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ANALYSIS OF PARTICLES THOROUGH THE AORTIC ARCH DURING TRANSCATHETER AORTIC VALVE REPLACEMENT. A Thesis. Presented to

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ANALYSIS OF PARTICLES THOROUGH THE AORTIC ARCH DURING TRANSCATHETER AORTIC VALVE REPLACEMENT A Thesis Presented to the Faculty of California Polytechnic State University, San Luis Obispo In Partial Fulfillment
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ANALYSIS OF PARTICLES THOROUGH THE AORTIC ARCH DURING TRANSCATHETER AORTIC VALVE REPLACEMENT A Thesis Presented to the Faculty of California Polytechnic State University, San Luis Obispo In Partial Fulfillment of the Requirements for the Degree Master of Science in Biomedical Engineering By, Andrew Joseph Janicki June 2015 2015 Andrew Joseph Janicki ALL RIGHTS RESERVED ii COMMITTEE MEMBERSHIP TITLE: Analysis of Particles Thorough the Aortic Arch During Transcatheter Aortic Valve Replacement AUTHOR: Andrew Joseph Janicki DATE SUBMITTED: June 2015 COMMITTEE CHAIR: Associate Professor David Clague, Ph.D., Department of Biomedical & General Engineering COMMITTEE MEMBER: Cameron Purcell, MS., R&D Engineer II at Claret Medical COMMITTEE MEMBER: Professor Dan Walsh, Ph.D., Department of Biomedical & General Engineering iii ABSTRACT Analysis of Particles Thorough the Aortic Arch During Transcatheter Aortic Valve Replacement Andrew Joseph Janicki Ischemia caused by particles becoming dislodged during transcatheter aortic valve replacement (TAVR) is a possible complication of TAVR. The particles that become dislodged can travel out of the aortic valve, into the aortic arch, and then into either the brachiocephalic artery, the left common carotid artery, the left subclavian artery or continue into the descending aorta. If the particles continue into the descending aorta it poses no risk of causing ischemia however if it travels into the other arteries then it increases the possibility of the particle causing an ischemic event. The goal of this study is to determine what parameters cause the particle to enter one artery over another. The parameters analyzed are the particle diameter, the particle density, the blood pressure, and the diameter of the catheter used in the surgery. This was done by creating a finite element model in COMSOL Multiphysics to track the particles flowing through a scan of an actual aortic arch. It was determined that the particle diameter, particle density, and the blood pressure affect which artery the particles take to exit the aortic arch. However the diameter of the surgical catheter used in a transaortic approach is not statistically significant when determining which artery the particles will exit. The study shows that larger diameter particle would lead to a higher transmissions probability into the brachiocephalic artery, the left common carotid artery, and the left subclavian artery while a smaller diameter particle would have a higher transmission probability for the descending aorta. Averaging all particle diameters, densities and blood pressure found that ± 13.66% of the particles released will travel into the cerebral circulatory system. iv TABLE OF CONTENTS LIST OF TABLES... vii LIST OF FIGURES... viii 1 INTRODUCTION Thesis Overview Motivation Previous Studies BACKGROUND TAVR The Aortic Valve/Arch Blood Flow through the aortic arch Complications of TAVR Cerebral Ischemia METHODS The Model Geometry Windkessel Model The Studies Fluid Flow Particle Tracing Parameters Particle Diameter Number of Particles Density of the particles Blood Pressure Catheter Size Meshing Studies Performed Statistical Analysis RESULTS Fluid Flow Particle Tracing Multivariate ANOVA Outlet v Outlet Outlet Outlet Not Out Overall Summary of MANOVA DISCUSSION Statistical analysis CONCLUSION REFERENCES APPENDICES A: CONVERTING CT SCAN INTO COMSOL MULTIPHYSICS B: MATLAB CODE FOR WINDKESSEL MODEL C: OUTPUT OF MANOVA vi LIST OF TABLES Table 1: Different settings for the Windkessel model Table 2: Transmission probability of particles leaving each outlet with 3mm included and excluded Table 3: Outlet 1 interaction of blood pressure and particle diameter Table 4: Outlet 1 interaction of blood pressure and particle density Table 5: Outlet 2 interaction of blood pressure and particle diameter Table 6: Outlet 2 interaction of blood pressure and particle density Table 7: Outlet 3 interaction of particle diameter and particle density Table 8: Outlet 3 interaction of particle diameter and blood pressure Table 9: Outlet 4 interaction of particle diameter and particle density Table 10: Outlet 4 interaction of particle diameter and blood pressure Table 11: Outlet 4 interaction of blood pressure and particle density Table 12: Not Out interaction of particle diameter and blood pressure vii LIST OF FIGURES Figure 1: Different Surgical approaches to TAVR [13] Figure 2: Physiology of the heart and the aortic arch [16] Figure 3: Pressure wave through the Aorta [19] Figure 4: Common aortic arch branching patterns [25] Figure 5: Original file G1-07-HH arch_001.stl opened in MeshLab Figure 