Double inlet left ventricle with transposition of the great arteries

Double Inlet Left Ventricle

In double inlet left ventricle, the most common double inlet connection, the dominant ventricle is of left ventricular morphology.L3,V1,V3 Apical trabeculations beyond insertions of the papillary muscles display a delicate criss-cross pattern. The septal surface is typically smooth in its superior half, and the crescentic margin bounding the VSD is smooth (Fig. 56-3). VSD morphology, however, can be variable. Of 46 patients with double inlet left ventricle carefully evaluated by Bevilacqua and colleagues, 24 had VSDs separated from the semilunar valves and completely surrounded by muscle (muscular defects), 19 had VSDs adjacent to the anterior semilunar valve (subaortic defect) in association with malalignment or hypoplasia of the infundibular septum, and 3 had multiple muscular defects.B3

The small incomplete (rudimentary) ventricle is of right ventricular morphology, with coarse apical trabeculations and frequently a recognizable trabecula septomarginalis (septal band) bounding the VSD anteriorly. A smooth-walled infundibulum is present when one or both great arteries arise from this chamber (Fig. 56-4). Otherwise, and rarely, the chamber exists as a blind pouch. It is always positioned on the anterosuperior shoulder of the dominant left ventricle (Fig. 56-5), usually to the left but sometimes to the right. The septum thus lies obliquely and never extends to the crux.

The typical morphology of double inlet left ventricle, with ventricular L-looping, left-sided incomplete right ventricle, and VA discordant connections, occurs in about half of all cases, with a wide variety of VA connections in the remainderU1 (seeTable 56-3). The relatively uniform internal cardiac architecture of the AV valves and myocardium in typical double inlet left ventricle may be more variable when double outlet right ventricle occurs with it.S3 Atrial situs is usually solitus, occasionally ambiguus, but rarely situs inversus.

Two variants of double inlet left ventricle warrant further description: (1) double inlet left ventricle with ventricular L-loop, left-sided incomplete right ventricle, and VA discordant connection and (2) double inlet left ventricle with ventricular D-loop, right-sided incomplete right ventricle, and VA concordant connection.

Arterial Switch Operation for Univentricular Heart with Subaortic Stenosis

Infants with DILV or tricuspid atresia with TGA (aorta arising from the outlet chamber of RV morphology), especially those with aortic arch obstruction, may be candidates for ASO with atrial septectomy.50 In these patients, systemic cardiac output may be limited by a restrictive bulboventricular foramen. ASO converts this subaortic stenosis to subpulmonic stenosis and establishes a controlled source of pulmonary blood flow without PA banding, which is known to accelerate subaortic stenosis in such hearts. This procedure has generally been abandoned in favor of the modified Norwood operation (arch repair with Damus-Kaye-Stansel connection and modified Blalock-Taussig shunt), but remains in our armamentarium for use in selected cases.

Anatomy and Anatomical Associations

Double-inlet left ventricle (DILV) is a term used to describe the cardiac malformation in which there are two atrioventricular (AV) valves that drain into a single, large dominant ventricle of left ventricular morphology, which is associated with a diminutive opposing rudimentary outflow chamber. Controversy surrounds the nomenclature of this malformation, and other terms used to describe this anomaly have includedsingle ventricle and auniventricular heart of the left ventricular type. The main ventricular chamber is of left ventricular morphology with characteristic fine trabeculations. The rudimentary outflow chamber of right ventricle (RV) origin consists only of trabecular and outlet portions and is often in communication with the single left ventricle (LV) through a ventricular septal defect (VSD). The VSD is also often referred to as abulboventricular, oroutlet, foramen. In this anomaly, the interventricular septum is displaced and malformed, but not absent.1 The rudimentary right ventricular chamber is located anterior to the main ventricle, either rightward (d-loop) or leftward (l-loop), and is separated by an anterior trabecular septum. Both AV valves are posterior to the trabecular septum and there is no intervening inlet septum between the two.

