4.5 Short-Axis, Bicaval, Branch PA & Arch Views

Short-Axis, Bicaval, Branch PA & Arch Views

The four-chamber, LVOT, RVOT, and three-vessel/trachea views form the core screening sweep, but the ARDMS Perform-the-Exam outline also requires proficiency with short-axis views, systemic venous (bicaval) views, branch pulmonary artery views, and dedicated aortic and ductal arch views. These planes answer questions the transverse sweep alone cannot settle.

Short-Axis Views (Ventricles and Great Vessels)

Rotate and angulate from the four-chamber plane to obtain short-axis cuts through the ventricles and then through the great vessels.

Ventricular short-axis

• Demonstrates circular left ventricular geometry versus a more triangular right ventricle with moderator band
• Shows papillary muscles and the ventricular septum in cross-section—useful for muscular VSD interrogation with color Doppler
• Allows comparison of ventricular wall thickness when cardiomyopathy or recipient-twin hypertrophy is suspected

Great-vessel short-axis

• Displays the classic “circle and sausage” relationship: the aorta as a circle in cross-section with the pulmonary artery wrapping anteriorly
• Confirms that the pulmonary artery bifurcates—critical when differentiating normally related great arteries from transposition (parallel vessels without normal bifurcation pattern)
• Provides a platform to follow the ductus arteriosus as it joins the descending aorta

Short-axis imaging is not optional ornamentation; it is the plane that often first reveals a large outlet VSD, crossed versus parallel outflow tracts, or asymmetric branch pulmonary arteries.

Bicaval and Systemic Venous Views

The bicaval view is a sagittal or parasagittal plane showing the superior vena cava (SVC) and inferior vena cava (IVC) entering the right atrium. Teaching points:

• Confirm uninterrupted IVC–right atrial continuity; an interrupted IVC with azygos continuation appears as absence of the intrahepatic IVC and a prominent azygos vein posterior to the aorta
• Evaluate for a persistent left SVC draining to the coronary sinus (dilated coronary sinus on four-chamber may be the first clue; the left SVC itself is traced in a left sagittal plane)
• Color Doppler should show antegrade flow into the right atrium without aliasing that would suggest obstruction

Systemic venous anomalies frequently coexist with heterotaxy; bicaval imaging therefore belongs in every complete study, not only when situs is obviously abnormal.

Branch Pulmonary Artery Views

After identifying the main pulmonary artery on RVOT or short-axis imaging, sweep to display the right and left branch pulmonary arteries.

Color and spectral Doppler across each branch help quantify relative flow when TOF, truncus, or ductal-dependent right-heart lesions are on the differential.

Aortic and Ductal Arch Views

The transverse 3VT suggests arch laterality and vessel number; sagittal views prove continuity.

Aortic arch (“candy cane”)

• Sagittal plane demonstrating ascending aorta, transverse arch, isthmus, and descending aorta
• Head and neck branches arise from the superior aspect of the arch
• Color Doppler shows antegrade flow throughout; aliasing or narrowing at the isthmus raises concern for coarctation

Ductal arch (“hockey stick”)

• Broader, flatter arch connecting the pulmonary artery to the descending aorta
• Normally lacks head-and-neck branches
• Spectral Doppler of the ductus arteriosus assesses for constriction (elevated peak systolic and diastolic velocities, especially with third-trimester NSAID exposure)

Side-by-side comparison of aortic and ductal arches clarifies which vessel is which when the 3VT is crowded or when a vascular ring (e.g., right aortic arch with aberrant left subclavian and left ductus) is suspected.

Integrating the Additional Views

A practical order after the core sweep is: short-axis great vessels → branch PAs → bicaval → sagittal aortic arch → sagittal ductal arch. Each view should be stored with and without color Doppler. When a pathology section later discusses coarctation, TAPVR, heterotaxy, or TOF, these acquisition skills are the reason the diagnosis can be made or excluded with confidence.

Acoustic Windows and Maternal Maneuvers for These Views

Short-axis, bicaval, and arch views fail more often from window choice than from unfamiliar anatomy. Use these practical maneuvers:

• For ventricular short-axis, start from a subcostal or apical four-chamber and rotate 90° while keeping the septum centered; if ribs shadow the apex, roll the mother slightly toward the side opposite the fetal spine.
• For great-vessel short-axis, slide cephalad from the ventricular short-axis until the aorta becomes circular and the pulmonary artery wraps anteriorly; freeze when both the bifurcation and ductal continuation are visible on a single sweep.
• For the bicaval view, align the transducer in a fetal sagittal plane through the right atrium; if only the SVC appears, angle caudal through the liver to capture IVC continuity—absence of that continuity is the teaching moment for interrupted IVC.
• For arch views, use a fetal sagittal plane slightly left or right of midline. The aortic arch rises higher and gives off head vessels; the ductal arch is flatter and inserts more inferiorly into the descending aorta. Color Doppler scale should be set high enough to avoid wall-motion artifact but low enough to fill the isthmus.

Document laterality: a right aortic arch on 3VT must be confirmed on sagittal imaging with attention to the ductal side, because a left ductus with a right arch creates a vascular ring around the trachea.

Common Pitfalls That Cost Exam Points

1. Calling the ductal arch the aortic arch because it is easier to obtain—always identify head-and-neck branches before labeling.
2. Accepting a single pulmonary vein color jet as proof that all pulmonary veins are normal—branch PA and venous mapping are separate tasks.
3. Skipping short-axis when the outflow tracts look “crossed enough” on long-axis; transposition and DORV differentials often become obvious only on short-axis circle-and-sausage analysis.
4. Failing to spectral-Doppler the ductus when third-trimester NSAID exposure is in the history; morphologic arch views alone can miss early constriction.

Mastery of these additional views is what separates a screening obstetric cardiac sweep from a complete fetal echocardiogram on the ARDMS outline.