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Feng Yuan: Preprocedural CT Evaluation of Transcatheter Aortic Valve Replacement can Improve Implantation Success Rate and Reduce Major Complications

Date:2016-11-18 14:32

Feng Yuan, Deputy Director of the Physician, Professor, Master of Medicine, West China Hospital of Sichuan University. 
Head of the center for minimally invasive diagnosis and treatment of structural cardiovascular and pulmonary diseases, Division of Vascular Surgery, West China Hospital, Sichuan University. Training Mentor of National Health and Family Planning Commission of the PRC’s Cardiovascular Disease Interventional therapy (CHD intervention); Standing Committee Member of the Cardiovascular Committee of the Association of Rehabilitation Medicine of Sichuan Province; Committee Member of the Asia-Pacific Heart Alliance Structural Heart Disease Branch; Former Committee Member of National Medical Examination Center Cardiovascular Disease Specialist Physicians Examination Committee and Former Interviewer of Cardiovascular Disease Specialist Physicians Licensing Examination; and Former Deputy Director of Cardiovascular Disease Committee, Sichuan Medical Association. Specializing in the diagnosis and interventional treatment of simple and complicated CHD, committed to pediatric complex congenital heart disease “hybrid” surgery, good at transcatheter heart valve implantation interventional therapy (aortic valve implantation and pulmonary valve implantation), having completed thousands of cases of interventional surgery for congenital heart diseases, structural and valve diseases with high success rate and few complications. Having published more than 20 SCI papers in the field of congenital and structural heart diseases. 
Transcatheter aortic valve implantation (TAVI) is one of the most advanced techniques for the treatment of aortic stenosis today, which has caught more and more attention and been put in wide application with less risk and similar effect compared to AVR. TAVI features high requirements of the coordination of each specialized department, from the patient screening to preoperative appraisal and the operation, each procedure playing the vital role in the operation’s success and good effect. Preoperative CT evaluation of TAVI is an essential procedure to improve the success rate of implantation and reduce the incidence rate of major complications. In this respect, Prof. Feng Yuan of West China Hospital shares his experience with us on improving the success rate and reducing major complications through preoperative CT evaluation of TAVI.
Objective establishment: to judge anatomical characteristics, and to make a plan for complication prevention 
Overall, pre-procedural CT evaluation of TAVR should achieve two major objectives, namely, the interpretation of anatomical characteristics and the planning for complications prevention. The main contents of judging anatomical characteristics include the possibility to implement TAVI, the selection of appropriate valve system and model, the selection of the preferred and alternative implant path and position, and supply of reference for estimating the difficulty of TAVI implementation; the complication prevention plan can predict the complication and the risk before TAVI and provide anatomical reference for dealing with the complications.
To determine whether anatomical features are suitable for TAVI, it needs: 1. Extensive experience in CT imaging and Surgery; 2. Familiarity with the advantages and disadvantages of the applicable ranges of various valve systems. In choosing valve systems, we should pay attention to different requirements of the aortic root’s anatomic system from self-expanding system, balloon-expanding system and other progressively expanding systems (such as Lotus, Driectflow) and different path requirements from the delivery system. While choosing the valve model, we should carefully consider the actual conditions like each patient's anatomical characteristics combined with clinical experience, rather than just refer to the recommended list provided by valve manufacturers. Meanwhile the surgeon should clearly recognize that the size of the valve model is closely related to the implantation effect. Only with rich experience and sufficient knowledge can we choose better valve system and obtain better effect.
Anatomical Features Analysis: Interpretation of key points of aortic valve root
In the interpretation of anatomical features, attention should be focused on: 1. Fine dissection of aortic root; 2. Ascending aorta and left ventricle; 3. Path(select the most appropriate path). Regarding the main aortic valve root, attentions should be paid to the following points, namely, the valve annulus , the leaflet, the coronary artery, the left ventricular outflow tract, sinus of aortic aneurysm, sinus tube joint,  department, the near ascending aorta and the calcification. TAVI operation correlation judgments should be made about each point, and the preferred/ alternative choice should be made with comprehensive analysis of the results.  
The valve annulus analysis should mainly check the basic condition of the annulus, which is perimeter, area, calcification, inner and outer diameter, and so on. After understanding the basic situations, we should further analyze the feasibility for TAVI at the valve annulus point, the most suitable system and model, the risk of the valve annulus rupture and the risk of paravalvular leakage.
The main artery leaflet is thin, with the total weight of normal leaflet less than 1 gram, and a 1000 mm² area. The area of the valve is 4 cm² when it is fully open. The tricuspid aortic valve is the optimal structure for TAVI treatment and is most common. The majority of the congenital malformations are single leaflet, bicuspid aortic valve or Quadricuspid aortic valve, among which bicuspid aortic valve accounts for a higher proportion in China. In 185 cases of TAVI patients in West China Hospital, the rate of bicuspid aortic valve was as high as 58%. This high proportion of bicuspid aortic valve in domestic patients is still destitute of final conclusion as to which cause takes the dominant role, and the possible explanations include race, patients’ age and treatment timing. In foreign countries, bicuspid aortic valve was classified as relative contraindication of TAVI, but in China, it is unavoidable to apply TAVI technique in patients with bicuspid aortic valve. It is shown from the pathological analysis of leaflet that the structures of the tricuspid aortic valve and bicuspid aortic valve are very different, leading to the obvious differences of preferred valve system and valve size. The main purpose of leaflet analysis is to estimate the effect of implantation, predict the stability of artificial valve, and reduce severe paravalvular leakage.
