Venoatrial MalconnectionsPartial
anomalous pulmonary venous connection Partial Anomalous Pulmonary Venous ConnectionIntroductionPulmonary venoatrial malconnections can involve a solitary vein, all the venous connections from one lung, or all of the connections from one lung and some or most of the connections from the other lung. Total anomalous pulmonary venous connection involves all of the venous drainage of both lungs. Partial anomalous pulmonary venous connection may be of no clinical importance, except when associated with a sinus venosus ASD, in which case it becomes of considerable surgical significance. Partial anomalous pulmonary venous connection is also of clinical importance in the setting of the scimitar syndrome, but taken overall, TAPVR is a more clinically significant lesion. MorphologyPartial anomalous pulmonary venous connection occurs most frequently on the right. In order of decreasing frequency, the sites of connection are to the superior vena cava, the right atrium, the inferior vena cava, and to coronary sinus. When the left pulmonary veins are anomalously connected, then the left innominate vein is the usual site of connection. The sinus venosus type of ASD is, in actuality, a unilateral PAPVR to the superior vena cava. The scimitar syndrome is a characteristic form of PAPVR to the inferior vena cava, in which the anomalous vein forms a curved shadow at the right lung base in the frontal chest film, an ASD is not present, and the right lung has varying degrees of hypoplasia and sequestration. The term ‘scimitar syndrome’ was first applied to a radiographic finding in a familial disease characterized by a right-sided heart (dextroverted) with partial anomalous pulmonary venous connection. The anomalous connection was to the inferior vena cava and the shadow produced was likened to the curve of a Turkish sword. Since then, it has become evident that similar features may be present in a range of cases, not all of which represent familial disease and not all exhibiting all features of the original cases. These features include dextroversion of the heart, sequestration of part of the lung, (sequestrated in terms of its bronchial supply and usually there is also an anomalous pulmonary arterial supply through systemic collateral arteries derived from the descending aorta, and the venous return is also anomalous in most cases, often for the entire right lung but sometimes for only part of it. The anomalous pulmonary venous connection pierces the diaphragm and terminates in the inferior vena cava. Clinical Findings The signs and symptoms of the partial anomalous pulmonary venous connection is related to the degree of left to right shunting. Isolated PAPVR from a single lobe results in asymptomatic shunting, whereas PAPVR of an entire lung results in significant shunting. The chest film will demonstrate evidence of right ventricular enlargement, hypoplasia of the right lung, and a snowman appearance to the mediastinum if there is a left vertical vein. Echocardiography may not reliably identify the abnormal venous drainage but can help exclude ASD from the differential diagnosis. Cardiac catheterization and angiocardiography are diagnostic. A step-up in oxygen saturation is present at the site of entry of the anomalous vein and calculations of pulmonary blood flow and shunt fraction can be made. Contrast injection into the pulmonary arteries defines any abnormalities of the branch arteries, and the venous phase reliably demonstrates the abnormal venous connection. The natural history of untreated PAPVR is probably similar to that of a secundum ASD. Anomalous drainage of one pulmonary lobe or less does not require operation whereas, larger shunts do require operative repair. Operative intervention is contraindicated in the presence of severe pulmonary hypertension. Operative technique Surgical correction of isolated PAPVR in which the left lung drains to the superior vena cava can be accomplished without the use of cardiopulmonary bypass. A left fourth interspace thoracotomy is used to expose the hilum, and the pericardium is opened. The left pulmonary artery can be temporarily occluded, or a side-biting clamp can be used. The left superior vena cava is clamped and divided at its point of entry into the innominate vein. The venous end is trimmed obliquely to facilitate creation of a wide anastomosis to the left atrium. The partial occlusion clamp is placed at the base of the left atrial appendage and the anastomosis is made with absorbable suture. Inflow to the pulmonary arteries is restored. Median sternotomy is customarily employed to repair PAPVR of the right lung. Cardiopulmonary bypass utilizing bicaval cannulation and a single aortic cannula is established, and a pericardial patch is used to baffle the anomalously draining right sided pulmonary veins to the sinus venosus ASD. If the ASD is small or not present, the atrial septum is excised prior to baffling. Correction of the scimitar syndrome may be technically demanding due to the infradiaphragmatic portion of the anomalous venous connection. Exposure of this portion of the vein is afforded by splitting the diaphragm to the venocaval hiatus. In some patients, the repair may only require removal of the inferior vena caval cannula to expose the anomalous venous ostium during a brief period of deep hypothermic circulatory arrest. In this instance, an intra-atrial baffle is used in much the same way as a PAPVR with a sinus venosus defect. A final alternative technique consists of extracardiac reimplantation of the scimitar vein into the posterior wall of the