Figure 4. Possible TBAD treatment selection algorithm.
Similarly reported by Tadros et. al (60). † Based on data summarised inTable 2 ; ‡ Based on data summarised in Table 3 .
Future directions
Next-generation biomarkers
Specific biomarkers for tissue inflammation, matrix degeneration, and
fibrinolysis are increasingly encroaching into the clinical realm to
better inform current predictors of unTBAD deterioration. There seems to
be growing evidence for a role for these novel serologic markers in
predicting the development of thoracic aortic aneurysm – many of these
are elusive based on small sample studies although CRP and TGF-β appear
to be of value (62). More recently, immunological metrics - such as
neutrophil-lymphocyte ratio (NLR) (63), monocyte to high-density
lipoprotein ratio (64, 65), and long ncRNAs (e.g. LUCAT1) (66) - have
all been suggested and further study in these areas is warranted.
Imaging advances
There are known limitations to measuring the diameters of true and false
lumens as a means of characterising aortic remodelling and predicting
aortic enlargement. The index CT scans could be volumetrically analysed
and the ratio of true lumen volume (TLV) to false lumen volume (FLV)
used to predict eventual aortic intervention (67). TLV/FLV <
0.8 (OR = 12.2; 95% CI 5-26; p < 0.001) is reportedly highly
predictive of aortic intervention whereas > 1.6 is highly
predictive of freedom from aortic intervention (67). Incorporating
personalized hemodynamic parameters in patient risk stratification could
also offer prognostic value. 4D-MRI could detect flow patterns in both
lumens and the entry tear, and recent clinical guidelines suggest that
these non-invasive methods can be used to deliver additional
quantitative information about the flow in the entry tear, and on
whether or not arterial vessels are involved (56, 68, 69). 4D-MRI
imaging has demonstrated that flow velocity, configuration (e.g.,
helical), and stroke volume are related to the rate of aortic expansion
(70, 71). Since it is challenging to accurately standardize these
parameters between patients based on differential aortic morphologies,
patient-specific approaches must be used to utilize 4D-MRI for both
predicting aortic expansion and as a tool for selecting patients who may
require additional procedures based on their clinical conditions (e.g.
organ malperfusion) (72, 73). Other innovations such as multidetector
CT, high-resolution ultrasound including color-coded Doppler, and
contrast-enhanced B-mode imaging have also been reported that may be
used to enhance aortic care (74).
Conclusions
TEVAR has enriched the surgical armamentarium to treat acute and
subacute TBAD and has reached maturation as a baseline strategy in many
patients. A specific subset of acute unTBAD patients at greater risk for
developing aortic complications should be strongly considered for timely
prophylactic TEVAR intervention. There are a variety of demographic,
clinical, laboratory and radiographic/morphological risk factors to
consider when selecting these patients. To guide selection, the
principles of the treatment scheme presented in this review could be
used. The scheme could be refined in future as the reporting of risk
quantification ratios across the literature becomes more consistent, and
advances in biochemistry and imaging techniques progressively enter the
clinical arena. Selection of high-risk patients should also be further
informed with randomized controlled trials and multicentre registry
analyses.