Clinical And Experiment Study On The Cardioembolic Stroke Prevention Of Atrial Fibrillation By Means Of Left Atrial Appendage Occlusion With Self-designed Nickel-titanium Shape Memory Alloy Left Atrial Appendage Occluder

PartⅠ. Value of echocardiography in evluating establishment of atrialfibrillation animal model and changes of cardiac function after rapidleft atrial appendage pacingBackground and Objective: With the development of interventionalcardiology, percutaneous left atrial appendage transcatheter occlusion hasbeen paid more attention to for the prevention of strokes in high-riskpatients with AF and contraindication for long-term anticoagulation.The establishment of atrial fibrillation animal model is the base to studyleft atrial appendage occlusion. The aim of the study was to evaluate thestructure and function of left atrial and ventrical of the heart induced byrapid left atrial appendage pacing of pigs.Methods: Twelve pigs were randomly divided into 2 groups: 1)experimental group (n=6): a left intercostal thoracotomy was performed and the pericardium was opened to expose the heart and the pacingelectrode was fixed on the base of the left atria appendage. The pulsegenerator was implanted subcutaneously in the left chest and rapid atrialpacing at the rate of 500 beats per minute was initiated one week afteroperation and continued for 8 weeks. 2) control group (n=6):pacingelectrode and pacemaker was implanted as pigs in experimental group butno pacing. Echocardiographic study was performed at baseline (beforeoperation), two, four and eight weeks after pacing to measure left atrialdimension (LAD), left atrial area systolic and diastolic diameters of leftventricle (LVDs, LVDd), fractional shortening (FS), eject fraction(LVEF).Results: Five pigs in experimental group and 6 pigs in control groupfinished the experiment. Atrial fibrillation was developed in one pig twoweeks and three pigs eight weeks after pacing in experimental group.There was no atrial fibrillation occurred in control group. After eightmonths of left atrial appendage pacing,the dimension of LAD, LADs-A,LADd-A,, LVDs and LVDd is significantly increased (2.5±0.12cm, 6.21±0.93cm~2, 3.63±0.35cm~2, 3.46±0.15cm, 2.14±0.09cm vs 3.44±0.21cm, 8.51±1.04 cm~2, 4.99±0.29 cm~2, 4.06±0.18cm, 2.92±0.15cm,respectively, p＜0.01) and FS, LVEF is decreased significantly (63.8％±0.04, 37.8％±0.03, 69.2％±0.04 vs 53.2％±0.05, 27.8％±0.02, 54.8％±0.04, respectively, p＜0.01) in group one. Conclusion: Rapid left atrial appendage stimulating is an effectivemethod in the establishment of a chronic atrial fibrillation model in pigs.Rapid atrial pacing could result in the increase of the left atrial andventricle and the decrease of the left ventricle function. Echocardiographycould monitor these changes during the establishment of atrial fibrillationmodel.PartⅡ. Study on the cardioembolic stroke prevention withself-designed nickel-titanium shape memory alloy left atrialappendage occluder in vivoBackgrounds: Patients with atrial fibrillation are at high risk ofthromboembolic stroke. Compared with people in sinus rhythm, those innon- and rheumatic atrial fibrillation have a six- and 18-fold increasedrisk of stroke respectively. In patients with non-rheumatic atrialfibrillation, more than 90％of thrombi form in the left atrial appendage.Closing the left atrial appendage may therefore be an effective way forthe prevention of strokes in high-risk patients with AF andcontraindication for long-term anticoagulation. Up to date, some devicessuch as PLATTO, Amplatzer and Watchman filter system are designed forthe catheter closure of LAA to avoid the systemic thromboembolism. Still,there is no ideal device because of non-stable implantation of the device and higher complications such as pericardial effusion etc. It is necessaryto design a new device which could be stably fixed in the LAA.Objective: A novel nickel-titanium shape memory alloy left atrialappendage occluder (LAAO) has been designed to seal the LAA. Thepurpose of this study was to test the feasibility and safety of the newself-designed left atrial appendage occluder (SLAAO) that wereimplanted in porcines and to detect the growth of endothelial cells to thesurface of the new LAAO in vivo.Methods: Seventeen pigs were randomly divided into experimental group(n=12) and control group (n=5).The SLAAO was implanted intoexperimental pig surgically. The control pig had the same operationprocedure and the SLAAO was not implanted. System study wasperformed pre-and post-operation.1. Echocardiographic studyTransthoracic echocardiography was reviewed to measure left atrial (LA)function parameters, left ventricle (LV) function parameters, mitral valve(MV) and pulmonary vein (PV) hemodynamic parameters atpre-operation, one, two and four weeks follow-up study.2. Blood sampling and assays·Enzyme-linked immunosorbent assay (ELISA) were used to measureplasma Von Willebrand factor (vwf), P-selection (Ps), D-dimer (D-D),fibrinogen (Fg) levels in experiment animals pre-operation, immediate, 4 weeks and 12 weeks after operation.