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.