5 Shunting Lesions

Brandy Hattendorf

Cardiac shunting lesions include atrial septal defects, ventricular septal defects, and patent ductus arteriosus as the most common lesions seen in congenital heart disease. These lesions may be seen in isolation or in association with other congenital heart disease.

Atrial Septal Defects

Atrial deptal defects represent defects in septation of the atria. They are common, representing as much as 10% of cases of congenital heart disease. Anatomic types of defects include (Fig. 5-1):

• Patent foramen ovale (PFO).

• Ostium secundum atrial septal defect (ASD).

• Ostium primum ASD.

• Sinus venosus ASD.

• Coronary sinus (CS) ASD.

Figure 5-1 Diagram of the atrial septum showing several types of atrial septal defects.

(Adapted from Fyler DC [ed], Nadas’ Pediatric Cardiology. Philadadelphia: Hanley & Belfus, 1992.)

Patent Foramen Ovale

• An interatrial communication between the superior limb of the septum secundum on the right side and the septum primum on the left atrial side (Fig. 5-2).

• The flap of the foramen ovale (FO) can often be seen (Fig. 5-3).

• Functionally closes after birth but may be present in as many as 25% of normal hearts during pathologic evaluation.

Figure 5-2 Diagram of atrial septal components, showing foramen ovale (FO; arrow), septum primum (Sept 1°), left atrium (LA), left ventricle (LV), fossa ovalis, superior limbic bands (SLB) and inferior limbic bands (ILB), atrioventricular septum (AVS), right atrium (RA), and right ventricle (RV).

(From Keane JF, Lock, JE, Fyler DC [eds], Nadas’ Pediatric Cardiology, 2nd ed. Philadelphia: Elsevier/Saunders, 2006.)

Figure 5-3 Subcostal image of a patent foramen ovale (PFO). A, A flap of tissue is seen partially occluding the communication. B, Subcostal image a PFO with color Doppler. Left-to-right shunting is seen. The size of the defect is overestimated by the width of the color jet compared with the two-dimensional size of the defect in part A.

Key Points

• Persists in a normal newborn to 6 months of age.

• Is not a congenital ASD.

Ostium Secundum Atrial Septal Defect

• Defect in the septum primum.

• Most common type of ASD.

• 70% of ASDs are secundum defects (Fig. 5-4).

Figure 5-4 Subcostal image of a secundum atrial septal defect (ASD). A, In this two-dimensional image, the true size of the atrial septal defect is seen. Septal rims are noted superior and inferior to the defect. Right atrial enlargement is also seen. B, With color on the same image, a red color jet is seen representing left-to-right flow across the defect.

Key Points

• Many secundum atrial septal defects may be closed percutaneously in the cardiac catheterization laboratory via device.

• Closure via device depends on the septal rims and size of the defect.

• A secundum atrial septal defect is best imaged from the subcostal plane.

Ostium Primum Atrial Septal Defect

• Located in the most anterior and inferior aspects of the atrial septum.

• Deficient atrioventricular (AV) septation.

Key Points

• Associated with trisomy 21.

• Usually seen in association with AV septal defects with a cleft in the anterior leaflet of the mitral valve, although primum defects can occur in isolation.

• Both AV valves (AVVs) appear at the same level.

• The tricuspid valve (TV) will not be apically displaced.

• Best imaged in apical view.

• Allows for assessment of the atrial septum in relationship to the crux of the heart.

Sinus Venosus Atrial Septal Defects: Two Types

• Superior sinus venosus defects: located in the most superior and posterior region of the atrial septum in close proximity to the right-sided pulmonary veins (PVs) and the entrance of the superior vena cava (SVC) into the right atrium (RA) (Fig. 5-5).

• Inferior sinus venosus defects: located posterior and inferior to the fossa ovalis and adjacent to the inferior vena cava.

Figure 5-5 Subcostal image of a sinus venosus defect located in the most superior and posterior region of the atrial septum. This defect is associated with partial anomalous pulmonary venous return.

Key Points

• Both types are associated with partial anomalous pulmonary venous return.

• Commonly the right upper PVs (Fig. 5-5).

Coronary Sinus Atrial Septal Defect

• Least common.

• The left SVC empties into the left atrium.

Key Point

• Associated with a persistent left SVC and unroofed CS.

The Echocardiography (Echo) Exam: Step-by-Step Approach

Step 1: Evaluate the Location of the Atrial Septal Defect

• Most ASDs are best imaged from a subcostal view.

• Parasternal short axis view may also be used.

• The apical view is not used for measurements or assessment of most ASDs.

