Atrial septal defects

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.

ASD occurs in the form of: 

• ostium secundum (fossa ovalis)
• ostium primum (inferiorly by the tricuspid valve)
• sinus venosus (near superior or inferior vena caval entry)
• and rarely, coronary sinus defects 

PFO is not a true deficiency of atrial septal tissue but rather a potential space or separation between the septum primum and septum secundum. 

Image 1 Atrial septal defect types

Silvestry FE, Cohen MS, Armsby LB, Burkule NJ, Fleishman CE, Hijazi ZM, Lang RM, Rome JJ, Wang Y; American Society of Echocardiography; Society for Cardiac Angiography and Interventions. Guidelines for the Echocardiographic Assessment of Atrial Septal Defect and Patent Foramen Ovale: From the American Society of Echocardiography and Society for Cardiac Angiography and Interventions. J Am Soc Echocardiogr. 2015 Aug;28(8):910-58. doi: 10.1016/j.echo.2015.05.015. PMID: 26239900.

Pathophysiology 

ASDs are associated with left-to-right shunt which causes volume overload of the right heart chambers, which is generally tolerated well for years.

The severity of the shunt is determined by the size of the defect and atrial and ventricular compliance and pressure.

The shunt flow due to an ASD moves from the left to the right atrium, right ventricle (RV), pulmonary circulation, back to the left atrium, and through the defect back to the right atrium.

The development of progressive pulmonary vascular disease and pulmonary hypertension is highly variable and depends not only on the size and duration of the shunt but also the presence of other left-to-right shunts such as partial anomalous pulmonary venous connection.

Clinical manifestation 

Very small ASDs (diameter <5 mm) may not have significant clinical consequences.

Defect of 5–10 mm may lead to symptoms in the fourth or fifth decade of life.

Larger defects (generally >10 mm) typically present with symptoms in the third decade of life.

It is estimated that most patients with an ASD and significant shunt flow (ie, pulmonary to systemic blood flow ratio [Qp:Qs] ≥1.5:1) will become symptomatic and require surgical correction or percutaneous repair by the age of 40 years. 

When symptoms occur, patients often first notice dyspnea, fatigue, exercise intolerance, or palpitations.

Some patients may present with syncope or even with peripheral edema from overt right heart failure and others may develop recurrent pulmonary infections.

Atrial tachyarrhythmias, including atrial fibrillation and flutter, are present preoperatively in about one-fifth of adults with ASDs.

In patients who have a stroke, transient ischemic attack, or peripheral arterial embolization, the clinical question commonly arises about paradoxical embolization as the underlying pathophysiologic mechanism.

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On physical examination, a patient with an ASD may have a right ventricular heave, systolic flow murmur in the pulmonary valve region due to increased pulmonary flow, a fixed split second heart sound, or a diastolic flow rumble across the tricuspid valve.

ECG signs of a secundum ASD include:

• right axis deviation
• right atrial enlargement
• voltage evidence of right ventricular hypertrophy
• incomplete right bundle branch block

Chest x-ray findings that are compatible with an ASD include cardiomegaly, pulmonary artery enlargement, or increased pulmonary vascularity.

ECHOCARDIOGRAPHY ASSESSMENT

TTE with Doppler is generally the initial test for diagnosis and evaluation of ASDs, as it identifies most secundum and primum ASDs.  

TEE provides superior image quality to TTE.

3D imaging provides unique views of the IAS and, in particular, allows for en face viewing of an ASD and the surrounding structures for accurate determination of ASD size and shape, to delineate the rims of surrounding tissue, and to determine the relationship of the ASD to the surrounding cardiac structures.

Transthoracic Echocardiography Imaging Protocol for Imaging the Interatrial Septum

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.

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.

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Basic echo principles when imaging patients with an ASD

What to look for on 2D:

• Classify ASD.
• Measure ASD size/area.
• Examine MV structure and function. Look for prolapse/cleft. Measure annulus.
• Examine TV structure and function. Look for prolapse. Measure annulus.
• Examine PV drainage especially right sided PVs.
• Assess for right atrial and ventricular enlargement.
• Assess biventricular function.
• Examine morphology/function of pulmonary valve. Look for doming leaflets, commissural fusion, and restricted motion. Measure PA size.
• Evaluate for evidence of Pulmonary hypertension.
• Look for an Left superior vena cava draining into the Coronary sinus, located between the Left upper pulmonary vein and Left atrial appendage. In a patient with an unroofed coronary sinus, a bubble study with agitated saline injected into a left hand intravenous line would opacify the LA before bubbles are seen entering the RA. If the above patient also has a bridging vein (innominate vein) opacification of the RA and LA may occur almost simultaneously. In a patient with any other ASD (except an unroofed CS ASD), opacification of both the RA and LA will occur because of the atrial communication, but opacification of the RA will precede the LA.

