| Objective: To evaluate and to compare the effects of the one point dipolar pacing at various ventricular sites on the mechanical synchrony of left ventricular wall and its effects on the left ventricular function using echocardiographic three-dimensional (3D) speckle tracking, so as to provide basic experimental database for optimizing the sites of the artificial cardiac pacing in clinic conditions.Method: The open-chest modes for cardiac pacing were prepared in 10 healthy beagles. The full volumetric real-time images of the left ventricle in one completed cardiac cycle were acquired respectively during baseline (BASE) and at the right ventricular apex pacing (RVAP), the left ventricular apex pacing (LVAP), the left ventricular lateral wall pacing (LVLP) states. The left ventricular pressure-time curves were recorded simultaneously for achieving left ventricular ejection pressure and the maximal upstroke velocity of left ventricular systolic pressure. The radial 3D strain maps and the peak radial 3D strain of the left ventricular wall, as well as the left ventricular end systolic volume, end diastolic volume, stroke volume, ejection fraction, cardiac output at different states were extracted respectively using echocardiograic 3D speckle tracking analysis software. The radial 3D strain synchrony of left ventricular wall during different states was qualitatively observed and compared. The pertinent parameter test and non-parameter test were applied for comparing the same kind quantitative parameters of the various states; and the linear correlation analyses were applied respectively between the peak global radial 3D strain of the left ventricular wall and the left ventricular volumetric parameters, as well as the pressure parameters.Results: (1) The results of the qualitative observation:â‘ The temporospatial changes of the radial 3D strain in the 16 myocardial segments of the left ventricular wall was not completely synchronic at the BASE, and embodied the characteristic of"orderly asynchrony".â‘¡The"orderly asynchrony"in the 16 myocardial segments of the left ventricular wall disappeared at all the various pacing states. Further more, the temporospatial asynchrony in the different myocardial segments of the left ventricular wall was worse at the LVAP or the LVLP state than that of the RVAP state. (2) The results of the quantitative analysis:â‘ To be compared with the BASE: The peak radial 3D strain decreased significantly in the left ventricular basal post-septum and the basal inferior wall at the RVAP state (P < 0.05). The peak radial 3D strain decreased significantly in 9 myocardial segments of the left ventricular wall at the LVAP state; including the whole left ventricular apex, the middle-post wall, the middle-lateral wall, the middle-anterior wall, the middle anterior-septum, and the middle post-septum (P<0.05). The peak radial 3D strain decreased significantly in 9 myocardial segments of the left ventricular wall at the LVLP state; including the whole left ventricular apex, the middle-post wall, the middle-lateral wall, the middle-anterior wall, the middle anterior-septum, and the basal anterior wall (P<0.05). The peak radial 3D strain in some myocardial segments of the left ventricular wall increased at various pacing states, but has no statistical significance (P>0.05).â‘¡There were more parafunctional myocardial segments,which peak radial 3D strain decreased significantly, within the left ventricular wall at the LVAP or the LVLP state than those of the RVAP state (both comparisons are 9/16 vs 2/16,P<0.05).â‘¢To be compared with the RVAP state; the peak global radial 3D strain of the left ventricular wall and the left ventricular stroke volume, ejection fraction, cardiac output decreased at the LVAP or the LVLP state (P<0.05). But the comparisons of the left ventricular pressure parameters between various pacing states has no statistical significance (P>0.05).â‘£There were statistic significant linear correlations between the peak global 3D strain of the left ventricular wall with the left ventricular stroke volume, and the ejection fraction, as well as the cardiac output in different states (P<0.05); but the linear correlation with the left ventricular pressure parameters was not established in all states (P>0.05).Conclusion:The study results of the left ventricular function, which based on the echocardiographic 3D speckle tracking technique, hint that: (1) All the one point dipolar pacing modes at the various ventricular sites in our study have destructive effects on the mechanical synchrony of the left ventricular wall, and the destructive effects of the LVAP or the LVLP are stronger than those of the RVAP. (2) All the one point dipolar pacing modes at the various ventricular sites have negatively affects on the systolic function of some myocardial segments within the left ventricular wall, and the region of pacing-induced dysfunction within the left ventricular wall is wider during the LVAP or the LVLP than that of the RVAP. (3) AS far as the destructive effects on the left ventricular function of healthy canine are concerned, the LVAP or the LVLP mode is more harmful than the RVAP mode. (4) Echocardiographic 3D speckle tracking technique provides medical workers with new visual pathway for insighting the left ventricular function, and may contribute its advantages to the electrophysilogical therapy of heart diseases at the scope of basic studies and clinical applications.
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