Anatomical description

To enter this category, a patient should present with pulmonary atresia, no persistent arterial duct and ‘hypoplastic’ but present central PAs. This excludes patients with ‘normal’ PAs vascularized through a ductal structure, with the atresia being simply at the valvular level or more complex. It excludes, of course, patients without any central PAs. In real life, it is not always easy at first examination to differentiate clearly between a tortuous arterial duct and an MAPCA but it is clear that none of these patients should be prostaglandin E1-dependent. ‘Hypoplastic’ PAs have to be determined according to the Nakata index (below 90 mm/m ² [or 100 mm/m ² , depending on the authors]). None of these patients should be readily accessible to complete repair without unifocalization, which means that a normal output will not be able to flow through the central PA before rehabilitation.

The origin of the pulmonary flow is completely due to the MAPCAs. The distribution of the native PAs and the MAPCAs to the pulmonary segments has to be appreciated and evaluated.

The location of the VSD is the same as in Tetralogy of Fallot – a conoventricular position. The anatomical investigations have to confirm that it is a single VSD. Furthermore, the position of the coronary arteries has to be checked. The aortic arch may be left- or right-sided, which may have importance for the surgical plans.

Some of the patients might have a 22q11 deletion (Di George syndrome), which seems to be correlated with smaller native PAs .

All of this information is established via echocardiography, tomodensitometry or angiography. In our hands, angiography is preferred because it has always permitted a more precise anatomical diagnosis. This point has to be re-evaluated with each improvement in the computed tomography scan technique. Typically, angiography shows the ‘sea-gull’ aspect, with retrograde filling of the extremely diminutive central PAs ( Fig. 1 A ). The Nakata index can then be calculated.

Initial angiographic evaluation. A. Angiography showing the extremely hypoplastic native pulmonary arteries and the famous ‘sea-gull’ (arrow). Right and left pulmonary arteries are measured (a and b). The pulmonary distribution is apparently complete. B. Angiography showing one major aorto-pulmonary collateral artery, emerging from the right side of the thoracic aorta to the middle and lower right pulmonary lobe.

Different features of each MAPCA should be analyzed ( Fig. 1 B): its origin from the descending aorta or – rarely, if ever – from the main branches of the ascending aorta; its size, with or without stenosis; its course, mainly in relationship with the esophagus, carina and bronchus and native PAs; and its distribution to the lungs.

The most important point to determine about the MAPCAs is if each of them is ‘communicant’; in other words, if the pulmonary segments they vascularize are also filled by the native PA or not. Each segment has to be considered separately, hence great differences in flow origin and pressure are possible between them.

However, detailed angiographical (or radiological) analysis may be easier after the first stage procedure than at the first work up and should always be re-evaluated afterwards. In our experience, we have to admit that complete distribution of the native PAs was, in fact, found more often than expected.

Clinical status

Early outcome after birth is usually good, with blood saturation usually around 80% or less. The mean age of the first surgical procedure is ideally around three months , depending on the patient’s growth. If cyanosis is problematic, the surgery has to be done earlier. If, however, the pulmonary blood flow is too high, medical treatment is given and early surgery is considered, if necessary.

One also has to be wary of management that is ‘too late’ in such a patient. In the lung territories filled by large MAPCAs, hypertensive PA disease can develop early, with no reversibility, which might compromise the patient’s future. Alternatively some segments can receive a very small part of the total pulmonary flow, which will impair vasculogenesis. Complete closure of central native PA is also a risk to consider. It is likely that some patients when diagnosed late and then described as having absolutely no native central PA, had, in fact, a diminutive and low-flow central PA to begin with. It should be understood that the flow in the central PA is dependent on a subtle difference of pressure between the left and right segments, with communication between native branching and MAPCAs.

In conclusion, even if the clinical status is good – meaning that the total pulmonary blood flow is adequate – this balance is unlikely to be as satisfactory at the segmental level and postponing the therapeutic decision can be very deleterious in the long-term.

Step 1: Surgical technique for right ventricle-to-pulmonary artery continuity establishment

The procedure is performed via a median sternotomy with the use of cardiopulmonary bypass (CPB) on a beating and ejecting heart. Aortic cross-clamping is not indicated because of the MAPCAs: the blood flow would be preferentially towards the lungs (if the pulmonary resistances are low) and would end up in dilated unable-to-eject ventricles; the systemic perfusion would be poor, whereas the lung would be overfilled.

Typically, analysis of external anatomy shows a diminutive main PA, connected to an atretic infundibulum. After controlling the right and left PAs, and in the case of no major coronary artery crossing the infundibulum, the main PA and the infundibulum are incised longitudinally. When the latter is opened (in the last minutes of the procedure), blood is, of course, ejected and resuctioned back in the CPB circuit. Despite this bleeding, the sucker is managed carefully to avoid air embolism through the VSD and to the aorta. A precisely tailored autologous pericardium patch treated with gluteraldehyde (and rinsed) is sutured to the edge of the arteriotomy and to the epicardium around the infundibulotomy ( Fig. 2 ).

Peroperative view of step 1. A and B. The arrow shows the hypoplastic main pulmonary arteries. The right and left pulmonary arteries are controlled and occluded by blue rubber loops. C. The main pulmonary artery is opened longitudinally (arrow). This incision will ultimately be extended to the infundibulum, as far as to obtain a sufficient opening of the right ventricle. D. An autologous pericardium patch is sutured to the edge of the arteriotomy and infundibulotomy.