6: Simplified G1-070HH arch _001.stl opened in MeshLab Figure 7: COMSOL model of an aortic arch Figure 8: Electrical circuit of the four element Windkessel model [37] Figure 9: Arterial pressure for three Windkessel Models: a measured pressure (solid line, black dots), b 4 Element Model (dashed line, red dots), c 3WM (dot line, blue dots), d 2WM (dot-and-dash line, green dots [36] Figure 10: Pressure over one cycle 78/40 mmhg Figure 11: Pressure over one cycle 120/70 mmhg Figure 12: Pressure over one cycle 150/90 mmhg Figure 13: Inlet 1 in purple Figure 14: Fluid Outlets: Panel A shows brachiocephalic (1), left common carotid (2), and left subclavian arteries (3). Panel B shows the descending aorta (4) Figure 15: Outlet velocities (m/s) of different blood pressures Figure 16: Velocity magnitude (m/s) with a catheter diameter of mm and a blood pressure 150/90 mmhg at different time intervals. Panel A at 0 seconds, panel B at 2.6 seconds, panel C at 5.2 seconds, panel D at 7.8 seconds, panel E at 10.4 seconds, and panel F at 13 seconds Figure 17: Particle tracing catheter diameter 7.33 mm, blood pressure 150/90 mmhg, particle diameter 0.25 mm, particle density 0.8 g/cm 3, Panel A at 0.5 seconds, panel B at 3.5 seconds, panel C at 6.5 seconds, panel D at 9.5 seconds and panel E at 13 seconds Figure 18: Particle tracing catheter diameter 7.33 mm, blood pressure 150/90 mmhg, particle diameter 3 mm, and particle density 0.8 g/cm 3. Panel A at 0.5 seconds, panel B at 3.5 seconds, panel C at 6.5 seconds, panel D at 9.5 seconds and panel E at 13 seconds Figure 19: LS Means Plot for outlet 1 interaction of blood pressure and particle diameter Figure 20: LS Means Plot for outlet 1 interaction of blood pressure and particle density Figure 21: LS Means Plot for outlet 2 interaction of blood pressure and particle diameter Figure 22: LS Means Plot for outlet 2 interaction of blood pressure and particle density Figure 23: LS Means Plot for outlet 3 interaction of particle diameter and particle density Figure 24: LS Means Plot for outlet 3 interaction of particle diameter and blood pressure Figure 25: LS Means Plot for outlet 4 interaction of particle diameter and particle density Figure 26: LS Means Plot for outlet 4 interaction of particle diameter and blood pressure viii Figure 27: LS Means Plot for outlet 4 interaction of blood pressure and particle density Figure 28: LS Means Plot for not out interaction of particle diameter and blood pressure Figure 29: Quadratic Edge Collapse Decimation dialogue box Figure 30: Mesh opened in SOLIDWORKS Figure 31: Cap Faces Bounding Edges ix 1 INTRODUCTION 1.1 Thesis Overview Currently there is no reliable way to predict if a person will have an ischemic event after Transcatheter Aortic Valve Replacement (TAVR). Many studies have been done on what causes ischemia and how TAVR patients have a high risk of ischemia, but none have analyzed more than the effects of particle size on ischemia. This thesis expands upon studies performed by Ian A. Carr and Shawn Shadden, in which they analyzed the effect of particle size and the path of travel in the aortic arch using computational fluid dynamic models [1] [2]. During TAVR, tissue fragments are released and can cause ischemia. These tissue fragments or particles come from various tissues and can vary in size and density. This leads to one of the questions that this thesis is trying to answer: do the physical properties of the particle affect the artery out of which the particles travel. The second question is related to the patient and how the surgery is performed. These questions are the backbone of this thesis and inspired the following two hypotheses. 1. The first hypothesis is that the size and/or the density of the particles affect which branch the particles will take to exit the aortic arch. 1 2. The second hypothesis is that the blood pressure of the patient and/or the catheter size used during the surgery impacts which branch the particles will take to exit the aortic arch. Overall the goal of this thesis is to analyze the effect of different parameters: particle size, particle density, blood pressure, and catheter size on the particles and to see if they exit the aortic arch via the Brachiocephalic artery, the left common carotid artery, the left subclavian artery or continue into the descending aorta. This was done using a finite element model to simulate blood flow and particle tracking through an aortic arch. Additionally, this thesis will lay the foundation for future TAVR models for Cal Poly Biofluidics Laboratory. Background research of previous TAVR and particle tracking studies, physiology and morphology of the aortic arch, properties of blood, flow rates, boundary conditions, and properties of particles was performed. To test the effect of these parameters, COMSOL Multiphysics was used to perform finite element analysis (FEA) using the creeping flow module to simulate blood flow through the aortic arch and the particle tracing module to track the particles through the arch. Nine simulations were run with the fluid and particles flowing through the simulations for 13 seconds. The effect of the parameters on the transmission probabilities of the particles was analyzed using multivariate analysis of variance (MANOVA) in JMP Pro 11 statistical software. 