The Initial Diagnostic Approach to Adult Congenital Heart Disease: A Practical Imaging Pathway for General Cardiologists and Cardiac Imagers

ACHD TTE Protocol

The standard adult TTE protocol, while comprehensive for acquired heart disease, can be limited for the evaluation of adults with CHD.¹⁰ A comprehensive ACHD TTE protocol must systematically assess unrepaired and repaired congenital lesions, including associated defects, residual lesions, and postoperative complications. Specialized surgical repairs require targeted protocol modifications and tailored imaging approaches. The protocol should include cardiac situs, morphology, and sequential segmental analysis, together with structural and functional assessment from additional echocardiographic windows and imaging planes beyond those used in standard adult or pediatric examinations.^11,12 Protocol implementation should remain consistent with the conventions and workflow of the individual laboratory, including apex orientation and preferred initial imaging window. Before image acquisition, the sonographer should review the patient’s clinical history, prior imaging, and operative reports to understand baseline anatomy, prior repairs, residual lesions, and potential complications, all of which should be documented in the echocardiographic report.

ACHD echocardiographic standards for imaging, interpretation, and reporting continue to evolve.^{7,8,12,13,14,15,16,17} A suggested ACHD echocardiographic assessment checklist is provided in Table 1. Intermediate windows and nonstandard planes are often necessary for comprehensive evaluation. A comprehensive ACHD TTE examination should include 2D imaging, M-mode, Doppler interrogation (color, pulsed-wave, continuous-wave, and tissue Doppler), and longitudinal strain assessment. Three-dimensional echocardiography provides additional information on valvular anatomy and mechanism of dysfunction, defect size and morphology, chamber volumes, and spatial relationships between cardiac structures that may aid procedural planning.

The examination should systematically assess:

1. Cardiac situs, cardiac position, apex orientation, and sequential segmental anatomy,

2. Systemic venous anatomy and flow, including the superior and inferior vena cava, innominate vein, hepatic veins, and coronary sinus,

3. Pulmonary venous connections and flow, ideally including all pulmonary veins,

4. Atrial morphology, size and function, and appendages,

5. Interatrial septum,

6. Atrioventricular valves morphology and function,

7. Ventricular morphology, size, and function,

8. Interventricular septum,

9. Ventricular outflow tracts size and patency,

10. Semilunar valves morphology and function,

11. Coronary artery origins and proximal patency,

12. Arch sidedness, aortic dimensions, and flow, including the aortic root, ascending, transverse, descending, and abdominal aorta,

13. Main and branch pulmonary artery anatomy and flow, and

14. Pericardial anatomy and effusion assessment.

Common congenital lesions encountered in adult echocardiography laboratories include bicuspid aortic valve, ASDs, ventricular septal defects, and pulmonary stenosis. However, patients with more complex disease—such as tetralogy of Fallot, TGA, multilevel left-sided obstructive lesions, SVP or complex repairs and palliations including cavopulmonary anastomosis, Ross procedure, Rastelli, conduits, and baffle repairs—should be evaluated at specialized ACHD centers whenever possible.

Imaging-specific Congenital Lesions

Left-Sided Obstructive Lesions

Bicuspid aortic valve and congenital aortic stenosis are among the most common forms of congenital heart disease and may coexist with aortopathy and multilevel left-sided obstruction such as congenital mitral stenosis, subaortic stenosis, and coarctation of the aorta, as seen in Shone’s complex. Echocardiographic assessment should define left ventricular (LV) size and function, left ventricular outflow tract (LVOT) size and patency, aortic valve morphology and hemodynamics, stenosis jet from multiple windows, aortic regurgitation, aortic dimensions, and associated lesions (Figure 2 A, B).

Figure 2

Management is guided by the level and severity of obstruction. Surgical options range from isolated aortic valve replacement to the Ross operation, which requires lifelong surveillance for right ventricle to pulmonary artery conduit degeneration, neoaortic valve dysfunction, and progressive neoaortic root dilation. Percutaneous interventions may include aortic balloon valvuloplasty, transcatheter aortic valve replacement, and stenting for coarctation of the aorta.

