Clinically silent cerebrovascular injury resulting from TAVR has come to the fore following a series of studies evaluating cerebral ischemic events using diffusion-weighted magnetic resonance imaging (DW MRI) (Table 20.3, Figs. 20.2 and 20.3). An initial study by Kahlert et al. [23] compared 32 patients undergoing transfemoral (TF) TAVR (22 with the Edwards SAPIEN valve [Edwards Lifesciences Inc., Irvine, CA] and 10 with the CoreValve [Medtronic, Minneapolis, MN]) to historical SAVR controls (n = 21) (Table 20.3). Patients underwent DW MRI at baseline, a mean of 3.4 (2.5–4.4) days, and again at 3 months post-index procedure. All patients were assessed by an experienced neurologist using both the National Institutes of Health Stroke Scale (NIHSS) and the Mini Mental State Examination (MMSE). Successful valve implantation was achieved in all TAVR patients with no obvious adverse neurologic event during the periprocedural period. No change was noted in the NIHSS scale or MMSE score of any of these patients. Repeat DW MRI post TAVR however demonstrated new hyperintense lesions in 86 % of the Edwards SAPIEN and 80 % of CoreValve TAVR patients. There were significantly fewer patients with new lesions in the control SAVR group (48 %, p = 0.016). These new lesions were typically identified in both hemispheres reflecting a probable embolic cause. Among individuals with new cerebral lesions, lesion size was significantly smaller in the TAVR groups compared with the SAVR patients. At 3 months, no new DW MRI findings or changes in clinical or neurocognitive testing were noted. Indeed, the authors reported that 80 % of post-TAVR lesions had no residual signal change on repeat DW MRI at the 3-month interval.

Ghanem et al. [24] performed a pilot study involving 22 patients to prospectively assess clinically silent and overt cerebral embolic events in the setting of TF TAVR. Cerebral DW MRI was carried out before, within 3 days post and at 3 months after valve implantation. Three patients (10 %) had a new neurological abnormality on examination post TAVR, but symptoms resolved in two. At the time of the first post-TAVR neuroimaging study, 72.7 % of patients had new ischemic lesions compared to baseline.

It had been suggested that the transapical (TA) approach may potentially minimize cardioembolic event rates as this method minimizes the need for extensive catheter manipulation within the aortic arch. Arnold et al. [25] performed a similar assessment using cerebral DW MRI in 25 patients undergoing TA TAVR with the Edwards SAPIEN system. Valve implantation was successful in all patients; however, neurological abnormalities were evident post procedure on clinical examination in five patients, one of who developed a major stroke. Analysis of DW MRI revealed new embolic lesions in 68 % of the patients, with more than one lesion in the majority. In those patients with new lesions, the posterior circulation territory was involved in greater than 50 % of cases. Rodés-Cabau et al. [26] compared the incidence of acute cerebral ischemic injury in those undergoing TAVR (employing the Edwards SAPIEN or SAPIEN XT valve) via the TF and the TA approach. In this multicenter study, 60 patients (TF: 29, TA: 31) underwent cerebral DW MRI prior to and within 6 days following TAVR. Additional neurologic and cognitive evaluation was performed at the same intervals as neuroimaging, using the NIHSS and MMSE tests. One patient in each group had clinical evidence of a stroke within 24 h of valve insertion. Up to 68 % of patients had new ischemic lesions on DW MRI post TAVR with a median number of three lesions per patient (range 1–36). Of those with new lesions, 76 % were multiple and 73 and 66 % involved both cerebral hemispheres and circulation (anterior and posterior) territories, respectively. Of note, most (91 %) lesions were small (<1 cm). There were no significant differences between groups with regard to the incidence of new ischemic lesions between the TF (66 %) and TA (71 %) approaches. Finally, no interval changes in NIHSS and MMSE test scores were recorded following TAVR.

Fairbairn et al. [27] examined quality of life data in addition to performing DW MRI pre and post TAVR with the CoreValve system in 31 AS patients. Two (6 %) patients were diagnosed clinically with stroke as a consequence of the procedure. DW MRI confirmed up to 26 new ischemic lesions in both of these. Overall, new cerebral ischemic lesions were seen in 24 (77 %) patients, with the infarcts distributed evenly between both hemispheres. The mean number of new lesions per patient was 4.2 ± 6.5 with a mean infarcted tissue volume of 2.05 ± 3.5 ml. The authors demonstrated that increasing age and aortic arch atheroma burden were independent predictors of new ischemic lesions post TAVR. General health status and quality of life improved at 30 days post TAVR with no functional cognitive decline recorded.

The significance of clinically silent cerebrovascular ischemic events post TAVR remains unclear. As detailed above DW MRI evaluation has shown that between 68 and 86 % of TAVR patients have evidence of acute ischemic insults [23–27]. General population studies have found that the prevalence of silent brain infarcts increases with age and may be as high as 28 %, fivefold more common than stroke [28–30]. Though the consequences of silent cerebral ischemia are not fully elucidated, they have been associated with visual defects, motor abnormalities, cognitive decline, and altered mood [31]. Further studies will have to elucidate the real clinical consequences of these DW MRI defects following TAVR procedures.