Experimental Study On Ultrasonography For Detecting Ventricular Myocardial Ablation With High-intensity Focused Ultrasound

Objective To explore suitable intracardiac echocardiography (ICE) views by endosonography catheter in order to make intracardiac ultrasonotomography standardize that wound be convenient for communication, and to evaluate the value of intracardiac Doppler tissue imaging (DTI) technique for showing the myocardial excitation and conduction (includes acceleration maps, velocity maps, M- mode and pulsed wave mode), for exploring new ways on mapping onset and propagation of myocardium excitation.Methods Healthy dogs underwent ICE with catheter intervened by jugular veins or femoral veins, so physiological parameters during and after examinations were recorded and compared with each other. Open-chest models of dogs with cardioventricular pacing were examined by intracardiac DTI to observe following targets (1) Acceleration mode (DTA):The high value distribution and movement of acceleration domains within the interatrial, interventricular septa and regional myocardium where the electrode were set (both in sinus and pacing rhythm); (2)Velocity mode (DTV): The different velocity value changes and distribution within ventricular wall; (3) M-mode (M- DTI): measure the electric- mechanical time T or T₁ from the beginning of Q wave or stimulating wave (in sinus and pacing rhythm) to the start of red contraction movement, comparing T and T₁ with different ventricular walls;(4) pulsed wave mode(PW- DTI): measure the electric- mechanical time T or T₁ from the beginning of Q wave or stimulating wave (in sinus and pacing rhythm) to the start of systolic wave, comparing T and T₁ with different ventricular walls; (5) Compare the ectopic excitation occurrence rate between transthorax echocardiography (TTE) and ICE in DTI mode, and compare the excitation conduction in long axis direction.Results The ICE can get the structure of the whole heart in high-quality images when the ICE transducer was put in different levels of right atrial, atrioventricular ring and intraventricular, and no significance was shown between the physiological parameters during and after examinations(P>0.05).The DTI shows the following phenomenon in observing cardioventricular pacing models: (1) The high value distribution and change of acceleration domains within the interatrial and interventricular septa in normal sinus rhythm was showed. The myocardial acceleration maps detected that the ventricular pacing onset changed first and the domain of the maximum acceleration induced by electrical stimulation was just the same position where the pacing electrode located.(2) The myocardial velocity maps detected that the domain contract firstly was just the same position where the pacing electrode located, and the contraction propagated during the pacing wave occurrence according to electrocardiogram (ECG.). (3) Comparing T and T₁ in different ventricular wall shows that: in sinus rhythm the base segment contract firstly, and there is significance in different level within same ventricular wall (P<0.05), and there is also significance between opposite segments of the same level (P<0.05). In pacing rhythm (pacing electrode in apex of heart), apex of heart contract firstly, and there is no significance between base and middle part within same wall (P>0.05), but there are significance between other different level segments (P<0.05); except apex of heart, there is no significance between opposite ventricular segments of the same level (P>0.05). In short axis level, under sinus rhythm except anterior septa and posterior wall (P<0.05), there is no significance (P>0.05) between other opposite ventricular segments (anterior vs inferior wall, lateral wall vs post septa); but in pacing rhythm, there is no significance in three pairs of opposite segments(P>0.05). (4)The ectopic excitation occurrence rate in ICE is higher than transthorax echocardiography (TTE) in DTI mode (58.3 % vs 11.7%, P<0.005).Conclusions ICE is safe and feasible. The intracardiac DTI with high frame frequency could real-time show the onset and propagation of myocardial electric activity and acceleration which is in response to the mechanical activity synchronously. With the development of equipments, this technique may provide a potential way for observing the occurrence and sequence of excitation.Part Two Experimental study on selective myocardium ablation with high-intensity focused ultrasoundObjective To observe acute biological effect on myocardium ablation with high-intensity focused ultrasound (HIFU) both in-vitro and in vivo hearts, in order to evaluate the feasibility of HIFU ablation on beating hearts, to explore new energy sources for latent excitation ablation.Methods 1. In-vitro experiment, the HIFU therapeutic apparatus was separately used to selectively destroy the different parts in myocardial tissue of 30 fresh normal swine in-vitro hearts. The myocardium was exposed to different HIFU dosages composed of different acoustic intensity and exposure time. The dissection was applied and then the lesion volumes were measured by software, and pathologic changes in border between normal and lesion area under each HIFU dosage were observed with a microscope. The temperature alteration in the focus was detected and recorded by a thermocouple probe that is just located in the focal field under the B-mode ultrasound monitoring. And each condition in this experiment was repeated five times.2. In vivo experiment: Open-chest models of healthy dogs were removal some rib to form enough focusing acoustic window, and fit quantity coupling medium gel were added in the pericardium basket. HIFU NIT9000 ablation equipments use 6 self-focusing acoustic transducer through two times focalization. The acoustic intensity is 500W/cm 3000W/cm². The energy emitted in one-point interrupted way: T₁(each emission time) = 200 ms, T₂ (the interval time between two emissions) were carefully set according to cardiac cycle for making the ablationhappened just during period of systolic phase (avoiding myocardium thinning in diastolic phase to breaking through ventricular wall). The ablation time were setting in 1.2s, 2.4s, 3.6s and 4.8s separately (emission times were 6, 12, 18 and 24 times separately). HIFU ablation with these 4 kinds of energy dosage were practiced under real-time ultrasonography monitoring, and each dosage repeated 5 times.The DTI spectrum, blood flow spectrum of mitral orifice, ejection fraction before and after ablation were recorded for comparison. Myocardium enzyme (AST, LDH, CK) and cardiac troponin T (CTnT) were detected in normal condition, pre-ablation and post-ablation separately. The hearts were dissected after ablation, then stained in 2% TTC solution at 37℃ constant temperature. The ablation range and volume were measured. Microscope and electron microscope were underwent for finding tissue microstructure and cells ultramicrostructure changes.Results 1. In-vitro experiment, the ablation volume varied from (11.2 ±1.9) mm³ to ( 283. 2 ±4. 5) mm³ with the change of exposed time between Is ⁸s and acoustic intensity varied between 11000 W/cm²-22200W/cm², and significant difference was found among different levels of both acoustic intensity and exposure time (F=3.387, 7.108, P =0.043, 0.002), and they effected each other (F=4. 430, P=0. 031) .The ablation shapes enlarged from ellipse to irregular triangles. Coagulative necrosis pathologic changes in regional myocardial ablation tissue were observed. And it was observed that the highest temperature in focal field varied from (66.4 ± 11.2)℃ to (85.8 + 7.4)℃ when HIFU dose changed between 11000 W/cm²-22200W/cm² and 1s ¹5s. And significant difference was also...