Diagnosis of DILV excludes those patients with an unbalanced common AV valve. Both AV valves in DILV are in fibrous continuity with the posterior great artery.2 The RV is variable in size ranging from slitlike to near 80% of the size of a normal RV. There may be either concordance (normal) or discordance (transposition) of the ventriculoarterial relations.

DILV is one of the most common forms of single ventricle and is regarded as the “classic form” because both AV valves communicate into a common chamber. Van Praagh and coworkers1 distinguished three primary subtypes of DILV based on the relationship of the great arteries: (1) type I DILV has normally related great arteries, (2) type II has a rightward and anterior aorta and rightward outlet chamber, and (3) type III has a leftward anterior aorta. DILV with a hypoplastic subpulmonary, rightward RV and normally related great arteries (type I) is classically referred to as the “Holmes heart” and is relatively rare in our current experience. Type II was observed in 21% of cases of DILV in Van Praagh and coworkers’ series. In this form, the outlet chamber is anterior and rightward, consistent withd-looped ventricles, and there isd-transposition of the great arteries, segments {S,D,D}. This type is associated with obstruction of the bulboventricular foramen and, therefore, subaortic stenosis, because the aorta arises from the small chamber. Arch anomalies are reported in approximately 50% of cases.

Type III is the most common form of DILV, accounting for 54% of the cases reviewed by Van Praagh and coworkers.1 Type III consists of DILV with a left-sided, subaortic, hypoplastic right ventricle (l-loop ventricles) andl-transposition of the great arteries, segments {S,L,L}. Subaortic stenosis is present in approximately 67% of patients with this morphology due to a small bulboventricular foramen or obstruction by left AV valve tissue (Figure 29-1).

Truncus Arteriosus, Double Inlet LV, and Other Mixing Lesions With Favorable Streaming

In some lesions, such as truncus arteriosus or double inlet LV, there may not be complete mixing, as there may be favorable streaming of pulmonary venous return to the aorta and systemic venous return to the pulmonary artery. For this reason, truncus arteriosus without branch pulmonary artery stenosis does not usually present with clinical cyanosis because of favorable streaming and increased QP/Qs. Similarly, infants with single ventricle, such as double inlet LV, may have favorable streaming and minimal cyanosis. Although infants with mitral and/or aortic atresia have complete mixing, they often have a high QP/Qs.

3 Atrioventricular Relationship

Once the situs of the atria is determined, one must assess the position of the ventricles in relation to the atria. The morphologic right ventricle has four characteristic features that distinguish it from the morphologic left ventricle: (1) a trabeculated apex, (2) a moderator band, (3) septal attachment of the tricuspid valve, and (4) lower (apical) insertion of the tricuspid valve. The tricuspid valve is always “attached” to the morphologic right ventricle (Fig. 75.5, and seeVideo 75.8

Themorphologic right ventricle is a triangular-shaped structure with an inlet, a trabecular, and an outlet component. The inlet component of the right ventricle has attachments from the septal leaflet of the tricuspid valve. Inferior to this is the moderator band, which arises at the base of the trabeculoseptomarginalis, with extensive trabeculations toward the apex of the right ventricle. The outlet component of the right ventricle consists of a fusion of three structures (i.e., the infundibular septum separating the aortic from the pulmonary valve, the ventriculoinfundibular fold separating the tricuspid valve from the pulmonary valve, and, finally, the anterior and posterior limbs of the trabeculoseptomarginalis).

Themorphologic left ventricle is an elliptical-shaped structure with a fine trabecular pattern, with absent septal attachments of the mitral valve in the normal heart. It consists of an inlet portion containing the mitral valve and a tension apparatus, with an apical trabecular zone that is characterized by fine trabeculations and an outlet zone that supports the aortic valve.

Subaortic Obstruction.

