Introduction
Anomalous pulmonary venous connection is categorized according to whether or not the entire pulmonary venous return is anomalous (total) or only partly anomalous, with some of the venous drainage being normal (partial).
Total Anomalous Pulmonary Venous Connection (TAPVC)
This is also called ‘total anomalous pulmonary venous drainage’ (TAPVD). The entire pulmonary venous return drains to the right side of the heart or the systemic venous system, usually via a common pulmonary venous confluence. An atrial communication is therefore essential to allow left ventricular filling. It makes up 1 to 2 per cent of congenital heart defects and occurs as in combination with other anomalies in one-third of cases.
Morphology
In most cases the pulmonary veins drain into an extra-cardiac chamber called the ‘pulmonary venous confluence’, which is a remnant of the embryo’s common pulmonary vein. This confluence drains through a separate channel into the systemic venous circulation.
There are four types of TAPVC:
Supra-cardiac. This is the commonest variant (45 to 55 per cent of TAPVCs), a connection of the pulmonary venous confluence via a vertical vein into the superior vena cava (SVC), the innominate vein or, rarely, the azygous vein. The confluence is horizontally oriented, lying immediately behind the pericardium, facing the back of the left atrium.
Cardiac. Here drainage is directly into the coronary sinus (10 to 15 per cent of TAPVCs).
Infra-diaphragmatic. The pulmonary venous confluence lies posterior to the pericardium behind the heart and drains via a descending vertical vein, through the diaphragm, into the portal circulation or the inferior vena cava (IVC; 20 to 25 per cent of TAPVCs). The orientation of the confluence is vertical rather than horizontal.
Mixed. This involves combinations of the above (5 to 10 per cent), typically with a confluence of the majority of the veins with one or two separate vein(s) draining directly into the SVC or innominate vein.
The common forms are shown in Figure 8.1.
Pathophysiology
The venous return from the pulmonary circulation drains to the right side of the heart (causing obligate mixing of the venous circulations and cyanosis), resulting in right heart volume loading, and the preload to the left side of the heart is entirely dependent on the atrial communication. Any restriction of the atrial communication causes further right heart pressure loading with under-filling of the left heart and poor systemic perfusion.
Furthermore, if there is any obstruction to the pulmonary venous return into the systemic circulation, then there will be venous congestion in the lungs and pulmonary oedema, setting up a potentially lethal combination of profound cyanosis, pulmonary hypertension and poor systemic cardiac output. More severe degrees of obstruction are associated with lymphatic abnormalities within the lungs.
Obstruction is most commonly seen in infra-cardiac types (most have some degree of obstruction), where the draining vein is obstructed in its passage through the liver. Less severe degrees of obstruction can be seen with (~50 per cent of) supra-cardiac types, where the draining vein can get trapped in the ‘vice’ between bronchus and pulmonary artery. Obstruction does not occur with cardiac types.
Any obstruction is usually at the level of the draining vein, but sometimes the individual veins themselves can be narrowed, particularly in the infra-cardiac group. Isolated pulmonary vein stenosis carries a particularly poor prognosis.
Presentation
If there is obstruction to pulmonary venous return, presentation is at birth with respiratory distress, cyanosis and collapse. Symptoms develop within 24 hours of birth, and death occurs without treatment in the first weeks of life.
In the absence of pulmonary venous obstruction, patients present in early infancy with variable degrees of cyanosis and right heart volume overload. There may be dyspnoea, failure to thrive, and recurrent chest infections. The degree of cyanosis can be relatively mild if there is unobstructed return.
Severity of symptoms depends on the degree of obstruction, but severe cases can present in extremis with profound cyanosis and require resuscitation and emergency surgery. ECG shows right ventricular hypertrophy.
CXR in obstructed cases shows plethoric and congested lung fields with a relatively small heart shadow; the venous obstruction creates a characteristic ‘ground glass’ pattern to the lung fields. In unobstructed cases, there tends to be cardiomegaly with less pulmonary plethora.
Echocardiography is diagnostic and demonstrates the absence of pulmonary venous connections to the left atrium in combination with right-to-left shunting across the atrial septal defect (ASD). The positions of all four veins should be identified. There is right ventricular and pulmonary artery volume loading. The left ventricle often appears small, but this is due to under-filling and compression from the enlarged right side – it is seldom due to inadequate development – and the aortic and mitral dimensions are normal.
CT scan and MRI are rarely necessary but can be used to further delineate the anatomy if there are doubts on echocardiography on the position of individual veins. Cardiac catheterization is not necessary.
Management
Management depends on the presentation. In obstructed TAPVC, the patient usually presents shocked, cyanotic and acidotic. This type of patient must be stabilized as much as possible with intubation, ventilation with 100 per cent oxygen and/or nitric oxide, prostaglandin infusion, inotropic support and correction of acidosis. The definitive treatment is surgical, and this must be undertaken emergently.
In unobstructed TAPVC there is no immediate urgency, and elective surgery can be planned before six months of age. Patients with minor degrees of obstruction usually have a degree of right heart failure and should be repaired as a priority.
Surgery
This is the only treatment for TAPVC, and the aim is to redirect pulmonary venous flow to the left atrium. Surgery is performed using moderate hypothermia and bicaval cannulation or with deep hypothermic arrest, according to preference – although the latter may be necessary in newborn obstructive cases where collateral return otherwise prevents an adequate view.
In infra- and supra-cardiac TAPVC, redirection can be achieved by laying open the confluence where it sits behind the pericardium, making a matching incision into the posterior wall of the left atrium/appendage and anastomosing the two together. The draining vein can be ligated (some recommend leaving this open in case recurrent obstruction occurs) and the ASD/PFO closed. Various approaches can be used, either dislocating the heart out of the pericardium or leaving the heart in position and cutting through the right atrium, across the septum and through the posterior wall of the left atrium. Alternatively, the confluence can be approached working between the aorta and SVC to access the posterior pericardium.
In cardiac TAPVC, the atrial septum can be partially resected, the coronary sinus unroofed back into the left atrium to create a large opening and a patch used to close the atrial septum, committing all the coronary sinus return into the left atrium (LA). This will inevitably also direct the coronary venous return to the LA, but this right-to-left shunt is small and not clinically significant.
Postoperative Management.
Obstructed cases will have varying degrees of pulmonary hypertension preoperatively and are at risk of pulmonary hypertensive crises postoperatively: a direct pulmonary artery (PA) pressure monitoring line can be helpful to direct inhaled nitric oxide (iNO) treatment if required. Since the left ventricle has been relatively under-filled, the sudden increase in preload can reveal a non-compliant left ventricle (LV) that is sensitive to volume changes, and monitoring LA pressure is also useful.
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