Congenital Anomalies of Vena Caval Connection

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Chapter 29 Congenital Anomalies of Vena Caval Connection

Anomalous vena caval connections comprise a wide range of malformations that vary from minor to major and that occur in isolation or with coexisting congenital heart disease. Persistent left superior vena cava occurs in 0.3% of the general population and in 4.3% of congenital heart disease.¹ A left-sided inferior vena cava occurs in 0.2% to 0.5% of the general population.¹ This chapter focuses on isolated anomalous vena caval connections in situs solitus hearts (Table 29-1). Anomalies of vena caval connection with cardiac malpositions or with atrial isomerism are dealt with in Chapter 3.

Table 29-1 Congenital Anomalies of Vena Caval Connection

In early embryonic development, the common cardinal veins are bilaterally symmetric and are potentially responsible for bilateral superior vena cavae.² The left common cardinal vein initially drains into the left portion of the sinus venosus, which becomes the coronary sinus.² Failure of obliteration of the left common cardinal vein results in persistent connection of a left superior vena cava to the coronary sinus (Figure 29-1),² a relatively common anomaly estimated at 0.3% to 0.5% of the general population and 1.5% to 10% of patients with congenital heart disease.³ An isolated left superior vena cava in itself produces no physiologic derangements when it drains harmlessly into the right atrium via the coronary sinus (see Figure 29-1). However, the coronary sinus dilates sometimes appreciably,⁴ especially if there is atresia of its right atrial orifice⁵ or absence of the right superior vena vava.^6,⁷ When the right superior cava is absent, the sinus node pacemaker is absent because the pacemaker is normally located at the junction of the right superior vena cava and the morphologic right atrium.⁸^–¹¹ A persistent left superior vena cava is a significant anomaly when it connects to the left atrium (Figures 29-2 and 29-3).¹²^–¹⁴ The coronary sinus is usually absent¹⁵ with partial or complete unroofing of its anterosuperior wall. Unroofing results in a connection between the left atrium and the right atrium—a coronary sinus type of atrial septal defect (see Chapter 15).¹⁶ A right-to-left shunt coexists through the left superior vena caval to left atrial connection.^14,¹⁷ An absent coronary sinus with bilateral superior vena cavae (right superior cava connected to the right atrium, left superior cava connected to the left atrium) is thought to represent a developmental complex.¹⁸ If the right superior vena cava is absent or atretic (see Figure 29-3), the innominate vein crosses the midline and terminates in the left superior vena cava.¹⁹ The left atrium occasionally receives the azygos vein, the hepatic vein, or the coronary sinus,¹⁴ variations that are not considered in this chapter.

Figure 29-1 A, Persistent left superior vena cava (LSVC) draining into the right atrium (RA) via the coronary sinus. The right superior vena cava (RSVC) and the inferior vena cava (IVC) drain normally into the right atrium. B, Left superior vena cava draining into the coronary sinus in a 3-year-old child.

Figure 29-2 A, Persistent left superior vena cava (LSVC) communicating directly with the left atrium (LA). The right superior vena cava (RSVC) and the inferior vena cava (IVC) drain normally into the right atrium (RA). The bilateral superior vena cavae communicate through a large innominate bridge. The direction of blood flow is from the left atrium into the anomalous left superior vena cava and then across the innominate bridge into the right superior vena cava. These pathways constitutes a left-to-right shunt. B, Restrictive innominate bridge offers resistance so that left superior vena caval blood is diverted into the left atrium with only a small portion flowing across the bridge. C, An atretic innominate bridge diverts left superior vena caval blood entirely into the left atrium. (PV’s = pulmonary veins.)

Figure 29-3 Persistent left superior vena cava (LSVC) connecting directly to the left atrium (LA). The right superior vena cava is absent. The inferior vena cava (IVC) drains normally into the right atrium (RA).

