Discussion
Accurate reimplantation of the coronary arteries is the key component in the success of the arterial switch procedure. This must be achieved without creating undue tension, torsion, or kinking of the stems of the coronary arteries or their proximal branches. During the evolution of the procedure, certain patterns have been identified as problematic. Of particular concern are the so-called intramural variants, and the arrangements when all arteries arise from a single sinus. During the evolution of the operative procedure, so-called “looping” was considered a potential problem, as was juxta-commissural origin of the arterial orifices. Presence of associated defects also created additional problems, as did side-by-side arterial trunks in the so-called Taussig-Bing variant.4,12,31,47 With ongoing experience, many of these potential problems have been mitigated. It is now generally considered that translocation is feasible for all variable patterns, although origin from the nonadjacent sinus may now be considered a contra-indication.29
In the initial technique as described by Jatene, the coronary arteries were not transferred to the new aorta until after anastomosis of the aorta to the initial pulmonary root.31 Translocation to a distended root was then recognised as helpful in avoiding the need for prolonged myocardial ischemia, preventing recurrent reperfusion injuries, and permitting visualization of the newly implanted buttons and suture lines prior to reconstructing the new pulmonary trunk.21,22,31,47,E1-E4 The approach, however, posed the risk of damaging the neoaortic valvar leaflets when creating the required openings in the neoaortic root. Placement of a marking stitch at the facing neoaortic commissure was proposed to mitigate this difficulty.E5 The essence of the technique is to punch appropriately sized holes, and then to anastomose the mobilized buttons to these openings.13 A key point is to bring the initial pulmonary root towards the buttons, rather than stretching the buttons towards the new root.E6 Good midterm results were reported using this strategy.59
Despite the success of the initial technique,31advantages came to be recognised of the trapdoor technique.33,39 In this modification, the arterial buttons are translocated to the neoaortic root prior to reconstruction of the neoaorta. This approach was considered of particular value in the setting of retropulmonary looping of the circumflex artery, which is the second commonest pattern, or the main stem of the left coronary artery. These variations create a shorter distance, and an acute turn, between the coronary artery and its new sinus, with potential kinking or distortion during translocation. Similar advantages were suggested for the trapdoor approach in the setting of anterior looping,12 which has the potential risk of stretching or bowstringing during translocation .4,13,E4 Further advantages were suggested if the arterial buttons were placed at or above the neoaortic anastomosis.33,35 Since reports of its success were published by the group working at Marie Lannelongue during the mid-1990s, the technique has gained significant popularity.12,52,54,E6 Some suggested changes, however, were not without their own problems. In the modification proposed by Vouhe, for example, with each button playing the role of the trapdoor flap for the other button, arterial obstruction within one year occurred in over one-quarter of patients. These findings understandably led to the abandonment of the modification.34 Another modification was to create trapdoor flaps in both arterial roots.44 Good short-term results then accrued for five consecutive individuals found to have looping in the setting of single sinus origin.44 Yet another successful modification was to augment the relocated coronary artery using a patch of autologous or treated pericardium or pulmonary artery.4,46 All of these modifications are designed to avoid kinking or stretching subsequent to transfer. It follows that identification of the optimal location for each anastomosis remains crucial. As yet, however, long-term results of these individual techniques are not available so as to determine which might be preferable.4,34,36,44,46
Problems were encountered initially when looping patterns were found in the setting of origin of coronary arteries from each of the adjacent sinuses. The techniques as described above have resolved most of the difficulties. Problems still remain when all arteries arise from the same aortic sinus,6 a finding in up to one-sixth of individuals in some series.40-43 The difficulties relate to the limited mobility when a short main stem feeds the looping artery or arteries. Comparable limited mobility is found should the arteries arise from the same sinus through double or triple orfices.2,4,5,8,10,12,19,27,28,52 Specific techniques have also been proposed to mitigate these problems. Thus, when arising from a solitary main stem, a button can be detached and inverted using the technique proposed by Yacoub,4 or else anastomosed to the neoaortic root using the trapdoor technique.33,39 When there are multiple orifices within the sinus, then as is the case for juxtacommissural origin from both adjacent sinuses, creation of an aortopulmonary window is a good option.40-43 The group working at Marie Lannelongue, however, had initially modified the technique of Yacoub as suggested above, only to abandon it because of kinking. Instead, they promoted the dual button trapdoor transfer as described by Asou and Mee.11,12,17,33,39 An additional high risk of direct implantation had been identified in specific situations when the angle between a line drawn between the centres of the arterial roots and that drawn from the neoaorta to the coronary arterial orifice exceeds 75 degree.20 In this setting, augmentation using a pericardial hood was shown to maintain a natural lie of the transferred coronary artery, and to produce a good long-term result.46 Others had suggested using a short autologous pericardial tube,E3 but this risks the formation of thrombus, as well as extrinsic compression by the newly constructed pulmonary pathways. Problems also occurred subsequent to augmentation using a pulmonary arterial flap, with the coronary artery being abnormally positioned even after successful translocation.21,44,E2,E3
