic guidance is less commonly used but should be available if needed The risks of complication can be as high as 10% depending on the clinical setting and include arrhythmia, cardiac puncture, hemothorax, pneumothorax, pneumopericardium, and hepatic injury.12 To reduce the risk of pericardial effusion recurrence in pediatric patients, it is recommended to place a pericardial drain for extended drainage at the ... clinical studies or tests, it is important to understand and interpret catheterization results within the context of the study limitations and environment obtained Furthermore, to maximize therapeutic... (represented by the partial pressure of oxygen [Po2]) The dissolved oxygen content is low in patients breathing room air and can be omitted from the equation When supplemental oxygen is used, the dissolved... pulmonary vein; RA, right atrial; Vo2, oxygen consumption (mL/min/m2); WU, Wood unit to as Qp:Qs, this ratio can be calculated by dividing the difference between the aortic and mixed venous saturations