Interatrial Communications

The interatrial septum should be systematically evaluated using comprehensive 2D and color Doppler sweeps from multiple imaging windows.¹⁸ Optimization of color Doppler settings is particularly important in the presence of pulmonary arterial hypertension. Evaluation should define defect location, size, number, morphology, shunt direction and magnitude, right atrial and RV size and function, RV systolic pressure (RVSP) and pulmonary artery systolic pressure (PASP), LV diastolic function, associated lesions, and residual defects.

Patent foramen ovale and secundum ASD are the most common interatrial communications (Figure 3 A-D). Transcatheter closure is standard for suitable defects. Postprocedural ACHD TTE should assess residual shunt, pulmonary or systemic venous obstruction, device impingement on the atrioventricular valves, device embolization, and device erosion.

Figure 3

Surgical repair includes primary closure of small defects and patch closure of larger ASDs with deficient rims. In patients with pulmonary hypertension and older adults at risk for heart failure with preserved ejection fraction, a fenestrated patch may reduce postoperative RV failure or diastolic dysfunction, respectively.

Sinus Venosus Defects

Sinus venosus defects are often underrecognized on standard adult TTE, which may delay diagnosis and intervention. Pulmonary venous anomalies are challenging to evaluate by TTE due to their marked anatomic variability. However, trained and experienced ACHD sonographers can detect the most common patterns with high diagnostic yield, including drainage of the right upper pulmonary vein to the superior vena cava (SVC), anomalous connection of the left upper pulmonary vein to the left innominate vein, and anomalous right pulmonary venous connection to the inferior vena cava (Scimitar syndrome)¹⁹ (Figure 4 A-D). CMR remains the modality of choice for comprehensive anatomic definition.

Figure 4

Postoperative anatomy may be challenging to assess without ACHD training. Key residual lesions include pulmonary venous stenosis and SVC obstruction.

Coronary Sinus Defects

Coronary sinus defects are uncommon and may be challenging to diagnose by TTE, requiring a high index of suspicion and careful imaging assessment (Figure 5). A persistent left superior vena cava draining into the coronary sinus is a common associated anomaly and often results in coronary sinus dilation.

Figure 5

Atrioventricular Septal Defects

Atrioventricular septal defect (AVSD) commonly includes an ostium primum atrial septal defect (Figure 6 A, B), an inlet VSD, and a cleft left atrioventricular valve, often with trifoliate valve morphology. Postoperative complications include residual patch leak and persistent or recurrent atrioventricular valve dysfunction.

Figure 6

Ventricular Septal Defects

Ventricular septal defects may occur in isolation or with more complex CHD. Systematic interrogation of the interventricular septum with 2D and color Doppler sweeps from apex to base is essential. Assessment should define VSD type (Figure 7 A), number, location, size, shunt direction and magnitude, VSD gradient (Figure 7 B, D), left heart size and function, RVSP, PASP, and aortic regurgitation. Associated lesions should also be assessed, including double-chambered RV, subaortic obstruction or ridge, aneurysmal tricuspid tissue, sinus of Valsalva rupture, aortic cusp prolapse, overriding or straddling atrioventricular valves (Figure 7 C), Gerbode defect, and coarctation.

Figure 7

Overlap of the VSD or Gerbode jet with tricuspid regurgitation may overestimate the RVSP and falsely suggest pulmonary hypertension. Similarly, double-chambered right ventricle may be missed when overlapping Doppler signals obscure RV outflow tract (RVOT) obstruction, leading to inaccurate PASP estimation if the RVOT gradient is not considered.

Patch closure remains the most common repair. Percutaneous closure may be feasible for selected muscular and perimembranous VSDs. Postprocedural evaluation should assess residual shunt and device impingement on adjacent structures.

Pulmonary Stenosis and Right-Sided Obstructive Lesions

Comprehensive TTE evaluation of the RV, RVOT, pulmonary infundibulum, pulmonary valve, and pulmonary arteries from multiple acoustic windows is required for accurate localization and grading of right-sided obstructive lesions and for optimal clinical management.

In the presence of a high-velocity tricuspid regurgitation jet, pulmonary stenosis (Figure 8 A-C) or RVOT obstruction should be considered before attributing the gradient to pulmonary hypertension. Peak RVOT and pulmonary arterial gradients should be interrogated from multiple imaging planes. The RV inflow-outflow view from the apical and subcostal windows is particularly useful in this assessment (Figure 8 D-F).

