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.