2 1.2 Motivation According to the American Heart Association more than five million Americans are diagnosed each year with heart valve disease. Heart valve disease can occur in any of the heart valves but is most common in the aortic valves accounting for 43% of all patients having heart disease [3]. Disease of the aortic valve is called aortic stenosis and in the United States around 1.5 million people suffer from aortic stenosis [4]. If the aortic valve is not replaced in people who suffer aortic stenosis 44% will not survive more than an average of 2 years after the onset of symptoms [5]. The main reason a valve would not be replaced is a high operative risk [6]. In a study of patients who were not considered suitable candidates for aortic value replacement TAVR was performed and the patient had a 20% lower rate of death versus standard therapy. However the study found that after TAVR there was a higher incidence of major stroke [7]. About 87% of all strokes are ischemic strokes where blood flow to the brain is blocked [8]. Embolism is the most common mechanism for stroke accounting for 40% of cases with the majority of embolisms having a cardiac or arterial origin [9]. Any way to reduce the number of embolisms released during TAVR could potentially save many lives. 1.3 Previous Studies Previous studies have been performed on the effects of TAVR and particle tracking in the aortic arch. One such study by Ian A. Carr analyzed 3 the effect of the particle size and the aortic anatomy on the cardiogenic embolic transport. In this study, Mr. Carr analyzed 10 computed tomography (CT) angiography of patients aorta and branch. The scans were converted into a computational mesh and finite element analysis software was run to simulate fluid flow and particle tracking. The study tested particle diameter ranging from 0 to 4 mm, in increments of 250 µm. The results showed peak particle transport to the branch arteries occurred for ± 0.25 mm diameter particles, and the total percentage of released embolic particles that entered the branch arteries was 60 ± 13% [1]. Another study took a different approach and examined in vivo data of embolic debris during TAVR. This study, performed by Nicolas M. Van Mieghem, MD, looked at 40 patients who underwent TAVR with a dual filter based embolic protection device. In 75% of the patients they captured material ranging in sizes from 0.15 mm to 4.0 mm that was traveling into the branch arteries. The debris consisted of fibrin, or amorphous calcium and connective tissue derived most likely from either the native aortic valve leaflets or aortic wall [10]. 4 2 BACKGROUND 2.1 TAVR Transcatheter Aortic Valve Replacement (TAVR also known as Transcatheter Aortic Valve Implantation or TAVI) is a therapy that treats aortic stenosis. Aortic stenosis is the narrowing of the aortic valve which blocks blood flow from your heart into the aortic arch. During TAVR a new valve is wedged into the damaged valve s place. In this surgery the original aortic valve is not removed instead the valve leaflets are pushed out of the way and the new valve is placed. The new valve is delivered using a catheter allowing TAVR to be a minimally invasive procedure. The catheter is most likely inserted between the sixth or the fifth intercostal space using 2 to 4 inch incisions without opening the entire chest [11] [12]. There are three different approaches to inserting the catheter as shown in Figure 1. First is the transfemoral approach where the valve is delivered via a catheter through the femoral artery shown in panel A. The second approach shown in panel B, is the transapical approach where the valve is delivered via a catheter through the apex of the heart. Finally there is the transaortic approach where the valve is delivered via a catheter through the ascending aorta, panel C [13]. 5 A B C Transfemoral Approach Transapical Approach Transaortic Approach Figure 1: Different Surgical approaches to TAVR [13]. In the past to replace the aortic valve, surgeons had to perform open heart surgery where they would make a 6- to 8-inch incision down the center of the sternum [12]. This surgery, surgical aortic valve replacement, is significantly more invasive for the patients and leaves a large scar. Obviously it is much preferred to us the noninvasive TAVR approach. However there are certain patients that are advised against TAVR due to disease and patient related factors. In addition one of the disadvantages with TAVR is it can cause more frequent neurological complications [14]. 