·ELISA were used to measure serum C reaction protein (CRP) and IL-6levels in experiment animals pre-operation, immediate, 4 weeks and 12weeks after operation.·Radioimmunoassay (RIA) and ELISA were used to measure plasmaANP and BNP levels in experiment animals pre-operation, immediate, 4weeks and 12 weeks after operation.·Atomic absorption spectrometry was used to measure Nickel serumconcentrations in experiment animals pre-operation, 4 weeks and 12weeks after LAA occlusion.·Whole blood WBC and PLT levels were measured before and afterocclusion.3. Endothelialization studyGross examination and scanning electron microscopic assessment wereused to evaluate the adherence and growth of endothelial cells to thesurface of the SLAAO.4. Pathological examinationThe animals were killed by exsanguinations and the spleen, liver, lungs,brain, and kidneys were examined for emboli. The heart, a section ofspleen, liver, lungs, brain, and kidneys were removed for furtherpathological examination. The hearts were fixed in bufferedformaldehyde for microscopic examination. Sections (5μm) were cut after dehydration and paraffin embedding of the tissue. Haematoxylin andeosin stained sections of spleen, liver, lung, brain and kidney wereexamined microscopically.Results:1. Echocardiographic studyTen pigs completed pre-operation, 1 and 4 weeks of follow-up study.New self-designed LAAO could seal the LAA effectively. Comparedwith pre-operation the data of left atrial function parameters showed nosignificant difference in all the perioda in experiment group (all p＞0.05).LVDs, LV EF, LV FS and E/A significantly decreased while Tei indexincreased significantly over the 1 and the 2 week follow-up period (p＜0.05). LVDs, LV EF, LV FS, E/A and Tei index showed no significantchange between four-week-follow-up and pre-operation (p＞0.05). Bothgroups showed no significant effect on the function of the LA and bloodflow of the MV and PV short term on follow-up study. The deviceremained stable at their sites of deployment with almost no residual flowaround them.2. Blood assays·Ten pigs completed pre-operation, 4 weeks and 12 weeks of follow-upstudy. The serum levels of IL-6 and CRP in both experimental andcontrol pigs immediate after SLAAO were higher than those beforeSLAAO (p＜0.05). Compared with pre-operation, serum levels of IL-6 and CRP showed no significant difference in 4 weeks and 12 weeksfollow-up study in both groups (p＞0.05). It showed no significantdifference in all the perioda of the two groups (all p＞0.05).·The plasma levels of vwf, D-D and the whole blood level of WBC werehigher at immediate after occlusion than those before in both groups butshowed no significant difference (p＞0.05). But the plasma levels of Ps,Fg and the whole blood level of PLT in both experimental and controlpigs immediate after SLAAO were higher than those before SLAAO (p＜0.05 or p＜0.01). Compared with pre-operation, the levels of vwf, D-D,Ps, Fg and PLT showed no significant difference in 4 weeks and 12weeks follow-up study in both groups (p＞0.05). Parameters aboveshowed no significant difference in all the perioda of the two groups (allp＞0.05).·The plasma level of ANP at 4 weeks and 12 weeks after SLAAO weresignificantly decreased compared with pre-operative values in experimentgroup (p＜0.05 or p＜0.01).The plasma level of BNP at immediate and 4weeks after SLAAO were significantly elevated compared withpre-operative values in experiment group (1.804±0.841pg/ml vs 1.085±0.615pg/ml, 1.857±1.131pg/ml vs 1.085±0.615pg/ml respectively, p＜0.01). And it decreased to the level of pre-operation at 12 weeks afterSLAAO. There were no significant differences of the plasma levels ofBNP and ANP between pre- and post-operation study in the control group.