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Target Audience
This document is designed for those with a primary interest and knowledge base in the field of echocardiography and for other medical professionals with a specific interest in the abnormalities of the interatrial septum and the use of cardiac ultrasonography. This includes cardiovascular physicians, other cardiovascular providers, cardiac sonographers, surgeons, cardiac interventionalists, neurologists, residents, research nurses, clinicians, intensivists, and other medical professionals.
Target Audience
This document is designed for those with a primary interest and knowledge base in the field of echocardiography and for other medical professionals with a specific interest in the abnormalities of the interatrial septum and the use of cardiac ultrasonography. This includes cardiovascular physicians, other cardiovascular providers, cardiac sonographers, surgeons, cardiac interventionalists, neurologists, residents, research nurses, clinicians, intensivists, and other medical professionals.
Objectives
On completing the reading of the proposed guideline, the participants will better be able to
- 1.
Describe the conventional two-dimensional, three-dimensional, and Doppler echocardiographic methodology required for optimal evaluation and characterization of the interatrial septum from transthoracic echocardiographic, transesophageal echocardiographic, and intracardiac echocardiographic ultrasound technologies.
- 2.
Describe the echocardiographic parameters to characterize the normal interatrial septum and the abnormalities of atrial septal defect, atrial septal aneurysm, and patent foramen ovale. This will include the best practices for measurement and assessment techniques.
- 3.
Identify the advantages and disadvantages of each echocardiographic technique and measurements of the interatrial septum as supported by the available published data.
- 4.
Recognize which images should be used and measurements that should be included in the standard echocardiographic evaluation of patients with atrial septal defect, atrial septal aneurysm, and patent foramen ovale.
- 5.
Explain the clinical and prognostic significance of the echocardiographic assessment of atrial septal defect, atrial septal aneurysm, and patent foramen ovale, including not only the interatrial septum assessment, but also evaluation of the chamber size and function and the pulmonary circulation.
- 6.
Recognize what are the relevant features used to evaluate patients for potential transcatheter (i.e., device) closure of atrial septal abnormalities.
- 7.
Describe the important features and potential findings in the echocardiographic assessment of the patient after surgical and transcatheter interventions for atrial septal abnormalities.
Introduction
Atrial septal communications account for approximately 6%–10% of congenital heart defects, with an incidence of 1 in 1,500 live births. The atrial septal defect (ASD) is among the most common acyanotic congenital cardiac lesions, occurring in 0.1% of births and accounting for 30%–40% of clinically important intracardiac shunts in adults. The patent foramen ovale (PFO) is more common and is present in greater than 20%–25% of adults. The clinical syndromes associated with ASD and PFO are extremely variable and represent a significant health burden that spans pediatric and adult medicine, neurology, and surgery. The evaluation of abnormalities of the interatrial septum and their associated syndromes require a standardized, systematic approach to their echocardiographic and Doppler characterization, including the use of transthoracic echocardiographic (TTE), transesophageal echocardiographic (TEE), and intracardiac echocardiographic (ICE) ultrasound, three-dimensional (3D) imaging, Doppler, and transcranial Doppler (TCD) modalities.
A thorough echocardiographic evaluation of PFO and ASD includes the detection and quantification of the size and shape of the septal defects, the rims of tissue surrounding the defect, the degree and direction of shunting, and the remodeling and changes in size and function of the cardiac chambers and pulmonary circulation. The emergence of 3D visualization, especially with the TEE-based characterization of septal abnormalities has contributed incremental information in the evaluation of the interatrial septum. As such, a guideline document to integrate the available diagnostic modalities is presented to aid clinical practice, training, and research.
Previous American Society of Echocardiography (ASE) guidelines have focused on the description of performing a comprehensive transesophageal examination, standards for acquisition and presentation of 3D echocardiographic imaging, echocardiographic guidance of interatrial defect device closure, and assessment of the right ventricle (RV). Guidelines for the comprehensive assessment of the interatrial septum (IAS) have the potential to reduce variation in the quality of echocardiographic studies, guide the complete characterization of defects, standardize the measurements and techniques used to describe the anatomy and physiology, and improve the assessment of suitability for surgical and transcatheter therapies.
As such, clinicians and researchers, device manufacturers, and regulatory agencies all stand to benefit from these standards, because they will bring greater uniformity into clinical care, clinical trial design, and the conduct of imaging core laboratories.
Finally, the echocardiographic and Doppler study of patients before and after surgical and transcatheter therapies involving the IAS also requires guidelines and standardization of the methodology. The results of these therapies and their complications must be fully and competently assessed, characterized, and reported by the modern echocardiography laboratory.
Development and Anatomy of the Atrial Septum
Normal Anatomy
Understanding atrial septal communications requires comprehension of the underlying development and anatomy of the IAS. The atrial septum has three components: the septum primum, septum secundum, and atrioventricular (AV) canal septum. The sinus venosus is not a component of the true atrial septum but is an adjacent structure through which an atrial communication can occur. Septal defects can be classified according to their anatomic location in the IAS ( Figure 1 ).
