Morphological Risk Factors For Type A Aortic Dissection

Background:Type A aortic dissection(TAAD)is an acute aortic adverse event(AAE)with rapid onset and a high fatality rate.One-fifth of patients die without emergency treatment,and the mortality rate increases by 1 – 2% every hour.Surgery should be performed immediately after diagnosis,but emergency surgery mortality is still high,prevention is particularly important.Ascending aortic aneurysm,a focal dilation of the ascending aorta,is the main cause of TAAD.Replacing the diseased blood vessel before it ruptures is the main preventive measure,greatly reducing the incidence and mortality of TAAD.Currently,the diameter of the ascending aorta is the only indication for surgical evaluation,and the guideline recommends 5.5 cm as an indication for surgery in ascending aortic aneurysm.However,studies have found that up to50% of TAAD occur in vessels with diameters less than the surgical threshold.The latest study by a Yale team suggested lowering the diameter threshold to 5cm.Relying solely on aortic diameter to formulate surgical indications might not be perfect,and it is particularly important to look for other indicators.Objective:We measured some aortic morphological indicators by computed tomographic angiography(CTA)imaging and additional analysis,attempting to identify their relationship with TAAD.The main contents include:(1)We measured ascending aortic diameter,ascending aortic length(AAL),ascending bending index(ABI)and other aortic morphological indicators by computed tomographic angiography(CTA)imaging and additional analysis,attempting to identify other risk factors for TAAD.(2)identify aortic morphological risk factors for TAAD below the diameter risk threshold.Methods:(1)A total of 112 patients from the Affiliated Hospital of Qingdao University between January 2020 and December 2021 were eventually included,The exclusion criteria were as follows:(1)poor imaging quality and lack of preoperative CTA;(2)hematoma or type B aortic dissection;(3)iatrogenic,traumatic dissection,and previous iatrogenic procedures that could damage the ascending aorta,such as ascending aortic cannulation and bypass;(4)Marfan’s syndrome and Behcet’s disease;(5)age <18 years old or lack of basic data,such as height;(6)aortic malformation.The patients were divided into a non-dissection group and a TAAD group(Group 3).The non-dissection group was further divided into an aneurysm group(Group 2)and a normal diameter group(Group 1)according to aortic diameter.We used AW Server software,version 3.2(General Electric Company),to further process the CTA data,measured ascending aortic diameter,AAL,ABI and other aortic morphological indicators.The clinical data and imaging data were compared among the three groups。(2)A total of 200 patients from the Affiliated Hospital of Qingdao University between July 2017 and July 2022 were eventually included.There were 135 males and 65 females with an age range of 28– 88 years old and a mean age of57.02 ± 12.81 years old.The exclusion criteria were as follows:(1)poor imaging quality and lack of preoperative CTA;(2)penetrating aortic ulcer or hematoma;(3)iatrogenic,traumatic dissection,history of type B dissection;(4)Marfan’s syndrome and Behcet’s disease;(5)age <18 years old;and(6)aortic malformation.The patients were divided into two groups: Group 1(ascending aortic diameter < 5.0 cm,n=156)and Group 2(ascending aortic diameter ≥ 5.0cm,n=44).All patients records were reviewed,and relevant clinical data were collected.We measured the maximum and minimum diameters of the ascending aorta,the AAL,ABI.The differences between the two groups were compared.For data adjustment,12 patients underwent thoracic aortic CTA before dissection were eventually included.we corrected the measured values by analyzing the morphological changes of the ascending aorta after TAAD.Results:(1)First,in Group 1,the univariate analysis results showed that ascending aortic diameter was correlated with patient age(r2 = 0.35)and ascending aortic length(AAL)(r2 = 0.43).AAL was correlated with age(r2 = 0.12)and height(r2= 0.11).Further analysis of the aortic morphological indicators among the three groups found that the median aortic diameter was 36.20 mm in Group 1(Q1–Q3:33.40–37.70mm),42.5mm in Group 2(Q1–Q3: 41.52–44.17mm)and 48.6mm in Group 3(Q1 – Q3: 42.4 – 55.3mm).There was no significant difference between Groups 2 and 3(P > 0.05).Group 3 had the longest AAL(median:109.4mm,Q1 – Q3: 118.3 – 105.3mm),followed by Group 2(median: 91.0mm,Q1–Q3: 95.97–84.12mm)and Group 1(81.20 mm,Q1–Q3: 76.90–86.20mm),and there were statistically significant differences among the three groups(P<0.05).The Aortic Bending Index(ABI)was 14.95mm/cm in Group 3(Q1 – Q3:14.42 – 15.78 mm/cm),13.80 mm/cm in Group 2(Q1 – Q3: 13.42 –14.42mm/cm),and 13.29mm/cm in Group 1(Q1–Q3: 12.71–13.78mm/cm),and the difference was statistically significant in comparisons between any two groups(P < 0.05).Regression analysis showed that aortic diameter + AAL + ABI differentiated Group 2 and Group 3 with statistical significance(area under the curve(AUC)= 0.834),which was better than aortic diameter alone(AUC = 0.657;P < 0.05).(2)The mean ascending aortic diameter increased by 8.9 mm(+23%)(p<0.05),and the AAL and ABI increased by 4.6%(p<0.05)and 1.3%(p<0.05),respectively,due to dissection.After adjustment according to this model,78% of patients with TAAD had ascending aortic diameter<5.0 cm(Group 1);they also had shorter AAL(median: 106.3 mm;Q1-Q3: 99.9-114.8 mm)than patients with ascending aortic diameter ≥ 5.0 cm(Group 2)(median: 120 mm;Q1-Q3:111.2-126 mm)(p<0.05).Group 1 and 2 both had a large ABI [(median: 14.99mm/cm;Q1-Q3: 14.19-15.84 mm/cm)versus(median: 15.04 mm/cm;Q1-Q3:14.02-16.02 mm/cm),p=0.99].Combining ascending aortic diameter and AAL to indication for preventive surgery can include 41% of patients with TAAD.The ascending aortic diameter combined with AAL and ABI could increase this value to 85%.Conclusions(1)We introduced the new concept of ABI,which has certain clinical significance in distinguishing patients with aortic dissection and aneurysm.Perhaps the ascending aortic diameter combined with AAL and ABI could be helpful in predicting the occurrence of TAAD.(2)The ascending aortic diameter will increase after acute onset of TAAD,but the AAL and ABI are relatively immune.It is not perfect to rely solely on aortic diameter and diameter-related indicators to determine the surgical indications for prophylactic aortic replacement.Combining aortic diameter with ABI and AAL may be more effective to prevent TAAD.