A total of 678 patients were included. Baseline characteristics are shown in Tab. 1. Median age was 69 years (64–72), and 439 patients (64.7%) were male. Median EuroSCORE II was 1.8% (1.1–3.2%).

Of the patients included, 292 underwent TAVI and 386 underwent SAVR. There was no significant sex difference between groups (63.0% vs 66.1% male in TAVI vs SAVR; p = 0.14). TAVI patients were older (70 vs 68 years, p < 0.001). More TAVI patients had a left ventricular ejection fraction (LVEF) < 50% (31.8% vs 18.7%; p < 0.001), diabetes (40.8% vs 26.4%; p < 0.001), atrial fibrillation (26.4% vs 14.2%; p < 0.001) or chronic kidney disease (estimated glomerular filtration rate < 60 ml/min in 29.1% vs 12.7%; p < 0.001). EuroSCORE II was higher in the TAVI population (2.2 vs 1.6%, p < 0.001).

The indication for valve intervention was AS in 95.0% of patients, with no significant difference between TAVI and SAVR (p = 0.52). Median length of hospital stay for TAVI patients was 4 days (2–7) vs 5 days (3–6, p < 0.001) for SAVR patients. SAVR was combined with coronary artery bypass surgery or other valve surgery in 40.2% of patients; TAVI was combined with percutaneous coronary intervention in 11.3% of patients.

Risk criteria distribution over the two cohorts is illustrated in Fig. 2a. Notably, six of the eight high-risk criteria and eight of the nine very high-risk criteria were significantly more prevalent in the TAVI group.

The risk profile distribution differed significantly between TAVI and SAVR patients (p < 0.001) (Fig. 2b). Of note is that 174 TAVI patients (59.6%) were at high risk based on the Dutch risk criteria as opposed to 75 SAVR patients (19.4%). Conversely, 230 SAVR patients (59.6%) versus 50 TAVI patients (17.1%) were deemed low risk.

TAVI and SAVR patients differed significantly within risk cohorts (Table S2, Electronic Supplementary Material). Across risk-category subgroups, TAVI patients were older than SAVR patients. Low-risk patients undergoing TAVI had more non-cardiovascular comorbidities (46.0% vs 30.0%, p = 0.029) and peripheral artery disease (20.0% vs 7.8%, p = 0.009) and were more often female (48% vs 29.6%, p = 0.012) compared to low-risk SAVR patients. High-risk TAVI patients were more often frail (50.6% vs 30.7%, p = 0.004) or had peripheral artery disease (38.5% vs 12.0%, p < 0.001). Of the high-risk TAVI patients, 15.5% were judged to be at prohibitive risk, defined by the presence of a porcelain aorta, a thoracic malformation or Child-Pugh class B or C liver cirrhosis (Fig. 2c).

The Kaplan-Meier survival percentages and the results of the Cox proportional hazards regression model are summarised in Table S3, Electronic Supplementary Material. There was no statistically significant difference in 30-day all-cause mortality between TAVI and SAVR patients (2.4% vs 0.8%, p = 0.083). Mortality at 1 year was higher for TAVI than for SAVR patients (12.5% vs 4.3%, p < 0.001), as was mortality at 5 years (36.8% vs 12.0%, p < 0.001) (Fig. 3).

Kaplan-Meier curves of all-cause survival. TAVI transcatheter aortic valve implantation, SAVR surgical aortic valve replacement

There were numerical differences between low-, intermediate- and high-risk patients, but no evidence for interaction between risk category and treatment group (pinteraction = 0.30 for low risk vs intermediate risk; pinteraction = 0.93 for low risk vs high risk). Hence, any statistical differences found may be the consequence of small treatment groups. The overall hazard ratio (HR) for TAVI vs SAVR was 3.3 [95% confidence interval (95% CI): 2.2–4.9; p < 0.001].

Prevalence of all cluster variables except demographics differed significantly between treatment groups (Table S4, Electronic Supplementary Material). Tab. 2 shows the simple and complex models of the 5‑year Cox regression analysis for all-cause mortality. The simple model suggests an increase in hazard of mortality from the cardiovascular comorbidities cluster [HR 1.7 (95% CI: 1.2–2.6)], the non-cardiovascular comorbidities cluster [HR 1.7 (95% CI: 1.07–2.6)] and the cluster of miscellaneous conditions [HR 4.2 (95% CI: 2.6–6.6)]. An isolated procedure was associated with a reduced hazard [HR 0.60 (95% CI: 0.38–0.95)]. No significant differences in HR were noted between TAVI and SAVR patients (pinteraction > 0.05 for all cluster variables). In the complex model, the cardiovascular comorbidities cluster [HR 1.6 (95% CI: 1.1–2.4)], isolated procedure [HR 0.55 (95% CI: 0.34–0.91)] and the cluster of miscellaneous conditions [HR 4.5 (95% CI: 2.8–7.4)] were independently associated with mortality at 5 years. For SAVR patients, the cluster of impediments to surgery also conveyed an increase in hazard of mortality.