Employment Of Novel High-Resolution Echocardiography In Murine Models Of Cardiovascular Disease

Novel high-frequency (≥20MHz) high-resolution (30μm) ultrasound techniques not only present characteristics of real-time, motion, economy, reproducibility, no radiation, but also are accustomed to the small heart size and rapid heart rates in the mouse, thus improving the image quality and facilitating researches and are being widely used in the studies using murine models of cardiovascular disease.As old saying goes, a workman must sharpen his tools if he is to do his work well. It is reported that anesthetics, anesthetic timing, heart rates and temperature are factors probably affecting the echocardiographic results in mice. We first investigated the possible roles of factors which may influence echocardiographic assessment, established a reliable and efficient murine high-frequency echocardiographic station, paved the way for in vivo evaluation in the future projects.Heart is supplied by coronary circulation, coronary flow reserve (CFR) mirrors cardiac load. We hypothesized the novel high-frequency micro-ultrasoud system can be applied to the estimation of coronary (both in LV and RV) structure and hemodynamics. Prior literature reported in the mouse with transverse aortic constriction (TAC), LV and RV experience identical coronary flow perfusion pressure but significantly different cavity pressure. We postulated that comparison of coronary flow perfusion in three major coronary arteries (left, septal and right coronary arteries) in mice by the novel high-frequency echocardiography and association of coronary perfusion with morphology, function and angiogenesis in LV and RV may yield interesting results, which widens our understandings in the pathophysiological links between coronary and cardiac function and the relations among mechanical stress, coronary perfusion and neoangiogenesis. Part ⅠEffects of Heart Rate and Anesthetic Timing on High-Resolution Echocardiographic Assessment Under Isoflurane Anesthesia in MiceBackground and Objectives:Anesthesia provides sedation and immobility facilitating echocardiography in mice. but it influences cardiovascular function and therefore outcomes of measurement. The present study aims to determine the effect of optimal heart rate (HR) and anesthetic timing on echocardiographic reproducibility under isoflurane anesthesia.Methods:Male C57BL/6J mice (9-10weeks old) underwent High-Resolution Echocardiography (HRE) with relative fixed heart rates and anesthetic timing. The same experiment was repeated once again after a week.Results:Echocardiography was highly reproducible in repeated measurements under low (350-400bpm) or high HR (475-525bpm) conditions, except some M-Mode parameters under low HR conditions. With similar anesthetic timing, mice with high HR demonstrated decreased preload indexes (inner diameter) and increased ejection phase indexes and Doppler flow indexes. Inversely, when the HR was similar, the echocardiographic results of mice under short anesthetic timing showed little difference from the ones under long anesthetic timing.Conclusions:The study demonstrates that echocardiographic assessment is greatly reproducible under high HR. HR is more important than anesthetic timing for echocardiographic evaluation in mice. Part II Coronary Flow Perfusion and Coronary Flow Reserve for the Left and Right Ventricles in Mice with Transverse Aortic Constriction-An Evaluation Using High Frequency Ultrasound ImagingBackground and Objectives:Transverse aortic constriction (TAC) in mice results in similarly elevated perfusion pressure to major coronary arteries, but significantly different loading conditions to left and right ventricles. Echocardiographic estimations of flow perfusion in different coronary arteries impose great challenges to conventional echocardiography techniques. We aimed to evaluate coronary flow perfusion in three major coronary arteries and the concomitant structural, functional and neoangiogenic changes in left (LV) and right ventricle (RV) in living mice using novel high frequency ultrasound imaging.Methods:Male C57BL/6J mice of12-13weeks of age were randomly divided into6groups. Three groups were subjected to transverse aortic constriction (TAC), and three other groups had sham surgery and served as controls. At each of three time points of observation (2,4and8weeks post-operation), one group of mice with TAC and one group with sham surgery underwent ultrasound estimations of flow perfusion for left (LCA), septal (SCA) and right (RCA) coronary and corresponding structure and function of left and right ventricles and big vessels. After ultrasound scanning, mice were sacrificed for histological assessments of cardiomyocyte size and neogenesis.Results:Doppler flow waveform analyses showed diastolic predominance in LCA and SCA of sham-operated mice was significantly blunted after TAC during the whole observation, while RCA always demonstrated similar diastolic and systolic components. Elevated flow perfusion and decreased coronary flow reserve (CFR) were present at as early as2weeks after TAC in LCA, such hemodynamic changes was delayed to present from4weeks in SCA and was generally absent in RCA. Correspondingly, after TAC, LV systolic function decreased after compensation while RV showed unchanged systolic function during the whole course. Moreover, echocardiography and histology always revealed increased cardiomyocyte size in LV and septum instead of in RV while capillary density was increased at2weeks and4weeks after TAC in LV and septum and only at4weeks in RV.Conclusions:We for the first time established an echocardiographic protocol of quantitatively evaluating the flow dynamics in all major coronary arteries of mouse heart, and demonstrated the significant differences in the flow waveform among three individual vessels. In spite of the generally elevated flow perfusion and deteriorated CFR in LCA and SCA after TAC, accompanied by the enhanced myocyte hypertrophy and neoangiogenesis in the LV and septal myocardium, those parameters in RCA and RV face relatively mild changes.