Evaluation Of Anatomical Characteristics Of Mitral Isthmus And Its Adjacent Relationship With Esophagus In Patients With Atrial Fibrillation Undergoing Ablation By CT Angiography

Background:Atrial fibrillation(AF)is the most common arrhythmia in the clinic.Catheter ablation has become a routine and effective method for the treatment of AF.In addition to the standard circum-pulmonary vein electrical isolation operation,some patients also need additional linear ablation.Mitral isthmus(MI)is a commonly used AF additional linear ablation site.Because MI is adjacent to the spatial anatomy of the esophagus,the ablation of the MI target may lead to complications of esophageal injury,even the occurrence of an atrio-esophageal fistula.Purpose:In this study,computed tomographic angiography(CTA)was used to evaluate the anatomical characteristics of MI in patients with AF ablation and its adjacent relationship with the surrounding esophagus.The purpose is to clarify the information about the MI ablation line and the anatomy of the surrounding esophagus before AF ablation,which is helpful for the operator to select the ablation method and ablation energy and reduce the complications of esophageal injury.Method:One hundred patients with radiofrequency or cryoablation(AF group)and 100 patients without AF(control group)who underwent cardiac CTA examination in the cardiovascular department of our hospital were included in each group.First,general information about the patients was collected:gender,age,history of tobacco and alcohol consumption,history of hypertension,coronary heart disease,diabetes,triglyceride,total cholesterol,and LDL cholesterol levels.Cardiac CTA images of patients were obtained,and the following data were measured:(1)the length of MI.(2)The distance of MI.(3)The depth of MI.(4)In three levels of MI(level 1:the junction of left inferior pulmonary vein(LIPV)and the upper end of MI;Level 2:midpoint of MI;Level 3:junction of the mitral annulus and lower end of MI;The shortest spatial distance between MI and esophagus was measured,and the number and proportion of patients with direct contact between MI and esophagus were recorded.(5)The shortest spatial distance between the esophagus and the right inferior pulmonary vein(RIPV)was measured.Six measurements(left atrium,left atrium(LA)before and after the maximum transverse diameter(LA1),maximum diameter(LA2),the largest diameter(LA3)from top to bottom,and analysis of the correlation of atrial size and the measure.Patients were divided into the linear type and curved type according to the depth of MI.MI depth≤2 mm was defined as linear type;curved type was defined as MI depth>2 mm.According to the morphology of MI,patients were divided into cristae and pocket types.MI was defined as the endocardial contour protruding from the vertical line and forming a narrow band on the surface.The morphology of MI was defined as the pocket type by its vestibule and crypt composition.The number and proportion of patients with linear,curved,ridge,and pocket types were recorded.The esophageal anatomy of the patients was divided into types A and B.In type A,the shortest distance between LIPV and RIPV was more significant than between LIPV and RIPV.The shortest spatial distance between the type B esophagus and LIPV was smaller than between the type B esophagus and RIPV.The differences in the above measurements between AF and control groups A and B were compared and analyzed.Results:The length(38.94±9.12 mm vs.36.45±8.28 mm,P=0.045)and distance(36.37±8.00 mm vs.34.06±7.35 mm,P=0.035)of MI in AF group were greater than those in control group.There was no significant difference in the depth of MI between AF group and control group[3.92(1.87,6.34)mm vs 4.25(2.57,7.14)mm,P=0.236].Linear and curved MI accounted for 27%(27/100)and 73%(73/100)of patients in AF group and 22%(22/100)and 78%(78/100)of patients in control group.In the AF group,23%(23/100)and 77%(77/100)of patients with cristae and saccule MI respectively accounted for,while in the control group,18%(18/100)and 82%(82/100)of patients with cristae and saccule MI respectively.There was no significant difference in MI morphology between the two groups(P>0.05).Among patients with type A esophagus,the shortest spatial distance from MI at level 1 to esophagus in AF group was greater than that in control group[5.76(3.97,9.54)mm vs 4.90(2.73,8.20)mm,P=0.039];There was no significant difference between the two groups in the spatial shortest distance from MI to esophagus at level 2[22.40(19.62,28.46)mm