The Experimental Study Of Radiofrequency Catheter Ablating At Coronary Sinus Ostium

Objective: Radiofrequency catheter ablation (RFCA) has been established as one of the treatment options for atrioventricular nodal reentrant tachycardia (AVNRT). Now, slow-pathway ablation has become the routine operation of modificating atrial ventricular node (AVN), one of its complications is to injure AVN or His bundle and result in A-V block. During a long time, people continually study slow-pathway ablation about its anatomic position, safe discharging time and energy. Recent studies demonstrated that almost AVNRT patients have dilated coronary sinus ostium (CSO), which is pathological basis of AVN slow pathway. CSO is the anatomic marker of AVN slow pathway. It isn't known the security and the influence of CSO ablation. This study took pigs whose heart structure is like to human's as the experimental animal, ablated near CSO for different amount of energy, studied the histopatholoical alteration in the ablated region and the influence in AVN and His bundle, eventually provided experimental data for the clinical work.Methods:Twenty Yorkshire pigs (3~4 month-old and 35~40kg weight) were enrolled in the experiment and broken down into control group and experimental group, the latter was broken down into 6 groups which were 3 pigs in each according to the ablation time. They were 10 second group, 20 second group, 30 second group, 40 second group, 60 second group and 80 second group. Anesthetized animal, killed control group pigs and put out their hearts for histological observation. Regress opacification was performed on experimental pigs to know the CSO shapes. Defined the position of CSO ablation target with the image data and endocardia electrocardiogram which presented little A wave, big V wave and no H wave. Under RAO30°fluoroscopic control, putted ablation catheter at right ventricular apex, withdrew it to AVN until endocardia electrocardiogram presented from big V wave to A, H and V waves, then defined His bundle zone where was biggest H wave. Under RAO30°and LAO45°fluoroscopic control, putted ablation catheter on CSO target away from His bundle zone, ablated here with 30W power as well as the following time: 10s, 20s, 30s, 40s, 60s and 80s in different groups. During RFCA, if junctional tachycardia,blocked reverse transmission to atrium, and longer P-R delay emerged or catheter shift, impedance heightened, then stopped discharge and chose again.Execute animal by aeroembolism after operating, put out the pig hearts and open them, observed the RFCA lesions characteristic, measured and calculated the maximal area of lesions, observed the relation among lesion, CSO, AVN and His bundle. Made sections and stained them with HE and Masson for microscopic examination to know the histopatholoical characteristic of lesions, AVN and His bundle. Analyze the relationship between the amount of RFCA energy and the size of RFCA lesions by statistics disposal.Results:1 Macroscopic findings1.1 The actual ablation targets were away from CSO within 10mm, which is taken as the valid range. The total effective rate of ablation site was 100%.1.2 Macroscopic characteristic RFCA targets were bright red or dark red bleeding focuses. Their shapes were approximate rotundity or ellipse, the endocardium was almost complete and without thrombus, yellow brown caseous necrosis was found in the sections, the bottom was almost curve. Surrounding the targets was normal tissue and no cardiac perforation was found.1.3 Distance between target and His bundle Among the 18 ablation targets, there were 7 whose distance to His bundle was long than 10mm and short than 15mm(7/18(38.9%)),there were 17 whose distance to His bundle was long than 15mm and short than 20mm (17/18 (93.4%)),there were 18 whose distance to His bundle was long than 20mm and short than 25mm(18/18(100%)),the mean distance between targets and His bundle was 20±3mm.1.4 CSO shapeThe CSO shape was funnel among experimental group and control group.2 Microscopic findings2.1 There were myocardial cells near CSO which were like to the transition cells in AVN, they were small, bent and light dyed. There were aplenty of fibrous connective tissue near CSO.2.2 The ablation targets were local regions with obvious demarcation. Their center was necrosis zone, the myocardial cells in endocardium and below it appeared to coagulated necrosis: the nucleoluses karyopyknosis or disappeared, muscle plasma agglutinated, a great quantity of contraction bands emerged. There was medium hemorrhage in necrosis zones and no obvious leukocytic infiltration. Around necrosis zone was degenerative zone, myocardial cells were oedema, a small quantity of contraction bands emerged. Myocardial cells around ablation targets were a little oedema or normal. There was a lot of fibrous connective tissue in ablation regions, fibrous connective tissue was obvious necrosis: its structure disappeared, cellular figure was unclear. No transition zone existed between ablation regions and normal tissue. All the ablation regions didn't cause thoroughly layer myocardium necrosis. The lesion size and necrosis degree increased with the improvement of RFCA energy.2.3 The influence in AVN and His bundle No A-V block appeared in the 6 groups and no lesion was found in AVN and His bundle.3 The relationship between the amount of RFCA energy and the size of RFCA lesionsDischarged with power of 30W, the area of RFCA lesions was not significant different in 10S and 20S group (P>0.05). Both of them were significant different to 30S, 40S, 60S and 80S groups(P<0.05); otherwise, the area of RFCA lesions was not completely same in 30S, 40S, 60S and 80S groups (P>0.05). The depth of RFCA lesions was significant different to other groups in 10S group (P<0.05), but the depth of RFCA lesions was not significant different in 20S, 30S, 40S, 60S and 80S groups (P>0.05).From 300J to 2400J, the area of RFCA lesions around CSO increased with the improvement of RFCA energy, they had positive linear correlation (r=0.9758,P<0.05), The depth of RFCA lesions tended to increase with the improvement of RFCA energy, but they had no linear correlation.Conclusions:The discharge site near CSO was far from real AVN and His bundle and the hurt was localized. Discharged with power of 30W, the area of RFCA lesions in 10S and 20S group was not significant different, it would be significantly increase when the time extended to 30s and more. The depth of RFCA lesions would be significantly deeper than that of 10s when the time extended to 20s and more. The area and degree of RFCA lesions around CSO increased with the improvement of RFCA energy which ranged from 300J to 2400J, the area of RFCA lesions and the amount of RFCA energy had positive linear correlation. The depth of RFCA lesions had no linear correlation with the amount of RFCA energy, but it tended to increase when RFCA energy improved. In order to decrease complication, exact fixing and taking proper RFCA energy were necessary in clinical work.