Subaortic or outflow tract obstruction is not uncommon in patients with double-inlet left ventricle or tricuspid atresia with transposed great vessels. A progressive restriction at the ventricular septal defect (VSD) is the most common site of systemic outflow obstruction in this subset of patients. Although not often used in the modern era, PA banding is known to promote outflow tract obstruction, particularly when aortic arch obstruction is present. Ventricular hypertrophy and diastolic dysfunction secondary to subaortic stenosis are significant risk factors for Fontan completion. Subaortic obstruction is considered significant when the size of the VSD is less than half the size of the aortic valve in end-systole. Surgical options to address subaortic stenosis include enlargement of the VSD and/or use of the subpulmonary outflow tract (Damus-Kaye-Stansel procedure). Although these strategies are sometimes inevitable, we feel that prevention of subaortic stenosis, particularly by recognizing the substrate that is likely to produce it, is paramount to the success of SV patients. When there is an anatomic risk for the development of aortic outflow obstruction, the use of a strategy to minimize this occurrence is paramount during the decision making for early palliation options.

Single Ventricle (Table 4-9)

Key Points

Includes hypoplastic left heart syndrome, single ventricle (SV) (double-inlet left ventricle [DILV] the most common variant), tricuspid atresia, unbalanced AVC, PA with an intact ventricular septum (PA/IVS), heterotaxy syndrome (Fig. 4-13).

In DILV, both AVV empty into the LV. A VSD (also referred to by its embryological name, the bulboventricular foramen [BVF]) leads to the outlet chamber. The ventricles and GVs are often transposed. Associated hypoplastic aorta, coarctation, and subaortic obstruction are common. PS/subpulmonary stenosis are also common. In less than 10%, the two coexist.

Diastolic Assessment in the Functionally Single Ventricle

Diastolic function in single-ventricle physiology impacts outcomes. In a large series of patients with a double inlet left ventricle from the Mayo Clinic, diastolic dysfunction (i.e., elevated LVEDP) was one of two independent risk factors for late death after the Fontan operation.155 However, assessment and characterization of diastolic function in the individual patient is even more difficult than in biventricular physiology. One of the important considerations is the stage of palliation and its relation to ventricular preload, which affect diastolic parameters. At the first stage of palliation, which, dependent on the lesion, often consists of a systemic to pulmonary shunt, the ventricle is typically volume overloaded. After the placement of a caval-pulmonary shunt, and after the Fontan procedure, there is a precipitous decrease in ventricular preload and increased mass/volume ratio. Ventricular filling is additionally affected by pulmonary vascular resistance.156 In this scenario it is often difficult to differentiate preload restriction from intrinsic diastolic dysfunction per se. Whether chronic preload deficiency affects intrinsic myocardial properties in and of itself is an open question. Nonetheless, in aggregate, single-ventricle patients after the Fontan operation appear to have diastolic dysfunction, which may be progressive.

Following this physiology, a high LV mass/volume ratio in the early postoperative period following Fontan palliation (in part due to the reduced preload) may be an indicator of increased early morbidity with pericardial or pleural effusions.157–159 However, normalization of the mass/volume ratio in Fontan patients may not lead to improved diastolic performance.160–162 Increased collagen deposition likely contributes to decreased compliance, as demonstrated in other cardiac anomalies.163 The additional presence of wall motion abnormalities, which are common in these patients, likely contributes further to altered diastology.164 These patients may show patterns consistent with abnormal relaxation and decreased early diastolic filling with increased compensatory late filling with atrial contraction, prolonged IVRT, and decreased peak early filling velocities,161,164,165 but also Doppler findings more consistent with decreased ventricular compliance such as shorter inflow deceleration time.166 Additional findings of mid-diastolic inflow (L wave) also suggest abnormal diastolic function.166 Thus children with either single or biventricular circulations may have mixed patterns of delayed relaxation and decreased compliance.

