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Verolino et al. Vessel Plus 2018;2:17 I http://dx.doi.org/10.20517/2574-1209.2018.32 Page 5 of 12

intermediate-risk (STS risk score between 4% and 8%) and at low-risk (STS risk score < 4%) [26,27] . Under cur-
rent guidelines, the choice to perform TAVI for that group of patients should be allowed only after a specific
cases selection by the Heart Team and, importantly, in centers with well-established procedural training.
Many trials are ongoing to demonstrate real advantage of TAVI in low risk subset but others have already
been published which show the true benefits for intermediate risk patients.

The PARTNER II was the first large randomized trial that evaluated the outcome of TAVI in intermedi-
[28]
[28]
ate surgical risk population . In this study Leon et al. randomized about 2000 patients with severe AS
and STS score between 4% and 8% to TAVI [mean STS- Prediction of Mortality (PROM) 5.8%] or SAVR. At
24-month follow-up, the composite endpoint of all-cause death or disabling stroke was 19.3% in the TAVI
group compared with 21.1% in those treated with SAVR (P = 0.25). Of note, a significant interaction between
TAVI approach and mortality was observed, with transfemoral TAVI showing superiority over SAVR (HR
0.79; 95% CI: 0.62-1.00; P = 0.05). Larger aortic valve areas, lower rates of acute kidney injury, severe bleed-
ing, and new-onset atrial fibrillation were also reported in TAVI group, whereas, SAVR caused fewer major
[28]
vascular complications and less paravalvular aortic regurgitation . In the Surgical Replacement and Trans-
[29]
catheter Aortic Valve Implantation trial (SURTAVI), Reardon et al. confirmed the feasibility of TAVI in
patients at intermediate risk (mean STS-PROM of 4.4%). They observed an incidence of the same end point
chosen in the PARTNER II trial (overall death and stroke) of 12.6% in patients receiving TAVI and of 14%
in those undergoing conventional surgery. A pre-specified analysis of the single components of the primary
end point has shown a similar rate of all-cause death between the two treatment strategies (11.4% and 11.6%),
whereas, at 24 months follow-up, a numerically lower rate of disabling stroke was found in the TAVI group
[29]
compared with the surgical group, although the difference was not significant (4.5% vs. 2.6%) . Similar pos-
itive results have been demonstrated also in low-risk AS population. In the Nordic Aortic Valve Intervention
[30]
Trial (NOTION), Thyregod et al. randomized 280 low-risk AS patients to TAVI or SAVR. The primary
endpoint of death for any causes, myocardial infarction and stroke after 1 year was observed in 13.1% of the
TAVI group and 16.3% of the SAVR group. The “intention to treat” analysis confirmed these results (11.3%
vs. 15.7%, respectively in TAVI and SAVR groups). Moreover, the 5-year follow-up of the NOTION trial was
[31]
recently reported at the latest ACC Congress . After five years, there were no differences in the incidence of
the composite primary end point (39.2% of TAVI patients and 35.8% of SAVR patients). Looking at the end-
points individually, the rate of all-cause mortality was 27.7% for both SAVR and TAVI. In addition, stroke
incidence was 10.5% in TAVI patients and 8.2% in those receiving SAVR, while 8.7% and 8.6% of patients
had experienced a myocardial infarction in the TAVI and SAVR groups, respectively. These results were also
[32]
[31]
observed for patients with STS score less than 4% . Similar evidence was reported by Wenaweser et al.
comparing clinical outcomes of patients with intermediate/low-risk and high-risk patients undergoing TAVI.
Patients with severe AS receiving TAVI showed a mortality rate of 3.9% and 2.4%, respectively for mid and
low risk groups (P < 0.001); these data are extremely positive and promising, especially in consideration
of the expected mortality estimates of 6.8% according to STS-PROM score. Finally, in the Italian registry
Observational Study of Effectiveness of SAVR-TAVI Procedures for Severe Aortic Stenosis Treatment (OB-
[33]
SERVANT) , enrolling patients surgical and TAVI treated, the 1-year mortality was not different in the two
groups (13.6% vs. 13.8%; P = 0.936), even if in the first 90 days after aortic procedure, mortality was numeri-
cally greater in patients receiving SAVR compared with TAVI. Furthermore, in this last group, the rate of
rehospitalization for cardiac symptoms and episodes of acute heart failure was lower (21.9% vs. 23.6% and
[33]
19.0% vs. 19.7%, respectively) . Several trials such as PARTNER 3 and NOTION 2 are ongoing and could
probably confirm the effectiveness and safety of transcatheter aortic approach compared with surgery also in
the low-risk subgroup.

However, although results of previously reported studies are very encouraging, nobody can demonstrate a
statistically relevant result that favours choosing TAVI in every patient, irrespective of risk profile. Moreover,