The present study comparatively displays the clinical, microbiological, and imaging characteristics of IE-SAVR and IE-TAVI, as well as their outcomes in 210 consecutive cases from tertiary referral centres with dedicated ET. The most relevant findings include: (1) patients with IE-TAVI were significantly older, more fragile, and with more comorbidities, compared to IE-SAVR; (2) early IE was more frequent amongst IE-TAVI; (3) the microbiological profile of both entities was comparable, except for a higher proportion of S. aureus infection in IE-TAVI; (4) abscesses were more frequent and larger in IE-SAVR, and these patients developed more frequently atrioventricular block; (5) regarding clinical presentation, IE-TAVI patients had more frequently constitutional symptoms; (6) the proportion of patients who did not undergo surgery in spite of having a surgical indication was higher in IE-TAVI; and (7) mortality during hospitalization and follow-up was similar in both groups.

Despite TAVI procedure has become less invasive and its indication has expanded to lower-risk patients, the incidence of IE-TAVI has remained stable along the years [14]. Initially, it was described that the incidence of IE was higher in TAVI, but recent large observational studies have shown no significant differences in comparison with SAVR [9, 11, 15]. On the other hand, and as it is shown in our cohort, the risk of early prosthetic valve IE is known to be higher in TAVI [15], with the highest incidence occurring during the first seven months after valve implantation [16]. In the Swiss TAVI registry, early IE episodes were significantly more common than late ones, and the highest incidence was noted in the first 100 days following valve implantation. These findings correspond to a risk of IE six times higher in the first 100 days after the procedure than after the first year [17]. Nevertheless, in a recent study which compared a historical cohort of TAVI patients with a contemporary one in which minimalist approaches are aimed, Del Val et al. observed a decline in early IE episodes in recent years, particularly in those occurring within the first 2 months after the procedure [18].

In high-income countries, IE is a disease which predominantly affects male older adults [19]. In our cohort, as expected, a predominant proportion of male sex was observed in both groups. We also found that patients with IE-TAVI had more comorbidities, such as diabetes, pulmonary diseases, and chronic anemia. Likewise, significant residual periprosthetic regurgitation and vascular complications, which are already known procedure-related risk factors for IE-TAVI, were more frequent in our IE-TAVI patients, compared to IE-SAVR [20].

In relation to all the above, and as previously described in other series [18, 20], a very high prevalence of healthcare associated cases was observed among IE-TAVI, although non-significant differences were found when compared to IE-SAVR, due to the limited sample size. We observed a higher proportion of cases referred from another hospital among IE-SAVR, which may be explained by the fact that these patients are more often considered surgical candidates, due to a lower operative risk.

Enterococci have been reported as a very common cause of IE-TAVI, due to their affinity for the groin region and the widespread use of transfemoral access for TAVI implantation [21]. In IE-SAVR, enterococci are less frequently isolated, although an increasing trend of their incidence as a cause of IE has been described within the last two decades [19]. In our cohort, coagulase-negative staphylococci, enterococci, and Staphylococcus aureus were the most frequently isolated microorganisms in both groups, which is consistent with prior studies [11]. We did not find significant differences in the proportion of enterococcal infections, but S. aureus was twice as frequent in IE-TAVI patients, compared to those with IE-SAVR.

Regarding clinical features, fever was the most frequent sign in both groups. Nonetheless, and in accordance with previous series, we found that TAVI patients, despite having a higher proportion of S. aureus infections, presented less frequently with fever, and had proportionally higher prevalence of nonspecific symptoms, such as constitutional syndrome and arthritis [18, 20]. These findings may be related to the fact that IE-TAVI occurs in older patients with a higher comorbidity burden and may be one of the reasons that led to the observed delay in diagnosis [14].

No significant differences were observed regarding heart failure or systemic embolisms at admission or during hospitalization between both groups of patients. Conversely, IE-SAVR patients developed more frequently atrioventricular blocks, and presented more and larger periannular complications, as recently reported by Panagides et al [22]. Contrary to our findings, some studies have described that the incidence of periannular complications is similar in both IE-SAVR and IE-TAVI patients, or even more frequent among the latter [14, 23, 24]. In a recent systematic review including 107 IE-TAVI cases who underwent surgery, Malvindi et al. found that 34% of episodes had annular abscesses [25]. Nevertheless, these results may be influenced by selection bias, as patients with periannular complications are more likely to be treated surgically.

