A 6-year-old presented for ostium primum atrial septal defect (ASD) closure. She had moderate right ventricular (RV) dilation and mild mitral regurgitation. She underwent surgical repair and had an uneventful postoperative course.
Morphologically, there are 4 types of ASDs: ostium secundum, ostium primum, sinus venosus, and coronary sinus (CS) (Table 1). Pathophysiology involves left-to-right interatrial shunting, which diminishes effective forward left ventricular flow and results in RV volume overload (RVVO). A pulmonary-to-systemic flow ratio >1.5 is indicative of significant left-to-right shunting and is an indication for repair to alleviate or prevent RVVO and possible pulmonary vascular resistance changes. Irreversible increases in pulmonary vascular resistance may result in development of pulmonary hypertension, but this is less likely and occurs later than with a ventricular defect or arterial-to-pulmonary communication. On transesophageal echocardiography, RVVO is noted by a late diastolic, leftward-shifting of the interventricular septum with associated tricuspid regurgitation (TR) and impaired left ventricular diastolic filling.1
Color-flow-Doppler (CFD) assists the detection of flow. Left-to-right flow is most common. Bidirectional flow indicates increased right atrial (RA) pressure, which is often a consequence of RV systolic dysfunction, TR, and/or impaired diastolic function. RV hypertension due to pulmonary vascular remodeling is an important cause of these changes. Doppler interrogation estimates pressure gradients by the formula: ΔP = (left atrial pressure – right atrial pressure [RAP]) = 4 (velocity).2 This gradient determines the direction of interatrial flow. RV systolic pressure, which may be increased because of pulmonary hypertension, can be calculated by Doppler interrogation of the TR jet.
A patent foramen ovale (PFO), the most common interatrial defect, is not technically an ASD but is discussed here. A PFO represents failure of the septum primum to completely fuse with the septum secundum, creating a flap. It occurs in 25% of the population2,3 (see Supplemental Digital Content 1, Video 1, http://links.lww.com/AA/A435). CFD examination of the septum is performed in multiple views, with the CFD scale decreased to 20 to 40 cm/second.2,3 If CFD is negative or inconclusive, echo contrast helps identify a PFO.3 In ventilated patients, echo contrast is given with and without the release of 20 to 30 cm H2O positive airway pressure. Release of positive airway pressure provokes a transient increase in RAP (RAP > left atrial pressure), which forces contrast across the defect. Visualization of contrast crossing into the left atrium (LA) within 3 to 5 cardiac cycles is consistent with a positive study.3,4
Secundum defects occur in the fossa ovalis (FO) and are the most common true ASD (75%).5 During embryologic development a thin pliable septum primum develops on the LA side of a thick muscular septum secundum (fatty limbus). During formation of these curtain-like septa, two gaps or foramina develop, the foramen primum and foramen secundum.6 Eventually both foramina close and the muscular septum secundum lies on the RA side of the thin pliable septum primum, with the septum primum acting as a flap covering the FO. Secundum ASDs are a defect in the embryologic septum primum in the area of the FO, which was the original fossa secundum; hence the name secundum.
Secundum ASDs are often oval shaped. The longest part of the oval or major axis runs cephalad-to-caudad as seen in a midesophageal (ME) bicaval view (size 4 to 30 mm; mean 15 mm). Usually there is a tissue remnant (rim) at both anteroposterior (superior vena cava [SVC] rim) and inferosuperior borders (inferior vena cava rim). This “rim” makes secundum ASDs amenable to percutaneous device closure.5,7
Secundum defects are visualized in the ME bicaval and modified ME aortic valve short-axis view (30 to 60 degrees) (see Supplemental Digital Content 1 and 2, Videos 1 and 2). In the bicaval view the defect is limited to the FO. This distinguishes it from a superior sinus venosus defect, which lies cephalad to the crista terminalis (Fig. 1, Supplemental Digital Content 1 and 2, Videos 1 and 2). Surgical repair involves a primary or patch closure.
Percutaneous device closure of ASDs is generally safe and effective.7 Embolization after transcatheter ASD device placement is a rare (<2%, 0.55%7) but potentially lethal complication. Other complications include device erosion (0.1%), residual shunts (<4%), atrial arrhythmias (<5%), and device size mismatch (<5%).
Sinus venosus ASDs are located near the SVC or inferior vena cava entrance into the RA. Superior defects are more common (Figs. 1, 2) (see Supplemental Digital Content 2, Video 2, http://links.lww.com/AA/A436). During the third week of development, the heart exists as a primitive tube with the most inferior portion divided into 2 horns (left and right horns of the sinus venosus). During development the horns of the sinus venosus move superiorly and posteriorly, where the sinus venosus lies posterior to the primitive atrium. The left horn forms the CS and the right horn forms both vena cavae while other portions of the sinus venosus are absorbed into the RA. Incomplete absorption of the sinus venosus into the RA combined with abnormal development of the septum secundum results in a sinus venosus ASD.
