This review shows that in patients with severe aortic stenosis, for several outcomes, transfemoral TAVI results in better outcomes relative to SAVR than the transapical approach relative to SAVR; this was true for mortality, stroke, acute kidney injury, and bleeding. These subgroup effects are highly credible. They are among a small number of a priori hypotheses with a prespecified direction, including a comparison within studies,8 chance is an unlikely explanation, and the effect is consistent across these related outcomes.34

Mortality was reduced with transfemoral TAVI compared with SAVR by about 3%, stroke by 2%, acute kidney injury by 5%, bleeding by 24%, new onset atrial fibrillation by 18%, and duration of index admission by three days. These benefits, however, come with associated harms. TAVI was associated with an increased risk of experiencing symptoms of heart failure by about 6% (2% of which were moderate or severe), permanent pacemaker insertion by about 15%, and aortic valve reintervention over the short term by about 1%.

The picture is quite different with transapical TAVI, which, though it probably shares benefits of less bleeding, less atrial fibrillation, and shorter hospital stay, increased the risk of stroke compared with SAVR by about 5% and could also increase mortality.

Strength and limitations

Strengths of this review include a comprehensive search for evidence; duplicate assessment of eligibility, risk of bias, and data abstraction; and assessments of risk of bias that included addressing loss to follow-up across studies (and found results robust to loss to follow-up).23 The review included rigorous assessment of the quality of evidence (and found the quality for many critical outcomes high and others moderate) and of the credibility of subgroup analyses (with crucial differences between transfemoral and transapical TAVR approaches). We have presented absolute and relative risks, which are crucial for making decisions between TAVI and SAVR.

Limitations include a modest total number of patients (3179) and questionable generalization of results to low risk patients (most patients were at intermediate rather than low surgical risk). The randomized controlled trials used bioprosthetic valves, typically used in older patients, in all SAVRs.5 6 Our results therefore apply only to patients who have already chosen to use a bioprosthetic valve instead of a mechanical valve. No trial reported recovery time—beyond length of hospital stay—or pain after the intervention, two outcomes that our patient representatives identified as important. The incidence of chronic pain after sternotomy is about 28% and 13% for any and moderate pain at one year, respectively, suggesting that chronic pain might be less common in TAVI.35 An unadjusted observational study that included both TAVI and SAVR patients, however, showed no difference in pain scores at three months.36 We are not able to ascertain how much of the increased risk of atrial fibrillation with SAVR represents transient postoperative atrial fibrillation—less important for patients than persistent atrial fibrillation. Further, we did not find a subgroup effect by type of TAVI valve on pacemaker insertion and thus present a single estimate of effect. We note, however, that there is evidence external to this review that self expanding valves impart a higher risk of need for pacemaker insertion than balloon expanding valves.37 Technology for TAVI38 39 and SAVR40 is continually changing, potentially further increasing the attractiveness of the TAVI option.

The most important limitation is that the relatively short duration of follow-up leaves uncertainty about one critical outcome: the need for reintervention over the longer term, a major concern with TAVI valves. We did find that TAVI is associated with a higher risk of aortic valve reintervention, although we were not able to determine whether this was because of paravalvular regurgitation or structural valve degeneration, and the absolute risk was low. The younger the patient, the greater the extent to which the uncertainty regarding the long term durability of TAVI valves is likely to influence the decision between TAVI and SAVR.

Our findings are consistent with those from recently published meta-analyses for many outcomes,9 10 but we have also provided absolute as well as relative risks and a formal rating of the quality of the evidence and documented the credibility of the crucial outcome differences between transfemoral and transapical TAVI approaches. Further, we quantified several new findings, including an increased risk of aortic valve reintervention, an increased risk of symptoms of heart failure with TAVI, and an increased risk of life threatening or disabling bleeding (rather than major bleeding, which is less important to patients) with SAVR.

In conclusion, we have clarified the trade-offs between TAVI and SAVR and identified issues of residual uncertainty. For patients with lower life expectancy (such as those aged over 85), in whom longer term valve deterioration is likely to be less of an issue, the benefits of transfemoral TAVI versus SAVR on mortality, stroke, life threatening or disabling bleeding, and a less invasive procedure are compelling. Younger patients (such as those aged 65-85), who are less concerned about the limited evidence regarding valve deterioration and the necessity for a second procedure, might (or might not) also find these mortality and morbidity benefits compelling. Even younger patients (such as those aged under 65), for whom valve longevity could be extremely important, are more likely to choose SAVR over TAVI or even to choose a mechanical over a bioprosthetic valve. Finally, patients in whom a transfemoral TAVI approach is not feasible are unlikely to view the transapical approach, which is associated with a higher rate of stroke and a possibly higher mortality rate than SAVR, as an attractive option.