Surgical aortic valve replacement (SAVR) has been the treatment for patients with aortic valve disease since it was first performed in 1960 (1, 2), with biological and mechanical prostheses most commonly used to replace the native diseased valve. The long-term outcome and freedom from structural valve degeneration for SAVR remain excellent (3, 4). However, the choice of the ideal valve in relation to the specific age group remains controversial.

The recent advancement of transcatheter aortic valve replacement (TAVR) provides an alternative treatment. The PARTNER 1, 2, and 3 trials have shown the benefits of TAVR in all patients with aortic stenosis, regardless of surgical risk (5–7). TAVR also provides an alternative to patients with the previous SAVR/TAVR with an option of valve-in-valve transcatheter aortic valve replacement (ViV TAVR). This has been suggested to result in a reduction in mechanical valve use worldwide (8, 9).

We aim to evaluate the trend and clinical outcomes in isolated SAVR in the United Kingdom and also focus on the volume of SAVR in the high-risk cohort, redo surgery, and the choice of prosthesis use. Finally, early clinical outcomes in patients who received mechanical or biological prostheses under the age of 65 were compared.

All patients undergoing elective or urgent isolated SAVR in the United Kingdom from 1996 to 2018 were extracted from the National Adult Cardiac Surgery Audit (NACSA) database. The NACSA database prospectively collects data on all major heart operations conducted on National Health Service patients in the United Kingdom since April 1996. The definitions of database variables were used, and a description of the database was previously described (10).

Patients were divided into five different age groups: less than 50 years old, 50–59 years old, 60–69 years old, 70–79 years old, and above 80 years old. The surgical volume and choice of aortic valve prostheses (biological vs. mechanical) across the five age groups were investigated. The choice of aortic valve prostheses used in patients with chronic kidney disease undergoing dialysis was also evaluated (As defined in one of the three categories—1. dialysis for acute renal failure: onset within 6 weeks of cardiac surgery, 2. dialysis for chronic renal failure: onset more than 6 weeks prior to cardiac surgery, and 3. no dialysis but pre-operative acute renal failure (anuria or oliguria <10 ml/h). The trend in patients who underwent previous cardiac surgery and the volume of SAVR performed in patients with low- (<2%), intermediate- (2–4%), and high-risk (>4%) as defined by the EuroSCORE II was also evaluated (11). The observed mortality was defined as 30-day or in-hospital mortality after the index operation. The expected mortality was calculated using the EuroSCORE II. Moreover, the early clinical outcomes in patients who received mechanical or biological prostheses under the age of 65 were compared using propensity score matching. Sixty-five was selected as a cutoff based on the 2020 ACC/AHA Guideline for the Management of Patients with Valvular Heart Disease (12).

Patients who underwent additional procedures, major aortic surgery, emergency, or salvage SAVR were excluded from the study. Missing data in the choice of prostheses were also excluded in this study (n = 3,309, 4.18%).

Continuous variables are reported as mean and standard deviation (SD). Categorical variables are reported as frequencies and percentages. Pearson’s chi-squared test, Wilcoxon rank-sum test, and one-way/multi-factor analysis of variance were used to compare two categorical variables, for comparison between two means of continuous, independent samples, and to compare between three continuous variables, respectively.

Propensity score matching (PSM) was performed to create a quasi-experimental design by balancing measured confounding factors between the two groups. A 1:1 nearest neighbor matching without replacement with a caliper width of 0.2 standard deviations of the logit of the propensity scores was performed using the pre-operative characteristics listed in Table 3. Missing continuous variables data (left ventricular ejection fraction and body mass index) were imputed with the median value in the data after the application the of exclusion criteria listed above. After matching, all standardized mean differences for the covariates were checked. The adequate balance was set to be below 0.1.

The effectiveness of the PSM was visualized with a Love plot to report the covariate balance with all variables before and after the matching. This is shown in the Supplementary Figure 1. Binary logistic regression was performed using the baseline patient demographics and comorbidities to predict factors associated with the use of biological aortic valve prostheses. The results are demonstrated as odds ratio (OR) and 95% confidence interval (95% CI). A P-value of < 0.05 is deemed statistically significant.