Figure 8

Surgical management may include pulmonary valvotomy or valvectomy (Figure 8 E), pulmonary valve replacement, RV to pulmonary artery conduit placement, RV muscle bundle resection, and pulmonary artery augmentation. Transcatheter therapies include pulmonary balloon valvuloplasty, transcatheter pulmonary valve replacement (Figure 8 G), and pulmonary artery stent implantation. Follow-up TTE should assess prosthetic valve function as well as residual or recurrent obstructive and regurgitant lesions.

Tetralogy of Fallot

Patients with tetralogy of Fallot (TOF) typically require closer TTE surveillance. Variants include TOF with pulmonary stenosis, pulmonary atresia, or absent pulmonary valve syndrome (Figure 9 A). Associated anomalies may include right aortic arch, persistent left SVC, ASD, patent ductus arteriosus, retroaortic innominate vein, anomalous coronary artery origin, AVSD, and major aortopulmonary collateral arteries. Palliation may include Blalock–Taussig–Thomas or central shunts, although primary neonatal repair is now standard. Patients should ideally be followed at specialized ACHD centers, and comprehensive TTE is essential.^8,10 Assessment should focus on residual pulmonary regurgitation or stenosis, RVOT obstruction, pulmonary artery trunk (Figure 9 B) and branch pulmonary artery dimensions and gradients, residual VSD, tricuspid regurgitation, biventricular size and function, atrial size, RVSP and PASP, proximal aortic dimensions, and associated lesions (Figure 9 C).

Figure 9

Transposition of the Great Arteries

In dextro-transposition of the great arteries (D-TGA), the aorta arises from the morphologic RV and the pulmonary artery from the morphologic LV, resulting in ventriculoarterial discordance. The aorta is anterior and to the right of the pulmonary trunk. Repair strategies include atrial switch (Mustard or Senning) (Figure 1, Figure 10 A) and arterial switch (Jatene) operations. Associated lesions include VSD, ASD, LVOT obstruction, patent ductus arteriosus, and coronary artery anomalies.

Figure 10

After atrial switch repair, systemic venous return is directed to the subpulmonary LV, whereas pulmonary venous return is baffled to the systemic RV (Figure 10 B-G, Figure 11). Echocardiographic assessment should focus on systemic and pulmonary venous baffle patency and leaks, systemic RV size and function, systemic tricuspid valve regurgitation, and PASP estimation and LV systolic pressure from the subpulmonary mitral regurgitation jet (Figure 10 B-G).

Figure 11

Published reference ranges for systemic RV size and function are limited, and guideline-based parameters for the subpulmonary RV are not validated for the systemic RV. Echocardiographic measurements should therefore be used primarily for serial comparison. Useful parameters include RV areas in diastole and systole from a focused apical four-chamber view, fractional area change, tissue Doppler S′ velocity, triplane or 3D estimates of RV volumes and ejection fraction, and RV longitudinal strain. Assessment should include both longitudinal and radial components of contraction. When more accurate quantification is required, CMR should be performed because it provides more reliable RV volumes and ejection fraction.

The arterial switch operation includes great artery translocation, coronary reimplantation, and the LeCompte maneuver, which may predispose to branch pulmonary artery stenosis. After repair, the left ventricle is systemic; the native aortic valve serves as the neopulmonary valve, and the native pulmonary valve as the neoaortic valve (Figure 10 H-J, Figure 12). Echocardiographic assessment should focus on neopulmonary valve or distal pulmonary artery obstruction (Figure 10 K), neoaortic root dilation and regurgitation, branch pulmonary artery stenosis, and ventricular size and function. Tricuspid regurgitation velocity may provide indirect evidence of RVOT obstruction or branch PA stenosis when the pulmonary arteries are not well visualized.

Figure 12

Congenitally Corrected Transposition of the Great Arteries

Congenitally corrected TGA (CCTGA) is characterized by atrioventricular and ventriculoarterial discordance, resulting in physiologically corrected circulation. The morphologic left atrium connects to the morphologic RV, which gives rise to the aorta and functions as the systemic ventricle, while the morphologic right atrium connects to the morphologic LV, which ejects into the pulmonary artery (Figure 13 A, B). In situs solitus, CCTGA is also referred to as L-transposition of the great arteries because the aorta arises anterior and leftward relative to the pulmonary artery.

