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.