Discussion:
In our study, we found that in patients undergoing SAVR with
preoperative MDCT imaging; (1) There was a strong correlation between
annular measurements on MDCT and actual SAVR size implanted; 2) Using
pre-procedural virtual valve implantation, all patients with AI were
predicted to be low risk for ViV TAVR coronary obstruction; (3) In
patients with AS, pre-procedural MDCT with virtual valve implantation
found that 38% of patients with tricuspid AS would be at high risk,
while no patients with bicuspid AS were at high risk.
To our knowledge, this is the first paper addressing the issue of
whether a patient undergoing SAVR will be a candidate for ViV TAVR in
the future based on pre-procedural MDCT. As our surgical and
transcatheter techniques evolve, focus has shifted to lifetime
management of valvular disease. Patients with bioprosthetic valve
failure are frequently at high surgical risk for reoperation, which is
why ViV TAVR has become a valuable option in such patients. (1) Coronary
artery obstruction more commonly occurs with ViV TAVR, and is a
potentially fatal complication that portends a mortality rate greater
than 50%. (6) Patients at high risk for coronary obstruction during ViV
TAVR still have options, however these options come at a higher risk.
Chimney stenting is associated with higher risk of procedural and
delayed clinical events. (8) Which prompted the advent of BASILICA
(Bioprosthetic or native Aortic Scallop Intentional Laceration to
prevent Coronary Artery obstruction). However, there are a significant
percentage of patients that are not candidates for BASILICA, and the
procedure may result in higher rates of procedural complications
including stroke. (3) Therefore, if we can classify patients who will be
high risk for future transcatheter procedures, it may factor into the
shared decision making between the patient and heart team. Options may
then include; 1) TAVR as primary strategy followed by SAVR for failure,
2) SAVR with surgical manipulation (e.g.- coronary re-implant, root
enlargement) to decrease subsequent risk for coronary obstruction, 3)
Standard SAVR (with the awareness that advanced adjunctive techniques
will likely be necessary or transcatheter options limited in the
future).
Though the majority of patients (74%) were correctly sized with MDCT,
the rest of the patients (26%) were oversized compared to actual SAVR
implanted. One would expect that virtual implantation of a larger valve
would increase the chance of falsely predicting high risk anatomy for
ViV TAVR. Interestingly, despite implanting a larger virtual valve in
almost ¼ of patients, MDCT did not predict any patients with AI to be at
high risk for coronary obstruction. These findings suggest that outside
of MDCT for root sizing/coronary evaluation, preoperative MDCT is less
helpful for patients with AI.
MDCT predicted the correct valve size implanted in all but one patient
with AS (94%). There was a strong correlation between MDCT annular
measurements and actual SAVR sizing. In patients with bicuspid AS, all
patients that underwent virtual valve implantation were predicted to
have low risk anatomy for ViV TAVR. Perhaps this is because root sizes
are generally larger in bicuspid AS patients. With virtual valve
implantation, 38% of patients with tricuspid AS were high risk for ViV
TAVR. This warrants a bigger question; would preoperative MDCT change
management in patients with tricuspid AS with plan for SAVR? Future
studies are needed to 1) compare preoperative virtual valve implantation
of the SAVR to postoperative MDCT and 2) determine if preoperative MDCT
can safely change the lifetime management in tricuspid AS patients.
As the heart team plans for the treatment of each individual’s aortic
valve pathology, it is important to determine what size surgical
bioprosthetic valve can be implanted. Surgical prosthesis with small
internal orifice diameters may predispose patients to transcatheter
heart valve under-expansion at the time of ViV TAVR. Smaller sized
surgical valves are associated with higher post-procedural gradients and
increased mortality in patients undergoing ViV TAVR. (4, 5) The ability
to predict SAVR sizing can therefore be useful to identify patients that
require smaller valves. For example, if preoperative workup reveals that
the annulus will only accommodate a 19mm valve, the heart team can then
discuss the most suitable option for the lifetime management of each
case. Options may include; standard SAVR, SAVR with root enlargement,
implantation of a prosthetic valve with an expandable frame (i.e.-
Inspiris, Edwards Lifescience, Irvine), mechanical valve, or the use of
TAVR instead of SAVR. This knowledge is especially useful in patients
with AS, who tend to have smaller annuli than patients with AI (annulus
area; 554.77mm2 ± 123.2 vs 474.18mm2± 135.41, P=0.049).
Among our studies limitations was the lack of patients with preoperative
MDCT. This is reflective of current standard practice, which does not
necessitate preoperative MDCT. Larger numbers are needed to evaluate
what percentage of AS patients would be high risk based on preoperative
MDCT. We also concede that virtual valve implantation has never proven
to predict feasibility for future ViV TAVR procedures. Though outer
stent diameters may be the same between valve manufacturers, valve sizes
may have different inner stent diameters, and therefore a patient may
end up with a different sized valve depending on the manufacturer. If a
smaller or larger prosthesis is implanted, it will skew measurements and
virtual valve implantation may be less accurate. Additionally, valves
may be canted one way or implanted at different depths, therefore
studies will need to address a pre-SAVR virtual valve implantation with
MDCT to post-SAVR measurements on MDCT. Unfortunately, it is not
standard protocol to obtain post-MDCT, so we were not able to
investigate this. However, the majority of valve implantations on pre-CT
were correctly sized for actual intraoperative measurements (or within 1
size at least), so this should not factor in largely to the limitations.
We believe that our study addresses a pressing need to investigate the
utility of MDCT to help guide management decisions for patients
undergoing isolated SAVR. Though the surge of TAVR has led to a
reduction in isolated SAVR volume, SAVR is still an option for low-risk
patients. (1, 9) It is the low risk/younger patients that are more
likely to need a valve re-intervention during their lifetime. Hence,
shared decision making between the patient and heart team is essential
in patients with high risk anatomy to discuss all options for lifetime
management.