Figure 13

Echocardiographic assessment is technically challenging and should focus on systemic RV size and function, systemic tricuspid valve regurgitation, pulmonary pressures, and associated lesions. Tricuspid regurgitation is common and may result from RV dilatation occasionally and/or Ebsteinoid tricuspid valve, requiring mechanical valve replacement in unrepaired patients.

Single Ventricle Physiology and Fontan Palliation

Functional univentricular hearts not amenable to biventricular repair are managed with Fontan palliation. Lesions include hypoplastic left heart syndrome, tricuspid atresia (Figure 14 A), severe Ebstein anomaly, TGA with large malaligned VSD and overriding or straddling atrioventricular valves, unbalanced AV canal/AVSD (Figure 14 B), and complex heterotaxy syndromes.

Figure 14

These patients should be managed at specialized ACHD centers with expertise in multimodality imaging and advanced therapies, including Fontan revision and heart transplantation. Assessment should focus on Fontan pathway patency (Figure 14 C, D), fenestration or leak, Glenn anastomosis patency, systemic ventricular size and function, atrioventricular and semilunar valve function, pulmonary venous flow, ASD patency, pulmonary artery flow, and thrombus.

Echocardiographic protocol must be individualized according to the underlying anatomy and surgical palliation. Key elements of assessment include cavopulmonary pathway patency, fenestration or leak, systemic ventricular size and function, atrioventricular and semilunar valve function, pulmonary venous flow, atrial septal communication patency, pulmonary artery flow, and the presence of thrombus or obstruction of the Fontan pathway.

Planning the ACHD CMR Study

Protocol selection should begin with a focused review of available echocardiographic data and the specific unanswered clinical questions. The initial objective is an accurate anatomic roadmap, typically achieved with an axial, interleaved 2D stack covering the entire chest using a bright-blood balanced steady-state free precession (bSSFP) sequence, followed by a double inversion recovery-prepared dark-blood T2-weighted single-shot fast spin-echo sequence (HASTE-type), acquired with ECG-gating during free-breathing. Coronal and sagittal reformats are optional and generally unnecessary when a high-quality MR angiographic dataset has been obtained.⁶ Cine imaging stacks can be valuable in complex congenital anatomies, such as atrial switch physiology and Fontan palliation, where they facilitate assessment for conduit or baffle obstruction, baffle leak, and fenestrations.

Ventricular Size and Function

Quantification of ventricular volumes and systolic function is among the most frequent indications for ACHD CMR. A standard contiguous short-axis cine stack is usually sufficient for this purpose. Long-axis cine views are often helpful to improve basal slice definition and reduce segmentation error near the atrioventricular junction. Breath-held, ECG-gated cine bSSFP remains the preferred approach when feasible. However, contemporary acceleration strategies including parallel imaging and compressed sensing have expanded the applicability of real-time, free-breathing cine acquisitions, which can provide reliable assessment of ventricular size and function in patients with limited breath-hold capacity or significant arrhythmia.²¹ Figure 15 shows a dilated systemic RV in a patient with D-TGA and atrial switch and Figure 16 shows a severely dilated RV in a patient with TOF and severe pulmonary regurgitation in the setting of a transannular patch repair.

Figure 15

Figure 16

Anatomical Assessment of Intracardiac Shunts

When atrial morphology or atrial septal evaluation is clinically relevant, a dedicated atrial short-axis stack should be obtained rather than simply extending the ventricular stack. Coverage should be contiguous, without an interslice gap, and should include both atria in their entirety. Spatial resolution should be optimized while maintaining adequate signal-to-noise ratio and breath-hold feasibility, as partial-volume effects can obscure small atrial septal defects. As a practical benchmark, many experienced laboratories target approximately 1.6 × 1.6 mm in-plane resolution with 4-mm slice thickness at 1.5T, with adjustments based on patient size and scanner performance. In good breath-holders, interpolation can be considered to improve apparent image sharpness and may assist assessment of atrial baffles, venous pathways, and fine valvular detail. However, interpolation improves reconstructed rather than acquired spatial resolution and may require phase oversampling, prolonging breath-hold time; its use should therefore be individualized. Similar principles apply when ventricular septal morphology or VSD assessment is clinically important, with imaging plane and coverage tailored to the suspected defect location, adjacent valves, outflow tracts, and prior patch or device material.²³ CMR can be particularly helpful to better define anatomy (including pulmonary veins) and plan surgery in patients with sinus venosus defects (Figure 17) and unroofed coronary sinus (Figure 18). When detailed septal anatomy is needed for transcatheter ASD or VSD closure planning, cardiac CT is often helpful, providing reproducible 0.5 mm to 0.6 mm isotropic voxels and excellent delineation of septal rims, defect margins, venous connections, adjacent valves, outflow tracts, and neighboring vascular structures.²²