right atrium followed by transposition of the atrial septum anterior to the new ostium, either directly or with a patch. Total Anomalous Pulmonary Venous ConnectionEmbryologyTotal anomalous pulmonary venous return commonly occurs as an isolated lesion, but may be associated with a patent arterial duct, ventricular septal defect or with the heterotaxic syndromes, especially right atrial isomerism. Recall that right atrial isomerism is associated with the presence of two right lungs, two right atria and no left atrium, so that, almost by definition, there is also anomalous pulmonary venous drainage. Early in fetal life, the common pulmonary vein develops as an endothelial out sprouting from the left atrium and grows towards the lung bud which is supplied by the splanchnic circulation. The common pulmonary vein of the left atrium then connects with the pulmonary venous plexus of the outgrowing lung bud, while connections between the pulmonary and splanchnic plexuses involute. Later on, the common pulmonary vein is annexed into the left atrium. If the common pulmonary vein is abnormally annexed into the right atrium, then connection with the pulmonary venous plexus results in total anomalous pulmonary venous return to the right atrium. If the common pulmonary vein of the left atrium fails to connect with the pulmonary venous plexus of the outgrowing lung bud, then adjacent systemic venous systems may drain the pulmonary blood flow. Connection to the right cardinal vein, destined to become the superior vena cava, results in total anomalous pulmonary venous return to the superior vena cava. Connection to the left cardinal vein results in total anomalous pulmonary venous return to the coronary sinus if the left cardinal vein involutes as it normally does, or in total anomalous pulmonary venous return to a left vertical vein which drains into the innominate vein if the left cardinal vein does not involute. Finally, If the connections between the pulmonary and splanchnic plexuses fails to involute, then the pulmonary plexus can drain into a common channel closely related to the esophagus and pierce the diaphragm at the esophageal hiatus, coming to communicate with either the portal system or venous duct. Site of anomalous connection and obstruction The anomalously connecting veins can be connected to any adjacent systemic venous channel, either within the thorax or within the veins can connect anomalously to different sites. The latter pattern is described as ‘mixed’ anomalous connection. Taken overall, the patterns are sufficiently constant to permit categorization. The anomalous connection can first be divided into supradiaphragmatic and infradiaphragmatic forms. The infradiaphragmatic variant is also infracardiac. The variant with anomalous connection above and within the thorax can be further divided into supracardiac and cardiac patterns. Several morphological variants can therefore possible:
Intracardiac (40%). The confluence of veins drain most commonly into the coronary sinus or less often directly into the right atrium. Infracardiac (20%). The confluence of veins behind the left atrium drains downward through the diaphragm through the esophageal hiatus to the portal system, reentering the heart through the venous duct or inferior vena cava. Mixed (rare). Any combination of anatomic entry is possible. Obstruction to pulmonary venous return along its abnormal pathway back to the heart greatly influences the presentation and pathophysiology of total anomalous pulmonary venous return. The approximate prevalence and most common sites of obstruction are given in the table below.
Supracardiac pulmonary venous connection is the commonest anomalous pattern, in which pulmonary veins join in a confluence immediately behind the left atrium and a venous channel usually ascends to the left and forms the left brachiocephalic vein. The venous return then reaches the right atrium through the superior vena cava. This arrangement gives a characteristic radiographic appearance known as the ‘snowman’ heart. The upper part of the radiographic image is the venous pathway while the lower part is the heart itself A characteristic feature of any form of totally anomalous pulmonary venous connection is the ease with which the heart can be deflected surgically or at autopsy from its pericardial cradle. This is an important pathological marker for the condition. Obstruction occurs with some frequency in the ‘snowman’ variant, and is due usually to trapping of the venous channel between the pulmonary artery and the bronchus. This arrangement has been graphically characterized as the ‘bronchopulmonary vice’. Although supracardiac connection involves a left-sided ascending channel in most instances, rarely the anomalous venous confluence may cross the midline and ascend within the right paravertebral gutter, picking up the right pulmonary veins as it ascends before joining the azygos vein. This pattern can also exist with the right-sided channel embedded within the substance of the right lung. Obstruction is much rarer with this variant. Cardiac connection is almost always to the coronary sinus. All four pulmonary veins may come separately into the sinus but usually there is a short confluence and a common channel behind the left atrium. The anomalous connection results in gross enlargement of the orifice of the sinus, and an extensive common wall is to be found between the sinus and the remnant of the left atrium. Observation of this feature led to the ingenious suggestion that this particular variant could best be repaired by removal of the common wall