**4. Indications of TAVI in low-risk patients**

Multiple death reasons analysis maintained by the National Center for Statistics from 2008 to 2017 [49] showed that the mortality rate due to aortic stenosis in the elderly in the United States has declined since 2013, while the number of TAVI hands has increased from 4627 in 2012 to nearly 35,000 in 2016. It is speculated that the observed death rate trend may be related to TAVI.

On March 17, 2019, in the American College of Cardiology (ACC) annual meeting, the low-risk patients TAVI studies PARTNER III and EVOLUT results were released, marking the comprehensive arrival of the TAVI era of severe aortic valve stenosis. Martin Leon of Columbia University Medical Center in New York officially released the results of PARTNER III study at the conference [17]. For low-risk patients with severe aortic stenosis, the incidence of 1-year death, infarction, and rehospitalization in patients with Edwards balloon-expandable TAVI valve implantation was significantly lower than that in patients undergoing open heart surgery. The study included 1000 patients from 71 centers, with an average age of 73 years and an average STS score of 1.9%. The main end point of the study was the compound end points, including 1-year death, infarction, and rehospitalization event rate. The results showed that the event rate of the main end point in the TAVI group was significantly lower than that in the surgical operation group (8.5% vs. 15.1%). The 30-day infarction rate (0.6 vs. 2.4%), infarction or death event rate (1.0% vs. 3.3%), and new atrial fibrillation rate (5.0% vs. 39.5%) in the TAVI group were significantly lower than those in the operation group. In addition, patients in the TAVI group had a shorter average hospital stay (3 days vs. 7 days) and a lower risk of a 30-day poor prognosis (death or low KCCQ score) (3.9% vs. 30.6%). There was no difference in the incidence of major vascular complications, permanent pacemaker implantation, and moderate or severe perivalvular leakage between the two groups.

The Evolut study included 1468 patients who underwent Medtronic selfexpanding TAVI valves, of which 1403 underwent TAVI or surgery [18]. The average age of these patients was 74 years, and the main end point of the study was a 24-month complex event of death or crippling infarction. The incidence of major end point events at 24 months in the TAVI group was 5.3%, while that in the surgical group was 6.7%. The incidences of 30-day disabled infarction (0.5 vs. 1.7%), bleeding complications (2.4% vs. 7.5%), acute renal injury (0.9% vs. 2.8%), and atrial fibrillation (7.7% vs. 35.4%) in the TAVI group were significantly lower than those in the surgical group. However, moderate or severe perivalvular leakage (3.5 vs. 0.5%) and permanent pacemaker implantation rate (17.4% vs. 6.1%) were higher than those in the surgical group. At 1 year, the mortality rate in the TAVI group was 0.4%, while that in the surgical group was 1.2% (no significant).

The TAVI group had lower all-cause mortality and incidence of disabled infarction (but not statistically significant) (2.9% vs. 4.6%), significantly reduced crippling infarction (0.8% vs. 2.4%), and significantly reduced hospitalization for heart failure (3.2%vs. 6.5%). In addition, in the TAVI group, the transvalvular pressure difference was lower (8.6 mmHg vs. 11.2 mmHg), and the effective valve orifice area was larger (2.3 cm<sup>2</sup> vs. 2.0 cm<sup>2</sup> ) at 12 months. Despite the high proportion of perivalvular regurgitation after TAVI, only 22% of the patients received the third-generation valve. The new valve increases the edge of the skirt to reduce perivalvular leakage, so it is expected that the regurgitation rate will decrease as the new device utilization rate increases.

At present, there are about 60,000 TAVI operations in the United States every year. This may increase to 75,000 if patients at moderate risk received TAVI and to 100,000 or more if extended to low risk. The ultimate goal of TAVI surgery is that TAVI can be performed in all comers. It means no matter what the risk, no matter what the anatomy, and even what age; as long as it is the need for intervention of aortic valve disease, TAVI always can be done.

The two studies of PARTNER III and EVOLUT in 2019 are an eye-catching new research progress of TAVI technology. On this basis, the FDA and the European Drug Regulatory Agency have approved the extension of TAVI surgical indications from surgical high-risk patients with severe aortic stenosis to surgical low-risk patients, which indicates that TAVI technology will continue to develop rapidly towards the goal of the whole population in the future. It is believed that more research evidence will be published one after another, the guidelines for the diagnosis and treatment of cardiac valvular disease will change greatly, and interventional valvular technology will play a more and more important role.