Because patients undergo catheter hemodynamic evaluation before stage 2 and 3 surgery in many institutions, there is an opportunity to correlate echocardiographic parameters with catheter hemodynamics in the single-ventricle population. In a small group of children with single-ventricle physiology,167 tau correlated well with the atrioventricular inflow E/A ratio and IVRT but also with lateral E/e′, which is thought to reflect filling pressures more than early diastolic relaxation.

In a study investigating patients with single right ventricles, ventricular filling pressures correlated significantly with early diastolic strain rate (SRe) and the E/SRe ratio.168 Conversely, there were no significant correlations between ventricular filling pressures and tissue Doppler measurements. Likewise, in a different study, diastolic strain rate correlated with RVEDP more strongly than Doppler-based parameters.169 However, results from different studies have been inconsistent. Menon et al. found that in patients with single-ventricle physiology, tissue Doppler velocities and pulmonary vein Doppler correlated, albeit modestly, with direct measurement of ventricular filling pressures. In that study, an E/e′ ratio above 12 was suggestive of ventricular end-diastolic pressures greater than 10.170 Of note, single left ventricles had better systolic and diastolic function than single right ventricles. This finding concurred with that of a large multicenter study that used mass/volume ratio, peak early diastolic velocity, and E/E′ ratio as well as the Tei index to characterize diastolic function in single ventricles.171 In a small study, invasively measured tau correlated well with the inflow Doppler E/A ratio, lateral E/e′, and IVRT derived from TDI.172 Thus there is inconsistency between studies on the correlation of echo parameters with near-simultaneously measured invasive parameters, likely influenced by factors such as small sample sizes, heterogeneous anatomy, physiology, and loading conditions, over and above measurement variability.

Strain and strain rate imaging may also be useful to follow diastolic function over time in the single-ventricle population. Michel et al. found in patients with hypoplastic left heart syndrome after the Fontan procedure that during serial evaluation, global early and late diastolic strain rate progressively decreased while conventional Doppler diastolic parameters did not change, suggesting that these parameters may be more sensitive to detect worsening in diastolic function over time.79 However, at this time, diastolic strain and strain rate measurements are not used routinely in clinical practice in most pediatric labs given factors such as low frame rates, messy strain rate curves, lack of validation, and lack of experience.

Loss of atrioventricular synchrony can induce failure in patients with a Fontan circulation, consistent with a significant reliance of atrial booster pump function for filling. Studies have shown reduced early atrial emptying and increased contribution from atrial contraction to ventricular filling,173 consistent with diastolic dysfunction.174 However, atrial function itself, especially reservoir function, may be impaired and insufficient to compensate for ventricular underfilling. Peak atrial strain (and hence atrial contractile function) correlates with ventricular filling pressures, highlighting atrioventricular interdependence.175 Thus pulmonary, ventricular, and atrial properties, as well as atrioventricular synchrony, influence diastolic function of the single ventricle.

Parasternal Short Axis View

Assess relationship between the dominant LV and the BVF. As mentioned, in the majority of cases of DILV, the BVF is the more anterosuperior and leftward chamber. This is best seen as the transducer is angled toward the base of the heart.

Commitment of both AVVs to the dominant ventricular chamber, architecture of the papillary muscles and the chordae tendineae.

Relationship of the GVs. Usually seen as two circles as the transducer is angled toward the base if they are transposed. If the GVs are normally related as in a Holmes heart, then the aorta is seen in cross section, and the PA is seen to the right of the aorta in a longitudinal plane.

Presence of size discrepancy between the AV and pulmonary valve.

Presence of aortic/pulmonary atresia.

Confluence of the PAs.

Presence and physiology of the PDA from a high left parasternal view.

Size and degree of restriction of the BVF. It is important to measure the BVF in two orthogonal views to calculate cross-sectional area (major diameter × minor diameter × Π/4) because it is usually elliptical in shape. Patients with a BVF cross-sectional area of less than 2 cm2/m2 are at a higher risk of late obstruction.

Ventricular systolic function.