Direct connections between vena cavae and left atrium are uncommon.^7,^20,²¹ Rarely, a right superior vena cava connects to the left atrium.²²^–²⁴ Still more rarely, a right superior vena cava connects to the left atrium, and a left superior vena cava connects to the right atrium.²⁵ Connection of a right superior vena cava to the left atrium must be distinguished from drainage of a right superior vena cava into both atria caused by a contiguous superior vena caval sinus venosus atrial septal defect (see Chapter 15).²⁰ When a right superior vena cava is congenitally absent (see Figure 29-3), brachiocephalic veins join a left superior vena cava that connects to the coronary sinus.^6,²⁶

Bilateral superior vena cavae ³ are illustrated in Figure 29-2. The innominate bridge that connects the two superior cavae may be widely patent, narrow, or atretic (see Figure 29-2), and the size of the left superior vena cava ranges from large to rudimentary.³ Bilateral superior vena cavae with atrial isomerism are dealt with in Chapter 3.

Anomalous connection of the inferior vena cava to the left atrium consists of a morphogenetic spectrum represented by combinations of persistence of the valve of the right sinus venosus, fusion of the valve with the septum secundum, and incomplete development of the atrial septum.²⁷ The inferior vena cava penetrates the diaphragm at its expected site. An enlarged azygos vein may arise from the anomalous inferior cava and convey inferior caval blood into the right atrium (Figure 29-4).^21,^28,²⁹ An isolated left-sided abdominal inferior vena cava usually crosses to the right after receiving the renal veins, then penetrates the diaphragm and enters the right atrium at the normal site. A distinction must be made between connection of the inferior vena cava to the left atrium and anomalous inferior vena caval drainage into the left atrium from persistence of a large Eustachian valve (right valve of the sinus venosus) that directs flow toward a patent foramen ovale or across an ostium secundum atrial septal defect (see Chapter 15).²⁷

Figure 29-4 Inferior vena cava (IVC) connecting directly to the left atrium (LA). An anomalous inferior vena cava gives rise to an enlarged azygos vein that joins a normal right superior vena cava (RSVC). A small portion of inferior vena caval blood is diverted through the azygos vein into the right superior vena cava and into the right atrium (RA; see curved arrow). (PV’s = pulmonary veins.)

Inferior vena caval interruption with azygous continuation is rare as an isolated malformation and is of no physiologic significance but can be mistaken for the descending thoracic aorta (Figure 29-5).³⁰ Interruption is immediately proximal to the renal veins and continues into a dilated azygos vein that enters the thorax to the right of the aorta, runs in the posterior mediastinum, and connects to a right superior vena cava (see Figure 29-5). There is an association with congenital absence of the portal vein.³¹ Inferior vena caval interruption with azygos continuation and left isomerism are dealt with in Chapter 3.

Figure 29-5 A, Inferior vena cavagram from a 28-year-old woman with isolated inferior vena caval interruption (IVC) and azygos (Az) continuation to a right superior vena cava (SVC). B, X-ray from same patient showing the azygos vein ascending along the right side of the vertebral column (lower Az) and forming a knuckle as it joins the right superior cava (upper Az).

Anomalous connection of either vena cava to the left atrium is rare enough, but connection of the right superior vena cava and the inferior vena cava to the left atrium—total anomalous systemic venous connection—is even rarer (Figures 29-6 and 29-7). ^7,^20,³² Survival depends on adequate mixing through an interatrial communication.

Figure 29-6 Electrocardiogram from a 28-year-old woman in whom the superior and inferior vena cavae both joined the left atrium—total anomalous systemic venous connection. A large ostium secundum atrial septal defect permitted interatrial mixing on which survival depended. The sinus node was absent because a junction between the superior vena cava and right atrium was absent. The P wave axis is directed upward and to the left, indicating an ectopic atrial focus. Broad notched P waves in leads 1, 3, and aVL reflect total caval drainage into the left atrium. The T wave abnormalities are nonspecific.