Figure 2 depicts a schematic of normal atrial septal development. The atria first develop as a common cavity. At approximately 28 days of gestation, the septum primum, derived from the atrial roof, begins to migrate toward the developing endocardial cushions. During this transition, the space between the septum primum and the endocardial cushion is termed the “embryonic ostium primum” or the “foramen primum.” The septum secundum, in contrast, is an infolding of the atrial roof rather than a true membranous structure; it develops adjacent to the developing truncus and to the right of the septum primum. In the normal heart, the ostium primum closes by fusion of the mesenchymal cells of the septum primum (the so-called mesenchymal cap of the vestibular spine) with the superior and inferior endocardial cushions. The leading edge of the septum secundum becomes the superior limbic band. By 2 months into gestation, the septum secundum and septum primum fuse, leaving the foramen ovale as the only residual communication. The flap of the foramen ovale is termed the “fossa ovalis” and is formed by the septum secundum, septum primum (which attaches on the left atrial [LA] side of the septum secundum), and the AV canal septum. The septum primum becomes contiguous with the systemic venous tributaries to form the inflow of the superior and inferior vena cavae. The sinus venosus septum is an adjacent structure to the atrial septum that separates the right pulmonary veins from the superior vena cava (SVC) and posterior right atrium (RA). The coronary sinus is separated from the LA by a wall of tissue called the coronary sinus septum. The anterosuperior portion of the atrial septum is adjacent to the right aortic sinus of Valsalva. A more detailed description of atrial septum development is available for additional information.
Anatomy of Atrial Septal Defects and Associated Atrial Septal Abnormalities
Patent Foramen Ovale
A (PFO is not a true deficiency of atrial septal tissue but rather a potential space or separation between the septum primum and septum secundum located in the anterosuperior portion of the atrial septum ( Figure 3 A,B). It is not considered a true ASD, because no structural deficiency of the atrial septal tissue is present. The foramen remains functionally closed as long as the LA pressure is greater than the RA pressure. In many cases, a PFO might be only functionally patent and have a tunnel-like appearance, because the septum primum forms a flap valve. The relative differences in left and RA pressure can result in intermittent shunting of blood. A PFO can also be a circular or elliptical true opening between the two atria. Some cases of PFO result from “stretching” of the superior limbic band of the septum secundum from atrial dilation and remodeling ( Figures 4–6 ). In other cases, the septum primum is truly aneurysmal and as such cannot completely close the atrial communication ( Figure 7 ). In fetal life, patency of the foramen ovale is essential to provide oxygenated blood from the placenta to the vital organs, including the developing central nervous system. After birth, the foramen ovale generally closes within the first 2 months of age. Up to 20%–25% of the normal population has a PFO present in adulthood.
The incidence and size of a PFO can change with age. In an autopsy study of 965 human hearts, the overall incidence of PFO was 27.3%, but it progressively declined with increasing age from 34.3% during the first 3 decades of life to 25.4% during the 4th through 8th decades and 20.2% during the 9th and 10th decades. The size of a PFO on autopsy in that series ranged from 1 to 19 mm in the maximal diameter (mean 4.9 mm). In 98% of these cases, the foramen ovale was 1–10 mm in diameter. The size tended to increase with increasing age, from a mean of 3.4 mm in the first decade to 5.8 mm in the 10th decade of life.
For purposes of consistency in nomenclature, a “patent foramen ovale” has been referred to when right to left shunting of blood has been demonstrated by Doppler or saline contrast injection without a true deficiency of the IAS. A “PFO with left to right flow” has been referred to when the atrial hemodynamics have resulted in opening the potential communication of the foramen, resulting in left to right shunting of blood demonstrated by Doppler imaging ( Figures 4–6 ). When a PFO is stretched open by atrial hemodynamics, thus creating a defect in the septum, it is referred to as a “stretched” PFO. This can result in left to right or right to left shunting of blood flow demonstrated by Doppler, depending on the differences in the right and LA pressure.
Closure of the foramen ovale occurs by fusion of the septum primum and septum secundum at the caudal limit of the zone of overlap of these structures. Incomplete fusion results in a pouch-like anatomic region that, in most instances, communicates with the LA cavity. The phrase “LA septal pouch” refers to the blind pouch from the residual overlap of the septum primum and septum secundum and has been suggested as a possible location for thrombus formation and embolism. This can mimic LA myxoma.
Ostium Secundum Atrial Septal Defect
An ostium secundum ASD most often occurs as the result of a true deficiency of septum primum tissue; it is the most common form of a true ASD. The superior and posterior margins of the defect are composed of the septum secundum, the anterior margin is composed of the AV canal septum, and the inferior margin is composed of the septum primum and left venous valve of the inferior vena cava. These defects can vary in shape and can be elliptical or round ( Figure 8 ). With large ostium secundum defects, the septum primum is often nearly or completely absent. In some cases, persistent strands of septum primum will be present and will cross the defect, resulting in multiple communications and creating multiple fenestrations ( Figures 9–12 ). These ASDs typically range in size from several millimeters to as large as more than 3 cm in diameter. For example, in an autopsy series of 50 patients with secundum ASD, all the defects were classifiable into one of four morphologic categories: (1) virtual absence of the septum primum such that the ASD was the entire fossa ovalis (n = 19, 38%); (2) deficiency of the septum primum (n = 16, 32%); (3) a fenestrated septum primum creating multiple ASDs (n = 2, 4%); and (4) fenestrations in a deficient septum primum creating multiple ASDs (n = 13, 26%). These anatomic variations can have significant implications for device closure and could favor the use of devices designed for multiple fenestrations or require multiple devices for closure. Secundum ASDs can enlarge over time with age and cardiac growth.
