| Objective Radiofrequency ablation of ventricular arrhythmias(VAs)originating from the epicardium and intramural parts of the left ventricular summit(LVS)is difficult due to its complex anatomy.Guidewire ablation(GA)is a novel alternative ablation method for the patients who had previous ablation failure.Howerer as a novel technology,the energy transmission process of GA is unknown.The purpose of this study is to explore the lesion size(lesion diameter),lesion characteristics and the incidence of steam pop in vitro and in vivo models with diverse ablation parameters so as to guide the application of this technology clinically.Methods1.In vitro experiment: We established an ablation model simulating blood vessel in isolated swine myocardial tissue.According to different ablation parameters,the follow aspects were investigated:(1)To explore the secure power and lesion characteristics of GA in different vessel diameters.According to the simulated vessel diameter,2 groups of 1.17 mm(4F)and 2.24 mm(8F)tissues were divided,and then each group was further divided into four sub-groups of10 W,15W,20 W and 25 W on the basis of the ablation power.During the ablation process,the baseline impedance,generator impedance(GI)changes,steam pop events and their occurrence time were recorded,and the lesion diameters were measured after operation.(2)To explore the secure power and injury characteristics of GA with different exposed lengths of guidewire.Myocardial tissues simulating the vessels were divided into 10 mm and 20 mm groups according to the length of the tip of the guidewire.In accordance with the power,each group was divided into four sub-groups of 10 W,15W,20 W and25W,and the same parameter changes were recorded,and the lesion diameters were measured as the study(1).(3)To explore the correlations between the lesion diameters and durations of GA with different lengths of guidewire exposure.As the secure power obtained in the study(2),the myocardial tissues were segmented into 10 mm group and 20 mm group for the exposed length of the guidewire,and then segmented into 7 sub-groups base on ablation durations(10s,20 s,30s,40 s,50s,60 s and 90s).The variations of parameters during ablation were recorded,and the correlations between the lesion diameter and ablation durations were analyzed.(4)The influence of the infusion velocity of normal saline on the diameter of the lesion.Using the secure power and duration of GA obtained from the previous studies,GA was performed according to the normal saline infusion speed of 0,1,2,3 and 4ml/min,and the relationship between the lesion diameter and the saline infusion speed was analyzed.2.In vivo experiment: Three beagle dogs were prepared,then the distal GCV and its branches undergone distinct angiography were selected as the target vessels.The guidewire was sent into the target vessels and used to deliver ablation energy.The secure power,duration and infusion speed of normal saline were determined according to the results of in vitro experiments.The cardiac vessel of each dog was ablated for 2 to 3 times,and the baseline impedance,GI drop and steam pop events during ablation were recorded.The gross lesions and histological features were observed 10 days after ablation.Results1.In vitro experiment:(1)In the 1.17mm(n=32)and 2.24 mm(n=32)simulating vessel diameter groups,we observed that steam pop rate raised with the increase of ablation power.The steam pop rates of 10W(n=8),15W(n=8),20W(n=8)and 25W(n=8)were 0%(0/8),50%(4/8),87.5%(7/8)and 100%(8/8)respectively,and the secure power of 1.17 mm group is 10 W possibly(1.17 mm group;10W,0%;15W,50%,P<0.01).In the 2.24 mm group,the steam pop rates were 0%(0/8),0%(0/8),0%,50%(4/8)at 10 W,15W,20 W and 25 W,therefore,we deem the safe power was 20W(2.24mm;20W,0%;25W,50%,P < 0.01).(2)The steam pop rates raised with the increase of ablation power in the 10 mm(n=32)and 20 mm(n=32)groups.As the power of 10W(n=8),15W(n=8),20W(n=8),and 25W(n=8),the steam pop rates of 10 mm group were 0%(0/8),12.5%(1/8)62.5%(5/8)and 100%(8/8),the secure power was identified as15W(10mm group;15W,12.5%;20W,,62.5%,P<0.01).In the 20 mm group,the steam pop rates were 0%(0/8),0%(0/8),25%(2/8)and 75%(6/8)at 10 W,15W,20 W and 25 W respectively,and the secure power might be 20W(20mm group: 20 W,25%;25W,75%,P<0.01).(3)The lesion diameter of 10 mm group(n=42)and 20 mm group(n=42)increased significantly within 10-40 seconds,however,when the ablation duration approximated 40 seconds,the increase slowed down,and the lesion diameter of 10 mm group was more extensive than that of 20 mm group in the same duration(P<0.01).(4)There was a strong negative correlation between the increasing saline infusion speed and the diameter of GA lesion,meanwhile the rate of steam pop decreased with the faster infusion speed.We recognized that 2ml/min may be the best infusion speed in the process of ablation,which can not only maximize the lesion area,but also reduce the incidence of steam pop.2.In vivo experiment: GA was performed 9 times in the cardiac vein of 3 animals and 6 lesions were created.At 10 days after ablation,the GA could form effective and continuous lesions via the GCV and its branches(maximum diameter: 3.2 ± 0.3 mm;minimum diameter: 2.8 ± 0.5 mm;n=6).It was found that the ablation results in vivo experiments were similar to those in vitro;however,with identical ablation parameters,the lesions in vivo study were not as big as those in vitro model.The lesion maximum diameters were 3.2 ± 0.3mm and 4.2 ± 0.5 mm(P=0.02)and the lesion minimum diameters were 2.8 ±0.5 mm and 3.8 ± 0.4 mm(P=0.03)in vivo group and in vitro group.Conclusions Data from in vivo and in vitro studies suggest that intravascular GA can safely form reliable lesions.The diameters and characteristics of the lesions formed by GA were related to ablation power,ablation duration,saline infusion rate,the exposed length of the guidewire tip and the diameter of the cardiac vessel.If the guidewire exposed was shorter and the target vessel diameter was smaller,high power and long duration ablation should be more cautious to decrease steam pop rate,and saline infusion should be provided to balance the effectiveness and safety of GA. |
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