Figure 29-7 X-rays from the 28-year-old woman with total anomalous systemic venous connection whose electrocardiogram is shown in Figure 29-6. A, The size and configuration of the heart are normal. Pulmonary vascularity is not reduced. Increased markings in the left lower lung fields are superimposed breast tissue. B, In the lateral projection, the inferior vena caval shadow is absent (arrow).

The physiologic consequences of anomalous vena caval connections to the left atrium take into account two variables: (1), the direction and volume of blood flow through the connection; and (2), the effect of the connection on the amount of blood flow entering the right and left sides of the heart. Flow patterns are complex when a persistent left superior vena cava communicates with the left atrium (see Figure 29-2).^14,¹⁷ The left superior vena cava may be the only superior cava (see Figure 29-3), or bilateral superior cavae may fail to communicate with each other because of stenosis or atresia of the innominate bridge (see Figures 29-2B and C). All or nearly all of left superior vena caval blood is then channeled into the left atrium (Figure 29-2B and C), so cyanosis is obligatory. Alternatively, when bilateral superior vena cavae communicate freely through a nonrestrictive innominate bridge, the direction of blood flow is from the left atrium into the anomalous left superior vena cava, across the innominate bridge and into the right superior vena cava (Figure 29-2A).^17,³³ The pathway constitutes a left-to-right shunt, so cyanosis is absent.¹⁴ With this exception, communications between vena cavae and left atrium result in right-to-left shunts and in a decrease in systemic arterial oxygen saturation. When a right superior vena cava connects to the left atrium, caval blood flow is into the left atrium, so cyanosis is inevitable. When the inferior vena cava connects to the left atrium, unoxygenated blood is directed into the left atrium despite a large azygos vein, so cyanosis is obligatory (see Figure 29-4).

Now consider the relative volume of blood flowing through the two sides of the heart in the presence of vena caval–to–left atrial connections. Normally, the entire systemic venous return from the superior and inferior vena cavae enters the right side of the heart, and the entire pulmonary venous return from the pulmonary veins enters the left side of the heart. If one vena cava connects to the left atrium, the right side of the heart is effectively bypassed, so right ventricular output and pulmonary blood flow fall reciprocally.³⁴ Left ventricular output theoretically remains unchanged because the increment in anomalous caval flow into the left atrium is matched by the reciprocal decrement in pulmonary venous flow. Accordingly, as systemic venous return to the left atrium increases, pulmonary venous return to the left atrium decreases by the same amount, so total blood flow to the left side of the heart remains unchanged. In the absence of compensatory mechanisms, anomalous caval connections to the left atrium should be associated with reduced pulmonary flow and normal systemic flow,³⁴ patterns that should pertain irrespective of whether the superior or inferior vena cava connects anomalously. Do these circulatory patterns really exist? Clinical and experimental observations indicate that right atrial and right ventricular pressures are normal or low³⁴ and pulmonary blood flow is usually,³⁴ but not always, reduced. Necropsy descriptions of a small right atrium and a small right ventricle are relevant.³⁵ However, left ventricular output tends to be moderately increased.³⁴ The mechanisms responsible for these deviations from theoretical blood flow patterns are not known.

When the superior vena cava and inferior vena cava both connect to the left atrium (total anomalous systemic venous connection), flow patterns are modified by obligatory mixing at atrial level. The left atrium receives blood from both cavae and from the pulmonary veins. Part of this mixture reaches the left ventricle directly across the mitral valve, and the remainder enters the right side of the heart across an atrial septal defect. Pulmonary blood flow is not increased even in the presence of a nonrestrictive atrial septal defect and normal pulmonary vascular resistance (see Figure 29-7).

The inferior vena cava normally carries about twice the volume of systemic venous return as the superior vena cava. Accordingly, an anomalously connecting inferior cava delivers a larger proportion of blood to the left atrium than an anomalously connecting superior vena cava. However, the magnitude of systemic blood flow (cardiac output) does not depend on which vena cava delivers its return to the left atrium, provided that pulmonary venous return falls by an equivalent amount.