Regarding patient’s management, the benefit of surgery in both native and prosthetic valve IE in patients with surgical indications is firmly endorsed by a large body of evidence [26]. However, the optimal therapeutic approach for IE-TAVI is not well established yet. Due to advanced age and comorbidities of patients undergoing TAVI, the proportion of patients receiving surgery in the context of IE, despite having clear indications, is consistently low (< 20%) [9, 18, 20]. Moreover, some studies assessing the outcomes of cardiac surgery for the treatment of IE-TAVI have shown no benefit in terms of survival during admission and at one-year follow-up [20, 27,28,29]. In our cohort, only 3 (7.3%) patients with IE-TAVI underwent cardiac surgery, and the survival rate of IE-TAVI patients who underwent surgery and those who were treated conservatively was similar.

On the other hand, a meta-analysis by Tinica et al. found that surgical treatment was associated with a lower mortality rate (OR 0.15, 95% CI 0.04 to 0.62), although they noticed the possibility of publishing bias [16]. In addition, Panagides et al. did observe a higher survival proportion with surgical treatment among patients with IE-TAVI and periannular complications [30]. Moreover, Saha et al. reported a survival to discharge rate of 88.4% in low-intermediate risk IE-TAVI patients who underwent surgery [31]. Therefore, surgical risk and patient selection are crucial when evaluating the results of surgery in this singular group of patients.

When comparing the outcomes between IE-TAVI and IE-SAVR, large national-based registries have reported a significantly higher in-hospital mortality in IE-TAVI patients compared to IE-SAVR, ascribing it to a more frequently conservative treatment strategy applied in a population with a higher age and more comorbidities. Of note, both, the proportion of patients with surgical indications and the percentage of those who actually undergo surgery, are often missing from these datasets [11, 15]. On the other hand, Moriyama et al. described no differences regarding in-hospital death between both groups of patients (20.0% in IE-TAVI vs. 32.1% in IE-SAVR, p = 0.44), although a lower proportion of TAVI patients received surgery [32]. In addition, Panagides et al. reported similar 1-year mortality rates among IE-TAVI and IE-SAVR [22]. Likewise, in our cohort, no differences in in-hospital and 1-year mortality rates were observed, despite the unbalanced proportion of surgery among groups.

We have not found definite reasons to explain this relatively “more benign” course in the case of IE-TAVI. Yet, we must bear in mind that patients with IE-TAVI had less frequently an indication for surgery, compared to the IE-SAVR group, and presented fewer periannular complications. In addition, 50% of patients with IE-SAVR in our series who underwent surgery presented periannular complications or signs of persistent infection, uncontrolled infection being the IE surgical indication associated to the highest mortality [33]. Therefore, it should not be surprising that these patients had poor outcomes, despite undergoing surgery.

In the setting of IE in elderly patients, Lopez-Wolf et al. observed a lower proportion of fever, less severe heart failure, a lower incidence of vegetations and abscesses, fewer surgical indications and a lower mortality among octogenarians with IE, in comparison with younger patients [34]. Furthermore, data from the ESC EORP EURO-ENDO registry showed that octogenarian patients with EI presented surgical indications less frequently than younger adults. Besides, among octogenarians, mortality was lower in patients without any indications for surgery, compared to those with surgical indications [35]. Conversely, other groups have reported better outcomes in elderly patients who were surgically treated [36].

Therefore, in the absence of clear evidence, patient selection, dedicated care and close follow-up by experienced ET become of capital importance when treating elderly patients. On this regard, the use of prolonged antibiotic therapy in our patients who did not undergo surgery may have played a role in the relatively low mortality and satisfactory evolution after discharge of the IE-TAVI group [37].

Our study has several limitations inherent to its observational design. Firstly, all participating centres were high-volume hospitals with experienced ET, so referral and selection bias may be present. Patients with severe comorbidities and considered not surgical candidates are less likely to be transferred to referral hospitals, and this could have occurred more frequently in patients with IE on TAVI. Secondly, since not all patients undergoing SAVR and TAVI in the participating centres were included, incidence of IE in both groups cannot be calculated. Thirdly, theoretical surgical indications of patients who did not undergo surgery are not available. Finally, the limited sample size, especially due to the low number of IE-TAVI cases, does not allow to formulate definite conclusions. Nevertheless, and contrary to large series comparing SAVR and IE-TAVI, all our data come from prospective cohorts of patients, from referral centres for IE with dedicated ET, which provide reliable information regarding clinical, microbiological, and imaging features.