Laboratory Studies
Arterial blood gas (ABG) values, including pO2, pCO2, pH, base excess, lactate concentration, and mixed venous oxygen saturations permit quantitative assessment of the patient's oxygenation and systemic perfusion. Acute ABG evaluation assists in the resuscitation of a neonate with obstructed total anomalous pulmonary venous connection (TAPVC). Severe metabolic acidosis and hypoxemia are often seen.
Hematocrit levels are checked to confirm adequate oxygen-carrying capacity.
BUN and/or creatinine levels are useful in critically ill neonates presenting with obstructed pulmonary venous return.
Imaging Studies
Chest radiography
In partial anomalous pulmonary venous connection (PAPVC), lung fields often demonstrate increased pulmonary vascular markings. In addition, an enlarged right-heart border from the volume loaded right heart is seen. In patients with scimitar syndrome, a diagnostic vertically-directed crescent shadow is observed to the right of the mediastinal silhouette.
In total anomalous pulmonary venous connection (TAPVC), obstruction to pulmonary venous drainage determines the appearance of the lung fields on chest radiography. In patients without obstruction, the pulmonary vascular bed is plethoric and pulmonary artery is prominent. In patients with obstruction, severe pulmonary edema is the commonest finding. A prominence of the pulmonary artery shadow and the right atrial (RA) silhouette are often observed. In supracardiac drainage, the prominence of the upper mediastinum can create the classic snowman or figure-8 appearance.
Echocardiography
In PAPVC, echocardiography is typically used to help delineate the anatomy of the pulmonary venous drainage and the atrial septum. Confirmation of the normal drainage of the remaining pulmonary veins is an important part of the echocardiographic examination. [16, 17]
In TAPVC, with 2-dimensional echocardiography and color-flow Doppler mapping, the anomalous venous anatomy is usually well defined. Diagnostic findings include distension of the right ventricle, the presence of a vascular confluence coupled with absent venous drainage to the left atrium on the Doppler interrogation, the presence of an accessory common vein, a dilated coronary sinus and turbulent flow in the right atrium with a right-to-left shunt. Demonstration of turbulence or flow acceleration in the pulmonary veins is also used to diagnose obstruction in the pulmonary venous circuit. In addition, right-heart pressures and other cardiac anomalies can be determined. Echocardiography has shown excellent sensitivity and specificity in fetal diagnosis [17] and as a prognostic tool and has supplanted angiography in the vast majority of cases. [18]
CT and MRI
In nonurgent cases of PAPVC or TAPVC, CT or MRI may be used to further delineate the cardiac anatomy. The ability to form 3-dimensional reconstructions with these imaging modalities is evolving rapidly.
In particular, contrast-enhanced magnetic resonance angiography (MRA) provides complete anatomical and functional assessment of the pulmonary circulation. When compared to echocardiography, MRIA has been shown to offer a better visualization of the whole length of the pulmonary veins, the communicating veins, and the accessory pathways. Additional benefits include the possibility of qualitatively and quantitatively evaluating the amount of anomalous pulmonary blood flow, the Qp:Qs (using phase-contrast MRI). The secondary effects of the shunt on pulmonary arteries as well as cardiac chambers are also detectable in the same study. [19, 20]
Diagnostic Procedures
Cardiac catheterization is used infrequently for diagnosis in routine TAPVC or PAPVC because of the refinements in echocardiography. Cardiac catheterization is helpful in patients in whom echocardiographic findings are ambiguous or in patients with other complex defects. As a result of the mixing of oxygenated pulmonary venous effluent and deoxygenated systemic venous blood (oxygen saturations) are almost identical in all chambers of the heart in patients with TAPVC.
The site of the anomalous connection is located precisely with angiography by locating the step-up in saturations along the systemic venous pathway. Catheterization is also helpful in defining the anatomy of pulmonary-vein stenosis, which may develop after TAPVC is repaired.
In older patients with PAPVC, cardiac catheterization may be required to exclude coronary artery disease, to assess right-heart pressures, to ascertain the reversibility of any pulmonary arterial hypertension, and to calculate the shunt fraction.
Balloon atrial septostomy (BAS) may assist in evaluating the hemodynamic status of patient by unmasking previously undetected severe venous obstruction. The persistence of pulmonary hypertension following BAS should raise the suspicion of an obstruction to the venous drainage in an extracardiac location.
Histologic Findings
TAPVC is associated with hypertrophy of the media of the pulmonary veins and arteries. This finding is most prominent in patients with evidence of pulmonary venous obstruction, and it is most important in the extrapulmonary and intrapulmonary veins. Intimal proliferation and fibrous thickening of the pulmonary veins, with lymphangiectasia, is a common microscopic finding in patients with TAPVC.
In patients with recurrent stenosis a diffuse fibrous proliferation of the intima is often seen, usually at the site of the surgical anastomosis, although these changes can be seen along the whole length of the vein. Occasionally, those nonspecific changes can involve the intraparenchymal portions of the venous bed, mimicking the pathological changes of the veno-occlusive disease.
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Types of total anomalous pulmonary venous connection.
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Partial anomalous pulmonary venous connection (PAPVC) of right-sided pulmonary veins to the right superior venoatrial junction. Note the enlarged confluence and superior vena cava. SVC = Superior vena cava; IVC = Inferior vena cava; RUPV = Right upper pulmonary vein; RMPV = Right middle pulmonary vein.
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(A): Patient with obstructed scimitar syndrome (magnetic resonance angiography). The right upper pulmonary vein (RUPV) is diffusely narrow and presents a discrete stenosis at the confluence with the right lower pulmonary vein (red arrow). (B): The confluence at the atrial level appears unobstructed (white arrow) in the 3D reconstruction.
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(A): Total anomalous pulmonary venous connection (TAPVC) of supracardiac type. All pulmonary veins drain into a long confluence and a short communicating vein is attached to the right superior vena cava (SVC). The left lower pulmonary vein appears stenosed (red arrow). (B): These findings are confirmed by the 3D reconstruction (white arrow).
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Follow-up CT scan performed after repair of total anomalous pulmonary venous connection (TAPVC). The right upper pulmonary vein (RUPV) appears severely stenosed (red arrow).
