Double Inlet Left Ventricle

Double Inlet Left Ventricle (DILV) is a significant congenital heart defect categorized under single ventricle lesions. These lesions are characterized by a single functional ventricle responsible for both systemic and pulmonary blood flow in a parallel configuration. Echocardiography is the primary diagnostic tool and gold standard for evaluating DILV and its associated anomalies. It provides precise anatomical details and functional information, often obviating the need for more invasive studies.

1. Ventricular Morphology and Atrioventricular Connection:

   • The most important diagnostic sign is the presence of a single ventricular chamber into which two AV valves open.

   • Cross-sectional echocardiography is ideal for displaying the type of univentricular AV connection.

   • The identification of a univentricular connection to a left ventricle (as in DILV) is made by finding an antero-superiorly located ventricular septum.

   • If a rudimentary chamber cannot be identified, it suggests a solitary (indeterminate) ventricle.

   • The competency and morphology of the AV valves are critical. If the AV valve is undivided, it may show significant regurgitation. Associated anomalies like overriding or straddling AV valves should be documented; an overriding valve is assigned to the ventricle supporting more than 50% of its circumference.

   • DILV is more frequent than double inlet right ventricle (extremely rare - in DIRV, the ventricle is coarsly trabeculated, which is the only differentiator to the single LV). Robert H. Anderson refers to a specific type of ventricle as "indeterminate". This term is used when the morphology of a main ventricle cannot be definitively classified as either a left or right ventricle, often because there isn't a second ventricle to compare it to, or other definitive anatomical markers are missing. "Ventricles of indeterminate type" are very likely almost always right morphological ventricles, even if their precise classification is challenging. DILV and DIRV are types of "single ventricle" physiology where both atria primarily connect to a single dominant ventricular chamber.

Double Inlet Left Ventricle (DILV)

• Primary Ventricle Morphology: The dominant ventricular chamber in DILV has a morphological left ventricular appearance. This is characterized by a smooth endocardial surface.

• Embryological Origin: This condition is generally considered an arrest in the normal development of the heart. This means the developmental process stopped at an earlier stage that somewhat resembles a primitive heart with a dominant left ventricle.

• Accessory Ventricle: DILV often features a small, rudimentary accessory right ventricle. This accessory chamber is typically positioned anterior or antero-superior to the main left ventricle. Even this rudimentary right ventricle tends to have a smooth surface and notably lacks a moderator band or septal band.

• Atrioventricular (AV) Valves: In DILV, there can be two permeable atrioventricular valves that open into the main left ventricle. These valves may not entirely resemble typical tricuspid or mitral valves but are often described as having two leaflets each. One of these valves can also be hypoplastic or atretic.

• Great Artery Relationships: The great arteries (aorta and pulmonary artery) are almost always transposed (in about 90% of cases) in DILV. This can manifest as either SLL (L-transposition) or SDD (D-transposition). Rarely, normal vessel relationships (SBS) can be observed, as seen in what is sometimes referred to as a "Holmes heart".

• Outflow Tract Obstruction: The type of outflow tract obstruction often depends on the great artery relationship: if the vessels are transposed, subaortic stenosis is generally expected; if normally positioned, subpulmonary stenosis is more common. However, subpulmonary stenosis can also occur relatively frequently even with transposed vessels.

Double Inlet Right Ventricle (DIRV)

• Primary Ventricle Morphology: The dominant ventricular chamber in DIRV has a morphological right ventricular appearance. This is characterized by prominent and coarse trabeculations. In cases where a secondary left ventricle is absent or difficult to identify, Robert H. Anderson might classify the main ventricle as "indeterminate" because the precise morphology is challenging to confirm without a comparison.

• Embryological Origin: DIRV is considered a total aberration or perturbation of normal development, indicating a more profound deviation from typical cardiac formation. It's embryologically "not at all logical" to have a double inlet right ventricle because the primitive cardiac tube initially contains only the left ventricle.

• Accessory Ventricle: In DIRV, there is often no recognizable accessory left ventricle. If a rudimentary left ventricle is present, it is typically small and located postero-inferiorly.

• Atrioventricular (AV) Valves: DIRV may have two similar atrioventricular valves, often described as having three leaflets, or a common atrioventricular valve, especially when associated with heterotaxy. These valves frequently have abnormal attachments.

• Great Artery Relationships: The connection to the great arteries in DIRV is almost always a double outlet right ventricle (DORV), meaning both the aorta and pulmonary artery arise predominantly from the morphological right ventricle. This often includes the presence of a bilateral conus (a muscular sleeve separating the atrioventricular valves from the arterial valves).

