Abstract
Comprehensive clinical and imaging-based surveillance represents a
fundamental aspect in the management of thoracic aortic aneurysms
(TAAs), affording the opportunity to identify intermediate-sized TAAs
before the onset of worrying symptoms or devastating acute aortic
dissection/rupture. Currently, size-based indices are favoured as the
major determinants driving patient selection for surgery, as supported
by aortic guidelines, although it is recognised that smaller
sub-threshold TAAs may still confer substantial risks. Prophylactic
aortic surgery can be offered within set timeframes at dedicated aortic
centres with excellent outcomes, to mitigate the threat of acute aortic
complications associated with repeatedly deferred intervention. In this
commentary, we discuss a recent article from the Journal of
Cardiac Surgery which highlights important socio-economic disparities
in TAA surveillance and follow-up.
Keywords: thoracic aortic aneurysm; surveillance; acute
dissection; socioeconomic
Surveillance is of paramount importance in the management of thoracic
aortic aneurysms (TAAs). Aortic guidelines clearly define the surgical
indications for operating on larger TAAs exceeding a diameter of 5.5
cm1-3, since the attributed dissection/rupture risks
are deemed to outweigh the predicted operative risks. However, the
optimal timing of aortic replacement in those with smaller TAAs not
fulfilling these surgical criteria is less well
established4. Such patients are traditionally enrolled
in an active surveillance programme, comprised of regular outpatient
clinic assessment and evaluation of aortic dimensions with serial
cross-sectional imaging with computed tomography (CT), or magnetic
resonance imaging (MRI) in younger individuals, combined with
echocardiographic follow-up. Annual and six-monthly CT/MRI is
recommended for aneurysms measuring 3.5-4.4 cm, and 4.4-5.4 cm,
respectively1,2.
In this issue of the Journal, Shang and colleagues draw our attention to
troubling variations in the surveillance and follow-up of patients with
lower socio-economic status5. In their retrospective
review, 465 patients diagnosed with an ascending TAA ≥4 cm in diameter
between 2013-2016 were stratified into quartiles according to the area
deprivation index as an indicator of socio-economic status, with the
primary outcome of interest being clinical follow-up with a
cardiovascular specialist and aortic surveillance imaging within two
years from an index scan. Interquartile differences in risk of death
preceding cardiovascular specialist follow-up were also determined
utilising competing risks analysis.
The authors discerned that patients in the top three quartiles,
corresponding to higher socio-economic status, were significantly more
likely to have been under pre-existing or new follow-up with a
cardiologist (p<0.001) or cardiac surgeon (p=0.002) for their
ascending TAA, than their counterparts in the lowest quartile
(p<0.001). Only 16% of patients in the lowest quartile
without pre-established follow-up were newly reviewed by a cardiologist
during the study period (p<0.001). Although there were no
significant interquartile differences between the top and lowest
quartile in ascending TAA size at the time of surgery, 92% of patients
in the lowest quartile displayed symptoms at the time of surgery,
compared to just 25% in the top quartile. Less disadvantaged quartiles
were more likely to undergo imaging within 2 years compared to the most
disadvantaged quartile (Q2 88% vs. Q4 71%, p<0.001), even
when adjusting for factors, including family history of TAA, active
malignancy, smoking history, congestive heart failure and COPD, which
should ordinarily prompt further imaging. Compared to the upper quartile
in which the competing event of death was reached in 11 patients in a
median time of 1.91 (IQR 1.49-3.08) years, in the lowest quartile, the
competing event of death was reached in 26 patients at a median time of
1.5 (IQR 0.95-2.29) years. On adjusted competed risks regression,
patients in the lowest quartile were significantly less likely to have
received follow-up prior to death (HR 0.46 [0.34-0.62],
p<0.001) compared to those in the upper quartile.
Two major themes warrant further discussion here. The first is that of
worrying disparities in the surveillance, follow-up and outcomes of
patients from lower socio-economic backgrounds with TAAs. In this first
reported study addressing surveillance outcomes in this population,
Shang and colleagues5 demonstrate that patients with
lower socio-economic status were less likely to be under the clinical
surveillance of a cardiovascular specialist, less likely to undergo
imaging at an appropriate time interval, more likely to have poorer
health at the time of surgery and more likely to have died before any
follow-up. The authors do not provide further explanation to account for
the significant discrepancies observed between those in the least- and
most-disadvantaged groups. In the US, access to healthcare is dependent
either on insurance coverage or self-funding by the patient. The
management of TAAs and their complications is resource-intensive, and
overall median cost for an index hospitalisation has been reported at
US$16,683 for TAAs and US$11,525 for type A dissections between
2003-20166. Those from more disadvantaged backgrounds
with more limited financial resources or lack of health insurance may
therefore be unable or unwilling to undergo referral to a cardiovascular
specialist owing to the significant monetary implications. This may then
preclude them from undergoing imaging evaluation, attending ongoing
clinic appointments, receiving prescription medications for symptom and
risk factor control, in addition to undergoing definitive surgical
therapy and potential future reinterventions. Though perhaps beyond the
scope of this paper, addressing these inequalities in healthcare access
and funding is certainly a complex, multi-faceted issue.