Sinus venosus defects are associated with partially anomalous pulmonary venous connections and/or drainage. Anomalous pulmonary venous drainage (normally connected pulmonary vein draining across the defect into the SVC/RA junction) may be closed with a patch. Anomalous pulmonary venous connection (anomalous pulmonary venous drainage due to a direct connection of the pulmonary vein to the SVC) is often corrected by a Warden procedure (Fig. 3).8
Sinus venosus defects are located posterior to the FO. They result from a deficiency in a common wall, which normally separates the pulmonary veins from the RA and SVC rather than a defect in the atrial septum or abnormal position of the pulmonary veins. This defect is not a true ASD but rather an unroofing of the anterior wall of the LA/pulmonary vein junction into the posterior wall of the SVC/RA junction. The most common anomalous pulmonary connection is where the right upper pulmonary vein drains directly into the lateral wall of the SVC above the SVC/RA junction at the level of the right pulmonary artery (PA) (Fig. 2) (see Supplemental Digital Content 2, Video 2, http://links.lww.com/AA/A436).
Superior sinus venosus defects are better visualized with transesophageal echocardiography than transthoracic echocardiography.5 In the ME bicaval view, the right PA is normally noted as a circular structure above the SVC. However, when a sinus venosus defect is present, the posterior wall of the right PA appears to be missing even though there is no true defect (Fig. 2) Supplemental Digital Content 2, Video 2, http://links.lww.com/AA/A436).
Primum ASDs (Fig. 4) (see Supplemental Digital Content 3, Video 3, http://links.lww.com/AA/A437) often occur in conjunction with a common atrioventricular (AV) valve orifice and are associated with inlet ventricular septal defect (VSD)s, cleft AV valve leaflets and trisomy 21. Embryologically the endocardial cushions help form the AV valves and the base of the interatrial septum. Failure of septum primum to fuse with the endocardial cushions, results in a primum ASD and abnormal (cleft) AV valve leaflets. A partial AV canal is a primum ASD with no associated VSD, where a separate complete fibrous ring encircles each AV valve. A primum ASD plus a restrictive inlet VSD constitutes a transitional AV canal, and a primum ASD with a nonrestrictive inlet VSD constitutes a complete AV canal defect. With transitional and complete canals, a single, common fibrous ring encircles both AV valves. Primum defects lie posterior and inferior to the FO near the AV valves and with these lesions the septal portions of both AV valves insert into the interventricular septum at the same level. As a consequence, the AV valves appear in the same plane and the defect is close to these valves (Fig. 4). Thus they are associated with cleft AV valve leaflets (often septal tricuspid and anterior mitral), which result in AV valve insufficiency.
The ME 4-chamber view shows a primum defect (Fig. 4). Three-dimensional echocardiography and 2D imaging (transgastric basal short-axis view) assist identification of the cleft(s).9 Severity of insufficiency can be assessed with CFD imaging.10 Repair usually requires patch closure of the primum ASD and repair of the cleft AV valve leaflet(s). Occasionally primum ASDs may be closed with transcatheter devices (see Supplemental Digital Content 3, Video 3, http://links.lww.com/AA/A437), but this is often not feasible because of the proximity of the AV valves.
CS ASDs result from unroofing of the posterior aspect of the CS such that LA blood drains into the CS and through the orifice of the CS into the RA. They are associated with persistent left SVC and a dilated CS. CS ASD may be seen in the ME 2-chamber or long-axis view. Normally the CS is a well-delineated circular structure; however, when a CS ASD is present, the CS wall closest to the LA appears to be missing, signifying communication between the posterior aspect of the LA and CS11,12 (see Supplemental Digital Content 4, Video 4, http://links.lww.com/AA/A438). When a left SVC is present, repair requires patch closure of the unroofed CS, directing left SVC flow into the RA. In the absence of a left SVC, the CS orifice may be oversewn, which closes the LA-to-RA communication while leaving a small (<5%) right-to-left CS to LA shunt.
Name: Thomas M. Burch, MD.
Contribution: This author helped prepare the manuscript.
Name: K. Annette Mizuguchi, MD, PhD.
Contribution: This author helped prepare the manuscript.
Name: James A. DiNardo, MD.
Contribution: This author helped prepare the manuscript.
This manuscript was handled by: Martin J. London, MD.
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