A comparison of patient characteristics and 30-day mortality outcomes after transcatheter aortic valve implantation and surgical aortic valve replacement for the treatment of aortic stenosis: a two-centre study

Abstract

Aims: It is unclear whether transcatheter aortic valve implantation (TAVI) addresses an unmet clinical need for those currently rejected for surgical aortic valve replacement (SAVR) and whether there is a subgroup of high-risk patients benefiting more from TAVI compared to SAVR. In this two-centre, prospective cohort study, we compared baseline characteristics and 30-day mortality between TAVI and SAVR in consecutive patients undergoing invasive treatment for aortic stenosis. Methods and results: We pre-specified different adjustment methods to examine the effect of TAVI as compared with SAVR on overall 30-day mortality: crude univariable logistic regression analysis, multivariable analysis adjusted for baseline characteristics, analysis adjusted for propensity scores, propensity score matched analysis, and weighted analysis using the inverse probability of treatment (IPT) as weights. A total of 1,122 patients were included in the study: 114 undergoing TAVI and 1,008 patients undergoing SAVR. The crude mortality rate was greater in the TAVI group (9.6% vs. 2.3%) yielding an odds ratio [OR] of 4.57 (95%-CI 2.17-9.65). Compared to patients undergoing SAVR, patients with TAVI were older, more likely to be in NYHA class III and IV, and had a considerably higher logistic EuroSCORE and more comorbid conditions. Adjusted OR depended on the method used to control for confounding and ranged from 0.60 (0.11-3.36) to 7.57 (0.91-63.0). We examined the distribution of propensity scores and found scores to overlap sufficiently only in a narrow range. In patients with sufficient overlap of propensity scores, adjusted OR ranged from 0.35 (0.04-2.72) to 3.17 (0.31 to 31.9). In patients with insufficient overlap, we consistently found increased odds of death associated with TAVI compared with SAVR irrespective of the method used to control confounding, with adjusted OR ranging from 5. 88 (0.67-51.8) to 25.7 (0.88-750). Approximately one third of patients undergoing TAVI were found to be potentially eligible for a randomised comparison of TAVI versus SAVR. Conclusions: Both measured and unmeasured confounding limit the conclusions that can be drawn from observational comparisons of TAVI versus SAVR. Our study indicates that TAVI could be associated with either substantial benefits or harms. Randomised comparisons of TAVI versus SAVR are warranted.

Tools & Techniques - Statistics: Propensity score techniques

“…In our group, we consider this issue when the Kernel probability density estimate permanently drops below 0.5, but we are not aware of a generally agreed cut-off. In any case, long thin tails of PS that spread near the null point indicate a high probability of residual confounding (here biological rather than chronological age, frailty, severity of comorbid conditions), which may severely distort results, as indeed was the case here 6 : conventional analyses with multivariable adjustment indicated a threefold increase in the odds of death with TAVI as compared with SAVR (OR 3.05, 95% CI: 1.09 to 8.51) at 30 days 6 , when the only randomised trial available at the time indicated a trend towards a lower overall mortality at 30 days with TAVI as compared with SAVR (OR 0.53, 95% CI: 0.24 to 1.14) 14 . Figure 1B shows the distribution of PS in an observational comparison of two cardioplegic solutions used in patients undergoing SAVR at our centre (unpublished).…”

“…Two simple approaches are also specified in Table 2. Our group has only little experience with these approaches 6 , and we are unaware of clear evidence to suggest that these methods are superior to PS matching and IPTW.…”

“…So, even if there are few patients with PS between 0.2 and 0.85, which corresponds to probabilities of 20% and 85% of SAVR patients to receive TAVI given their pretreatment characteristics, the thin long tail spread along the null between 0.2 and 0.85 indicates that we cannot be certain that the actual probability of these patients to receive TAVI is anything else but zero. An 81-year-old SAVR patient with a PS of 0.5, for example, may look on paper as if she has had a 50% chance to receive TAVI, but at clinical inspection one would immediately grasp that she appears biologically much younger, has only minor severity of her comorbid conditions, is participating fully in life and shows no signs of frailty, which made her an extremely likely candidate to receive SAVR despite her age and rendered her practically ineligible for receiving TAVI 6 . In our group, we consider this issue when the Kernel probability density estimate permanently drops below 0.5, but we are not aware of a generally agreed cut-off.…”

“…We use smoothed Kernel probability density estimates 12,13 of the PS of the two groups to do so, but simple histograms will also do the job. Figure 1A shows the distribution of PS in the above-mentioned comparison of TAVI with SAVR in patients with aortic stenosis 6 . The distribution of PS in experimental patients receiving TAVI is almost uniformly distributed between zero and one.…”

“…Observations in both groups that have PS beyond these two cut-offs are dropped 16 . We do not advocate trimming based on the common support assumption, even though we previously used it 6 , since the cut-off will depend heavily on the parameters used for the Kernel probability density function 12,13 . After trimming, the study population becomes more selected and, again analogous to an RCT, results after trimming may not be generalisable to all patients seen in routine clinical practice.…”