An ostium secundum ASD is often amenable to percutaneous transcatheter closure. The evaluation for the suitability of transcatheter closure is reviewed in detail in the present document.
A rare form of ostium secundum ASD occurs when the superior limbic band of the septum secundum is absent. In such cases, the atrial communication is “high” in the septum, in close proximity to the SVC. However, these defects should not be confused with the sinus venosus defect of the SVC type. Importantly, the high ostium secundum ASD is not associated with anomalous pulmonary venous return. An absence of the septum secundum can also occur in the presence of left-sided juxtaposition of the atrial appendages. Juxtaposition of the atrial appendages describes the condition in which both atrial appendages (or one appendage and part of the other) lie beside each other and to one side of the great arterial vessels. The juxtaposition is commonly associated with significant congenital heart disease, including transposition of the great vessels. In juxtaposition, the normal infolding of the atrial roof (that forms the septum secundum) often does not occur because the great arteries are positioned abnormally (such as is seen with a double outlet ventricle or transposition of the great arteries). Although these defects do not involve the vena cavae, AV valves, pulmonary veins, or coronary sinus, it is important to recognize how close the defect is to these surrounding structures when considering catheter-based device closure.
Ostium Primum Atrial Septal Defect
An ostium primum ASD is a congenital anomaly that exists within the spectrum of an AV canal defect ( Figure 13 ). In early embryologic development, these defects occur when the endocardial cushions fail to fuse because of abnormal migration of mesenchymal cells. With an endocardial cushion defect, the canal portion of the AV septum and the AV valves can all be variably affected. Ostium primum ASD is otherwise known as partial or incomplete AV canal defect; these names are used interchangeably. The defect is characterized by an atrial communication resulting from absence of the AV canal portion of the atrial septum in association with a common AV valve annulus and two AV valve orifices. The AV valve tissue is adherent to the crest of the ventricular septum such that no ventricular level shunt is present. The leaflets of the two AV valves are abnormal with two bridging leaflets that straddle from the RV to the left ventricle (LV) rather than a normal anterior mitral valve leaflet and septal tricuspid valve leaflet. The bridging leaflets (superior and inferior) meet at the ventricular septum and are thus often erroneously termed “cleft mitral valve.” This term is indelibly in the lexicon of congenital heart disease. However, it is more accurate to use the left and right AV valves when describing an ostium primum ASD because both valves will always be abnormal in this setting. AV valve regurgitation through the so-called cleft is extremely common because of an abnormality or absence of valve tissue.
The borders of an ostium primum ASD include the septum primum superiorly and posteriorly and the common AV valve annulus anteriorly. Because these communications have the AV valve orifice as one of the margins, percutaneous transcatheter device closure is not possible.
Sinus Venosus Defects
Sinus venosus defects are less common than ostium secundum ASDs and are not true ASDs. These defects occur as a result of a partial or complete absence of the sinus venosus septum between the SVC and the right upper pulmonary vein (SVC type) or the right lower and middle pulmonary veins and the RA (inferior vena cava [IVC] type; Figures 14–16 ). In most cases of sinus venosus defects of the SVC type, the right upper pulmonary vein is connected normally but drains anomalously to the RA. However, in some cases, the right pulmonary vein or veins will be abnormally connected to the SVC superior to the RA. The shunt that occurs is therefore similar to that seen in a partial anomalous pulmonary venous connection in that the pulmonary venous flow is directed toward the RA. The resulting left-to-right shunt is typically large. Occasionally, the patient will be mildly desaturated because SVC blood is able to enter the LA. Sinus venosus defects of the IVC type are more unusual and typically involve anomalous drainage of the right middle and/or lower pulmonary veins. Sinus venosus defects cannot be closed by device and typically require baffling of the right pulmonary veins to the LA by way of an ASD patch. Reimplantation of the SVC (Warden procedure) is sometimes required if the right pulmonary veins are connected directly to the SVC.
Coronary Sinus Defects
A coronary sinus septal defect or an “unroofed” coronary sinus is one of the more rare forms of atrial communication. In this defect, the wall of the coronary sinus within the LA is deficient or completely absent ( Figures 17–19 ). In a heart without other major structural anomalies, LA blood enters the coronary sinus and drains into the RA through the coronary sinus os, which is typically enlarged to accommodate the increased flow. When a patent left SVC is associated with a coronary sinus septal defect, it is termed “Raghib syndrome.”
Contrast injection with agitated saline is often helpful to make the diagnosis. Two-dimensional (2D) and 3D TEE could be particularly useful in establishing the diagnosis and correlating with the surgical findings. In the setting of partial coronary sinus unroofing, percutaneous transcatheter device closure might be possible in some cases.
Common Atrium
Rarely, all components of the atrial septum, including the septum primum, septum secundum, and AV canal septum are absent, resulting in a common atrium. This is typically seen in association with heterotaxy syndrome. Some remnants of tissue might still be present in these patients.