• Septal/Moderator Bands: Crucially, DIRV lacks the typical septal band and moderator band found in a normal right ventricle. Therefore, the coarse trabeculations become the primary anatomical feature for its identification.

• Associated Conditions: DIRV is frequently associated with heterotaxy.

• Outflow Tract Obstruction: Subaortic stenosis is more common in DIRV.

2. Ventricular Septal Defect (VSD) and Outflow Tracts:

   • The size, location, and number of VSDs are vital for diagnosis and treatment planning. In DILV, the VSD is commonly subaortic.

   • VSDs can be imaged directly using various echocardiographic planes.

   • The relationship of the VSD to the arterial outlets and the presence of any narrowing or obstruction in the outflow tract should be assessed. This includes evaluating localized posterior bulging of the septum, subpulmonic membranes, or fibromuscular shelves at the outflow level.

3. Great Arteries:

   • The relationship of the great vessels to each other and to the ventricles should be determined.

   • The pulmonary artery can be recognized by its rapid posterior dip after emerging from the heart and its early bifurcation. In contrast, the aorta assumes an ascending retrosternal course and does not bifurcate (except rarely in double aortic arch).

   • Arch sidedness, hypoplasia, or coarctation of the aorta are important associated anomalies to rule out. Suprasternal imaging is particularly useful for assessing the aortic arch.

   • The ductal anatomy and patency, as well as the direction and velocity of flow through the patent ductus arteriosus (PDA), must be assessed. The best view to image a left PDA is the ductal view from the high left parasternal area.

4. Atrial and Venous Connections:

   • The presence and importance of the atrial septal defect (ASD) should be evaluated.

   • Systemic and pulmonary venous anomalies are often associated with single ventricle lesions, especially heterotaxy syndrome. A dilated coronary sinus can strongly suggest a persistent left superior vena cava (LSVC). Or a TAPVR draining to the coronary sinus. 

   • Pulmonary vein connections and drainage must be visualized, ideally from the suprasternal frontal view using color Doppler, with spectral Doppler to assess for stenosis.

5. Associated Valvular Anomalies:

   • Mitral valve lesions, including mitral valve prolapse, are sometimes encountered in children with ASD. Congenital mitral stenosis morphology can include a restrictive annulus, limited leaflet mobility, or a combination. Mitral valve regurgitation can also be detected ultrasonically.

   • Severe isolated tricuspid valve stenosis may be indicated by a small valve ring, rudimentary cusps with restricted doming motion, and a small right ventricular cavity.

6. Ventricular Function:

   • Assessment of ventricular size, wall thickness, and systolic and diastolic function is critical.

   • In functionally single ventricles, diastolic function is frequently abnormal. Qualitative assessment of ventricular performance by an experienced echocardiographer is common for single ventricles. While ejection fraction (EF) and shortening fraction (SF) are used, their reliability can be limited due to variable ventricular size, geometry, and loading conditions in congenital heart disease. Advanced techniques like myocardial velocities or strain rate imaging may detect myocardial dysfunction even with normal EF/SF.

   • The degree of AV valve regurgitation and pulmonary artery growth are important factors in deciding eligibility for Fontan palliation.

7. Coronary Arteries:

   • Coronary artery origins and course should be evaluated. While rarely the primary focus in single ventricle patients, this information is available from parasternal views.

Fetal Echocardiography

Fetal echocardiography plays an increasingly important role, with over 40-50% of DILV patients now being diagnosed prenatally. This early diagnosis allows for delivery and treatment in specialized centers, potentially improving outcomes. Fetal echo can identify the anatomical features of DILV and its occasional association with heterotaxy syndrome. The comprehensive echocardiographic assessment informs the initial management plan and helps determine the most appropriate surgical repair strategy. This includes deciding between biventricular repair versus single-ventricle palliation (e.g., Fontan operation), based on the size and adequacy of the ventricles and AV valve function. Follow-up echocardiograms are essential for monitoring outcomes, residual lesions, and ventricular function.

Case 1

Case 2

Double inlet univentricular connection of left ventricular morphology with outlet chamber. Normal tricuspid valve but mitral valve hypoplasia. Moderate bulboventricular foramen in univentricular heart with no obstruction of 6mm. L-malposition of the great arteries with the pulmonary artery posterior and right, arising from the main ventricular chamber, and the aorta anterior and to the left, arising from the outlet chamber. 

Pathological example from the Maude Abbott Medical Museum