R (Version 4.1.1) and R Studio (Version 1.4.1103, RStudio, PBC) were used to perform the statistical analysis. The following packages were used: tidyverse, MatchIt, sjPlot, and ggplot2. Graphs and tables were created using R Studio (Version 1.4.1103, RStudio, PBC) and Microsoft Office 365 (Version 16.0.14026, 64 bits).

A total of 79,173 patients underwent isolated SAVR in the study period. The mean age was 67.99 (SD 12.48) years old, and 32,799 (41%) were female. The mean BMI was 28.35 (SD 5.64), and LVEF was 53.60 (SD 10.89). About 81% (n = 64,457) were performed in an elective setting. The median post-operative length of stay was 6 days (IQR 5–7 days). The most common surgical incision was median sternotomy (88.7%), followed by partial/hemisternotomy (9.05%). In patients who underwent minimally access SAVR, 4.9% required conversion to median sternotomy.

The most common etiology was aortic stenosis (66.8%) followed by mixed aortic stenosis and regurgitation (18.3%) and aortic regurgitation (14.9%). The native valve pathology was most likely due to degeneration (76.1%) followed by congenital (9.4%). Infective endocarditis and rheumatic heart disease accounted for 3.6 and 2.3% of total cases, respectively.

Our study demonstrated that SAVR remains an effective treatment with low mortality for patients with isolated aortic valve disease. The number of patients with high-risk, octogenarians undergoing isolated SAVR, and those requiring redo surgery has reduced in recent years, likely due to the advancement in TAVR. The use of biological aortic prostheses has increased significantly in recent years in all age groups.

Despite the increment in EuroSCORE II, the overall mortality rate has continued a downward trend to 1.06% in 2018. The observed mortality rate has outperformed the predicted mortality rate by nearly 50% in 2016–2018. The mortality rate in the United Kingdom has further reduced since the last report (13) and other reports in the literature (9, 14).

The increased use of bioprostheses we observed reflects a similar trend in the literature. Jiménez-García et al. (9) reported a five-fold use of bioprostheses from 2001 to 2015 using the Spanish National Hospital Discharge Database, although the age groups were not specified. Alkhouli et al. (8) reported the age group-specific use of bio/mechanical prostheses in the United States using the Nationwide Inpatient Sample. They observed a significant reduction in the use of mechanical prostheses among patients aged 50–70 years between 2008 and 2017. This is similar to our finding in which more than 80% of patients aged 60–69 received a biological aortic valve. However, the use of mechanical valves remains higher in the 50–59 age group in the United Kingdom (58% in 2018) compared with 37 and 22% among the 56–60 and 50–55 age groups in the United States (8).

The durability of bioprostheses remains an important topic when used in young patients. The freedom from structural valve deterioration has been reported at 81.7% at 15 years and 52% at 20 years post-SAVR (15); hence, the need to repeat interventions should be taken into consideration. The advancement of TAVR, valve-in-valve transcatheter aortic valve replacement (ViV TAVR), has become an alternative treatment in patients with the previous SAVR. In addition to avoidance of anticoagulation, these may be the explanation for the observed reduction in the use of mechanical prostheses. However, a higher rate of prosthesis–patient mismatch, paravalvular leak, and coronary obstruction, in ViV TAVR compared to native valve TAVR has been reported (16, 17).

In our report, we observed a higher proportion of mechanical valves used in patients requiring dialysis. With the high risk of early structural deterioration in biological prostheses, there seems to be a preference for the use of the mechanical valve in this subgroup. This is in line with literature reports. Uzuka et al. (18) reported the risk of early structural deterioration in the biological valve to be approximately 50% at 6 years (compared to 0% in the control arm). Chi et al. (19) also demonstrated the survival benefits of implanting mechanical prostheses in patients with dialysis.