and closure of the mouth of the coronary sinus, this procedure restoring, more or less, the anatomy of the normal heart. Congenital stenosis in this form of connection is exceedingly rare, but has been reported as the consequence of a persistent Thebesian valve. Totally anomalous connection of the pulmonary veins can also be directly to the right atrium but this is much rarer. Taken overall, connection directly to the heart is the rarest form of totally anomalous return. Infracardiac and infradiaphragmatic pulmonary venous connection is usually to the portal venous system or directly to the venous duct. Rarely it is to the inferior vena cava. When the connection is to the portal system men patency of the venous duct determines the natural history of the condition. While the duct remains open, the pulmonary venous return will achieve a relatively unobstructed pathway to the heart. As soon as the venous duct closes, all the pulmonary flow must pass through the sinusoids of the liver before reaching the right atrium. Severe obstruction can also occur as the consequence of the anatomical anomaly itself. In the most extreme example, the descending channel split into a leash of veins which men anastomosed with the gastric veins. Mixed totally anomalous connection can involve any of the sites of anomalous connection but most usually is a combination of cardiac and supracardiac connections. The major effect of totally anomalous pulmonary venous connection is that all the venous return, systemic and pulmonary, is to the morphologically right atrium. Because of this, the right heart chambers and the pulmonary trunk are much larger than their left-sided counterparts. Because all the venous return is to the right atrium, the circulation is dependent upon flow of blood through the atrial septum. The oval fossa, therefore, is usually widely patent, although it is rare to find a true deficiency of the floor. In contrast, the finding of an intact, or virtually intact, atrial septum is a significant feature. In most cases, the anomalous connection of the pulmonary veins is the only lesion within the heart. Anomalous connection can coexist with other lesions. Sometimes, as with complete transposition, it is beneficial in the natural history of the associated condition. As already indicated, in other instances the anomalous pulmonary venous connection is an integral part of a complex of lesions. Right atrial isomerism is the prime example of this but anomalous connection of the right pulmonary veins is a very common accompaniment of the sinus venosus interatrial communication. The anomalous connection which is part of the ‘scimitar syndrome’ is discussed below. The anomalous route of venous circulation imposing an increased load on the right heart has a major effect upon the structure of the pulmonary vasculature. Changes are to be found even in neonates. The muscularity of the pulmonary arteries is increased and the degree increases further with age, even in those with low pulmonary flow. The pulmonary veins are also masculinized. Studies of large numbers of specimens permit the calculation of am index of pulmonary vascular disease. The index is higher in cases with obstructed pulmonary venous flow. Multiple anastomoses develop between the pulmonary and bronchial veins. The evidence indicates that most of these changes are already present during fetal life, so the excellent results of surgery in most cases indicate that such changes are not inimical to survival. Hemodynamics Total anomalous pulmonary venous return is associated with the return of all systemic and all pulmonary venous blood to the right atrium, which can either cross the tricuspid valve to the right ventricle or shunt to the left atrium across an ASD to the left ventricle. Pulmonary vascular resistance, obstruction to pulmonary venous drainage, and the presence of arterial and venous level shunts are key factors in the hemodynamics and clinical features of the different forms of total anomalous pulmonary venous return. Following birth, pulmonary vascular resistance drops sharply, and pulmonary blood flow increases. Increased pulmonary blood flow due to total anomalous pulmonary venous return in the absence of pulmonary venous obstruction results in an increased return of blood to the anomalous pulmonary venous drainage, and hence flow back to the right atrium and right ventricle. Depending on the presence and degree of right-to-left shunting at the atrial level, left ventricular output is either maintained or decreased, while right ventricular output is greatly increased. The presence of obstruction to pulmonary venous return, due for example to restriction of flow at the patent foramen ovale or venous duct, may result in pulmonary venous hypertension and pulmonary edema, and the propensity towards pulmonary hypertensive episodes. Pulmonary venous hypertension also results in pulmonary arterial hypertension and decreased pulmonary blood flow, resulting in severe cyanosis, a small heart and edematous lungs. The arterial duct may remain patent for days or weeks after birth, particularly in infants hypoxic with pulmonary venous obstruction. If the pulmonary vascular resistance is very high, blood will shunt from the pulmonary artery to the aorta, effectively stealing blood from the pulmonary circulation and rendering the baby even more cyanotic. Conversely, if the resistances are reversed, the direction of shunting will also reversed. Arterial-level or ventricular-level shunting, the latter occurring in the presence of a ventricular septal defect, in conditions of high pulmonary