Figure 17

Figure 18

Intracardiac Shunt Assessment with Phase Contrast

For intracardiac shunt evaluation, imaging plane selection is critical. As in echocardiography, a shunt may be missed entirely if the acquisition plane does not intersect the jet. A practical approach is to review prior Doppler data to characterize jet direction, then reproduce an analogous CMR plane using cine bSSFP to identify flow-related signal heterogeneity followed by targeted phase-contrast interrogation. When in-plane phase-contrast imaging is used to localize shunt flow direction, the velocity-encoding axis must be oriented along the expected direction of shunt flow, as an incorrect orientation may underestimate or obscure the jet. Because many atrial-level shunts generate relatively low-velocity flow, velocity encoding should be set low enough to maintain sensitivity, typically around 100 cm/s initially, then increased incrementally if aliasing is observed.²⁴ Once localized, through-plane phase-contrast imaging prescribed perpendicular to the jet can directly quantify shunt flow volume, and this measurement should be correlated with Qp:Qs quantification as a measure of internal validity.

Role of Magnetic Resonance Angiography

Given the frequency of anomalous arterial and venous connections in ACHD—and the need to evaluate stenosis, aneurysmal dilatation, and surgical pathways including conduits, baffles, and anastomoses—a 3D MR angiography (MRA) dataset is often essential and is typically obtained prior to detailed phase-contrast interrogation. MRA should balance spatial resolution, motion control, and acquisition efficiency. Breath-held, ECG-gated approaches reduce motion artifact and improve vessel edge definition, though free-breathing methods may be required in patients with limited compliance. Contrast-enhanced MRA remains widely used and highly reliable for vascular mapping. Noncontrast, free-breathing MRA techniques are increasingly available and may obviate gadolinium in straightforward cases (Figure 19), although bSSFP-based readouts can be susceptible to off-resonance effects, particularly at 3T.^25,26,27

Figure 19

Time-resolved contrast-enhanced MRA is particularly valuable for pulmonary venous evaluation in ACHD because it depicts the temporal sequence of contrast transit through the circulation. This dynamic information can help distinguish anomalous pulmonary venous drainage from systemic venous pathways, complex collateral flow, or postoperative venous obstruction, especially when anatomy is ambiguous on static imaging. Although spatial resolution is lower than single-phase high-resolution MRA, modern accelerated acquisitions can improve voxel size in selected implementations ²⁸ (Figure 20).

Figure 20

This should be integrated into a deliberate multimodality strategy. Echocardiography remains first-line and may show indirect findings such as right-sided chamber dilation, elevated pulmonary pressures, or abnormal Doppler flow, but pulmonary venous anatomy may be incompletely visualized because of acoustic windows, posterior vessel location, and complex postoperative anatomy. CMR and CT should therefore be used when pulmonary venous disease is suspected or right-sided dilation is unexplained. CMR can define anomalous pulmonary venous connections, quantify shunt burden, and assess ventricular remodeling without ionizing radiation, whereas CT provides higher spatial resolution for small pulmonary veins, pulmonary venous stenosis, scimitar anatomy, airway or lung relationships, and procedural planning.

Ferumoxytol-enhanced CMR is increasingly recognized as a valuable alternative contrast strategy, particularly in patients with renal dysfunction. An additional advantage is its prolonged intravascular residence time exceeding 12 hours, attributable to its large molecular size and carbohydrate shell coating.^29,30

Optimization of Phase Contrast Flow Imaging for Accurate Qp:Qs Assessment

The MRA dataset serves as the roadmap for planning phase-contrast acquisitions and enables precise prescription of imaging planes perpendicular to the target vessel, improving accuracy and reproducibility of flow quantification in the main pulmonary artery, branch pulmonary arteries, great veins, aorta, and major branches, supporting reliable calculation of Qp:Qs and assessment of differential pulmonary blood flow.