vs.23.02(19.15,28.34)mm,P=0.996]and level 3(35.16±8.53 mm vs.34.87±6.68mm,P=0.952).In patients with type B esophagus,there was no significant difference between the three levels of MI and the shortest spatial distance between the two groups(P>0.05).Three levels of MI in patients with type A esophagus[Horizontal 1:5.48(3.42,8.91)mm vs 17.61(14.00,25.06)mm,P<0.001;Horizontal 2:22.75(19.50,28.40)mm vs 35.08(30.60,39.39)mm,P<0.001;Horizontal3:35.02±7.64 mm vs.45.87±8.78 mm,P<0.001]The shortest space distance to the esophagus was significantly smaller than that of type B esophageal patients.In patients with type A esophagus,the overall distribution of the shortest spatial distance from MI level 1,2,and 3 to the esophagus was statistically different(H=439.63,P<0.001).Among them,there were statistically significant differences in the shortest spatial distance from level 1 and level 2,level 1 and level 3,level 2 and level 3 to the esophagus(P<0.001).In patients with type B esophagus,the overall distribution of the shortest spatial distance from MI level 1,2,and 3to the esophagus was statistically different(H=23.95,P<0.001).Among them,there was statistical significance in the difference of the shortest distance from the esophagus between level 1 and level 2(P=0.021),level1 and level 3(P<0.001).In patients with type A esophagus,the proportion of MI level 1,2,and 3 in direct contact with the esophagus was 47.6%,25.1%,and 14.4%,respectively.Among them,the difference between level 1 and level 2,level 1 and level 3,level 2 and level 3 in direct contact with the esophagus was statistically significant(P<0.05).In patients with type B esophagus,the proportion of MI level 1,2,and 3 in direct contact with the esophagus was 46.2%,23.1%,and 23.1%,respectively.There was no statistically significant difference in the overall distribution of the three groups of data(P=0.503).The maximum transverse diameter of LA[66.99(60.44,73.23)mm vs.63.52(57.84,69.74)mm,P=0.011],the maximum anteroposterior diameter(41.26±8.59 mm vs.37.72±7.09 mm,P=0.002),the maximum upper and lower diameter[54.44(49.80,60.00)mm vs.51.64(47.24,54.41)mm,P<0.001]and the volume of LA[158.65(113.72,200.20)cm~3 vs 126.45(92.31,150.02)cm~3,P<0.001]in the AF group were significantly greater than those in the control group.Correlation analysis showed that LA volume was positively correlated with the length and distance of MI,and the distance from MI level 2 and 3 to esophagus(P<0.05).Conclusion:1.The MI shape of different patients varies greatly.The MI length and distance of AF patients are longer than that of non-AF patients,which may increase the length and time of MI line ablation.2.AF and non-AF patients have a relatively high proportion of curved and baggy MI,which may increase the difficulty of ablation and the possibility of catheter insertion into MI.3.In patients with type A esophagus,the distance from the junction(level1)between the upper end of MI and LIPV in the AF group to the esophagus is more significant than that in the control group,which may be related to the increase of epicardial adipose tissue in AF patients.4.AF and non-AF patients have a high proportion of type A esophageal anatomy patients.The shortest spatial distance from the different levels of MI in the type A esophagus to the esophagus is smaller than that in the type B esophagus,so it is more vulnerable to injury during ablation.5.Compared with the middle point of MI(level 2)and the horizontal point of the mitral annulus(level 3),the spatial distance from the junction of the upper end of MI and LIPV(level 1)to the esophagus is the shortest.Nearly 50%of patients are in direct contact with the esophagus,where ablation is more likely to damage the esophagus.6.The maximum transverse diameter,anteroposterior diameter,upper and lower diameter,and LA volume of AF patients were more significant than those of non-AF patients.There is a positive correlation between LA volume and the length and distance of MI,and the distance from the middle point of MI and the horizontal point of the mitral annulus(levels 2 and3)to the esophagus.In conclusion,CTA has the advantages of being non-invasive,convenient,short examination time,high resolution,and powerful image post-processing and reconstruction technology,which can enable the operator to know the anatomical characteristics of the MI ablation line and its adjacent relationship with the surrounding esophagus before catheter ablation,thus helping to select the individualized ablation scheme and energy,and reducing the complications of esophageal injury.