Currently, the European guideline recommends that patients above the age of 75 should consider TAVR after Heart/Valve team evaluation (20), while the American guideline had a cutoff of 65 years old (12). The National Institute for Health and Care Excellence recommends SAVR as a first-line interventions and TAVR for patients who are at high surgical risk or if surgery is unsuitable (21). However, with the results of the UK TAVI trials, the authors predicted that the volume of TAVR will continue to increase and exceed SAVR in the United Kingdom (22). Indeed, in the NACSA 2022 reports, the ratio of TAVR to SAVR rose from 1.2:1 to 2.3:1, which dramatically accelerated during the COVID-19 pandemic (23). The annual volume of TAVR has already exceeded SAVR in the USA and Germany (24, 25).

Our study demonstrated similar short-term outcomes regardless of the valve of choice in non-elderly patients, which echo the findings reported in the literature. Most studies showed the risk of re-intervention is higher in bioprostheses although the risk of major bleeding is lower. However, the long-term survival benefits remain controversial with some studies demonstrating a survival benefit with mechanical valves (26–28) while some did not (29–32). Although the survival benefits could be due to primary valve failure, which could be less of an issue due to the advancement of TAVR, particularly in patients who are at high risk for a redo of SAVR.

There are several limitations of the study. First, the impact of SVAR on the clinical practice may not be fully evaluated, in a patient with extra pathology such as mitral valve/aortic/coronary artery disease requiring concomitant procedures. The choice of prostheses in these patients was not evaluated in this report. In addition, patients with aortic stenosis and coronary artery disease may undergo TAVR and their coronary artery disease managed at a later stage, while in the surgical arm, these patients will undergo both coronary artery bypass graft and SAVR at the same time. The morphology (bicuspid and tricuspid) was not coded in the database and remains an important limitation as patients with bicuspid valves are more likely to be referred for a SAVR. The lack of TAVR registry data to compare the volume of SAVR against TAVR is another major limitation.

The lack of pre- and post-operative precise echocardiographic data limited the sub-analysis for patients who underwent SAVR with different pathologies. In addition, the database did not collect certain post-operative outcomes and follow-up data; hence, information on pacemaker implantation, repeat valve intervention, endocarditis, and structural valve deterioration is not available. Finally, the database requires input from all healthcare professionals, missing data are seen in several non-mandatory items, and these are instead presented as a percentage. Overall, the mandatory items, particularly items essential for EuroSCORE II risk stratification, are well maintained with an acceptable rate (<5%) of missing data since the 2,000s.

Despite the application of PSM, it is possible that residual bias is present in the analysis since the propensity-matched model can account only for measured confounders and not for the unmeasured confounders (e.g., frailty).

Our data show that isolated SAVR is a safe and effective treatment with very low in-hospital mortality for patients with aortic valve disease. The advancement of transcatheter aortic valve replacement is the likely explanation for the reduction of SAVR in patients with high-risk, octogenarians, and those requiring redo surgery. The option of valve-in-valve transcatheter aortic valve replacement may also be one of the causes for the observed use of biological aortic prostheses which has increased significantly in recent years in all age groups.

The datasets presented in this article are not readily available because Ethical approval required. Requests to access the datasets should be directed to NICOR, nicor.auditenquiries@nhs.net.

The studies involving human participants were reviewed and approved by Health Research Authority (HRA) and Health and Care Research Wales (HCRW) (IRAS ID: 278171). Written informed consent for participation was not required for this study in accordance with the national legislation and the institutional requirements.

JC: conceptualization, data curation, formal analysis, methodology, writing—original draft, and writing—reviewing and editing. AD: data curation, formal analysis, methodology, writing—original draft, and writing—reviewing and editing. TD: data curation, formal analysis, methodology, and writing—reviewing and editing. DF, SS, and PN: conceptualization and writing—reviewing and editing. GA: conceptualization, supervision, methodology, and writing—reviewing and editing. All authors contributed to the article and approved the submitted version.