In markedly dilated pulmonary arteries, turbulence and partial-volume effects can underestimate flow at the main pulmonary artery level, making branch pulmonary artery measurements often more reliable. When prescribing branch pulmonary artery imaging planes, slices should be positioned as proximally as feasible while avoiding regions of early branching, as distal placement may underestimate total pulmonary flow. In patients with partial anomalous pulmonary venous return, MRA identifies the anomalous vein or veins and guides targeted phase-contrast measurements for quantification of anomalous venous return and shunt magnitude (Figure 20).

Accurate Qp:Qs assessment is a fundamental component of ACHD CMR. Because phase-contrast flow measurements are susceptible to artifacts related to motion, arrhythmia, through-plane motion, and background phase offset, repeated or supplementary acquisitions are often necessary. In many patients, paired measurements across the aorta and main pulmonary artery are sufficient for routine Qp:Qs quantification. However, in complex anatomies—particularly with multilevel shunts or single ventricle physiology—additional acquisitions involving the SVC, inferior vena cava, descending aorta, and pulmonary veins are essential for comprehensive hemodynamic assessment and internal validation of flow consistency.⁶

When breath-holding is reliable and initial flow data are technically robust, free-breathing acquisitions may be omitted or limited to repeat measurements of the main pulmonary artery and ascending aorta. In patients with limited breath-hold capacity, arrhythmia, or discrepant measurements, free-breathing or repeated acquisitions help confirm results.

In patients with patent ductus arteriosus, the level of shunt must be considered when interpreting Qp:Qs. Pulmonary arterial flow measured proximal to the ductal insertion reflects systemic rather than total pulmonary flow; in this setting, ascending aortic forward flow includes ductal runoff and may serve as the Qp.³¹

4D Flow Cardiac Magnetic Resonance Imaging in ACHD

4D flow CMR is an emerging technique providing time-resolved, 3D velocity encoding across a prescribed volume, enabling retrospective visualization and quantification of complex cardiovascular flow.³² This is particularly appealing in ACHD, where abnormal anatomy, repaired outflow tracts, conduits, baffles, Fontan pathways, branch pulmonary arteries, aortopathy, collaterals, and shunts can make conventional 2D phase-contrast plane prescription challenging.³³ Potential advantages include retrospective flow quantification, visualization of eccentric jets, and assessment of advanced hemodynamic markers such as vortices, helicity, wall shear stress, kinetic energy, and energy loss.³³ Limitations include long acquisition times, lower spatial and temporal resolution compared with targeted 2D phase-contrast imaging, sensitivity to arrhythmia and respiratory motion, and substantial post-processing time and expertise.³⁴ Broader adoption will require faster acquisitions, standardized post-processing workflows, multicenter validation, and evidence that 4D flow-derived metrics meaningfully improve clinical decision-making and patient outcomes.³⁵

Safety and Logistical Considerations in ACHD CMR

CMR is a practical and increasingly accessible modality for ACHD patients. Most adult examinations can be performed without sedation, and anesthesia is almost never required. Pre-scan planning should identify limited breath-hold capacity, arrhythmia, claustrophobia, renal dysfunction, and implanted devices so the protocol can be tailored appropriately.

Most contemporary pacemakers, defibrillators, and intracardiac devices are MRI-conditional or can be scanned under established institutional protocols.^36,37 MRI-nonconditional devices and abandoned leads require review by the MRI technologist, supervising physician, and device team before scanning.³⁸ Insufficient data exist to definitively comment on MRI safety in the presence of permanent epicardial leads.³⁹ Device-related artifact should not automatically preclude CMR, as newer sequences and protocol adjustments can often preserve diagnostic image quality.⁴⁰

Gadolinium use should be individualized. With contemporary macrocyclic agents, the risk of nephrogenic systemic fibrosis is very low when renal function is preserved.^41,42 Improved noncontrast cine, phase-contrast, and MRA techniques allow many ACHD questions to be answered without contrast. Advances in device safety, artifact reduction, and noncontrast imaging have made CMR substantially more feasible for ACHD care over the past decade.