3 Comment
Leg malperfusion after aortic dissection occurs in 10.3% of cases with
aortic dissection.3 There are two pathophysiological
mechanisms of malperfusion: static obstruction and dynamic
obstruction.4 Static obstruction can cause
malperfusion because the branch vessels dissociate, and stenosis or
occlusion occurs due to thrombus. This condition can be easily diagnosed
by CT. In contrast, dynamic obstruction causes malperfusion because the
false lumen expands, and the dissection flap covers the vessel origin.
The diagnosis of this complication is difficult because the dissection
flap usually remains unstable and moves easily. Previous reports have
found that postural change1 and exercise
echography2 are helpful for diagnosing leg
malperfusion due to dynamic obstruction. In our case, since postural
change did not cause any symptoms, and given that echography requires a
high level of skill, the Ex-ABPI test was performed. This examination
demonstrated that the patient’s right ABPI fell significantly after
exercise, which was helpful for detecting this complication. To our
knowledge, this is the first report of leg malperfusion caused by
dynamic obstruction after aortic dissection being diagnosed by the
Ex-ABPI test.
Of note, the Ex-ABPI test suggested an interesting finding of a negative
correlation between leg malperfusion and BP. In experimental models, the
entry size and physiological factors have a complex influence true lumen
collapse.5 However, what aggravates dynamic
obstruction in vivo remains unclear. In the present case, BP
elevation may have been a factor that exacerbated the dynamic
obstruction. From that perspective, leg malperfusion was also
exacerbated at BP elevation and restored at BP reduction in a previous
report.2 It is difficult to explain the exact
mechanism underlying this unique feature, but it may involve an increase
in the cardiac output because of exercise resulting in an increased
inflow into the false lumen, with the false lumen consequently expanding
and compressing the true lumen further; alternatively, the stenosis of
the true lumen may have been exacerbated by the contraction of the aorta
itself by exercise, which diminished the blood flow to his right leg and
exacerbated peripheral malperfusion. Even after TEVAR, the slight
decrease in the right ABPI by BP elevation after exercise can be
attributed to residual re-entry at the peripheral side.
An important finding from this case is that dynamic obstruction should
not be ruled out, even if the symptoms and examinations are not marked
at rest. Stress can be a key factor in the diagnosis of this
complication. However, the degree of stress in such cases remains
unclear, and symptoms can be caused either by postural change
alone,1 or by some degree of stress as observed in
both the previous case2 and ours. Exercise echography
may also be useful, but the Ex-ABPI test has more advantages, such as a
low cost, low invasiveness, high reproducibility, ease of testing, and
ease of interpreting test results. Lower limb ischemia caused by aortic
dissection is a predictive factor for death and visceral
ischemia.6 Therefore, we recommend an aggressive
evaluation of the symptoms and the performance of medical examinations
not only at rest but also under stress, with an increase in the BP
required to make an accurate diagnosis of leg malperfusion following
aortic dissection.