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Aortic dissection is a low-incidence, high-impact and potentially catastrophic condition if not treated adequately and in time. Acute aortic dissection is diagnosed within 2 weeks of onset of symptoms, which is the high-mortality period. Patients surviving 2 weeks are considered to have subacute disease, and chronic aortic dissection is diagnosed after 8 weeks. The anatomical classification is based on the involvement of ascending aorta (type A according to Stanford) or not (type B).1 Historical data for untreated type A aortic dissection show a mortality rate of 1%–2% per hour within the first 24 hours, resulting in a mortality rate of up to 50%–74% during the acute phase.2 Uncomplicated acute type B dissection is less frequently lethal, with survival rates for medically treated patients of 84% at 1 year. Within the risk factors, arterial hypertension is dominating. It affects arterial wall composition, causing intimal thickening, fibrosis, and calcification and extracellular fatty acid deposition. The extracellular matrix also undergoes accelerated degradation, apoptosis and elastolysis with hyalinisation of collagen. Other risk factors in the elderly are atherosclerosis, prior cardiac surgery and known aortic aneurysms. On the contrary, hereditary conditions of aortopathology (eg, Marfan syndrome and other genetic factors) are the main cause of dissection in younger patients. The pathophysiological denominator is a weakened aortic tunica media, which predisposes to dissection by splitting the cohesive layers of aortic wall. This weakening of the tunica media could be due to either a derangement or possibly a loss of structural elements in the media layer, including elastin, collagen, non-fibrous matrix and smooth muscle cells. The anatomical criterion based on aortic diameter, which is the only criterion in the latest guideline, is currently the best-evaluated predictor for aortic dissection and rupture with specific ‘hinge points’ (6 cm for the ascending aorta and 7 cm for the descending aorta).3 However, the majority of patients dissect at an aortic diameter less than these hinge points, which was shown in the International Registry of Aortic Dissection (IRAD) registry, in which nearly two-thirds of type A dissection patients had an aortic diameter of <5.5 cm.4 Similarly, Rylski et al reported that of the 343 patients who had undergone CT angiography <2 years before and within 12 hours after aortic dissection onset, 334 (97%) patients had an ascending aorta diameter of <5.5 cm, and 315 (92%) patients had a diameter of <5 cm before dissection,5 which underlines the need for more powerful aortic event predictor tools.
An elegantly work about diameter, volume and length of the aorta in predissection phase was presented by the Maastricht group in the current issue of Heart. They compared in a two-centre matched cohort 25 patients suffering from acute type A aortic dissection (ATAAD) and undergoing CT within 2 years before dissection with 258 healthy subjects and 75 patients with thoracic aortic aneurysm using a propensity score matching strategy.6 More strongly accentuated than in IRAD registry, 96% did not meet the guideline-defined threshold of 5.5 cm in diameter. They could confirm a larger length and volume without any differences in diameter of ascending aorta in patients with ATAAD in the predissection phase as compared with propensity-matched controls with superior diagnostic accuracy. Similarly, the aortic length was significantly larger in patients with pre-ATAAD when compared with controls.
The same Maastricht group identified in a previous publication an age-depending elongation of the aorta in healthy subjects and in patients with ATAAD. The length of the thoracic aorta increased by 59 and 66 mm in healthy men and women, respectively, between the ages of 20 and 80 years with a predominance on the ascending aorta (142%), the aortic arch (169%) and the proximal part of the descending aorta (247%).7 A comparison of the ATAAD and control groups with adjustment to predissection dimensions revealed that elongation of the ascending aorta and diameter proved both to be independent predictors of dissection. Thus, the ascending aorta was longer and more dilated in patients with ATAAD compared with healthy controls, whereas longitudinal elongation in both the aortic arch and the descending aorta was not predictive.8 The aorta and the large elastic arteries become tortuous, and there is an elongation with increasing age. Similarly, there is vascular stiffening as the reduction of elastin content, which is highest in the aortic arch and the descending aorta, impairs vessel compliance. Despite the fact that current guidelines try to define a user-friendly solution by restricting the prediction to diameter, this may not be sufficient. Dimensional anatomical parameters such as diameter, length and volume are certainly factors to be considered in the predictive analysis of aortic dissection. However, these parameters often represent the result of long-lasting influences of hypertension or connective tissue disorders, and a prediction tool based on anatomy only would leave many aspects unconsidered (figure 1). Even the Aortic Dissection Detection risk score, which summarises baseline conditions with pain features, exam features and D-dimer values, is only an approximation of the multifactorial genesis of the disease. In addition to the classical cardiovascular risk factors, haemodynamic and anatomical conditions, genetics, traumatic, iatrogenic and inflammatory factors certainly play a role and should be taken into consideration, perhaps in a complex algorithm employing artificial intelligence brought to the bedside. For the time being and without access to such a tool yet, the need for an individual patient-specific management plan designed by a multidisciplinary aortic team is unchallenged.
Contributors Both authors wrote and edited the manuscript.
Competing interests None declared.
Patient and public involvement Patients and/or the public were not involved in the design, conduct, reporting or dissemination plans of this research.
Patient consent for publication Not required.
Provenance and peer review Commissioned; externally peer reviewed.
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