History

Isolated anomalous vena caval connection to the left atrium has an equal gender distribution. Cyanosis dates from birth or infancy ^20,²⁷ unless bilateral superior cavae are connected by a nonrestrictive innominate bridge (see Figure 29-2A). Despite conspicuous cyanosis, there is a paucity of symptoms.^21,²⁷ the syndrome of cyanosis and clubbing with normal heart. Adult survival is expected, with longevities recorded in the sixth, seventh, and eighth decades.^12,²⁰ Effort intolerance, dyspnea, and light-headedness develop late if at all and are generally mild.^20,²¹ One man tolerated training in the armed forces.²⁷ Brain abscess and paradoxical embolus have been reported.^20,²³

The cause of death is usually unrelated to the isolated congenital anomalies of vena caval connection. However, unexplained sudden death has been reported with isolated left superior vena caval connection to the coronary sinus, especially if the right superior vena cava is absent.⁹

Physical appearance

Cyanosis and clubbing are the only abnormalities of physical appearance.²⁰ Cyanosis increases with effort because caval venous return increases. Cyanosis is greater when the inferior vena cava connects to the left atrium because approximately twice as much blood is delivered to the heart via the inferior vena cava (see previous).^34,³⁶ A large azygos venous system allows substantial inferior vena caval flow into the right atrium and proportionately less flow into the left atrium (see Figure 29-4), so cyanosis is relatively mild.²¹ A superior vena cava that connects to the left atrium (see Figure 29-3) is accompanied by conspicuous cyanosis. When a nonrestrictive innominate bridge joins bilateral superior vena cavae, cyanosis is absent because the direction of flow is from the left atrium into the anomalous left superior vena cava (see Figure 29-2A).¹⁷

Arterial pulse and jugular venous pulse

The arterial pulse is normal because left ventricular stroke volume increases little if at all.

Attention has been called to a new physical sign: namely, relative prominence of the left internal jugular venous pulse because of persistence of the left superior vena cava. When there is congenital absence of the right superior vena cava, the jugular venous pulse is confined to the left side of the neck.

Precordial movement and palpation

The left ventricular impulse is normal or only moderately increased, which reflects the normal or only moderate increase in systemic output. A right ventricular impulse is absent. These physical signs indicate that cyanosis is occurring with a dominant left ventricle, an important observation in the clinical recognition of cyanotic congenital heart disease (see Box 1-1).

Auscultation

Left ventricular stroke volume is seldom sufficient to generate a flow murmur into the aorta.^20,²¹ The second heart sound is single because decreased right ventricular stroke volume and decreased pulmonary capacitance result in early pulmonary valve closure and synchrony or near synchrony of the two components.²⁰ The intensity of the pulmonary component is normal or reduced because pulmonary arterial pressure is normal or low.³⁴

Electrocardiogram

When a left superior vena cava connects to the coronary sinus (see Figure 29-1), the atrial rhythm may be ectopic and abnormalities of atrioventricular conduction may coexist.^2,^8,⁹ When a right superior vena cava is absent or connects to the left atrium, the sinus node is absent, so the atrial focus is ectopic and the P wave axis is abnormal (see Figure 29-6).¹¹ Atresia or absence of the segment of superior vena cava adjacent to the right atrium is accompanied by developmental abnormalities of the sinus node and an ectopic atrial focus.⁹

The QRS pattern is normal with vena caval–to–left atrial connections (Figure 29-8). Adult survival anticipates age-related electrocardiographic abnormalities.^12,^20,²¹ Right ventricular hypertrophy is absent because flow into the right side of the heart is normal or reduced. Left ventricular electrical forces retain their normal adult dominance (Figures 29-6 and 29-9), but the modest increment in left ventricular volume is seldom sufficient to cause hypertrophy.

