5.1. TEVAR risks and risk mitigation
TEVAR remains an imperfect procedure. Early survival in unTBAD patients receiving OMT is ± 90% (34, 35) which is appreciably lower than patients managed with TEVAR (36-40). Nonetheless, 30-40% (36, 41, 42) of surviving patients will experience aneurysmal dilatation or dissection progression despite being under cautious clinical surveillance which could mandate downstream TEVAR intervention. TEVAR is associated with moderate risk of ischemic stroke and spinal cord ischemia (SCI) / paraplegia even when preventative actions (e.g., CSF drainage) are taken (43, 44). A recent multicentre study found an incidence of SCI post-TEVAR is ± 3.6% with ± 60% being permanent (45). In addition to CSF drainage (46), other potentially more effective strategies to reduce paraplegia risk include permissive hypertension and left subclavian revascularization (47). Further trials using these strategies to characterise TEVAR outcomes are warranted. Accordingly, a list of significant SCI-predicting factors (45) is shown inTable 1 .
The aetiology and management of TEVAR-related stroke is still not fully understood and further evidence can add value to the management approach. The MOTHER registry reports a higher incidence of TEVAR-related strokes in procedures where endovascular stent extends to cover the left subclavian artery (LSA), which usually manifests as posterior territory strokes and may cause left upper limb ischemia (48, 49). However, other aetiologies may be present due to the increased embolic load during the procedure which usually leads to middle cerebral artery territory strokes (50). Nonetheless, a recent observational study showed non-significant association between LSA revascularization and SCI (p = 0.58) or stroke (p = 0.37) incidence in patients undergoing TEVAR (51).
Other less commonly reported post-procedural complications include acute myocardial infarction, left upper limb ischemia, acute kidney injury, malperfusion, access-related pseudoaneurysm, or groin hematoma (38, 51). Aorta-specific TEVAR-related complications including retrograde type A aortic dissection (RTAD) and stent graft-induced new entry (SINE) are serious TEVAR-related complications. RTAD has an incidence of 2.5% and a mortality rate of up to 37.1%. (52). The incidence of RTAD is higher in patients undergoing acute procedures, whereas SINE occurs with higher incidence in chronic procedures. Incidence of these TEVAR-related complications and associated mortality can be reduced with using more appropriately sized stents and better developed aortic facilities (53, 54). Other aorta specific post-TEVAR complications include rupture, endoleaks, or stent failure, which are usually managed by reinterventions (55). Therefore, pre-procedural risk identification, interventional expertise, choice of appropriate stents, and the availability of well-developed aortic centres are necessary factors when offering early TEVAR for patients with unTBAD to achieve optimal outcomes.
Table 1 . Predictor of increased risk for spinal cord ischemia for TEVAR procedures reported by Mousa et. al (45).