·The serum level of nickel at 4 weeks and 12 weeks after SLAAO weresignificantly elevated compared with pre-operative values in experimentgroup (0.055±0.013μg/mL vs 0.017±0.005μg/mL, p＜0.001; 0.030±0.075μg/mL vs 0.017±0.005μg/mL, p＜0.01).3. Endothelization studyOn gross examination at 4 weeks follow-up study, the surface of theimplanted occluder is covered with a smooth intact, half-parentneointimal layer and thrombus formation was not observed. Neointimalgrowth is continuous with the atrial walls and the interfaces are sealed.High-power view of appendage/device interface shows well-organizedfibromuscular coverage of the device surface covered with endothelialcells. Scanning electron microscopic study showed that the outer surfaceof the occluder near the atrial wall is covered with well-formedendothelial layer. Toward the center of the implant, the endotheliumappears more loosely arranged. At 12 weeks follow-up study, the smoothintact neointimal layer is thicker than that at 4 weeks study and thesurface of the implant was covered with more endothelial layer.5. Pathological examinationThere were no macroscopic signs of embolism or infarction in the spleen,liver, lungs, brain and kidney. There were no signs of thrombus formationand corrosion of the metal surface. Acute inflammatory reaction (histiocytic cells, neutrophils, multinuclear cells, etc) was presentobviously in the atrial tissue at 2 weeks follow-up study after left atrialappendage occlusion. There was a milder inflammatory reaction at 4weeks than that at 2 weeks follow-up study. The inflammatory responsediminished at 12 weeks follow-up study.Conclusions:1. Echocardiography plays an important role in selecting animalspre-operation, evaluating occlusion effect of the SLAAO and monitoringcardiac function and structure after SLAAO.2. The SLAAO achieved an adequate seal of the neck of the left atrialappendage without significant influence on the LA function and bloodflow of MV and PV in short term. Significantly change could be seen inleft ventricle function parameters at pre-operation, one and two weeksfollow-up while the change recover to the level of pre-operation atfour-week-follow-up.3. Endothelialization of the SLAAO surface has come into being at 4weeks after left atrial appendage occlusion.4. Nickel seems to be released from the SLAAO, causing a systemic risein serum levels of nickel. The maximum value of serum nickel appears at4 weeks after implantation. Nickel released could be hampered byendothelialization of the device surface.5. The inflammatory response, high platelet activity and high coagulation appeared after left atrial appendage occlusion in both groups and theyrecovered to the level of pre-operation. It showed that SLAAO hadexcellent biocompatibility.6. The plasma level of ANP and BNP could be affected by left atrialappendage occlusion.7. Light microscopic examination of brain, kidney, spleen, lung and livershowed no evidence of emboli or infarct after SLAAO implanted.PartⅢ. The Morphologie Study of Left Atrial Appendage inChinese Patients with Atrial FibrillationBackgrounds: Left atrial appendage (LAA) is the most important sourceof cardiac embolic events. Left atrial appendage occlusion is a promisingtechnique in high-risk patients with AF unable to take warfarin for theprevention of cardioembolic strokes. Up to date, many devices such asPLATTO, Amplatzer and Watchman filter system are designed for thecatheter closure of LAA to avoid the systemic thromboembolism. Still,there is no ideal device because of non-stable implantation of the deviceand higher complications. There is no angiographic study on the shape and size in the patients with AF and non-AF.Objective: The aim of the study was to observe morphology of LAA inAF and ASD patients on angiography so as to design a new LAAoccluder to reduce systematic thromboembolism in patients with AF.Methods: One hundred consecutive patients with either AF or ASD wereenrolled in the study. Before angiography procedure all the patients wereexamined by TEE to exclude people with left atrial appendage thrombi.Twenty-five patients were excluded because of emboli in the LAA.Seventy-five patients were enrolled and divided into AF (45 patients) andASD (30 patients) group. All the patients were treated with eitherradiofrequency catheter ablation of AF or catheter closure of ASD (Ⅱ)after the angiography of LAA. The morphology of LAA was visualizedand the orifice diameter, length, maximum and minimum area of LAAwere measured directly and emptying ejection was calculated.Results: The shape of LAA was divided into eight categories. They aretube-shaped, sphere-like-shaped, claw-shaped, tadpole-shaped,duckbill-shaped, sword-shaped, willow-leaf-shaped and irregular. Of 58％patients with AF the typical LAA body was tube-shaped while the typicalLAA body of patients with ASD was sphere-like-shaped and irregular,20% and 23% respectively. Mean dimensions of orifice diameter, length,width, height and inner diameter in patients with AF are bigger than thatin patients without