DISCUSSION
This work is the first study to determine an ELI cutoff value associated
with postoperative mortality. When using all-cause mortality as the
primary outcome, our analysis found increased cumulative survival time
in patients with ELI > 1.34 for nine years post-TAVR. We
discovered that ejection fraction and aortic valve effective orifice
area increased post-TAVR while mean transvalvular, and peak
transvalvular gradients decreased post-TAVR. Multivariate analysis
indicated that advanced age and SAPIEN valves were associated with
increased mortality post-TAVR.
Over 276,000 patients have undergone the TAVR procedure in the United
States 12. TAVR has
been widely available in the US since 2011 and has surfaced as an
alternative to SAVR. Although the PARTNER I trial demonstrated similar
valve performance and cardiac hemodynamics post-TAVR and SAVR
implantation 13, TAVR
has grown in popularity. One key difference between the two procedures
is that in TAVR, the native aortic leaflets are not removed. Instead,
they are displaced into the Valsalva sinus, reducing the sinus volume
and blood velocity in the sinus14. This decrease in
speed may increase the chances of thrombus formation. Despite these
risks, TAVR has been proven much safer based on one-year follow-up than
surgical valve replacement15. While enough time
elapsed to examine the longevity of the prosthesis, there was no
significant increased risk of thrombotic events post-TAVR in our sample.
Our study corroborates prior research showing ELI offers clinical
benefits and provides additional prognostic information in classifying
aortic stenosis. One study reported that decreases in ELI predicted
increased aortic events and increased total mortality and
hospitalizations for heart failure. However, after reclassification
analysis, ELI improved the prediction of aortic valve events but no
longer predicted total mortality or hospitalizations16. Other research
found that patients with small aortic roots or aortic sinotubular
junctions were associated with higher rates of ischemic cardiovascular
events, non-hemorrhagic stroke, and mortality17.
Blood pressure in the left ventricular outflow tract (LVOT) is high
while the velocity is low, and the pressure in the aortic valve area is
low while the velocity is high. The pressure in the receiving aorta is
again high while the velocity is low. This decrease in velocity in the
aorta and subsequent increase in pressure is known as pressure recovery18. The amount of
pressure recovery increases with more severe aortic stenosis. A more
accurate fluid dynamics model considers the third variable outside of
velocity and pressure, which is the heat. The turbulent flow or friction
through a valve can cause energy to be lost as heat. This loss of energy
due to heat will decrease the pressure recovery in the aorta. Thus,
patients who have higher energy losses are more likely to survive
following TAVR as they experience less turbulent or shear forces.
As the aortic valve becomes increasingly stenotic, turbulent flow
increases in a non-linear fashion19. Patients with
increased turbulent flow experience more shear forces, which in turn
cause structural instability20.
We concluded that ELI should be used as an additional factor when
considering all-cause mortality following TAVR. It is reasonable to
implement this factor during the pre-op risk assessment process as we
have shown lower ELI values predictive of increased post-op mortality.
ELI is indirectly related to body surface area and body weight.
Therefore, delaying TAVR in non-emergent cases to allow patients to
engage in weight reduction strategies may improve patient outcomes
post-TAVR. Additionally, ELI may be used to highlight the efficacy of
different prostheses in different patient populations.
The external validity of this study was low, given that most patients
were Caucasians living in the western New York area who received newer
generation valves. Additionally, the location at which the sinotubular
junction measurement was obtained from an echocardiogram may have
differed slightly between patients due to human error. It is important
to consider patients’ native anatomy as patients with a smaller
ascending aorta have a more significant pressure recovery and thus a
larger ELI. Future studies may be designed to improve the longevity of
these prosthetics by deciding on the appropriate size of the valve
according to the established ELI criterion.