6.5 Double Outlet Right Ventricle (DORV)

Defining Double Outlet Right Ventricle

Double Outlet Right Ventricle (DORV) is not a single, uniform disease entity but rather a complex, heterogeneous spectrum of conotruncal malformations. The defining anatomical requirement for DORV is that both the aorta and the main pulmonary artery arise entirely or predominantly (more than 50%) from the morphological right ventricle.

Because both exit routes are situated over the right ventricle, the left ventricle has no direct connection to a great vessel. Consequently, a ventricular septal defect (VSD) is universally present and absolutely essential for survival, as it represents the sole egress for oxygenated blood leaving the left ventricle.

Classification Based on VSD Location

The clinical presentation, hemodynamics, and surgical approach to DORV are dictated almost entirely by two factors: the spatial relationship of the VSD to the great arteries, and the presence or absence of right ventricular outflow tract (RVOT) obstruction (pulmonary stenosis).

DORV is classified into four main types based on the location of the VSD:

1. DORV with Subaortic VSD

This is the most common form. The VSD is located directly beneath the aortic valve. Left ventricular blood preferentially streams across the VSD and directly into the aorta, while deoxygenated right ventricular blood enters the pulmonary artery.

• Physiology: This hemodynamically mimics a simple VSD if there is no pulmonary stenosis.
• With Pulmonary Stenosis: If infundibular pulmonary stenosis is present, this variant acts physiologically and sonographically exactly like Tetralogy of Fallot (TOF). The differentiating factor is simply the degree of aortic override. If the aorta overrides >50% into the RV, it is DORV. If <50%, it is TOF.

2. DORV with Subpulmonary VSD (Taussig-Bing Anomaly)

The VSD is located directly beneath the pulmonary valve. Left ventricular oxygenated blood streams preferentially across the VSD into the pulmonary artery, while right ventricular deoxygenated blood streams into the aorta.

• Physiology: Because the aorta is pumping deoxygenated blood to the body and the pulmonary artery is pumping oxygenated blood to the lungs, this variant physiologically mirrors d-Transposition of the Great Arteries (d-TGA). The infant will be profoundly cyanotic at birth.

3. DORV with Doubly Committed VSD

A rare variant where the VSD is exceptionally large, extending superiorly to lie directly beneath both the aortic and pulmonary valves. Both great arteries sit squarely over the massive defect.

4. DORV with Non-Committed (Remote) VSD

The VSD is situated far away from both semilunar valves, typically in the muscular or inlet portion of the ventricular septum. Blood must traverse a significant distance within the right ventricle to exit. This is highly challenging surgically, as routing the left ventricle to the aorta requires constructing a long, complex intraventricular baffle.

Sonographic Evaluation in Utero

The standard 4-chamber view is frequently normal unless the VSD extends inferiorly enough to be seen as an inlet defect.

Diagnosis relies on careful multiplanar sweeping of the outflow tracts:

1. The Overriding Rule: In the long-axis view, evaluate the septal-aortic continuity. If a vessel is seen overriding the septum, determine the percentage of the vessel that sits over the right ventricle. If it is clearly more than 50% for both vessels, DORV is present.
2. Loss of Normal Crossing: The normal perpendicular relationship of the great arteries is lost. In many forms of DORV (particularly Taussig-Bing), the great arteries exit the heart parallel to each other.
3. VSD Localization: Color Doppler is essential to track the flow of blood from the left ventricle, across the VSD, and into the respective great vessel to determine commitment (subaortic vs. subpulmonary).
4. Assessing Obstruction: Continuous-wave and color Doppler must be used to interrogate the pulmonary and aortic valves to rule out stenosis, as this radically alters the postnatal management pathway.

Surgical Implications

Surgical repair of DORV aims to connect the left ventricle exclusively to the aorta and the right ventricle exclusively to the pulmonary artery.

• For a subaortic VSD, surgeons patch the VSD to create a "tunnel" routing LV blood directly to the aorta.
• For a Taussig-Bing anomaly, because routing the LV to the aorta is impossible (the PA is in the way), an Arterial Switch Operation (ASO) is performed concurrently with the VSD closure, exactly as managed for d-TGA.