Closed-chest Ablation Of The Cavotricuspid Isthmus Using Higth-intensity Ultrasound In Canines In Vivo

PART1THE FEASIBILITY OF CLOSED-CHEST ABLATION OFTHE CAVOTRICUSPID ISTHMUS USINGHIGTH-INTENSITY ULTRASOUND INBackgrounds: Cavotricuspid isthmus(CTI) as the critical conductionarea for typical atrial flutter, is the first choice of treatment targets withradiofrequency ablation via catheter. However, the anatomic differences ofCTI and the limited injury depth of radiofrequency ablation requires newenergies as an alternative strategy. Moreover, the catheter manipulationneeds X-ray induction, and both the catheterization and X-ray have someside-effect for body, especially the radioactive injuries for doctors andpatients, so it requires new strategies independent of catheterization andX-ray. High-intensity focused ultrasound(HIFU) can ablate tumor inside thebody via extracorporeal method in the previous studies, and it also caninduce point and linear injuries on cardiac tissue in vitro. Furthermore, it hasbeen identified to induce atrial septum injury via open-chest way in vivo. Based on these, HIFU is chose to explore the feasibility of cardiac ablation invivo via closed-chest ways.Aims: To study the feasibility of CTI ablation using HIFU viaimprovement of cardiac acoustic environments.Methods: Ten healthy mongrel dogs, anesthesized, removing hair,degreased and degassed skin, constructing bilateral pleural effusion model,then using JC-200HIFU apparatus to localize the CTI and performingablation strategy as400W X2s from the TV to IVC. The average grey-scaledifference was observed, and ECG monitoring the process. One week afterablation, the experimental animal was sacrificed and the structure during theacoustic process was observed, the CTI specimen was observed on theaspects of morphology and histology. Meanwhile, the side-effect wasobserved. Results: Eight of ten reached the ablation termination of wholetransmural necrosis of CTI via closed-chest using HIFU. The average valueof total ablation time was (54.5±12.0)s，and the actual average time was17.0±3.4s except the waiting interval time. Occasional single premature beatwas observed on two animals and one lung injury was observed in oneanimal which could be ablation to the whole transmural necrosis oftermination. No injuries of pleural effusion and pericardial effusion wasobserved one week after ablation. No injuries of RCA was observed in thesection.Conclusions: Through improvement of cardiac acoustic environment, it can acquire clear ultrasonic image of CTI. Furthermore, this studyindicates the feasibility of CTI ablation using transthoracic HIFU and themethod is safe and effective. PART2THE ELECTROCONDUCTION INSIDE THE RIGHTATRIUM VIA CAVOTRICUSPID ISTHMUS AND SAFTEYOF ABLATION DURING THE MID-TERM PERSPECTIVEINTERVALS USING HIGH-INTENSITY FOCUSEDULTRASOUNDBackgrounds: The whole transmural necrosis of Cavotricuspidisthmus(CTI) is usually the anatomic ablation target for treatment of typicalatrial flutter, as a result, bilateral conduction block(BCB) is the alternativeoptimal ablation target for clinical treatment instead. Because of anatomicdifferences of CTI and the limited injury depth of radiofrequency energy,about10%patients cannot be cured via classic radiofrequency ablation.Based on the findings from experiments in part one, the safety andeffectiveness should be identified for further study.Aims: To study the electric conduction characteristics inside the rightatrium after CTI ablation using transthoracic HIFU and to estimate the safetyof the method at the30d.Methods: Eight canines were divided into two groups, four in theablation group and four in the control group. The ablation group followed the strategy of preparation and ablation as in the first section. And30d later, thetwo groups received open-chest cardiac electricity conduction test undertracheal tube and artificial breath. The bilateral jungular veins and rightfemoral vein were centesised for putting into electrodes, one into coronarysinus, one at the superior RA and one at the inferior RA. And the conductiontime inside the RA from the inferior RA to CS was recorded. The animalswere sacrificed after the test. The CTI specimen was preserved formorphology and histology observation including immunohistochemical testfor cadherin and connexin expression in the ablation area and the controlgroup. Results:The average value of total ablation time was (61.4±9.0)s，andthe actual average time was （19.0±2.6）s. The average difference ofgrey-scale value was30.5±3.0. All of the animals survived during theperspective interval time30d. The electricity conduction test identified theBCB of CTI, indicating the effectiveness of ablation. And little expression ofconnexin in the ablated CTI identified the deadly necrosis of atrial myocytes,but the decreasing level of endothelial cadhesin indicated the weakenfunction of endothelial cells inspite of its contact structures.Conclusions: The accurate location for canine CTI in vivo could beperformed under two-dimensional ultrasonography integrated in the HIFUapparatus. Based on this, the study demonstrated it could ablate canine CTIto the termination of whole transmural necrosis in vivo by closed-chest wayusing HIFU for the first time, via non-catheter and without X-ray inducing, and the security and effectiveness was indentified during the30d afterablation.