Common views in TTE: 

• Subxiphoid frontal

Allows imaging of the atrial septum along its anterior-posterior axis from the SVC to the AV valves.

• Subxiphoid Sagittal

Is acquired by turning the transducer 90 clockwise from the frontal view. 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.

• Left Anterior Oblique

Is acquired by turning the transducer approximately 45 counterclockwise from the frontal (4C) view. This view allows imaging of the length of the atrial septum and is therefore ideal to identify ostium primum ADSs and for assessment of coronary sinus dilation.

• Apical Four-Chamber

Is used to assess the hemodynamic consequences of ASDs, such as RA and RV dilatation, 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.

• Modified Apical Four-Chamber

In the patients in whom the subcostal view is difficult to obtain, the modified apical 4C view is an alternative method for imaging the atrial septum.

• Parasternal Short-Axis

Is ideal to identify the aortic rim of the defect. Also highlights the posterior rim (or lack thereof) in sinus venosus and posteroinferior secundum defects.

• High Right Parasternal 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 defect,particularly when the subxiphoid windows are inadequate.

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What to look for with Doppler:

• Color Flow Doppler (CFD) and Pulse Wave Doppler (PW) for direction of flow through ASD. (Predominant L to R in uncomplicated ASD’s).
• CFD/PW to locate PV flow.
• CFD/CW to grade MR, TR.
• Estimate PASP if TR is present.
• CFD/CW to assess for pulmonary valve stenosis. Velocities up to 2.5 m/sec may result from ASD flow alone.
• CFD used to localize an LSVC.

• The direction of shunting through an ASD by color Doppler is typically left to right. The color scale settings should be optimized for the expected low velocity of shunt flow (i.e., 25–40 cm/sec).
• ASD shunt flow can be right to left or bidirectional in the setting of significant pulmonary hypertension or impaired RV compliance. Pulse wave spectral Doppler can be used for detection of bidirectional shunting in addition to color Doppler.
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• Color flow Doppler can detect shunting across a PFO when it has been stretched open by differences in atrial pressure; however, the shunting is often intermittent and might not be readily detectable using color flow Doppler. 
• TEE is considered the reference standard for detection of a PFO.
• Echo bubble study - agitated saline with provocative maneuvers to transiently increase the RA pressure.  
• Bubble studies can provide false-negative findings owing to inadequate opacification of the RA, an inadequate Valsalva maneuver, a prominent eustachian valve directing venous return from the IVC to the IAS and preventing microbubbles entering from the SVC to cross the IAS, an inability to increase the RA pressure above the LA pressure, and poor image quality. 
• The most pronounced echocardiographic finding associated with a left-to-right shunt is dilatation of the RV, for which multiple echocardiographic methods are available for measurement.  Echocardiographic assessment of the magnitude of shunting by Qp/Qs estimation and the assessment of RV function completes the assessment of patients with an ASD.
• Once a PFO has been identified, if catheter closure is being contemplated, a detailed evaluation of the atrial septal anatomy should be performed using TEE or ICE. 
• The anatomic details of the atrial septum when a PFO is present that should be routinely evaluated include the location of the PFO, thickness and extent of septum secundum, total length of the atrial septum, length of the PFO tunnel, size of the PFO at the RA and LA ends, distance of the PFO from the venae cavae, presence of an ASA, and presence of additional atrial septal fenestrations or defects.

 ASD secundum rims

• SVC or superior margin
• IVC or inferior margin
• Posterior margin
• Anterior or retroaortic margin
• Mitral rim

‍Views to identify the ASD rims:

1) PSAX view at great vessel level: Aortic and Post rim

2) A4C view: Mitral Rim

3) Subcostal view: SVC and IVC rim

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ECHO BUBBLE STUDY

Is performed to detect shunts (PFO, ASD, persistent left superior vena cava).

In case of ASD or PFO; the bubbles should appear on the left side of the heart within the first 3 to 4 cardiac cycles.

If no bubbles appear in the left side then the patient is instructed to perform Valsalva maneuver (which leads to opening of PFO during it’s release) and bubbles appear in the left side in case of PFO.

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PFO videos and images

Video 1a  Suspicion on PFO was established already from TTE, A4C view

Video 1b  Patent foramen ovale (PFO) with applied agitated saline filling the right heart, A4C view - note the bubbles travelling to the left atrium through the PFO right-to-left shunt (withing 4 beats)

Video 1c  Patent foramen ovale (PFO) with applied agitated saline.  The Valsalva Maneuver is performed to transiently increase the RA pressure over the LA pressure to reveal presence of right-to-left shunt. Below you can see the echo contrast moved through the PFO to the left heart.

