Introduction

Systemic venous anomalies can occur in isolation or in association with other structural heart defects. The identification of systemic venous anomalies can have a significant impact on procedural planning for catheterization interventions and surgical procedures in patients with congenital heart disease. Echocardiography is an essential tool in the diagnosis and management of these patients [1–4]. When found in isolation, systemic venous anomalies often have little hemodynamic significance. Because of the wide variability seen within this class of anomalies, the evaluation of systemic venous return must involve a systematic approach with a comprehensive description of each individual segment: the superior vena cava (SVC), the inferior vena cava (IVC), the azygos and hemiazygos veins, the hepatic veins, the coronary sinus (CS), and the innominate vein.

Atrial situs is a key factor in the understanding of the systemic veins [5]. If there is lateralized situs (situs solitus or situs inversus totalis), the CS is usually present, and systemic venous anomalies are infrequent and fairly predictable. The most common anomaly in situs solitus is a persistent left SVC connecting to the CS. In situs inversus totalis, the systemic venous return is usually a mirror image of the normal pattern. If there is abnormal situs, such as in heterotaxy syndrome (right or left isomerism), there are often complex systemic venous anomalies that may be suspected based on the type of heterotaxy (e.g., asplenia or polysplenia type) [6–10]. In asplenia‐type heterotaxy (right isomerism) the CS is often absent and there are often bilateral SVCs connecting directly to the roof of the atria. In polysplenia‐type heterotaxy (left isomerism), the CS is usually present and there may be bilateral SVCs with the left SVC connecting to the CS. Many additional systemic venous abnormalities can coexist, including anomalous hepatic venous connections and interrupted IVC with azygos continuation.

Systemic venous anomalies can have important implications in the management of any patient who requires a cardiac catheterization or surgical intervention with cardiopulmonary bypass, since the systemic venous return is accessed or cannulated in these procedures. Additionally, there are important implications for orthotopic heart transplantation that require complete elucidation of any systemic venous abnormalities. Preoperative identification and complete characterization of systemic venous return is also crucial in patients with single ventricle physiology, because their surgical palliation and unique circulation ultimately requires connecting the systemic veins directly into the pulmonary arteries.

Prevalence

Systemic venous anomalies are uncommon in isolation, and their frequency is higher in association with other structural heart defects. A persistent left SVC (the most common systemic venous anomaly) occurs in about 0.3–0.5% of the general population [11–13], but is seen in up to 2–10% of patients with congenital heart disease [14–17]. In the setting of heterotaxy syndrome (right or left isomerism), systemic venous anomalies occur in more than half of all cases [18,19].

Etiology and embryology

With increasing knowledge pertaining to the development of abnormal visceroatrial situs, systemic venous anomalies represent one component of the morphologically diverse lesions that comprise heterotaxy syndrome. It remains unknown, however, whether heterotaxy syndrome and the development of laterality defects are predetermined in the genetic code.

The embryologic origins of the major systemic veins are outlined in Table 11.1, and the embryologic origins of common systemic venous anomalies are outlined in Table 11.2. There are three separate venous systems in the early human embryo that contribute to the systemic venous return: the umbilical, vitelline, and cardinal veins. The paired umbilical veins (from the chorionic villi) and the paired vitelline veins (from the yolk sac) appear during the third week of gestation. The sinus venosus develops by enlargement of the confluence of the umbilical veins and communicates with the atrial heart segment through the sinoatrial foramen [20]. The vitelline veins then join the umbilical veins as they drain into the rightward and leftward aspect of the developing sinus venosus, thus forming the right and left horns of the sinus venosus.

The anterior and posterior cardinal veins appear during the fourth week of gestation. The anterior cardinal veins appear first, draining blood from the cranial end of the embryo and the developing central nervous system. The posterior cardinal veins appear shortly thereafter, lateral to the spinal cord, draining blood from the caudal end of the embryo. The anterior and posterior cardinal veins converge into the common cardinal veins that join the umbilical and vitelline veins as they drain into the right and left horns of the sinus venosus.