Atrial Septal Aneurysm
An atrial septal aneurysm (ASA) is a redundancy or saccular deformity of the atrial septum and is associated with increased mobility of the atrial septal tissue. ASA is defined as excursion of the septal tissue (typically the fossa ovalis) of greater than 10 mm from the plane of the atrial septum into the RA or LA or a combined total excursion right and left of 15 mm ( Figure 10 ). The prevalence of ASA is 2%–3%. ASA has been associated with the presence of a PFO, as well as an increased size of a PFO, and an increased prevalence of cryptogenic stroke and other embolic events. ASA has also been associated with multiple septal fenestrations, and this should be evaluated for carefully using color Doppler imaging.
Eustachian Valve and Chiari Network
The eustachian valve is a remnant of the valve of the IVC that, during fetal life, directs IVC flow across the fossa ovalis. A large or prominent eustachian valve in the setting of a PFO might indirectly contribute to paradoxical embolism by preventing spontaneous closure of the foramen. The eustachian valve extends anterior from the IVC–RA junction.
A Chiari network is a remnant of the right valve of the sinus venosus and appears as a filamentous structure in various places in the RA, including near the entry of the IVC and coronary sinus into the RA ( Figure 20 ). A Chiari network is present in 2%–3% of the general population and is associated with the presence of PFO and ASA.
Key Points
PFO
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PFO is not a true deficiency of atrial septal tissue but rather a potential space or separation between the septum primum and septum secundum that occurs in up to 20%–25% of the population.
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PFO is defined by the demonstration of right to left shunting by contrast or color Doppler, and a “stretched” PFO is present when atrial hemodynamics have opened the foramen and result in left to right or right to left shunting demonstrated by Doppler imaging.
ASD
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Ostium secundum ASD occurs as a deficiency in septum primum and is the most common form of ASD.
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Ostium secundum ASD is often amenable to percutaneous transcatheter closure.
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Ostium secundum ASD defects can vary in shape and can be elliptical or round and can contain multiple fenestrations.
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Ostium primum ASD occur as a result a failure of fusion of the endocardial cushions and are within the spectrum of AV septal defects.
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Sinus venosus defects are not true ASDs and result from the absence of sinus venosus septum between right upper pulmonary veins and SVC (SVC type) or right middle and lower pulmonary veins and RA (IVC type).
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Coronary sinus defects (or unroofed coronary sinus) are not true ASDs and permit a left-to-right shunt from the LA to coronary sinus to the RA.
ASA
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ASA is defined as an excursion of septal tissue of >10 mm from the plane of the atrial septum into the atrium or a total excursion of >15 mm.
Imaging of the Interatrial Septum
General Imaging Approach
The most widely used ultrasound modality to evaluate the IAS is TTE, which remains the preferred initial diagnostic modality for the detection and diagnosis of PFO, ASD, and ASA. TTE is especially useful in small children in whom the ultrasound image quality will typically permit a full diagnostic study. It can also be used for patient selection and real-time transcatheter ASD or PFO closure procedural guidance in pediatric patients.
TTE can be used for the initial evaluation of ASD and PFO in adults; however, TEE is required to further characterize the atrial septal abnormalities, because the TTE image quality will not always permit a comprehensive evaluation of the IAS. TEE is not invariably required for assessment of a PFO if transcatheter closure is not being considered. Also, 2D and 3D TEE offers significant incremental anatomic information compared with TTE and should be performed in all adult patients being evaluated for percutaneous transcatheter closure or surgical therapy. In adults, TEE can identify the margins or rims of the ASD (see section on Assessment of ASDs: Standards and Characterization) and assess the surrounding structures (e.g., aorta, cavae, pulmonary veins, AV valves, and coronary sinus).
ICE has been used extensively to guide percutaneous ASD/PFO closure procedures and provides comparable (but not identical) imaging to TEE. ICE is discussed extensively in the subsequent sections (see sections on Intracardiac Echocardiographic Imaging Protocol for IAS and Role of Echocardiography in Transcatheter Device Closure).
Contrast echocardiography with agitated saline plays an important role in the evaluation of PFO and assessing residual shunts after transcatheter closure and has a more limited role in the diagnosis of ASD. Contrast echocardiography and contrast TCD is discussed further in sections on Assessment of Shunting; Techniques, Standards, and Characterization Visualization of Shunting: TTE and TEE; and Transcranial Doppler Detection/Grading of Shunting.
Table 1 summarizes the recommended general imaging approach to atrial septal abnormalities stratified by the patient characteristics, imaging modality, and intended application (e.g., diagnosis, procedure selection or guidance, follow-up).
| Patient population | Establishing diagnosis of ASD or PFO | Imaging for transcatheter procedure guidance | Routine postprocedure follow-up study |
|---|---|---|---|
| Pediatric patients <35–40 kg | TTE or TEE ∗ | TEE or ICE † | TTE |
| Pediatric patients >35–40 kg | TTE, TEE, 3D TEE | TEE, 3D TEE, or ICE † | TTE |
| Adult patients | TTE, TEE, or 3D TEE | TEE, 3D TEE, or ICE † | TTE |
∗ Depending on body surface area and adequacy of image quality, TEE is highly recommended for assessment of an ASD but is generally performed in intubated patients; if the weight is >35–40 kg, 3D TEE can be performed.
