3 DISCUSSION
The argument for heart-lung transplantation for patients with pulmonary arterial hypertension (with or without a giant PAA) is no longer compelling with the knowledge that even the most adversely remodeled right ventricle, such as those preoperatively requiring inotropic or VA ECMO support, will reverse remodel after lung transplantation alone [9]. Most centers try to avoid heart-lung transplantation when possible, due to the shortage of donor organs as well. In the most recent analysis of the International Society of Heart Lung Transplantation (ISHLT) registry the 1,3 and 5 year survival in heart-lung transplantation for PAH was 87.3%, 68.6 and 61.8 respectively. In comparison the 1,3 and 5 year survival for all lung transplant recipients for PAH transplanted between 2008 and 2015 were 80.7%, 63.4% and 55.2% respectively [10]. Consequently, the decision for heart-lung transplant in PAH is reserved for patients with severe left ventricular failure or those with anticipated difficulty in repairing complex congenital heart disease [11-13]. Case 2 required heart-lung transplantation due to the underlying complex congenital heart disease and severe PH with PAA.
In PAH patients the prostacyclin analogue intravenous epoprostenol has been found to significantly increase transplant free survival [10, 14, 15]. Intravenous epoprostenol is reserved for patients with WHO class IV symptoms, where it is used in combination with one or both of an endothelin receptor antagonist and a phospho-di-esterase 5 inhibitor [16, 17]. In addition to initiating epoprostenol therapy, early referral of patients with WHO class III or IV symptoms to a transplant center is appropriate given their higher rate of disease progression and mortality [16].
However, with PAA in the setting of PAH, an increase in size is independent of normalized pressures [18], and progression of dilation and chest pain are indications for urgent transplant due to the risk of dissection and rupture. The rare complication of PAA poses substantial problems for lung transplantation and traditionally, combined heart-lung transplantation has been recommended as the treatment of choice. Sole lung transplantation is being increasingly recognized as an alternative in experienced lung transplant centers. In a relatively large 12-year series, Schwarz et al. reported 7 of 127 patients with PAH presented with severe PAA in their 12 year series. Their institutional experience with a lung-only strategy, where donor PA trunk was procured along with the lungs, and the main PA was reconstructed along with the implantation of the right lung. The left lung was then implanted and the left PA was reconnected to the main PA. Their series demonstrates feasibility of this approach in this complex group of patients [19]. Shayan et al. reported a case where the donor pulmonary trunk was procured with the lungs [20]. They implanted the lung allograft bloc by positioning it posterior to the heart and anastomosing the trachea instead of separate bronchial anastomoses. Force et al. and Noda et al. described techniques where donor thoracic aorta was fashioned to replace the recipient PAA which we employed in Case 1. It is important to carefully assess the pulmonary arterial and right ventricular pressures following replacement of the pulmonary arteries, especially in cases where extensive reconstruction was required.