Down the yellow brick road: Transcatheter aortic valve insertion and patient risk

In this issue of the journal, Tamburino et al. [1] report on the results of a single center series of patients undergoing transcatheter aortic valve insertion (TAVI). They have assessed outcomes by dividing patients into a high risk, logistic euroSCORE 20, and a lower risk group with a euroSCORE of less than 20. There are several limitations to the study, the two major ones being first: it is a single center registry potentially reflecting a unique cohort and the second a relatively short term of follow-up. An additional problem is the use of non-standard end points that do not, for example, use VARC definitions of vascular complications. Nonetheless the differences in outcome between the two groups are stark with the lower risk group having universally superior outcomes. Now comes the hard part, what can be recommended based on the results of this article. Unfortunately, it is really hypothesis generating rather than a clear road to use this exciting technology in a lower risk population. Although it is difficult to compare different studies; the randomized PARTNER A high risk data is probably our best look at TAVI outcomes compared to standard surgical valve replacement. That study showed TAVI was non-inferior to surgery [2]. However, there were signals that do give us pause, particularly the incidence of stroke or TIA, which appeared to be higher in the TAVI arm of the trial. A stroke is an important event in anyone’s life but is particularly devastating and sometimes life ending in the elderly frail patient. Obviously this important adverse event must be weighed heavily when TAVI is considered for the patient at lower risk. Although we do not know if the rate of stroke will be lower in the lower risk patients, it is a critical determinant of any recommendation to perform TAVI in this patient population since the rate of stroke with surgical aortic valve replacement is also likely to be lower as well. The PARTNER II trial, which is currently enrolling patients, will specifically look at this issue in a lower risk population (STS risk of > 4 vs. > 10 in PARTNER I). It may be that specifically designed vascular protection devices will decrease the stroke rate in TAVI but the data to support that contention at this point is immature. The a priori suggestion, without the data to support it, that the use of vascular protection devices will decrease this significant complication is not a valid contention and should not be used to mitigate the concern over this very important complication. Tamburino et al. also suggest that to really assess the risk of patients undergoing TAVI we need a specific risk score for TAVI. I could not agree more. All who have performed these procedures realize that the current tools are inadequate. For example, the predicted mortality in the PARTNER high risk surgical cohort using the STS risk calculator was 11.8% for mortality, but the observed mortality was actually much lower at 8% in the surgical arm of the trial [2]. Although the euroSCORE and STS risk calculator have been used to categorize these patients, they have significant limitations in this particular patient population primarily because they were never designed to assess risk in patients undergoing a novel new procedure like TAVI. However, I do take exception with Tamburino that a TAVI risk model should include institutional experience as a modifier. This procedure should only be performed by centers with the experience and infrastructure to yield the best outcomes irrespective of center experience. Although institutional and individual learning curves are inevitable the impact on patients can and should be mitigated by adequate training and proctoring prior to a center being made independent for the delivery of TAVI. Therefore, a modifier based on institutional experience is a non-starter. We should accept nothing less for these very ill and frail patients or anyone being offered