• The atrial septum is thin, particularly in the region of the fossa ovalis.

• From an apical view, the septum is parallel to the ultrasound beam, resulting in dropout.

• Evaluate surrounding structures including PVs, the SVC, inferior vena cava, and CS.

• Pulmonary venous anomalies are associated with sinus venosus defects.

• Agitated saline solution is the preferred contrast used in pediatrics.

• Contrast echocardiography is performed by rapid injection of agitated saline solution into a peripheral vein.

• Upper extremity veins are preferred.

• Filling of the left atrium with contrast echoes confirms the presence of an interatrial communication.

Key Points

• Ostium primum defects are best imaged from an apical four-chamber (4C) view.

• Dropout can occur in the region of the fossa ovalis, giving the impression that an ASD exists in a normal heart or making an existing defect appear larger when imaged from an apical view.

• Evaluate AVV regurgitation, especially in the presence of a primum ASD or a cleft in the anterior leaflet of the mitral valve.

• Injection into the left arm in a patient with a persistent left superior vena caval draining to a CS may cause confusion by resulting in contrast seen in the left atrium.

Step 2: Evaluate the Atrial Septal Defect Dimensions and Position

• A PFO is a defect in the septum primum less than 3 mm in size without associated right atrial or right ventricular dilation and typically with a flap of tissue partially occluding the communication.

• ASD size is quantified as:

• Small: 3 to 5 mm in size.

• Moderate: 5 to 8 mm in size.

• Large: 8 mm or larger.

Key Points

• ASDs may enlarge over time as the right ventricle (RV) becomes more compliant.

• ASDs may also become smaller over time and close spontaneously.

• Spontaneous closure is more common in the first few years of life.

• Evaluate for additional defects and fenestrated defects.

• In ostium secundum ASDs, septal rims and total septal length should be measured to assess for possible transcatheter device closure.

• Contrast echocardiography (echo) can be used to detect interatrial communications if the atrial septum is not well visualized.

Step 3: Evaluate the Direction of the Shunt

• Can be determined primarily by color Doppler.

• Shunting can be phasic, varying during systole and diastole.

Key Points

• Most shunting is left to right.

• Spectral Doppler may be helpful if the ultrasound beam can be aligned in a parallel fashion. However, velocity of flow is not usually helpful in that a pressure gradient between left and right atria greater than 2 to 3 mm Hg is rare.

Step 4: Determine the Size of the Shunt

• The degree of shunting is determined by ventricular compliance.

• The left-to-right shunt across an ASD is often minimal during infancy as the RV is initially less compliant.

Key Points

• Left-to-right shunt increases with age.

• Shunting is usually low velocity and biphasic.

Step 5: Evaluate the Effects of Shunting

• In hemodynamically significant shunts, volume overload may result in:

• Right atrial enlargement.

• Right ventricular enlargement.

• Main and branch pulmonary artery (PA) enlargement.

• Left atrial enlargement.

• The interventricular septum (IVS) may appear flat during diastole.

• Right ventricular dilation with paradoxical septal motion may be present.

Post-Device Atrial Septum Defect Closure Evaluation: Special Considerations

• Evaluate the location of the device monitoring for device migration.

• Evaluate for impingement or distortion of surrounding structures.

• Aortic erosion is a rare but serious complication after device closure of an ASD.

Key Points

• Determine whether a residual shunt is present.

• “Speckling” may be seen representing blood swirling within the device without the presence of a shunt across the septum.

• Residual shunts may close spontaneously with endothelialization of the device over time after device closure.

Postoperative Evaluation: Special Considerations

• Primary closure: pericardial patch or artificial material such as GORE-TEX may be used to close the defect.

• An intra-atrial baffle may be present for sinus venosus or CS defects.

• Evaluate the atrial septum for any residual shunting as well.

• If a baffle is present, evaluate the baffle for leaks and stenosis.

Key Point

• The patch or baffle should appear well placed without dehiscence or impingement of surrounding structures.

Ventricular Septal Defects

A ventricular septal defect is a communication within the interventricular septum that seperates the left ventricle (LV) and RV, allowing for shunting for blood between the ventricles. VSDs represent 20% of congenital heart disease. VSDs can be classified as follows (Fig. 5-6):

• Membranous (Gerbode defect).

• Perimembranous.

• Also called infracristal.

• Muscular.

• Supracristal.

• Also called subpulmonic, doubly committed subarterial defect, and/or outlet ventricular septal defects (VSDs).

• Inlet.

• Also called AV canal (AVC) type defects.

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2. The Pediatric Transthoracic Echocardiogram
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