At around the same time, rightward lateralization of the systemic venous return begins. First, there is invagination of the junction between the left horn of the sinus venosus and the common atrium, separating the left horn from the left atrium (LA). This is followed by a rightward shift of the sinus venosus to commit the three paired venous systems to the right atrium (RA). Now that the systemic venous return has lateralized to drain into the RA, the individual systemic veins can start to form.

Superior vena caval anomalies

The right SVC receives blood from the upper half of the body via the two brachiocephalic or innominate veins. It also receives the azygos vein and several small veins from the pericardium and other mediastinal structures.

Left SVC to the coronary sinus (bilateral SVCs)

A persistent left SVC is the most common systemic venous anomaly. It occurs in about 20% of patients with tetralogy of Fallot [21]. In the majority of cases, a persistent left SVC drains into the RA via the CS (Figure 11.1a). It can also drain directly into the LA because of the absence or unroofing of the CS (Figure 11.1c) [22]. Additional variations are demonstrated in Figure 11.1.

Embryologically, this anomaly results from failure of regression of the left anterior cardinal and left common cardinal veins. If a connection forms between the right and left anterior cardinal veins, it can persist as a connecting or bridging vein, as seen in the majority of cases with bilateral SVCs [15]. In general, the size of the connecting vein is inversely proportional to the size of the persistent left SVC. A persistent left SVC normally courses anteriorly to the left pulmonary artery and aortic arch, between the LA appendage and left pulmonary veins, and then into the CS as it traverses the left atrioventricular groove. Rarely, it courses behind the left pulmonary artery with potential for obstruction as it passes between the left pulmonary artery and the left bronchus, an area that has been referred to as the “anatomic vise.”

Pathophysiology and clinical significance

In bilateral SVCs with the left SVC to an intact CS, all the systemic venous return still drains into the RA so there is no hemodynamic significance. From a practical standpoint, identification of bilateral SVCs prior to surgical intervention can have significant impact on the cannulation approach during initiation of cardiopulmonary bypass support [23]. In addition, identification of a well‐developed connecting vein can allow for surgical ligation of the left SVC in the operating room if necessary. In patients with single ventricle physiology, staged surgical palliation involves a superior cavopulmonary anastomosis (bidirectional Glenn procedure). Bilateral SVCs without a connecting vein may require bilateral bidirectional superior cavopulmonary anastomoses or, occasionally, surgical ligation of the left SVC [24]. Failure to identify a persistent left SVC in a patient with single ventricle circulation would ultimately result in a persistent right‐to‐left shunt and decreased oxygen saturation. In single ventricle patients with an interrupted IVC and azygos continuation to one of the SVCs, a Kawashima procedure is required and may affect the timing of stage 2 palliation.

Imaging

A suprasternal frontal view (in a transverse plane or horizontal orientation) can display both SVCs and their relationship to the ascending aorta (Figure 11.2, Video 11.1). In addition, a connecting vein, if present, can usually be visualized in this view, particularly with the use of low‐scale color mapping. A high left parasternal view (in a sagittal plane or vertical orientation) is best to delineate the left SVC and its continuity with the CS (Figure 11.3, Video 11.2). Color mapping sweeps in a subxiphoid sagittal view can also show the flow from both SVCs and the IVC into the heart.

A persistent left SVC is the most common cause of a dilated CS [25]. A dilated CS can be seen during the posterior/inferior to anterior/superior sweep of a subxiphoid frontal or subxiphoid left anterior oblique (LAO) view (Figure 11.4, Video 11.3), from an apical four‐chamber view with posterior angulation (Figure 11.5, Video 11.4), and in the posterior left atrioventricular groove in a parasternal long‐axis image (Figure 11.6, Video 11.5). If the left SVC cannot be easily delineated by 2D imaging and/or color mapping, agitated saline injection into the left arm will result in the presence of contrast in the dilated CS before its presence in the RA. Prenatal diagnosis of a persistent left SVC usually involves a dilated CS as seen during the posterior sweep in four‐chamber views and in the long‐axis view of the left ventricle in the area of the left atrioventricular groove [26]. The persistent left SVC itself can be identified by fetal echocardiography in the three‐vessel tracheal view [27], as an additional vessel in cross‐section to the left of the main pulmonary artery.