† Some centers use ICE for procedure guidance of all defects; others use ICE for uncomplicated small ASD closure only, reserving TEE or 3D TEE for complicated or larger septal defects.
Three-Dimensional Imaging of the Interatrial Septum
Most recently, 3D TEE has been described to improve the visualization of PFO and ASD, their surrounding tissue rims, and surrounding structures and can be used for guidance during percutaneous transcatheter closure. Because the IAS is a complex, dynamic, and 3D anatomic structure, limitations exist in its evaluation using any single form of 2D echocardiography. The IAS (and associated abnormalities such as ASD or PFO) does not exist in a true flat plane that can be easily aligned or interrogated using 2D imaging. Both ASD and PFO exist in a wide variety of heterogeneous sizes, shapes, and configurations ( Figures 8 and 21 ). Also, 3D imaging provides unique views of the IAS and, in particular, allows for en face viewing of the ASD and surrounding fossa, allowing for accurate determination of the ASD size and shape. Furthermore, 3D imaging offers the potential to clearly and comprehensively define the dynamic morphology of the defect, which has been shown to change during the cardiac cycle. Also, 3D imaging delineates the relationship of the ASD to the surrounding cardiac structures and the rims of tissue surrounding it ( Figure 22 ).
Two-dimensional biplane (or triplane) imaging, a feature of currently commercially available 3D imaging systems, is a unique modality that takes advantage of 3D technology. The advantages of biplane imaging include the display of simultaneous additional echocardiographic views, with high frame rates and excellent temporal resolution. Complimentary simultaneously displayed orthogonal plane imaging provides incremental information compared with that from a single plane, and this imaging modality is uniquely suited to transcatheter procedure guidance. Numerous reports of the advantages of 3D TEE in guiding catheter interventions have been published and include the use of biplane imaging. Figure 23 illustrates the use of biplane imaging during percutaneous transcatheter closure of ASD before deployment of the device.
Also, 3D imaging allows for multiple acquisition modes, including narrow-angle, zoomed, and wide-angle gated acquisition of multiple volumes. Once 3D volumes are acquired, postprocessing using commercially available 3D software packages such as QLAB (Philips, Best, The Netherlands) or 4D Cardio-View (TomTec, Munich, Germany) is performed to align the plane of the IAS with multiple 3D plane slices. This approach facilitates an assessment of the shape of an ASD and allows for measurement of the en face diameters in multiple orthogonal views, without the potential for bias due to malalignment of the ultrasound planes ( Figure 24 ). The images should be reviewed in both systole and diastole to assess for the dynamic change in size that can occur. This 3D en face display can also aid in the recognition and quantification of rim deficiencies, because the extent of the deficiency relative to the surrounding structures such as the aorta can be easily demonstrated and quantified. The distance between the defect and the aorta can be easily measured, just as can the area of the defect and length of rim deficiency when present.
Role of Echocardiography in Percutaneous Transcatheter Device Closure
The role of TTE, TEE, and ICE during the assessment and transcatheter management of ASD/PFO is essential. Echocardiography in patients undergoing transcatheter closure is critically important for appropriate patient selection, real-time procedure guidance, assessment of device efficacy and complications, and long-term follow-up.
TTE provides information about the type of defect, its hemodynamic significance, and any associated anomalies and can be used comprehensively in smaller pediatric patients for the diagnosis of ASD and PFO and for patient selection and procedure guidance. TTE has the advantage of offering unlimited multiple planes to evaluate the atrial septum, but it has limited ability to interrogate the lower rim of atrial septal tissue above the IVC after device placement because the device shadowing interferes with imaging in virtually all planes. In addition, because the septum is relatively far from the transducer, the image quality is often suboptimal in larger pediatric and adult patients. If percutaneous closure is clinically indicated, a detailed assessment of the IAS anatomy and surrounding structures using TEE is typically required for patient selection and procedure guidance or ICE for procedure guidance in such patients.
Transesophageal echocardiography provides real-time, highly detailed imaging of the IAS, surrounding structures, catheters, and closure device during transcatheter closure. It requires either conscious sedation, with the attendant aspiration risk in a supine patient, or general anesthesia, with an endotracheal tube placed to minimize aspiration risk. This approach also requires a dedicated echocardiographer to perform the TEE, while the interventionalist performs the transcatheter closure procedure. The advent of 3D TEE has enhanced the evaluation of ASD and PFO by clearly defining the IAS anatomy and enables an en face view of the defect and its surrounding structures. Multiplanar reconstruction of the 3D data set allows accurate measurement of the minimum and maximum dimensions of the defect or defects, facilitating selection of the optimal size and type of closure device. Moreover, intraprocedural real-time 3D TEE provides superior visualization of wires, catheters and devices, and their relationships to neighboring structures in a format that is generally more intuitively comprehended by the interventional cardiologist ( Figure 25 ).
