RESUMO
Objective To assess the change of left ventricular wall motion at ventricular pacing(VP)by using global circumferential strain (GCS) and segmental circumferential strain of speckle tracking imaging(STI). Methods Seven adult pigs were sedated,followed by median sternotomy and opening of the pericardium. Temporary pacing leads were placed on the right ventricular (RV) epicardium and LV epicardium for RV or LV pacing. A LV short axis view at the mid-level LV was acquired at sinus and VP rhythm. Analysis of circumferential strain by STI was performed offline. The onset of QRS wave was used to characterize the beginning of the cardiac cycle, and the ratio of beginning systolic time, end systolic time and total systolic time to cardiac cycle dyssynchrony was analyzed at sinus and VP rhythm. Results Compared with sinus rhythm,in VP rhythm all of the ratio of the beginning systolic time,end systolic time and total systolic time to cardiac cycle were increased (all P ＜0.05), and the construction of six segments were dyssynchrony,even segmental paradoxical movement. At VP ≥130 beats/min,both LV global and LV segments sometimes showed irregular motion while the EKG remained normal, which included: ( 1 ) multiple construction and diastole in one heart cycle; (2) A large variability of construction amplitude in several consecutive cardiac cycles. Conclusions VP can lead to several kinds of disturbance of left ventricular wall motion, including delay and lengthening of LV systole, dyssynchrony, and irregularity of systole and diastole.