2.2 The Aortic Valve/Arch The aortic valve is located between the left ventricle and the largest artery in the body, the aorta (Figure 2). The function of the aortic valve is to maintain one-way blood flow out of the heart and into the aortic arch. Blood leaves the heart through the aortic valve and passes into the ascending aorta, from there it can either flow up into three smaller arteries or down into the 6 descending aorta. If the blood travels into the descending aorta then it will flow to the lower half of the body. If the blood travels through the ascending aorta it can exit the aortic arch through three outlets: Brachiocephalic artery, the left common carotid artery, the left subclavian artery shown in Figure 2. The Brachiocephalic trunk bifurcates into Right Common Carotid and Right Subclavian. The Right Subclavian flows into the arm and the Right Common Carotid flows in the cerebral circulatory system. The Left Common Carotid artery leads directly into the cerebral circulatory system (CCS). The Left Subclavian Artery bifurcates into the Vertebral Artery and the Left Subclavian Artery. The Vertebral Artery leads into the CCS and the Left Subclavian does not [15]. Figure 2: Physiology of the heart and the aortic arch [16]. 2.3 Blood Flow through the aortic arch The flow of fluid through the aortic arch is pressure driven flow based on the contracting of the cardiac muscles. The blood pressure in the aortic 7 arch is determined by three major factors: the total peripheral resistance, the blood viscosity and the cardiac output [17]. A typical persons peripheral resistance is dictated by the geometries of their circulatory system and does not change over short periods of time and, thus, can be considered constant during a surgery. The viscosity of blood can also be considered constant during a surgery. The only factor that influences blood pressure during a surgery is the cardiac output. Cardiac output is how much blood is pumped out of the heart each minute. Cardiac output is determined by two factors: heart rate and stroke volume. The heart rate can increase or decrease based on the amount of activity a person is doing or stress level. The stroke volume of an individual is fairly constant but can fluctuate during exercise. Typically the blood pressure is measured using two numbers, systolic pressure and diastolic pressure. A person with average blood pressure, for example, should have a systolic pressure of around 120 mmhg and a diastolic pressure of around 80mmHg, or 120 over 80 mmhg (120/80 mmhg). Systolic pressure measures the pressure in the arteries when the heart is fully contracted. Diastolic pressure is the pressure between heart beats when the cardiac muscles are relaxed [18]. However these two numbers don t tell the whole story when it comes to blood pressure. In reality the typical aortic pressure over one cycle is not constant and changes over time as shown in Figure 3. 8 Figure 3: Pressure wave through the Aorta [19]. The pressure wave as shown in Figure 3 changes due to a large variety of factors. The factors that change the pressure wave are heart rate, age, high or low blood pressure, and medications that the patient is taking. As the heart rate increases the pressure wave becomes compact and has a shorter cycle time. Increased age can result in higher systolic and diastolic blood pressures [20]. Depending on what medications a patient is on dictates how the pressure wave will change. For example if the patient is on β-blocker the heart will beat more slowly leading to a longer cycle time. In addition the heart may not be contracting as forcefully leading to lower blood pressure. All of these factors affect the blood pressure and in turn affect the blood flow through the aortic arch. Another factor that affects the fluid flow through the aortic arch is the geometry of the arch. Like a snowflake each person s aortic arch is different. The changes in the aortic arch s size are based on the age and sex of the person, the amount the person exercises, and the workload of the heart [21]. 9 Both the length and the diameter of the aortic arch change with age [22]. The diameter of the arch is different between the sexes but when averaging both men and women the mean diameter for the ascending arch is 33.2 ± 4.1 mm and 24.6 ± 3.0 mm for the descending aorta [23]. An increase in exercise and the workload of the heart can lead to a larger aortic diameter. In addition to the size variability, the normal anatomy of the aortic arch is subject to considerable variation [24]. Aortic Arch morphologies are differentiated by looking at the relationship between the brachiocephalic artery and the aortic arch. Figure 4 shows the three common aortic morphologies. The most common geometry is the classic picture shown in panel A of Figure 4 which has separate origins for the brachiocephalic (innominate in Figure 4), left common carotid, and left subclavian arteries. Panel B depicts the second most common pattern of aortic arch branching where the left common carotid artery has the same origin as brachiocephalic artery. Panel C shows the common carotid has its origin on the brachiocephalic artery [25]. The morphologies in panels B and C are 10 commonly referred to as bovine aortic arches; however this anatomy is not generally found in cattle so the name is a misnomer [26]. Figure 4: Common aortic arch branching patterns [25]. 2.4 Complications of TAVR Research
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