vascular resistance may occasionally be important in maintaining systemic blood flow, particularly when the left atrium and left ventricle are hypoplastic or the patent foramen ovale restrictive. Clinical Presentation and Management The age at presentation depends largely on the presence of obstruction to the pulmonary venous return. Infants with obstructed total anomalous pulmonary venous return become symptomatic very early in the neonatal period, while children with completely unobstructed total anomalous pulmonary venous return may present somewhat later with congestive heart failure. Thus neonates with total anomalous pulmonary venous return can present with signs of symptoms of pulmonary venous obstruction and/or excessive pulmonary blood flow, including pulmonary plethora, dyspnea, cyanosis, and poor cardiac function. Imaging studies. The chest film varies depending on the presence or absence of pulmonary venous obstruction. Patients with unobstructed total anomalous pulmonary venous return have a large heart, plethoric lung fields, and may have an extra shadow of the vertical vein, while those with obstructed total anomalous pulmonary venous return have a small heart, pulmonary edema, and Kerley B lines. 2-D echocardiography, Doppler and color flow mapping are important diagnostic modalities in total anomalous pulmonary venous return, often identifying all of the pulmonary veins, the venous connection to the systemic circulation, the sites of obstruction, in addition to allowing for an estimation of the presence of pulmonary hypertension and identification of the presence of associated lesions. Cardiac catheterization in these ill infants is not without risk, and is currently performed on a selective basis. Medical Management Untreated patients with obstructed total anomalous pulmonary venous return have a high mortality within the first few weeks of life, while those with unobstructed total anomalous pulmonary venous return may survive longer, although suffer from failure to thrive, poor feeding, and recurrent chest infections. Medical treatment is generally supportive, consisting of treatment of congestive heart failure, respiratory support, and correction of acid-base abnormalities and electrolyte disturbances. Administration of PGE1 may effectively open the venous duct, which may be beneficial in cases of infracardiac total anomalous pulmonary venous return, as well as the arterial duct, which may be beneficial when left ventricular output is poor. Maintaining patency of venous and arterial ducts may also effectively decompress the right ventricle which is operating at supra-systemic pressures. Balloon atrial septostomy is occasionally beneficial in cases of a restrictive patent foramen ovale, which may improve left ventricular filling, ameliorate features of low cardiac output and decrease pulmonary venous pressure. Surgical Management Infants with pulmonary venous obstruction are considered surgical emergencies. Repair[115, 179] consists of connecting the common pulmonary venous channel to the left atrium, division of the vertical pulmonary vein, and closure of interatrial shunts, if present. Ligation of a arterial duct is especially important prior to repair in order to prevent air from entering the systemic circulation and possibly causing cerebral damage. The surgical approach in all forms of TAPVR is via sternotomy and cannulation using a single venous and a single arterial cannula. In all cases, the arterial duct is identified and doubly ligated immediately after establishing cardiopulmonary bypass. The patient is cooled to 20° C, the aorta is cross-clamped and the heart arrested with an infusion of cold blood potassium cardioplegia.
For TAPVR to the coronary sinus, the enlarged coronary sinus ostium is identified through the opened right atrium. The coronary sinus is cut back into the left atrium, to essentially unroof it as widely as possible. The left and right atria are then separated by closing the newly created ASD and coronary sinus ostium using a patch. The defect remaining in the coronary sinus within the confines of the left atrium allows drainage of pulmonary venous blood, as well as the cardiac veins, into that chamber. Although infracardaic TAPVR is the least common form of total anomalous connection, it is the type most often associated with pulmonary venous obstruction. These neonates may be profoundly hypoxemic and severely acidotic. Following establishment of deep hypothermic circulatory arrest, the anatomy of the confluence of the pulmonary veins is confirmed, again by raising the apex of the heart towards the right shoulder. The descending vertical vein is identified and ligated at the level of its entrance into the diaphragmatic hiatus. This can be accomplished by a left-sided approach while the heart is still elevated, or by a right-sided approach after lysis of pericardial adhesions to the atria and vena cava. An incision is then made in the anterior aspect of the pulmonary venous confluence which is extended along the anterior wall of the descending vertical vein. A corresponding incision is made in the left atrium and into the left atrial appendage. As wide an anastomosis as possible is then achieved between the two incisions just made. Mortality following repair of TAPVR ranges from 2 to 20% depending on the number of neonates in the series and the degree of severe pulmonary venous obstruction present prior to operation. Long term prognosis is generally good although the risk of pulmonary vein stenosis is always present. Cor triatriatumAs mentioned above, persistence of the valves