Figure 29-8 Left anterior oblique projection from a 9-year-old girl with isolated inferior vena caval connection to the left atrium. One catheter entered the right atrium (RA) from the superior vena cava, and a second catheter entered the left atrium (LA) from the inferior vena cava (see Figure 29-6 for electrocardiogram).

(With permission, from Venables AW. Isolated drainage of the inferior vena cava to the left atrium. British Heart Journal 1963;25:545.)

Figure 29-9 Normal electrocardiogram from a 9-year-old girl with isolated connection of the inferior vena cava to the left atrium.

(With permission, from Venables AW. Isolated drainage of the inferior vena cava to the left atrium. British Heart Journal 1963;25:545.)

X-Ray

The size and configuration of the heart are normal (see Figure 29-8),^20,^21,³⁵ even when both superior and inferior vena cavae connect to the left atrium (see Figure 29-7). A left superior vena cava may form a concave or crescentic shadow as it emerges from beneath the middle third of the left clavicle.^14,^17,³⁷ When the inferior vena cava communicates with the left atrium, the inferior vena caval shadow is absent from its expected location at the angle formed by the posterior cardiac silhouette and the diaphragm (see Figure 29-7B). An inferior vena caval shadow is also absent when there is inferior caval interruption with azygos continuation (see Figure 29-5). The azygos vein ascends along the right edge of the vertebral column, forming a knuckle as it courses anteriorly to join the right superior vena cava (see Figure 29-5).

Echocardiogram

Echocardiography with color flow and contrast imaging establishes the diagnoses of most if not all anomalies of vena caval connection described in this chapter,^1,^16,³⁸^–⁴³ including intrauterine.⁴⁴ A dilated coronary sinus in the parasternal long-axis view arouses suspicion of a hitherto unsuspected connection of a left superior vena cava to the coronary sinus (Figure 29-10 and Video 29-1).⁴⁵ The coronary sinus is absent when a left superior vena cava connects directly to the left atrium (see Figure 29-2). Color flow imaging confirms the course of a persistent left superior vena cava (Figure 29-11 and Video 29-2), which can sometimes be visualized together with the innominate bridge associated with bilateral cavae (see Figure 29-2). When the right superior vena cava is absent, a persistent left superior vena cava is imaged along the left side of the aorta.^46,⁴⁷

Figure 29-10 A, Echocardiogram (parasternal long-axis view) from a healthy 9-month-old male with a coronary sinus (CS) that was dilated by connection to a persistent left superior vena cava. The large size of the coronary sinus is evident when compared with the cross-section of the descending aorta (Ao) (Video 29-1). (LV = left ventricle, LA = left atrium.) B, Echocardiogram from a healthy 12-month-old girl with a normal-sized coronary sinus.

Figure 29-11 Color flow image showing the course of a persistent left superior vena cava (LSVC) that communicated with a dilated coronary sinus in a 3-day-old male with an ostium secundum atrial septal defect (Video 29-2).

Contrast echocardiography identifies specific vena caval to left atrial connections.^38,^40,⁴⁸ When a left superior vena cava connects directly to the left atrium, injection of echo contrast into the left antecubital vein is followed by immediate opacification of the left atrium.³⁸ Conversely, when a right superior vena cava connects directly to the left atrium, injection of contrast into the right antecubital vein promptly opacifies the left atrium.³⁸ Contrast echocardiography is more complex when the inferior vena caval connects to the left atrium⁴⁹ because contrast material injected into the femoral vein may appear in the right as well as the left atrium depending on the size of the azygos vein that leaves the inferior vena cava and joins the right atrium via a right superior vena cava (see Figure 29-4). When a right superior vena cava and an inferior connect both connect to the left atrium (see Figure 29-7), injection of contrast into the right antecubital vein and into the femoral vein result in a combination of the patterns just described.