Intracardiac echocardiography has been used extensively to guide percutaneous ASD/PFO closure procedures and is the imaging modality of choice in many centers in the cardiac catheterization laboratory. The advantages of ICE include an image quality that is similar (but not identical) to that of TEE, facilitating a comprehensive assessment of the IAS, location and size of the defects, the adequacy of the rims, and location of the pulmonary veins. It also retains an advantage compared with TEE in imaging the inferior and posterior portions of the IAS. Finally, the use of ICE eliminates the need for general anesthesia and endotracheal intubation and can be performed with the patient under conscious sedation. An interventionalist can perform ICE without the need for additional echocardiography support personnel. However, the potential disadvantages of ICE include a limited far-field view, catheter instability, the expense of single-use ICE catheters, the need for additional training, the risk of provocation of atrial arrhythmias, and increased technical difficulty for a single operator. Table 2 provides a summary of the advantages and disadvantages of TTE, TEE, and ICE in percutaneous transcatheter guidance of PFO and ASD.
| Modality | Advantages | Disadvantages |
|---|---|---|
| TTE | Readily available Low cost Unlimited multiple planes to evaluate IAS Noninvasive Does not require any additional sedation Excellent image quality in pediatric patients | Image quality in larger patients could be suboptimal Requires technologist or echocardiographer to perform study during closure Lower rim of IAS not well seen after device placement owing to shadowing in virtually all views |
| TEE | Improved image quality over TTE 3D technique adds incremental value over 2D technique in evaluating ASD size, shape, location Provides en face imaging that might be more intuitively understood to nonimagers | Requires additional sedation or anesthesia to perform Risks include aspiration and esophageal trauma Could require endotracheal intubation if prolonged procedure performed Requires additional echocardiographic operator to perform Patient discomfort |
| ICE | Comparable image quality to TEE Can be performed with patient under conscious sedation Reduces procedure and fluoroscopy times Superior to TEE for evaluating inferior aspects of IAS Interventionalist autonomy (can perform without additional support) | Invasive Risks of 8F–10F venous access and catheter, including vascular risk and arrhythmia Role of 3D technique to be defined Cost of single-use ICE catheters Limited far field views with some systems Need for additional training of ICE operator Operator might have two tasks (imaging and procedure) |
Transthoracic Echocardiography Imaging Protocol for Imaging the Interatrial Septum
The atrial septum can be evaluated fully using TTE. Ideally, multiple views should be used to evaluate the size, shape, and location of an atrial communication and the relationship of the defect to its surrounding structures ( Figures 9 and 13–17 and 26–28 ). In particular, special attention must be paid to determine the relationship of the defect to the venae cavae, pulmonary veins, mitral and tricuspid valves, and coronary sinus. Assessment of the amount of the surrounding rims of tissue present is crucial. A deficiency of rim tissue between the defect and pulmonary veins, AV valve, or IVC will preclude transcatheter closure, and a deficiency of aortic rim can increase the risk of device erosion in certain circumstances.
Additional views of other structures such as the ventricles and great arteries are necessary to assess for secondary findings related to the hemodynamic consequences of an ASD such as RA, right ventricular (RV), and pulmonary artery (PA) dilation. In the pediatric population, the subxiphoid window typically allows the best visualization of the atrial septum and its related structures. In adolescence and adulthood, the subxiphoid window is often inadequate because of the distance from the probe to the atrial septum. Thus, other views such as the parasternal windows should be used to assess the atrial septum. In some cases, a full assessment of the atrial septum might not be possible with TTE. Thus, TEE could be required.
Subxiphoid Frontal (Four-Chamber) TTE View
The subxiphoid frontal (four-chamber) view allows imaging of the atrial septum along its anterior–posterior axis from the SVC to the AV valves. This is the preferred view for imaging the atrial septum, because the atrial septum runs near perpendicularly to the ultrasound beam, providing the highest axial resolution and permitting measurement of the defect diameter along its long axis. Because the septum is thin (especially in its midportion), placing the septum perpendicular to the ultrasound beam helps distinguish a true defect from dropout resulting from an artifact. Aneurysms of the atrial septum primum composed of tissue attached to the edges of the ASD are also well visualized from the subcostal frontal view. ASAs could be fenestrated ( Figure 9 ) but also can be intact with no resultant atrial level shunt. Color Doppler interrogation and contrast studies should be used to detect shunting. The surrounding rim from the defect to the right pulmonary veins can be measured in this view. Sinus venosus defects will be difficult to visualize because the venae cavae are not viewed longitudinally in this view.
Subxiphoid Sagittal TTE View
The subxiphoid sagittal TTE view is acquired by turning the transducer 90° clockwise from the frontal view. This view is ideal for imaging the atrial septum along its superior–inferior axis in a plane orthogonal to the subxiphoid frontal four-chamber view. Sweeping the transducer from right to left in this axis allows determination of the orthogonal dimension of the ASD ( Figures 15 and 17 ). This dimension can be compared with the dimension measured in the subxiphoid frontal view to help determine the shape (circular or oval) of the defect. This view can be used to measure the rim from the defect to the SVC and IVC and is an excellent window to image a sinus venosus type defect ( Figures 14B and 15 ).