It is the intramural arrangement, nonetheless, that still poses the greatest risk to the patient. If undetected prior to the procedure, the artery may inadvertently be transected during the initial aortotomy. The aortotomy should be performed in a safe area, revealing the location of all the arterial orifices before the aorta is transected.E7,E8 If the intramural artery is para-commissural, or inseparable from the other arterial orifice arising from the same sinus, the commissure itself should be detached, permitting harvesting of the button as a single disc. If the intramural component is stenotic, it must be completely unroofed prior to resuspending and reconstructing the neopulmonary valve.11,17,39,46,47,E7-E9
Once recognised, two methods have evolved to mitigate the problems of the intramural arrangement. The first is to separate the orifice of the intramural artery from its sinus, either as a confluent button containing the other artery, or as separate buttons. The second method is to leave both arteries within the sinus, and to create an aortopulmonary window roofed by a patch or autologous tissue. Each technique has advantages and disadvantages.11,17,39,46,47,E7-E9 If two buttons are to be successfully created, there should be more than 2 millimeters between the orifices. Each button can then be handled using the trapdoor approach.33,39 This technique, however, is technically demanding. An insufficient cuff of sinusal wall has been found to lead to more angled rotation of one or both buttons.11,17,33,39,48 Transfer of a confluent button can be achieved using a medially based trapdoor supplemented by pericardial or pulmonary hood augmentation, with this approach avoiding turbulent flow within the neopulmonary system.47Creation of an aortopulmonary window, in contrast, by maintaining the native geometry, is claimed to reduce the possibility of tension, torsion, kinking or overstretching.37,38,40-44 Use of a hinged aortic sinus pouch and flap in the latter approach is also claimed, irrespective of the location of the arteries, to reduce the risks of thrombosis, shrinkage, distortion, late obstruction, compression, and neopulmonary arterial stenosis.37,38,40-44
The commonest reason for early mortality following anatomical correction has proved to be postoperative ventricular dysfunction.19,48,49,60 Reports on etiology, however, are limited and conflicting.E8-E10 Studies conducted to date have been hindered by the small number of included patients, and hence their limited statistical power ranging between 20% to 35%.25,26,53,54 We were able to identify nine retrospective, one prospective, and one meta-analysis specifically addressing the relationship between coronary arterial patterns and short and long-term outcomes.12,13,25,26,30,34,36,57-59,E11-E13 Reported events have varied from 2% to 11%, with a high early and low late incidence. Most have been related to kinking, torsion, or stretching.12,13,25,26,30,34,36,57-59,E11-E13 As with the operative problems, the events are associated with the intramural arrangement, retropulmonary looping, and single sinus origin with multiple orifices. Residual stenosis due to intimal proliferation is commonly reported.47,51-54,57,E14,E15 Complications occurring with favourable arterial patterns have been less well explained. One meta-analysis,26 for example,26 found looping in the setting of a single sinus origin to be associated with a 3 fold increase in mortality, whereas looping when each adjacent sinus supported a coronary artery was not associated with increased risk. The underlying problem is again considered to be kinking or stretching of the looping coronary arteries.26,53,E13-E15 In up to one-tenth of cases, evidence has been found of extensive lengths of stenosis, or even occlusion, explaining well some catastrophic clinical consequences.12,33,39 A small number of individuals suffer late events, either death or myocardial infarction, following anatomical correction,54,56,59,E4,E12 with myocardial revascularization reported at periods of between three months and three years after the switch.53,54,E15,E16 The causes were again mostly related to stretching of the translocated coronary arteries with ongoing somatic growth, and progressive fibrocellular-intimal hyperplasia..E12,E14,E15 Studies assessing the capacity of non-invasive methods to predict such obstruction have thus far been inconclusive.E12-E20 With the increased resolution of three-dimensional clinical techniques, nonetheless, it is becoming much easier specifically to identify the postoperative coronary arterial anatomy, thus offering hope that the reasons for complications will soon become obvious.E21-E23 Already, when using coronary angiography, the group working at Marie Lannelongue had identified postoperative lesions in two-thirds of their patients at a median of 7 years of follow-up.53 Another angiographic study, however, identified problems in less than one-twentieth of their patients after a median follow-up of just over one year.E12 Others have demonstrated long term problems in between one-twelth and one fifth of patients, mostly in the setting of single sinus origin, with the findings considered an important cause of late death.E13-E15 The optimal management of the lesions, once identified, remains to be determined. Percutaneous coronary angioplasty, or surgical revascularization, have thus far been performed with satisfactory mid-term results.51-53,E13,E15,E17-E19,E24,E25