In this nationwide, registry-based all-comers study of late stroke after TAVR, we could demonstrate a stroke rate between 2–3% per year during long-term follow-up. The majority (89%) suffered an ischemic stroke, and the 30-day mortality was 20%.
One key question that we tried to address in this study was whether having a TAVR valve is associated with an increased risk of stroke. Patients receiving TAVR are usually old, have risk factors that could predispose them to stroke, and subsequently, already carry an increased background risk for stroke. Any attempts to address this question need to take this into account. By combining official population data to obtain the number of individuals for each age and sex, we used Riksstroke to calculate an estimated standardized incidence for each individual and compared it to the actual outcome in this cohort. The standardized incidence ratio varied between 1.15% and 1.75% during the follow-up. The intention was not to make a direct comparison but to get a perspective on the risk of stroke after TAVR. A direct comparison between the actual outcome and standardized incidence falls short for two reasons. Firstly, the diagnosis of stroke in the TAVR cohort was taken from two sources, where the National Patient Registry accounted for 3% of patients. For the standardized incidence estimation, only Riksstroke was used, since the NPR could not be accessed for the entire Swedish population. In the TAVR population, we found an underreporting of 3%, but validation studies have reported figures between 5–11% missing cases in the registry (21). Secondly, the TAVR cohort had more comorbidities than the general population. In the present study, 37% of patients had atrial fibrillation, whereas the same age group in Sweden has a 21–24% prevalence of atrial fibrillation (22). The group also had a 74% frequency of hypertension, whereas the general population has lower numbers (58–63%). Diabetes on the other hand was not overrepresented, with 24% prevalence compared to 21–25% prevalence in the general population (23). Given that the TAVR cohort had a higher prevalence of comorbidities and that we have underestimated the standardized incidence slightly, the higher number of strokes in the TAVR cohort may be explained by these observations. However, we cannot exclude that the stent frame, the pericardial valve tissue, or immobilized native leaflets affects stroke rate. Given the observation that there was no difference between low frame valves (BEVs) and valves with frames expanding into the LVOT and ascending aorta (SEVs), this effect is probably not that large.
The present study identified reduced estimated GFR (eGFR < 30 ml/min/1.73 m2), diabetes, a history of stroke, patient age, and male sex as pre-disposing factors for stroke after TAVR. These findings are in concordance with other reports describing risk factors for stroke both in the general population and in the TAVR population (8, 24). Interestingly, a valve-in-valve procedure was associated with a reduced stroke rate. The only explanation for this unexpected finding could be that either valve-in-valve patients are generally healthier as the threshold for accepting them for TAVR is higher, they are better anticoagulated after the procedure or that the finding is simply a type II error. The model created yielded a Harrell's C-index of 0.64, which should be considered as relatively good given the heterogeneity of the material.
Almost 90% of the patients suffered an ischemic stroke, whereas 10% had a haemorrhagic stroke and in one patient, the stroke type was not known. Patients with ischemic stroke had more hypertension and presented with a higher level of consciousness at admission.
There were no statistical differences in anti-platelet therapy or anticoagulation between ischemic and haemorrhagic stroke. However, the tendency was that ischemic stroke patients were more often on acetylsalicylic acid and clopidrogel, whereas patients with haemorrhagic stroke were more often on anticoagulation. In the ischemic stroke group, 21% were not on any antithrombotic treatment, whereas in the haemorrhagic stroke group, 33% were not on any antithrombotic treatment. The databases do not provide any information on the indication for different antithrombotic treatment or the reason why patients had no treatment. Given these figures, it is hard to get any indication as to whether the current regimen with acetylsalicylic acid in the long-term after TAVR is as appropriate as antithrombotic treatment.
The outcome after stroke showed an expected 30-day mortality of 20%. The short- and long-term survival was very much in line with what is seen after stroke in a corresponding age group in the general population in Sweden and in similar studies (25, 26). In terms of functional class, 40% could be discharged home, whereas 35% were discharged to a nursing home or rehab. There was some difference in outcome depending upon type of stroke. Patients with ischemic stroke were more often discharged home and had a better short-term prognosis. By far, the strongest predictor for outcome after stroke was level of consciousness at admission. This pattern also is seen in the general population (25).
Atrial fibrillation is a strong pre-disposing and treatable causative factor for a stroke. This was seen in the univariable analysis but surprisingly not in the multivariable analysis. The plausible explanation for this is that we measure atrial fibrillation at the time of implant and have no records of atrial rhythm for all patients years later when the risk for stroke presents. It is reasonable to believe that quite a few patients have developed atrial fibrillation after the implant and not received adequate treatment. This hypothesis is supported by the fact that only 42% of patients with ischemic stroke were on OAC/NOAC. This observation warrants further studies on the low grade of anticoagulation in these stroke patients.
A retrospective registry-based study is limited by the amount and quality of data available. The strength of this study is its comprehensiveness, where all TAVR procedures in Sweden during the study period were included and where we were able to cross-reference the SWEDEHEART data with Riksstroke and National Patient Registry: three registries with a high level of completeness and accuracy (15, 16, 21, 27). The primary weakness is shared with all registry-based studies, i.e., incompleteness or inaccuracy of data depending on human factor or missing information. Despite a relatively large sample of 4000 + patients, a larger cohort would have yielded more robust data, but as all procedures in Sweden were included, a larger dataset was not possible. With the increasing number of TAVR, a study follow-up at 5 years would probably increase the number of individuals by a factor of three and would also have more individuals in the later follow-up period. We used the general population as bench-mark, but the best comparison would have been to create a cohort of SAVR patient that exactly matched our population. However, this is close to impossible to perform as most TAVR patients in this study were in prohibitive risk-category where no matching cases can be found in the SAVR population. Also, many patients are burdened by co-morbidities that do not show up in registries (frailty, malignancy, liver function cognitive function, etc.) and matching will inherently be skewed. One of the limitations is the lack of data on anticoagulation in the period after TAVR. Another issue that can be raised is the competing risk for death in this type of patient cohort. However, competing risk analysis did not change the spectrum of risk factors for stroke (eTable 7).
In this study, we could demonstrate an increased risk of stroke in this patient category, but it was unclear whether this was dependent on the TAVR valve per se or the higher frequency of pre-disposing risk factors in this cohort. In any case, the risk increase is modest and should not affect decision-making in the treatment of aortic valve stenosis.