Step 2: Multistage catheterization

After a delay of two months, we believe that catheterization can be safely performed. This procedure has several objectives ( Fig. 3 ):

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  the diagnostic objectives are:

  
  
  
  
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    visualization of the enlarged now-established right ventricle-to-pulmonary artery (RV-PA) continuity,

    
    
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    quantification of the growth of native PAs, with an increased Nakata index,

    
    
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    re-evaluation and identification of the distribution of the native PAs,

    
    
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    and re-evaluation of the pre-existing MAPCAs and research of new ones;

  
  
  
  
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  the haemodynamic objective is:

  
  
  
  
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    evaluation of PA pressures in the different pulmonary segments, downstream of the MAPCAs;

  
  
  
  
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  the interventional objectives are:

  
  
  
  
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    angioplasty/stenting of the native PAs,

    
    
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    and coil occlusion of communicant MAPCAs.

  
  

Example of incomplete pulmonary artery distribution. A. Angiography showing an incomplete distribution of the right pulmonary artery. Only the upper pulmonary lobes are perfused. B. Major aorto-pulmonary collateral artery perfusing the middle and lower right pulmonary lobes.

A computed tomography scan is often very useful at this point to prepare for the catheterization procedure. Occlusion of communicant collaterals is important, even if the PA has not yet reached the expected diameter, to promote the flow, which will itself promote growth and presumably angiogenesis. The expected antegrade flow is always in competition with collateral flow and this has to be well understood and studied branch by branch. When a native pulmonary branch and MAPCA both fill one or several pulmonary segments, the occlusion of this MAPCA is performed as soon as the antegrade circulation (with or even without dilatation/stenting) is considered sufficient. When one or several pulmonary segments are only filled by a MAPCA ( Fig. 3 B), it will be ‘unifocalized’ (disconnected from origin and anastomosed to the now enlarged native PA) at the time of step 3 or during an additional step, before the total correction.

At this point of the pathway the dilatation/stenting process focuses on the central PAs, to promote growth of hilar and segmental branches and to allow safe occlusion of the communicant MAPCAs.

Sometimes an ‘ideal’ catheterization procedure cannot be done in one step; several procedures may be necessary, according to the development of the native PAs. Of course, the pulmonary blood flow and the subsequent oxygen saturation have to be evaluated throughout the whole process.

If the pulmonary blood flow has already increased before the first surgical step, occlusion of the communicant collaterals may be done earlier than two months, if necessary. As a matter of fact, in these specific cases, the first surgical step is necessary but does not improve and even impairs clinical status, increasing the failure to thrive and signs of congestive heart failure.

Step 3: ‘Complete’ correction

When all the communicant MAPCAs have been occluded and the Nakata index is considered sufficient (usually > 150 mm/m ² ), a complete repair can be performed under CPB, this time with aortic cross-clamping and cardioplegic cardiac arrest. In patients with a Nakata index between 90 and 150 mm/m ² , other criteria, such as transcutaneous oxygen saturation (SaO ₂ ) greater or equal to 85% (without open MAPCA), might be considered as good evidence of feasibility of VSD closure.

The repair includes: reconstruction of the pulmonary bifurcation and branches as far as possible in both directions (the stents, if any, are longitudinally open and most of the time almost totally removed; some well included and perfectly endotheliarized parts can be left in place; both the right and left PAs, from origin to hilum, are enlarged with PA homograft wall patches); patch closure of the VSD; and establishment of another RV-PA continuity with a cryopreserved pulmonary homograft. At the end of the procedure, even if the haemodynamics are perfect, the RV/left ventricle (LV) pressure ratio has to be calculated. Upon a 1/1 ratio, VSD reopening (perforating the patch with a hole punch) should be considered.

Additional steps

The management of MAPCAs that provide the only supply to one or several pulmonary segments may necessitate other surgical steps. Those MAPCAs have to be unifocalized to the homolateral native PA, when it is considered sufficiently well developed. This may be performed as an additional step, through a lateral thoracotomy, between two stages of catheterization; it can also be performed at the time of step 3. The choice between these two different approaches depends heavily on the feasibility of midline unifocalization. The course of each MAPCA with respect to the other structure is of importance. Easy access to the aortic origin of the MAPCAs depends also on the right or left position of the descending aorta.

Moreover, additional catheterizations should be performed after the last surgical step, in order to continue the PA rehabilitation programme. Those subsequent percutaneous procedures aim to: evaluate haemodynamic status (PA and RV pressures); continue to promote the development of native PAs with angioplasty and stenting, if necessary (this will now mainly address hilar and lobar branches); diagnose and occlude new aorto-pulmonary collaterals; if necessary and as soon as possible, occlude a fenestrated VSD patch; and, eventually, redilate the central homograft and/or revalvulate the RV outflow tract.

The schedule and frequency of those additional catheterization procedures are determined according to each patient’s characteristics. Clinical status (even if the patient is doing well) and RV pressures (even if pleasantly low) have to be taken in account. The distribution can also be still very heterogeneous between the right and left side (perfusion scans are very helpful) and in each side between lobes and segments.