17.3 Adult Recognition of ASD, VSD, PFO, PDA, and Congenital Clues

Let chamber remodeling point toward the shunt

The adult RCS role is to recognize congenital clues during a comprehensive adult examination, document anatomy and hemodynamics that are actually seen, and prompt appropriate review. It is not a substitute for a complete pediatric or RCCS segmental protocol, advanced device planning, or final congenital diagnosis. Begin with situs and connections when uncertain, then examine chamber proportions, septa, valves, pulmonary veins when visible, great arteries, arch, and prior repair material. An unexplained remodeling pattern should trigger directed sweeps rather than a premature label.

Left-to-right atrial shunting primarily volume-loads the RA and RV and increases pulmonary flow. Diastolic septal flattening can accompany RV volume overload. Left-to-right ventricular or ductal shunting more often enlarges the LA and LV because increased pulmonary blood returns to the left heart. Pulmonary vascular disease can reduce, equalize, or reverse a shunt, so absence of classic dilation does not exclude a defect. Record shunt direction, chamber response, pressure evidence, and oxygen or loading context.

Connect adult findings to cardiac development

Embryology helps explain why defects cluster near particular septa, valves, and great vessels. The primitive heart tube loops rightward, bringing the future ventricles into their characteristic relationships while the atrial and venous portions move posteriorly and superiorly. Abnormal looping can accompany complex positional and connection abnormalities; on an adult study with unexpected chamber or great-artery relationships, describe what is seen and escalate rather than forcing a simple ASD/VSD label.

Atrial septation uses two overlapping tissues. Septum primum grows toward the endocardial cushions; its initial opening, the ostium primum, closes as secondary perforations form an ostium secundum. Septum secundum then develops to the right and leaves the foramen ovale, while septum primum acts as its flap valve. In fetal life, right-to-left flow through the foramen ovale bypasses the lungs. After birth, falling pulmonary resistance and rising LA pressure normally press the flap closed. Failure of tissue formation can produce a true secundum ASD, whereas incomplete fusion can leave a PFO without a tissue-deficiency ASD. Endocardial cushions contribute to AV septation, AV valves, the lower atrial septum, and the membranous ventricular septum; developmental failure helps explain primum ASD and AV-septal-defect associations.

The muscular interventricular septum grows upward, and cushion/conotruncal components close the remaining membranous region. Incomplete closure produces VSDs whose valve relationships depend on location. Neural-crest-derived conotruncal ridges separate and align the aortic and pulmonary outflow tracts; abnormal septation or alignment contributes to outflow lesions such as persistent truncus arteriosus, tetralogy-type malalignment, or transposed great-artery relationships. The fetal ductus arteriosus derives from the distal (dorsal) portion of the left sixth aortic arch, while its proximal portion contributes to the proximal left pulmonary artery. The ductus carries pulmonary-artery flow to the descending aorta; postnatal oxygen and prostaglandin changes normally constrict it. Persistence produces PDA. These links are recognition tools, not permission to infer a complete congenital diagnosis from one adult TTE view.

Distinguish ASD from PFO

Interrogate the atrial septum with 2-D and low-scale color from several planes. Apical ultrasound travels nearly parallel to the septum and can create dropout; the subcostal beam is more perpendicular and better for confirmation. For an ASD, report number and location, two orthogonal dimensions when feasible, direction and timing of flow, RA/RV size, pulmonary pressure clues, and Qp:Qs when technically valid. TEE, 3-D, CT, or CMR may be needed to define superior defects, pulmonary veins, rims, or complex anatomy.

A PFO is a potential flap communication rather than a true ASD. During agitated-saline imaging, completely opacify the RA and record rest plus cough or Valsalva release when safe and ordered. A useful maneuver shows septal shift from increased RA pressure. Early bubbles entering the LA support an intracardiac right-to-left shunt; delayed appearance after several cycles suggests intrapulmonary transit, but timing alone is imperfect. Report image quality, maneuver effectiveness, amount and timing, and likely location. A negative study with weak RA opacification or ineffective Valsalva does not exclude PFO. Chronic RV dilation should prompt a search for a true ASD or another volume load rather than attribution to an incidental PFO.

Recognize VSD location and pressure behavior

Sweep the septum from parasternal long axis, short axis at aortic through apical levels, apical views, and subcostal planes using color at a scale capable of showing a narrow high-velocity jet. Perimembranous VSD lies near the membranous septum and aortic and tricuspid valves; muscular defects can occur anywhere in the trabecular septum; inlet and outlet defects have distinct valve relationships. Report number, location, dimensions in two axes when seen, direction, peak velocity and gradient, chamber response, PA pressure evidence, and adjacent valve findings. Look for aortic cusp prolapse or AR near outlet or perimembranous defects.

For a well-aligned restrictive VSD jet, peak LV-RV systolic gradient = 4V². A 5.0-m/s jet gives 100 mm Hg and generally indicates a large pressure difference, not a large defect. A large nonrestrictive VSD may have lower velocity because LV and RV pressures approach each other. The equation assumes the signal is the VSD jet and there is no important serial obstruction or mismatched pressure timing. Shunt importance depends on size, direction, chamber volume load, pulmonary pressure and resistance, and associated lesions—not velocity alone.

Find a PDA and quantify cautiously

A PDA connects the proximal descending aorta to the pulmonary artery near the left pulmonary artery origin. Use parasternal short-axis or ductal-focused, high parasternal, and suprasternal views. Color may show continuous flow entering the PA near the left branch; CW or PW documents direction and systolic-diastolic velocity. A small restrictive PDA can have a high-velocity continuous signal with little chamber enlargement. A larger left-to-right duct can enlarge LA/LV and pulmonary arteries. With high PA pressure, velocity falls and flow can become bidirectional or right-to-left, so the classic bright continuous jet may disappear.

Report PDA location and diameter when visible, shunt direction, peak gradient when the envelope is valid, left-heart size and function, PA pressure evidence, and any repair device or residual flow. Distinguish ductal flow from PR, branch PA acceleration, a coronary fistula, or artifact by origin, timing, and multiple planes. Qp:Qs may support shunt magnitude: Doppler pulmonary stroke volume divided by systemic stroke volume. Annular diameters are squared, and valve regurgitation, multiple shunts, arrhythmia, or poor alignment can invalidate the ratio. Do not use one Qp:Qs value for closure decisions.

Unexpected clues—dilated coronary sinus suggesting persistent left SVC, bicuspid aortic valve with aortopathy or coarctation, anomalous pulmonary venous course, unusual arch flow, or unexplained right-heart enlargement—should prompt additional adult-lab views and recommendation for congenital expertise through the interpreting clinician. State what was not visualized. Recognition is successful when it prevents a simple lesion or repair from being overlooked without claiming a complete congenital examination.

High VSD velocity does not mean a large shunt

A high velocity reflects a large LV-RV pressure difference and often a restrictive defect. Shunt significance requires defect anatomy, direction, chamber volume load, pulmonary pressure and resistance, and associated lesions.