Left SVC to the coronary sinus with an atretic right SVC

Rarely, a persistent left SVC occurs without a right SVC because of regression of the right anterior cardinal vein [28,29], and this has been associated with an increased incidence of arrhythmias such as sinus node dysfunction, Wolff–Parkinson–White syndrome, third‐degree atrioventricular block, atrioventricular nodal reentrant tachycardia, and atrial fibrillation [30].

In this anomaly, the right‐sided head and neck vessels drain via the right innominate vein into the left SVC, which in turn drains via a dilated CS into the RA (see Figure 11.1b). Echocardiographic imaging reveals the absence of a right SVC connecting to the RA in the subxiphoid LAO or subxiphoid sagittal view. The dilated CS and the left SVC are then visualized with the same techniques described earlier. The suprasternal frontal view (in a transverse plane or horizontal orientation) can also display the left SVC and absence of the right SVC (Figure 11.7, Video 11.6).

Left SVC to the left atrium

A persistent left SVC can also drain directly into the LA [22]. The vessel runs anteriorly to the left pulmonary artery and connects directly to the LA between the left upper pulmonary vein and the LA appendage [31]. It has been suggested that this anomaly results from persistence of the left anterior cardinal vein and failure of the invagination between the left sinus horn and the LA (with consequent failure of development of the CS) [32]. Another theory suggests that this anomaly (direct left SVC to LA connection) may result from a completely unroofed CS, due to full incorporation of the left horn of the sinus venosus into the LA [33,34]. Nevertheless, the most common scenario involving direct connection of a left SVC to the LA is in heterotaxy syndrome (isomerism) with drainage of bilateral SVCs into both sides of the atrial mass.

In the case of a partially unroofed CS, there is still a connection between the LA, the left SVC to CS pathway, and the ostium of the CS in the RA. Typically this leads to a left‐to‐right shunt from the LA to the CS and to the RA. The CS ostium is often dilated, acting as the point of interatrial shunt in this “coronary sinus‐type” atrial septal defect. The presence of a dilated right heart (of unclear etiology) with a dilated CS ostium should alert the echocardiographer to the possibility of a partially or completely unroofed CS.

Pathophysiology and clinical significance

When there is no connecting or bridging vein between the bilateral SVCs and no interatrial communication, patients with a left SVC directly to the LA may present with decreased oxygen saturation and usually no cardiac murmur. If there is a connecting vein between the bilateral SVCs and a small or absent interatrial communication, however, the left SVC and connecting vein can decompress the LA blood into the right SVC and RA (since the RA has a lower pressure than the LA). Color mapping may reveal retrograde (cephalad) flow along the left SVC. Hemodynamically, this anomaly represents a left‐to‐right shunt similar to an atrial septal defect or partial anomalous pulmonary venous return and can cause right ventricular volume overload. Surgical repair of this anomaly is often indicated.

A persistent left SVC to the LA can cause cyanosis after a Glenn or Fontan procedure, and interventional catheterization with coil occlusion of the vein can be beneficial and preclude the need for another operation. However, in the case of a persistent left SVC to the CS, detailed imaging and test occlusion of the left SVC to CS pathway is important because of the rare occurrence of coronary sinus ostial atresia. In the case of a CS with an atretic os, the left SVC serves as the only way to decompress the coronary vein flow and therefore should not be ligated, coiled, or occluded.

Imaging

The diagnosis of a persistent left SVC with direct connection to the LA can be made by echocardiography using the same high left parasternal (Figure 11.8, Video 11.7

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