DISCUSSION
In our experience, root replacement in TAAD with stentless PAR is a feasible alternative to the CVG, especially in older patients. Our decision for root replacement in TAAD was based primarily on the requirement for biological substitutes, either due to the patient’s age or known contraindication to anticoagulation, as a suitable alternative to a bio-Bentall. The need for clarity on patient and procedure selection is crucial in TAAD, especially given the excellent outcomes reported by several institutions using widely varying techniques(11).
Acute type A aortic dissection (TAAD) has a mortality of 50% within the first 48 hours if not operated on(12). The choice of root replacement versus conservation varies from centre to centre, although certain cases render the need for root replacement in TAAD quite necessary, especially if the dissection extends to at least one sinus of Valsalva. Avoiding root replacement in such cases is associated with late dilation of the aortic sinuses and recurrence of aortic regurgitation, making the risk of re-operation unacceptably high(13).
Root replacement using a CVG has been considered the gold standard for all acute TAAD when the aortic root is dilated greater than 4.5 cm, contains an intimal tear, or if there is known connective tissue disease(14,15). A mechanical CVG is usually offered to younger patients, due to proven valve durability(16). However, the need for surgical alternatives is important, especially in cases where anticoagulation may be contraindicated. Furthermore, the impact of anticoagulation on the prognosis of the distal aorta is important to consider and may in fact increase the incidence of false lumen patency(17). This claim has however been refuted by other studies, finding that anticoagulation did not lead to an increased incidence of distal aortic events or impact false lumen thrombosis(18,19). The present study has demonstrated that the performance of aortic root replacements (ARR) using porcine stentless aortic roots (PAR) have comparable short and midterm outcomes to composite valve grafts (CVG) and can be safely used for the management of type A aortic dissection (TAAD).
The Freestyle bioprosthesis (Medtronic, Minneapolis, MN) is a complete porcine aortic root with ligated coronary arteries and a thin skirt over the porcine septal muscle bar. Their design have very comparable advantages to stented bioprosthetic valves, including suitable durability in the elderly population whilst making anticoagulation redundant (20). Furthermore, stentless valve technology has long been shown to offer superior hemodynamic performance when compared to stented counterparts(9,21). Flow patterns are remarkably similar to normal native aortic valves(22). Echocardiographic studies have demonstrated lower mean aortic valve gradient and improved left ventricular mass regression at 6 months post operatively(23). This is supported by our data (Table 4) which demonstrates that the improved valve haemodynamic profile and consequent positive LV remodeling is achievable in emergency TAAD cases, with results potentially evident by 6 weeks follow up.
In the literature, evidence for the use of PAR in patients with TAAD has been sporadic. Smith et al(24) demonstrated the use of the Medtronic Freestyle bioprosthesis in TAAD with satisfactory early and midterm outcomes in 24 patients, although this was not compared with a valid control. Similarly, larger centres have reported the use of porcine stentless aortic roots as the biological conduit of choice in TAAD with good results(25,26). Despite this, there is limited evidence comparing the use of porcine stentless aortic bioprosthesis with alternative root surgery in TAAD.