Video 2a PFO apparent on TEE examination

Video 2b Hypermobile septum with PFO in the same patient

Image 2c Measurement of PFO (21x3 mm)

‍Image 2d  Patent foramen ovale (PFO), TEE view of the interatrial septum in bicaval view = 20 mm

Video 3a PFO with L-R shunt documented with Colour Doppler

Video 3b Positive bubble study in the same patient with PFO

‍Video 4a  Aneurysm of the IAS with patent foramen ovale (PFO) and left-to-right shunt, A4C view colour Doppler - the aneurysmatic septum is seen fluttering to the right atrium. 

Video 4b  Aneurysm of IAS with PFO assessed using contrast on TTE - apart from the L-P shunt visible on colour Doppler, a right-to-left shunt was revealed after application of the contrast. The bubbles are seen traveling to the left side of the heart even without the need of Valsalva Maneuver.

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Atrial septal defects videos and images

Video 5a TEE assessment of atrial septal defect, secundum type

 Video 5b  TEE view of secundum ASD, colour Doppler reveals blood flowing through the shunt

Video 6 ASD type secundum - TEE

Image 3 TEE, 3D view of atrial septal defect, secundum type with diameter of the defect measurement (16x17 mm)

 Image 4 TEE, Secundum ASD measurement

Image 6 Rim measurement by aortic valve (3 mm)

‍Video 7  Hemodynamically significant Secundum ASD with left-to-right shunting, PSAX - note the greatly enlarged right ventricle with dilation of the tricuspid annulus, PSAX at the level of the tricuspid and mitral valve.

Video 8a  Ostium secundum ASD with left-to-right shunting, colour Doppler applied - the small flow through the shunt to the right atrium is visualized with the colour Doppler. Vena contracta of the flow is 5 mm. This ASD is deemed insignificant at this point (Qp:Qs 1,1-1,2).

Video 8b  The same secundum ASD, PSAX view -  note the flow through the ASD

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ASD secundum device closure criteria

1. “Significant” ASDs (Qp/Qs > 1.5 or ASDs associated with right ventricular volume overload)
2. Secundum ASD that has a stretched diameter of less than 38mm and more than 10mm
3. Adequate rims (5mm) to enable secure deployment of the device 
4. Anomalous pulmonary venous connection of proximity of the defect to the AV valves or coronary sinus or systemic venous drainage, intracardiac trombie absent

PFO closure indications

1. Cyptogenic stroke
2. Migraine
3. Platypnea-orthodeoxia syndrome
4. Decompression illness.

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Video 9a  TEE navigation for Amplatz occluder placement

 Video 9b  Amplatz occluder in situ

 Video 9c  Amplatz occluder in situ, colour Doppler shows no residual shunt

 Video 9d  Amplatz occluder as seen on TTE, A4C view

References

1.  Martin SS, Shapiro EP, Mukherjee M. Atrial septal defects - clinical manifestations, echo assessment, and intervention. Clin Med Insights Cardiol. 2015;8(Suppl 1):93-98. Published 2015 Mar 23. doi:10.4137/CMC.S15715
2. Silvestry FE, Cohen MS, Armsby LB, Burkule NJ, Fleishman CE, Hijazi ZM, Lang RM, Rome JJ, Wang Y; American Society of Echocardiography; Society for Cardiac Angiography and Interventions. Guidelines for the Echocardiographic Assessment of Atrial Septal Defect and Patent Foramen Ovale: From the American Society of Echocardiography and Society for Cardiac Angiography and Interventions. J Am Soc Echocardiogr. 2015 Aug;28(8):910-58. doi: 10.1016/j.echo.2015.05.015. PMID: 26239900.
3. Atrial Septal Defects - Congenital Cardiac Anesthesia Society. Congenital Cardiac Anesthesia Society - Congenital Cardiac Anesthesia Society [online]. Copyright © 2020 The Congenital Cardiac Anesthesia Society [cit. 04.09.2021]. Available from: https://ccasociety.org/education/echoimage/asd-echo/
4. Echocardia - Wiki. Echocardia - Overview [online]. Available from: https://echocardia.com/en/wiki.html/ASD
5. Asd echo assessment. Share and Discover Knowledge on SlideShare [online]. Available from: https://www.slideshare.net/zaber15/asd-echo-assessment
6. Naser M Ammash, Heidi M Connolly, Susan B Yeon. Clinical manifestations and diagnosis of atrial septal defects in adults. Available from: https://www.uptodate.com/contents/clinical-manifestations-and-diagnosis-of-atrial-septal-defects-in-adults?search=atrial%20septal%20defect%20&source=search_result&selectedTitle=2~150&usage_type=default&display_rank=2