of the embryonic venous sinus is often described as ‘cor triatriatum dexter’. When used in isolation, the term ‘cor triatriatum’ almost always refers to division of the left atrium. Several patterns exist in which the left atrial chamber is divided, often in association with anomalous pulmonary venous connections or other lesions. The greater majority of cases, nonetheless, are of a pattern which can be considered as the ‘classic’ lesion. In this variant, an oblique partition separates a proximal atrial chamber, to which are connected the pulmonary veins, from a distal chamber in free communication with the vestibule of the mitral valve and the mouth of the atrial appendage. Most frequently, the fossa ovalis (which may be deficient, probe-patent or intact) is in actual or potential communication with the distal chamber. Cases are well described, however, in which the fossa is in communication with the distal chamber. The severity of the lesion depends upon the size of the orifice between the divided components of the left atrium. This communication is usually seen in the part of the shelf where it joins inferiorly with the atrial septum and, in cases coming to autopsy, is usually of pin-hole size. Cor triatriatum is seen most frequently as an isolated lesion but it can coexist with any other defect. Notable associations are with atrioventricular septal defect or totally anomalous pulmonary venous connection, where the presence of the obstructive shelf may be masked clinically. Clinical presentation Patients become symptomatic if the ostium between the proximal and distal and atrial chambers is small. The signs and symptoms are those of pulmonary venous and arterial hypertension and low cardiac output. Poor feeding, growth failure, recurrent respiratory infections, tachypnea, congestive heart failure are the usual symptoms. Echocardiography is accurate in the diagnosis of cor triatriatum. The dilated and thick walled proximal chamber is well visualized and the membrane can often be demonstrated. Cardiac catheterization is usually unnecessary, unless there is suspicion of associated defects. At catheterization, an elevated pulmonary artery wedge pressure is often present, and it is often possible to enter both proximal and distal chambers and record any gradient. Pulmonary arteriography will delineate the atrial membrane during the venous phase. Signs, symptoms, along with the natural history are dependent on the communication between the proximal and distal atrial portions. If the communication is small and the restriction severe, patients will become severely ill within the first few months of life and approximately three-fourths will die in infancy if not surgically corrected. A less restrictive fenestration may delay the development of symptoms until adolescence, whereas a communication with no gradient may be asymptomatic and confirm a normal life expectancy. Medical and surgical treatment A treatment of cor triatriatum is surgical. Because life expectancy is limited, prompt operation is indicated for all patients with a restrictive opening. The surgical approach is dependent on the specific anatomy. Either a right or left atrial approach is used according to the size of these chambers. Cardiopulmonary bypass is established and the heart is arrested. The opening into the common pulmonary venous chamber is enlarged and the orifices of the four pulmonary veins and the fenestration into the left atrium are identified. This fenestration is enlarged so that the mitral valve and atrial appendage are easily identified. The membrane has been widely excised taking care not to injure the mitral valve or the intra-atrial septum. Operative results for the repair of cor triatriatum are generally good. Perioperative mortality is reported to be between 15 and 20%, with virtually all deaths occurring in patients with Serres associated cardiac defects. Late survival rates are generally between 80 and 100% at five years |
Supracardiac
(40%). The pulmonary veins drain into a confluence of veins (the common pulmonary
vein) located behind the left atrium, and then upwards through a vertical vein into the
innominate or azygous vein to return to the right atrium via the superior vena cava.
For supracardiac
TAPVR, the anatomy of the pulmonary veins and their connections to the systemic venous
system are established. Often, it is useful to retract the apex of the left ventricle
towards the right shoulder in order to facilitate exposure. The usual left-sided vertical
vein is then ligated at its junction with the innominate vein. An incision is made in the
anterior wall of the pulmonary venous confluence and a corresponding incision is made in
the adjacent wall of the left atrium. The longest, widest possible anastomosis is then
performed. This supracardiac approach is performed in the space between the right superior
vena cava and the aorta, the latter which is retracted to the left side. When supracardiac
connection is to the right superior vena cava, a similar approach as described may be
used. The anomalous connection of the veins to the right superior vena cava can then be
ligated. Alternatively, through a right atrial approach, a baffle may be placed to direct
flow from the entrance of the pulmonary veins into the right superior vena cava through a
surgically enlarged intra-atrial communication to the left atrium. When supracardiac
connection is to an azygous vein, it is advisable to ligate the connection and perform a
direct anastomosis of the confluence of the pulmonary veins to the posterior aspect of the
left atrium as described above.