Spectrum of TOF/PA
TOF/PA with confluent branch
PAs In milder forms of TOF/ PA, the branch PAs are confluent and can be only mildly hypoplastic. In the best case, the MPA can even be present such that eventual repair can involve a short conduit or even a TAP. A general rule of thumb is that the larger the branch PAs, the more likely it is that APCs (PBF derived from a ductus) are absent and the more likely it is to achieve early biventricular repair.
In more severe forms of the disease, the branch PAs are severely hypoplastic or even absent. Pulmonary blood flow is then exclusively dependent on APCs (when ductus is absent), which is undesirable for several reasons. (1) The circulation mandates complete mixing, with partially oxygenated blood perfusing the lung, which is inefficient. (2) APCs are high resistance, unreliable vessels and do not grow reliably over time, compromising lung perfusion over time. Flow dynamics through such vessels are abnormal.
Due to pulmonary atresia, PGE must be started at birth. In the newborn period, the goal is to establish a reliable source of pulmonary blood flow. In the most favorable anatomic subtypes, it may be possible to establish a complete biventricular repair in the newborn period including a TAP (sometimes with a monocusp valve), closure of the VSD, and fenestrated ASD closure. If the PA anatomy is less favorable (i.e. the PAs are diminuitive), it is important to determine whether any of the PBF is ductal dependent. If the branch PAs are confluent, PBF may be ductal dependent (rather than exclusively APC dependent) such that a definitive procedure (PDA stent or BTS) is considered. In other cases, PBF is all via APCs in which case initial intervention can be deferred out of the newborn period absent significant hypoxemia. The drivers of care in patients TOF/PA/MAPCAs are to encourage growth of the PAs as early as possible and to perfuse all lung segments with the ultimate goal of a complete biventricular repair including closure of the VSD
Management of the pulmonary arteries. Generally, it is thought that PA growth is optimized by establishing antegrade (i.e. from the RV) PBF early (when possible), removing competitive dual supply PBF (i.e. coiling APCs to segments also fed by native PAs), and relieving PA stenosis. At the first operation, the goal is to incorporate as much of the APC circulation into a single circulation as possible, either reconstructed with the native branch PAs and brought to an RVPA conduit (preferable) or alternatively to a central aortopulmonary shunt; this is often performed in stages, some via thoracotomy and others via sternotomy. In some cases, reconstructed PAs are anastamosed to an RVPAC and a shunt added for supplementary PBF to encourage PA growth and decrease hypoxemia. It is important to note that APCs are abnormal, unreliable, high resistance vessels that are prone to occlusion; this may lead to a permanent loss of blood flow to the affected segment of lung. Following manipulation (dilation/stenting or surgical plasty), anticoagulation and ensuring good flow (by preventing atelectasis) is a high priority. Bronchomalacia, atelectasis, and frequent pulmonary infections are unfortunately common in the most severe cases, and excellent pulmonary toilet in the postoperative period is imperative. Even following biventricular repair, close monitoring of PA growth and PA pressure are important. Catheterizations for PA dilations are common but wane with time and growth.
Management of the VSD. In more severe cases, VSD closure is not possible in the initial procedure due to hypoplastic PAs which create a high resistance to PBF (and would cause RV failure were the VSDs closed). Generally, timing of VSD closure can be determined by Qp/Qs (i.e. direction of VSD flow; as the PAs grow, the saturations increase and the VSD shunts more left to right). When the VSD is closed (sometimes with a fenestration), postoperative monitoring and treatments for restrictive RV physiology are important (maintain preload and SVR).
Repair. In the most favorable anatomies, RV-PA continuity can be established using the native PA, one or two dominant APCs (if present) can be incorporated into the PA circulation, and the VSD closed. A fenestrated ASD is often left, allowing for right to left atrial flow (and maintenance of LV preload in the setting of a less compliant RV). A fenestrated VSD may also be left, allowing an additional site of right to left shunting. These fenestrations allow hypoxemia but preserve cardiac output.
Postoperative considerations. (1) In the setting of multiple redo sternotomies and/or multiple APCs, thoracic bleeding may be present and clinically dominate the initial postoperative period. RAP should be closely monitored and maintained at a sufficient level to ensure adequate RV preload. Coagulation factors should be optimized. Bleeding is also a prothrombotic state, placing recently anastamosed APCs at risk for thrombosis. (2) Due to RV hypertrophy, VSD closure, an infundibular incision with RVPAC placement, restrictive RV physiology may be present. Ensuring RV preload via replacing volume loss and maintaining some degree of vasoconstriction improves stroke volume and diminishes swings in blood pressure. Inotropic support with catecholamines is also helpful (NE has excellent B1 and vasoconstrictive properties). (3) Because PVR increases with atelectasis, pulmonary toilet and lung recruitment are important to maintaining patency of small PAs.
Procedure. In more severely affected patients, there is often an absent MPA and hypoplastic (even absent) native branch PAs. In this setting, the initial procedures often include unifocalization of APCs to a central shunt to promote PA growth as an iterative step towards a complete unifocalization and ventricular septation. APCs from the descending aorta may be unifocalized via thoracotomy.
Postoperative considerations. (1) In the setting of multiple redo sternotomies and/or multiple APCs, thoracic bleeding may be present and should be addressed by correction of medical coagulopathy and occasionally by administration of thrombostabilizing agents. Once bleeding is controlled, thrombus formation within the aortopulmonary shunt or within an APC is considered, and anticoagulation is often indicated. Treatment with antiplatelet agents, including aspirin and tirofiban, are common. (2) Any patient with a central shunt must be monitored for insufficient systemic blood flow (weak pulses, low SvO2, elevated lactic acid), though the PA resistance is commonly elevated such that the concern is more commonly the development of shunt thrombosis. The time of extubation is a particularly high risk period for the development of thrombosis due to valsalva (decreasing PBF transiently) and atelectasis.