Left Anterior Oblique TTE View
The left anterior oblique TTE view is acquired by turning the transducer approximately 45° counterclockwise from the frontal (four-chamber) view. This view allows imaging of the length of the atrial septum and is therefore ideal to identify ostium primum ASDs and for assessment of coronary sinus dilation ( Figures 13B and 17 B). In addition, it allows evaluation of the relation of the SVC to the defect. Furthermore, this view can be used to evaluate the entrance of the right-sided pulmonary veins into the heart.
Apical Four-Chamber TTE View
In the apical four-chamber TTE view, the diagnosis and measurement of ASDs should be avoided because the atrial septum is aligned parallel to the ultrasound beam. Thus, artifactual dropout is frequently seen in this view, which could result in overestimation of the defect size. This view is used to assess the hemodynamic consequences of ASDs, such as RA and RV dilation, and to estimate RV pressure using the tricuspid valve regurgitant jet velocity. This view is also used to evaluate for right-to-left shunting with agitated saline ( Figure 29 ).
Modified Apical Four-Chamber TTE View (Half Way in Between Apical Four-Chamber and Parasternal Short-Axis View)
The modified apical four-chamber TTE view is obtained by sliding the transducer medially from the apical four-chamber view to the sternal border. This view highlights the atrial septum at an improved incidence angle to the sound bean (30°–45°). In the patients in whom the subcostal views are difficult to obtain, the modified apical four-chamber view is an alternative method for imaging the atrial septum in the direction of the axial resolution of the equipment.
Parasternal Short-Axis TTE View
In the parasternal short-axis TTE view at the base of the heart, the atrial septum is visualized posterior to the aortic root running in an anterior–posterior orientation. This view is ideal to identify the aortic rim of the defect ( Figures 26 and 27 ). It also highlights the posterior rim (or lack thereof) in sinus venosus and posteroinferior secundum defects. The size of the defect itself should not be measured in this view, because the beam orientation is parallel to the septum, and drop out resulting from artifact can occur.
High Right Parasternal View
The high right parasternal view is a parasagittal view performed with the patient in the right lateral decubitus position with the probe in the superior–inferior orientation. In this view, the atrial septum is aligned perpendicular to the beam and is ideal for diagnosing sinus venosus defects, particularly when the subxiphoid windows are inadequate ( Figure 16 ).
Table 3 summarizes the key imaging views for TTE for the evaluation of the IAS and surrounding structures.
Transesophageal Echocardiography Imaging Protocol for the Interatrial Septum
As with TTE, multiple and sequential TEE views should be used to completely and systematically evaluate the IAS, the size, shape, and location of any atrial communication present, and the relationship of the defect to its surrounding structures. A comprehensive guide to performing multiplane TEE has been previously published by the ASE and the Society of Cardiovascular Anesthesiologists, and should be referred to for recommendations on performing a comprehensive TEE examination.
We recommend sequential interrogation and the digital capture of images starting from the standard views and then by stepwise increases in the transducer angle in a series of 15° increments to pan or sweep the ultrasound beam through the areas of interest. Two-dimensional images should be optimized and color Doppler mapping subsequently applied. The color Doppler scale can be reduced slightly to approximately 35–40 cm/sec to capture low-velocity flow across a small fenestration, PFO, or smaller ASD. Pulsed and continuous wave Doppler should then be used to measure the velocity, direction, and timing of flow in the representative views.
Capturing 3D volumes with and without color Doppler of the IAS allows for even greater data acquisition without the need for sequential multiplane interrogation and acquisition and is discussed separately in the section on 3D TEE Acquisition Protocol for PFO and ASD.
When an ASD or PFO is present, attention must be given to determining the relationship of the defect to the venae cavae, pulmonary veins, mitral and tricuspid valves, and coronary sinus. An assessment of the amount of the surrounding rims of tissue is critical for evaluation of patient candidacy for percutaneous transcatheter closure. A deficient rim is defined as less than 5 mm in multiple sequential views, and this should be evaluated in at least three sequential related multiplane views in 15° increments.
As with TTE, additional views of the other cardiac structures are necessary to assess for secondary findings related to the hemodynamic consequences of an ASD such as right heart and pulmonary arterial dilation. Please refer to the ASE guidelines on comprehensive TEE assessment and the assessment of the right heart.
When using TEE, five base views are used to assess the IAS and surrounding structures, which are summarized in Table 4 . These key views include the upper esophageal short-axis view, midesophageal aortic valve (AoV) short-axis view, midesophageal four-chamber view, midesophageal bicaval view, and midesophageal long-axis view.
Upper Esophageal Short-Axis View
The upper esophageal short-axis view is obtained from the upper esophagus starting at multiplane angles of 0°, with stepwise sweeping and recording at 15°, 30°, and 45°. This view facilitates imaging of the superior aspects of the atrial septum, including the septum secundum, the roofs of the RA and LA, and the surrounding great vessels (SVC and ascending aorta). Entry of the right pulmonary veins can be demonstrated by insertion into the mid-esophagus and by clockwise rotation of the probe in these views ( Figure 30 ). Anomalous pulmonary venous drainage and an SVC type sinus venosus defect can be noted in this view.
