Coarctation of the aorta manifests as the narrowing of stenosis, which occurs due to ductus arteriosus closure. This closure causes increased left ventricular afterload and decreased lower body circulation. While patients are often diagnosed in the neonatal period and promptly undergo treatment with surgical repair, delays in diagnosis may occur, albeit rarely. For instances, delays may occur if thestenosis is moderate or severe but progresses slowly, and if sufficient collateral vessels have developed [4]. The approach for coarctation of the aorta repair in neonates is controversial, particularly if the transverse arch is hypoplastic [5]. Furthermore, EEA, extended EEA, end-to-side aortoplasty, or subclavian aortoplasty is performed through either a left thoracotomy or median sternotomy, depending on the aortic arch anatomy and the policy of the individual institution. The extended EEA procedure through a left lateral thoracotomy may be optimal in older children due to two reasons: (1) many patients have localized coarctation of the aorta without the hypoplasia of the transverse arch, and (2) the lack of tissue extensibility compared with that in neonates requires dissection to the distal side of the descending aorta.

The risk factors for paraplegia following a simple aortic clamp include the cross-clamp time [6], body temperature [7], distal aortic pressure [8], and an aberrant right subclavian artery [6]. There have been various reports of acceptable limits for these parameters, but definitive cutoff values have not been identified. Regardless of the surgical technique, prolonged aortic clamp time due to intraoperative problems (such as tear, residual gradient, change of planned procedure) could occur. Therefore, it is necessary to develop a safe partial CPB technique as a bail-out strategy. The femoral artery and vein are commonly used in adult patients as access vessels for partial CPB. However, careful judgment is required in pediatric patients because vascular injury during cannulation with spasms may occur, even with an adequate femoral artery-vein diameter [9]. In addition, there are concerns regarding complications, such as infections, lymph fistulas, and neuropathy, due to the creation of a new incision in the groin.

A left heart bypass through the left atrial appendage and the descending aorta is an excellent alternative to CPB under a left thoracotomy [1, 3]. Unfortunately, the left atrial wall in children is very fragile, making cerebral complications from air embolization associated with left atrial cannulation potential risks [3]. In addition, a left heart bypass without an oxygenator does not solve lung problems associated with ventilation during the coarctation of the aorta repair. Sandrio and colleagues reported on 15 patients aged 7–48 years, with a minimum weight of 19.7 kg, who underwent partial CPB through a left thoracotomy using alternative cannulation sites (namely, main pulmonary artery and descending aorta), with no instances of paraplegia observed [10]. In this study, where we extended this technique to younger infants, we also chose the main pulmonary artery as the venous cannulation site for the following reasons. One, the vessel wall of the main pulmonary artery is more solid than that of the left atrium tissue. Two, since the venous cannulation site is in the right heart system, the possibility of air embolization into the systemic circulation is extremely low. Finally, because blood is drawn from the pulmonary artery, excessive blood supply to the ventilated right lung is suppressed, potentially reducing pulmonary complications, such as pulmonary congestion or hemorrhage. We achieved a stable targeted flow rate during assisted circulation in infants by using a straight cannula and ensuring its tip remained in the main pulmonary artery.

There is no absolute preoperative evaluation method for determining whether the collateral blood supply to the lower body is adequate, especially if the degree of coarctation is moderate. Additionally, determining the necessity of partial CPB is difficult. The intraoperative descending aortic clamp test, to measure the perfusion pressure, has been reported as a potential evaluation method [8, 11]. However, it still lacks reliability and reproducibility, as it may be influenced by the peripheral circulation status under general anesthesia with mild hypothermia. Particularly in older children, poor elasticity of vascular tissue or unexpected bleeding associated with a higher blood pressure than that of neonates may necessitate a change in surgical procedure or a prolonged aortic clamp time. Further, rectal temperature regulation with blankets is challenging in older children and can lead to uncontrolled hyperthermia [11]. The main pulmonary artery-to-descending aorta partial bypass allows reliable assisted circulation and lower body thermoregulation with fewer complications and without wound formation. This considerably lowers the threshold for the decision to use partial CPB for coarctation of the aorta repair.

Coarctation of the aorta repair through a median sternotomy with total body perfusion is another method for preventing lower body ischemia and may be preferable when other intracardiac comorbidities are present [12]. However, studies have shown balanced growth of the aortic arch with extended EEA repair via left thoracotomy [3, 13]. Utilizing a safer method of partial CPB, such as main pulmonary artery-to-descending aorta bypass, would expand the indications for more complex aortic arch repairs through a left thoracotomy. We extended the indications for main pulmonary artery-to-descending aorta partial CPB to infants weighing approximately 3 kg. Two of our infant patients needed reoperations for re-coarctation of the aorta (cases #9 and #10), and another (case #4) underwent a second aortic clamping for residual coarctation of the aorta. The prolonged aortic clamp times in these cases allowed us to perform a complex aortic arch reconstruction procedure. Even in infants, the cannulas inserted in the descending aorta and main pulmonary artery did not interfere with the surgical field during the left thoracotomy. In addition, we obtained good results using partial CPB during graft replacement, for a distal tortuous thoracic aortic aneurysm in a 1-year-old girl weighing 12.3 kg and with PHACE syndrome [14].

This study has some limitations. First, this was a retrospective study involving a small number of patients. Second, the background of the patients in the non-CPB group did not align with our indications for using a partial CPB, and we were unable to rigorously examine the protective effects on the lower body organs.