The Establishment Of Stanford Type B Aortic Dissection Model In Canine And The Application Of IVUS For Model Effect Evaluation

Objective:This study is aimed to establish a model of Stanford type-B aortic dissection in canine,and to evaluate the feasibility of the modified method and the accuracy of intravascular ultrasound(IVUS)as an examination method for aortic dissection.Methods:12 local healthy mongrels of Tianjin(age: 24 to 36 months,weight: 20 to 25 kg)were used in this study.After tracheal intubation under general anesthesia,an incision was made on the left chest between the fourth and fifth rib to perform thoracotomy,and then five centimeters of thoracic descending aorta distal of the third intercostal artery was separated from the surrounding soft tissues.The artery block band was placed at superior border of the third intercostal artery.Then two thirds of circumference of the aorta was clamped partially and was cut alone the long axis.The aortic wall was separated into two layers,which were inner layer(including the intima and two thirds of media)and outer layer((including one third of media and adventitia),and then one centimeter of the proximal inner layer was excised.Flushing the aorta with heparin,then the inner layer was sutured as much as possible with 5-0Prolene line and the out layer continuously with a 4-0 Prolene line.Loosening the clamp and stanching validly,0.05 mg/kg of Intravenous epinephrine was used,then the chest was closed after one-hour observation.IVUS was used to examine the aortic dissection on the operation day and 7 days,14 days,30 days after operation respectively.The experimental dogs were killed at the 30 th day after operation to obtain the descending aorta,then,the aortic dissection is observed directly.At the same time,the parts of aorta wall were paraffin sliced for HE staining in order to observe the pathological changes of the aorta wall Results:1.10 dogs survived healthily after operation,with a fine state of activity,mentality and appetite.The incision healed well without complications such as infection or rupture;one died during the operation and one died on the day of operation and aortic dissection was found in neither of them.2.Aortic dissection was formed in eight of ten living dogs on the day of surgery,and one of which with distal tears located 3cm proximal from the ostial of celiac trunk,but then healed after 14 days.Finally,seven cases of aortic dissection met the standard of our model with total distal tears of twelve.One case with one tear involved the site 2.5cm proximal from the ostial of celiac trunk.In two cases the aortic dissection with single tear involved the site 1cm proximal from the ostial of celiac trunk,three cases of aortic dissection with two tears and one case of aortic dissection with three tears involved celiac artery and superior mesenteric artery.3.In the successful model group,on the operation day and 7 days,14 days,30 days after operation,the average length of the dissection measured with IVUS was(11.4±1.2)cm,(11.4±1.3)cm,(11.8±1.1)cm,(12.6±1.4)cm respectively.There were no statistically significant difference among groups(P>0.05).The average diameter of false lumen at the site 3.0cm distal from the first tear was(3.1±0.5)mm,(3.5±0.3)mm,(4.1±0.3)mm,(4.2±0.2)mm at every point-in time.The measured value of the operation day and 7days postoperation compared with the value of 14 dyas and30days postoperation,There were statistically significant difference(P<0.05).4.The length of the aortic dissection separated from bodies of successfully modeled dogs ranged from 11.3 to 15.5 cm with an average of(12.4±1.2)cm;the length of the aortic dissection measured by IVUS ranged from 10.0 to 16.2cm,with an average of(12.6±1.4)cm,There were no statistically significant difference between the two measuring methods(P>0.05).The number of tears counted in vitro was 12,which was the same as the number measured by IVUS.There were no statistically significant difference between the two measuring methods(P>0.05).5.The expression of pathologic sampling from the aortic dissection after hematoxylin-eosin staining was consistent with the pathologic change of aortic dissection.Conclusion:1.The model of Stanford type-B aortic dissection involving visceral arteries can be established in vivo by combining thoracotomy and intravenous medicine.2.The patency of false lumen is relatively high among aortic dissections with distal tears,and the result of a 30-day follow-up was satisfactory.3.The length of aortic dissections and locations as well as quantities of distal tears revealed by Intravascular ultrasound(IVUS)coincide with direct observation,and the diameter of false lumen can be observed dynamically.So IVUS can be an effective method to examine the aortic dissection model.4.The principle of the establishment of our model is similar to that of human pathology in the formation of aortic dissection,so it can be used to explore the next step of endovascular treatment and provide a model for the treatment of aortic dissection.