The second theme for discussion concerns moderate-size TAAs, their
associated complication risks and selection for surgery. Alongside
rupture, acute dissection remains the most devastating complication
affecting proximal TAAs. With an incidence of approximately 10 per
100,000 patient-years7, the vast majority of TAAs are
clinically silent and may only declare themselves at the time of a
potentially catastrophic adverse aortic event. Acute type A aortic
dissection bears a 20% pre-admission mortality risk, increasing to 30%
during the index hospital admission8, with emergent
open aortic repair representing the current gold standard
management9. A large proportion of these dissections
originate within significantly aneurysmal aortic segments, and insights
gleaned from natural history studies indicate that the risk of
dissection and rupture, as well as aneurysm growth rate, correlate
closely with the absolute aortic diameter10,11. A
landmark study published almost twenty years ago by Elefteriades’ group
in Yale depicted an annual dissection/rupture risk of around 2% in TAAs
measuring 4.0-4.9 cm, rising to almost 7% in those exceeding 6
cm12, a critical hinge-point beyond which diameter
dissection would be anticipated in over 30% of
patients12,13. An earlier study reported a
dissection/rupture rate as high as 45.2% with TAA diameter
>6 cm14. In the present study by Shang
and colleagues, there was no significant difference in TAA sizes at
surgery (p<0.94) with median diameter of 4.85-5.00 cm across
all quartiles5.
This valuable information provides the supporting evidence for the
size-based surgical intervention for TAAs, as currently proposed in
international guidelines1-3. Whilst surgical
replacement of TAAs is generally undertaken at a diameter of 4.5-5.5 cm
in both tri-leaflet and bicuspid aortic valve populations, it should be
considered at 4.0-4.5 cm in those with a genetic predisposition to
aortic disease, including those with inherited aortopathies such as
Marfan and Ehler-Danlos syndromes, whilst accounting for additional risk
factors, such as family history of dissection or rapid aneurysm
expansion at >3mm/year1,2. Nevertheless,
it is not uncommon for acute dissection to occur at aortic diameters
smaller than these thresholds, fuelling the notion that prophylactic
surgical intervention should be performed at more conservative aortic
diameters. Indeed, dissection/rupture risk has been described in an
important natural history study in 7.1% of patients at a diameter
<4 cm, 8.5% at 4.0-4.9 cm, 12.8% at 5.0-5.9 cm, with 22% of
patients overall experiencing dissection/rupture below the guideline
cut-off of 5.5 cm14. Notably, an analysis of the
International Registry of Acute Aortic Dissection (IRAD) database
revealed that 59% of acute type A dissection occurred in patients with
ascending aortic diameter <5.5 cm15. Our
group’s previous work examining the relationship between absolute aortic
diameter and cross-sectional aortic area indexed to patient height
demonstrated that significant proportions of TAAs possess smaller aortic
diameters below the size cut-offs mandating surgical replacement,
although their indexed aortic areas >10
cm2/m signified their increased propensity for acute
aortic dissection/rupture16,17.
Many will share the viewpoint that TAA diameter in isolation does not
accurately reflect dissection/rupture risk. However, until other
uncomplicated, reproducible and validated indicators of aortic risk
emerge, size-dependent criteria remain the major determinants that drive
aortic replacement surgery worldwide, as endorsed by contemporary
guidelines. Therefore, once even a relatively small TAA is identified,
close clinical and imaging surveillance is warranted to determine the
associated aortic risks and optimal timepoint for surgery. One should
not become complacent when judging these smaller aneurysms. Ascending
aortic dilatation to 4.0-4.4 cm represents an 89-fold increase in
dissection risk, and dilatation to ≥4.5 cm confers a 348-fold
risk18.
In conclusion, this interesting article by Shang and
colleagues5, serves to highlight the importance of
ensuring that patients with TAAs, whose smaller diameters do not satisfy
surgical criteria, participate in a stringent surveillance programme
with timely clinical, radiological and echocardiographic follow-up in
adherence to established guidelines. Of equal importance, specialists
involved in the management of aortic diseases should work to enhance
access to the aortic services they provide to all corners of society,
irrespective of their socio-economic status. There is the chance here to
afford a great deal of benefit for those who might otherwise not receive
it. Proactive surveillance would identify patients harbouring dangerous
TAAs at greatest risk of life-threatening complications, facilitate
their selection for effective surgical repair and theoretically save
untold numbers from serious acute aortic events. To strive for
excellence in care, means delivering excellent care for all.