| The left atrial appendage occluder is an implant medical device used to prevent cardioembolic stroke.Patients with atrial fibrillation are often accompanied with dysfunction in left atrial appendage during systole and diastole.This results in abnormal hemodynamic conditions in the auricle of left atrial,inducing cardiogenic embolism.The left atrial appendage occluder is designed to block the thrombus leakage in the left atrial appendage.During closure process,the occluder is implanted into the right atrium through the venous system.It is released in the left atrial appendage through septal puncture.After occlusion,the left atrium is isolated from the left atrial appendage,preventing drifting of embolism.The morphology of left atrial appendage is highly individualized.However,existing classification of occluders is relatively simple and the selection of which is highly dependent on the experience of clinicians.Device-related complications shift of occlude,incomplete occlusion or the use of two occluders for one block are often reported,due to improper selection of occluders for particular patients.Therefore,improvement on design of occluders that are able to consider individual conditions under the requirements of the existing medical devices regulations is needed.In this study,morphological analysis has been conducted and key characteristics parameters for left atrial appendage shape have been proposed.Occluders with improved design based on these key parameters were manufactured.At the same time,an in vitro experimental platform that mimics the heart circulatory environment was established,in order to verify the performance of the occluder.Morover,based on this platform,a training system for left atrial appendage occlusion has been proposed.The main achievements of this thesis include the following aspects:1.Morphological analysis of left atrial appendage and key characteristics parameters of occluders.In this study,3-D reconstructed models of left atrial appendage of 116 patients with atrial fibrillation were established.Based on the shape of the left atrial appendage,the models mainly contain four types: chicken-wing type,cactus type,wind-socks type and cauliflower type.They were accounting for 12.93%,8.62%,50.86% and 17.24% of the total cases,respectively.The diameter of plugging zone,anchoring zone,opening diameter,opening depth and remaining depth were measured and analyzed.The results of correlation analysis showed that only the opening diameter was significantly correlated with the parameters(r = 0.937,P < 0.01;r = 0.855,P < 0.01;r = 0.731,P < 0.01),and the opening diameter was significantly different in various types of left atrial appendage.No significant correlation was found between the remaining depth and the parameters(r = 0.075,P > 0.05;r = 0.144,P > 0.05;r =-0.030,P > 0.05;r = 0.060,P > 0.05;and R = 0.060,P > 0.05).Therefore,in this study,the remaining depth is taken as a constant,and the opening diameter provides a basis for the subsectional design of the occluders.According to the distribution of the mean and standard deviation of each block,the comprehensive sectionalization of the 3 mm and 2 mm intersecting intervals was selected for the subsectional design of occluders.Based on the difference test among sample datasets,it indicates that the distribution of opening depth is not statistically related to the shape of left atrial appendage.The diameter of occlusion area,anchorage area and remaining depth should be classified according to the shape of left atrial appendage.Through regression analysis and verification,the regression equation of each parameter is determined.Finally,the characteristic parameters such as the diameter of plugging disc,the length of connecting rod and the diameter of plugging umbrella are obtained.It provides a guide for the size design of the plugger,and explains the rationality of separating design for the plugging disc,connecting rod and plugging umbrella.2.Design and manufacture of characteristic left atrial appendage occluder and mechanical performance verification.Based on material tests,the Ni-Ti alloy wire with 0.1mm diameter was selected as the raw material(tensile strength 1370 MPa,elongation at break 12.45%).The structural design and fabrication of the firstgeneration occluder were completed,and the feasibility of the processing technology was verified.Through the design of three-stage parameters,the second generation occluder was improved,and then the manufacture process and key parameters were designed.The occluders with opening diameters of 30,24 and 20 mm were manufactured.In this paper,anchorage performance,pull-off performance,radial compression performance,plugging disc elasticity and connection performance experiments are conducted to verify the mechanical performance of the occluder.The maximum anchoring force of single hook is 0.035 N,and the anchoring force of the whole anchoring area is 1.284 N,which is larger than the anchoring resultant force of single hook.It is proved that the structural design of the anchoring area can effectively increase the anchoring performance.The matched left atrial appendage model is used to test the pulling force of anchoring area,and the maximum pulling force is 0.9761 N,which proves that the anchoring area is irregular.The anchorage performance can also be maintained under the atrial appendage morphology.In the compression test of plugging disc,the compression range is 100% to 70%,and the results show that the radial support force of plugging disc varies in the compression range;the full compression test results of plugging disc show that the maximum wall pressure of plugging disc in sheath is 14.642N;and the elastic coefficient measured by the longitudinal tensile test of plugging disc is(0.05931N/mm,0.09597 N/mm,0.06234 N/mm),indicating that the occluder is not easy to deform after implantation.The mechanical parameters of human aortic wall were measured,the average thickness was 1.249 mm,the average maximum compressive force was 10.985 N,the average sample thickness was 1.031 mm,the average circumferential rupture stress was 1.236 MPa,and the average longitudinal rupture stress was 1.184 Mpa.The key parameters of delivery sheath and others are designed and the delivery system were produced.3.Design and manufacture of the mock circulatory system for testing left atrial appendage occluder and in vitro performance verification of left atrial appendage occluder.Based on the characteristics of circulation system,similar fluid mechanical components are designed to imitate and a pulsatile cardiopulmonary bypass test device is established.The system can simulate the blood circulation under the condition of heart beating as well as the state of atrial appendage movement under atrial pressure.The required hemodynamic characteristics of the circulatory system can be achieved by adjusting the output conditions of mechanical components and power units.By collecting pressure and flow waveform data,the changes of hemodynamic characteristics before and after implantation were analyzed,and the function of the test system in device implantation was expanded.In this study,a mock heart model and an elastic left atrial appendage model were made to simulate the diastolic and systolic state of the left atrial appendage during pulsation.Ultrasound was used to observe the change of the flow field before and after the occluder was implanted.The occlusion performance,the occlusion state and the safety of the occluder were analyzed.This study focuses on the design and performance verification of the left atrial appendage occluder with characteristic parameters.The analysis method of characteristic parameters provides guidance for the design of the device,and clarifies the design principle of the left atrial appendage occluder.The method of mechanical performance verification provides a basis for the structural design of the device.The occluder and expand its research function in the field of interventional medicine apparatus.This study has a theoretical significance and application value for the design and production of left atrial appendage occluder,and lays a foundation for clinical trial and marketing in the future. |
PDF Full Text Request