Midesophageal Aortic Valve Short-Axis View
The midesophageal AoV short-axis view is obtained from the mid-esophagus starting with a multiplane angle of approximately 30° and stepwise sweeping through and recording additional views at 45°, 60°, and 75°. This progression of transducer angles allows transitional interrogation of the IAS from the AoV short-axis view to the modified bicaval tricuspid valve view. The AoV short-axis view is typically obtained to present short-axis views of the AoV and its surrounding septum. This view facilitates imaging of the anterior and posterior planes of the atrial septum (and aortic and posterior rims if an ASD is present), the anteroposterior diameter of the ASD, and the overlap of septum primum and septum secundum when a PFO is present ( Figures 31 and 32 ).
Midesophageal Four-Chamber View
The midesophageal four-chamber view is obtained from the mid-esophagus beginning with a multiplane angles of 0° and stepwise increases of the multiplane angle to 15° and 30°. This view is used to evaluate the AV septum (deficient in primum ASD) and the relationship of any ASD to the AV valves ( Figure 33 ). Larger devices used to close secundum ASD can interfere or impinge on AV valve function, and this must be carefully evaluated before device deployment ( Figure 34 ).
Midesophageal Bicaval View
The midesophageal bicaval view is obtained from the mid-esophagus with multiplane angles of 90°, 105°, and 120°. It is used to image the inferior and superior plane of the atrial septum and the surrounding structures, such as the SVC and right pulmonary veins ( Figures 4, 5, 7, 10A–C,11A and B, 12A, 35, and 36 ). This view is important for evaluating sinus venosus defects of the SVC type and to evaluate for anomalous pulmonary vein insertion. This view is also important in evaluating the roof or dome of the RA, which must be visualized before release of ASD closure devices.
Mid-Esophageal Long-Axis View
The midesophageal long-axis view is obtained from the mid-esophagus with multiplane angles of 120°, 135°, and 150° to evaluate the roof or dome of the LA when a percutaneous device is placed (see the section on the Role of Echocardiography in Percutaneous Transcatheter Device Closure). Rotation past the LA appendage demonstrates the entry of the left pulmonary veins into the LA ( Figure 37 ).
3D TEE Acquisition Protocol for PFO and ASD
Three-dimensional transesophageal images of the IAS should be acquired from multiple views and multiple 3D imaging modes for analysis. A comprehensive description of overall 3D image acquisition, formatting, and presentation can be found in the 2012 ASE guidelines.
A comprehensive 3D examination usually begins with a real-time or narrow-angled acquisition from the standard imaging views. To obtain images with higher temporal and spatial resolution, electrocardiographically gated, 3D wide-angled acquisitions are then performed. When evaluating the IAS using TEE, we recommend narrow-angled, zoomed, and wide-angled acquisition of 3D data from several key views:
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Midesophageal short-axis view: acquired from the mid-esophagus starting at a multiplane angle of 0°. The probe is rotated toward the IAS. This view is particularly suited to narrow- and wide-angled acquisitions.
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Basal short-axis view: acquired from the mid-esophagus starting at 30° to 60° multiplane angles. This view is particularly suited to narrow- and wide-angled acquisitions. This view can also be used for zoom mode imaging during procedure guidance. Processing the 3D images from this view facilitates the demonstration of an ASD en face and demonstrates the relationship to the surrounding structures (e.g., the aorta and aortic rim) ( Figures 38 and 39 A and B ). Wide-angled acquisition from this view should be acquired with and without color Doppler flow mapping for precise offline measurements of ASD size, shape, dynamic change, and relationship to surrounding structures.
Figure 38
Real-time 3D TEE images from the midesophageal short-axis views of a PFO during a saline contrast study. The PFO exit into the LA is apparent ( blue arrow ). This is performed to help localize the site of bubble entry into the LA and not to quantify the size of the shunt. (A–C) Progressive saline contrast microbubbles crossing through the PFO into the LA. Blue arrow indicates PFO tunnel. See also Video 18 .
Figure 39
Real-time 3D TEE images of an ostium secundum ASD from the (A) RA perspective demonstrating an ASD en face from the midesophageal short-axis view, (B) RA perspective demonstrating the aortic rim ( arrow ) from the midesophageal short-axis view, and (C) LA perspective from the four-chamber view also demonstrating the aortic rim. MV , mitral valve.
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Bicaval view: acquired from the midesophageal level with the transducer starting at the 90° to 120° multiplane orientation. This view can also be captured by each of the 3D imaging modalities. The depth of pyramidal data sets should be adjusted to include only the left and right sides of the atrial septum in this view. This specific setting will allow the entire septum to be acquired in a 3D format without incorporating the surrounding structures. With a 90° up–down angulation of the pyramidal data set, the entire left-sided aspect of the septum can shown in an “en face perspective” ( Figure 40 ). Once the left side of the atrial septum has been acquired, a 180° counterclockwise rotation will show the right side of the atrial septum and the fossa ovalis as a depression on the septum ( Figure 41 ). Sometimes the use of fine cropping using the arbitrary crop plane will be necessary to remove the surrounding atrial structures that can obscure the septum. A gain setting at medium level is usually required to avoid the disappearance of the fossa ovalis and creating a false impression of an ASD. This view is also used to measure the size and shape of the ASD in systole and diastole.