AF (20.9±2.9mm vs 12.0±2.5mm, 40.4±5.7mm vs 28.5±6.5mm, 21.1±4.1 mm vs 14.6±3.6mm, 10.3±3.9 mm vs 3.1±0.9mm, 15.8±2.7mm vs 12.6±3.1mm, p＜0.001). And maximum areaand minimum area in patients with AF are larger than that in patientswithout AF (529.6mm~2±63.7mm~2 vs 362.0±105.1mm~2, 352.8±60.1mm~2 vs 207.0±66.2mm~2, p＜0.001). Nevertheless, emptyingfraction of LAA in AF patients is less than that in patients without AF(33.6%±0.05 vs 41.0%±0.05, p＜0.001).Conclusions:1. LAAs are multi-shaped. In AF patients, most are tube-shaped withsingle lobe and in ASD patients most are either sphere-like-shaped orirregular with two-or multi-lobe.2. Atrial fibrillation could decrease emptying fraction of LAA and lead toits dilatation.3. Device design should be up to the size and shape of LAA in AFpatients.PartⅣ. Atrial Velocity, Strain and Strain Rate Study in AtrialFibrillation Patients Before and After Radiofrequency CatheterAblation by Doppler Tissue ImageBackgrounds: Atrial fibrillation is the most common arrhythmia. Thestructural change in the atrial myocardium contribute to local impairment of electrical conduction and then to AF recurrences. The Atrial anatomicremodeling leads to the increase of atrial stiffness. Atrial compliance isaltered by AF before atrial structural remodeling occurs.Radiofrequency catheter ablation based on the electroanatomic approachwas an effective approach in eliminationg AF. There is little study onatrial myocardium feature before and after RFCA. Accurateechocardiographic parameters to predict maintenance of sinus rhythm inpatients with AF are poorly defined.Objective: Based on the information from standard TTE and TEE, wewould like to study the atrial myocardial properties in patients with AFbefore and after radiofrequency ablation and in normal people throughmyocardial velocity, strain rate, and strain and to compare theirprognostic value in maintaining sinus rhythm.Methods: Twenty-six AF patients and fifteen normal people underwentTTE, TEE, and myocardial velocity and strain and strain rate imagingexaminations before and after successful RFCA. The apical four chamberview and apical two chamber view of people enrolled were stored byusing QTVI. The LA septum, LA lateral wall, right atrial free wall LAinferior wall and LA anterior wall were analyzed. LA appendage flow wasobtained by placing the pulsed Doppler sample volume at the orifice ofthe LAA, after which peak flow velocities were measured and averagedwithin an RR interval of six consecutive cardiac cycles. LAA flow was defined as the peak forward or emptying flow velocity. Moreover, clinicaland echocardiographic parameters of patients with maintenance of sinusrhythm over the 3-month follow-up period were compared with thosefrom patients with AF recurrence.Results:1. Campared with healthy subjects, AF patients had significantly largerLA dimensions (p＜0.01). Emptying flow velocity of LAA and its TVIrecorded by multiplane TEE were significantly different between groups(P＜0.05)2. Campared with healthy subjects, peak systolic and early diastolic atrialmyocardial strain and strain rate values in each studied atrial wall weresignificantly lower in the AF group (p＜0.001) . Peak systolic and earlydiastolic atrial myocardial velocity in each studied atrial wall except earlydiastolic atrial myocardial velocities of right atrial free wall weresignificantly lower in the AF group (p＜0.001).3. Campared with AF recurrence group, LA diameter in the maintenanceof sinus rhythm group was significantly lower and recovered to normalthree months after RFCA (p＜0.05). And emptying flow velocity of LAArecorded by multiplane TEE were significantly different between groups(P＜0.05)4. Peak systolic atrial myocardial velocities were lower in the AFrecurrence group, but this difference was not significant (p＞0.05). Peak systolic atrial myocardial strain and strain rate values in each studiedatrial wall were significantly lower in the AF recurrence group (p＜0.05or p＜0.01). Early diastolic atrial myocardial velocity, strain, and strainrate were not significantly different between groups (p＞0.05).Conclusions:1. DTI, combined with TTE and TEE, is a new quantitative parameterwhich can find the regional systolic dysfunction. It is important toevaluate the changement of left atrial function.2. AF patients have obviously larger LA diameter and could recover tonormal three months after successful RFCA. There is significantrelationship between procedural success and LA size.3. Patients with higher emptying flow velocity of LAA, atrial strain andstrain rate appear to have a greater likelihood of staying in sinus rhythm.