In terms of the coronary arteries, CT can observe and analyze the anatomic location of the coronary artery and its adjacent structure. The full use of CT evaluation can predict whether it will obstruct coronary artery inTAVI, and estimate the probability of coronary occlusion, so as to choose reasonable prevention and avoidance plan. When examining left ventricle and outflow tract, we mainly focus on the size of left ventricle, the degree of myocardial hypertrophy, thrombus, ventricular aneurysm, and diverticulum and so on. At the same time, special attention should be paid to whether the outflow tract is narrow or is it "suicide left ventricle". The evaluation of left ventricular and outflow tract is helpful to predict the risk of ventricular perforation and to guide the selection of steel wire. In addition, the CT evaluation of aortic arch (whether there’s dilation, dissection, calcification, thrombus or artificial blood vessel), angle of the valve annulus and ascending aorta, working posture and merger should also be performed. These factors are directly related to the feasibility of TAVI and the avoidance of the risk of complication.
To consider the problem from the angle of finding the most suitable path, we should pay attention to the thoracic aorta and peripheral blood vessels, including basic vessel profiles (diameter, etc.), whether there are distortions, stenosis, aneurysm, calcification, thrombosis and femoral artery bifurcation and so on. Through CT evaluation of thoracic and abdominal aorta and peripheral blood vessels, we can determine the blood vessel path and provide adequate anatomical basis for the treatment of vascular complications. 
Problem solving: prevention of common complications
The rupture of the valve annulus usually occurs in the balloon implantation, balloon pre-expanding and the posterior expanding. The rupture is closely related to the calcification of the annulus and the surrounding structure and the over large size of the selected balloon. Once the rupture of the valve annulus occurs, the mortality rate is very high. Therefore, the risk of valve annulus rupture should be actively prevented and avoided: 1. The anatomical features of the valve annulus should be evaluated carefully; 2. Appropriate balloon should be chosen without too large expansion pressure; 3. To evaluate the patients with high-risk of posterior annulus rupture(such as the mass calcification of the valve annulus, the calcification in the left ventricular outflow tract, and so on), it is necessary to avoid choosing the balloon-expanding valve system as far as possible. 4. Reduce the unnecessary (or overly adequate) balloon pre-expansion and posterior expansion.
Paravalvular leakage is related to the type, the calcification degree and location of valve, the depth of prosthetic valve implantation, the type and size of prosthetic valves, and etc. The accumulation of operation experience and the improvement of new valve system can obviously improve paravalvular leakage, but it cannot be completely avoided at present. It is necessary to analyze the anatomic characteristics, predict the possibility and location of paravalvular leakage; for those patients with high risk of paravalvular leakage, valve system can be recycled and relocated to adjust the depth of the implantation; the valve system with skirt can help to reduce paravalvular leakage; the selection of larger valves may reduce paravalvular leakage; In addition, the selection of larger valves may reduce paravalvular leakage, but may also increase other risks. After implantation of valve, some types of valve can adopt interventional occlusion, but the operation is very difficult, our center has such a successful case, and the effect is satisfactory.
To predict the risk of coronary occlusion, it is necessary to evaluate the height of coronary arteries, the length of the leaflets, the calcification of the leaflets, the diameter of sinus of aortic aneurysm and other related structures. The following conditions are likely to cause coronary occlusion: 1. female patients; 2. Coronary artery height is less than 12mm; 3. The sinus of aortic aneurysm is small; 4. The ball-expanding valve is higher than self-expanding valve 5. The implanted valve is too large; 6. The position of the implanted valve is too high. For clinical patients with high risk of coronary artery occlusion, timely prevention precautions should be adopted, for example: select the valve system with relatively low risk of coronary occlusion; select a system that can be recycled or relocated; select small types of valves as much as possible; balloon pre-expansion should be assisted with imaging evaluation; preset protective steel wire and/or balloon, stent; imaging and ultrasound assessment after valve implantation; give up TAVI for cases that cannot avoid coronary artery occlusion.
Attention should be paid to the complication of ascending aorta, including aortic dissection, hematoma, rupture and embolus shedding. If the ascending aorta diameter is larger than 50mm, the risk is increased and surgical treatment is more suitable for the case. The difficulty of horizontal ascending aorta to pass its valve in the conveying system is increased and paravalvular leakage is likely to happen.  Especially difficulty would increase in the second valve implantation (intraoperative valve-in-valve) increased, and sometimes need other equipment assistance (such as net bar). Using the net bar to lift the valve stent to change the depth of the implanted valve is more dangerous and aortic dissection is prone to occur. So this approach is limited to the cautious use by experienced physicians. In addition, if the prosthetic valve is displaced into the ascending aorta, coronary occlusion and dissection are likely to happen.
The American Society of Cardiovascular Computed Tomography (SCCT) issued a TAVI/TAVR CT policy statement, recommending that preoperative CT scan be taken before TAVI/TAVR, and emphasizing the importance of the imaging model for patients receiving catheter-aortic valve. SCCT said that all patients considering TAVI surgery should get CT imaging examination in the evaluation process, except for patients with CT contraindications. At the same time, CT images should be interpreted by the members of the TAVI operation group or examined by the surgeons before the operation to ensure good results. 
This article is reproduced from Clinic

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