Effect Of Right Ventricular Outflow Tract Pacing And Right Ventricular Apex Pacing On Cardiac Function By Tissue Doppler Imaging

Background: As a traditional permanent ventricular pacing mode, right ventricular apex pacing(RVAP) is widely used in clinic for its lead being easily set and uneasily fall off. But RVAP induced cardiac abnormality and the simultaneous movement ventricular systolic function, asymmetric septal hypertrophy, left ventricular uneven tension. myocardial fibers disorder, ventricular filling affected, left ventricular function damaged. Compared to the normal atrioventricular conduction, the morbidity and mortality in heart failure increased conspicuously. Therefore, it is necessary to choose a new pacing site in order to reduce the bad influence of heart function. Right ventricular outflow pacing (RVOTP) changes the traditional pacing site from apex to right ventricular outflow. Because it can keep nearly normal physiological ventricular activation sequence and ventricular systole synchronism, the whole heart systole and diastole can be coordinate. Hemodynamics is superior to that of RVAP. With the increasing clinical application of the spiral electrode wire,RVOTP is easily fixed compared to RVAP. It provides more using ways for the new pacing site as it has better pacing and sensing function.At present, the investigation involes the immediate and medium-term, short-term hemodynamic and electrophysiological evaluation of the fields. The results demonstrate that RVAP may lead to impaired left ventricular systolic and diastolic function . But there are many disputes exiting to these results. Nowdays, the reseach about the ventricular mechanical synchronous change resulted from different site pacing are limited. So it causes more and more attention to detect the myocardical motion synchronism. Cardiac synchronization movement should include the following three elements : by the time sequence of atrial and ventricular synchronous coordination between campaigns; Synchronous coordination between the left ventricle and right ventricle of the ventricular wall motion and left ventricular internal coordination synchronized movement. The synchronous movement of the heart wall is not only reflected in the time period between the systolic and diastolic phase is the same, but also myocardial performance for the same direction. However, there is not an ideal method for evaluating cardiac resynchronization campaign.TDI is a new technique which can assess the myocardical motion through the semi-qualitation and quantitative. It bases on the Doppler principle and it can analyse brachytely tissue motion, to detect the signal of wall motion which are low frequence but high amplitude and show the myocardical tissue motion. Therefore, it can assess the different segment of ventricular wall motion objectively and all around. From its appearance, the experts attempt to assess the heart function through this new technique. The intial effect has been abtained. TDI can directly extract the frequency shift signal from myocardial tissue and measure the velocity of wall motion, discriminate different phase in cardiac cycle clearly. For its very high time resolution, TDI can clearly display not only all phases in the same cardiac cycle but also myocardial longitudinal direction of the movement. So we can utilize the velocity imaging to observe and assess the left ventricular myocardial synchronization at different time phase. It provides the possible of assessing the cardiac function through the measure of the time index. TDI is a new technique which is being widely used not only without damage but also cheap value and safety and without radioaction. Many experts apply it to study the left ventricular wall segment motion in physiological and different pathological state. But it is less in the change of heart function result from different pacing site.Objective: To discuss the left ventricular systole situation and the value in myocardic synchronism motion by TDI. To compare the effect of right ventricular outflow tract ( RVOT) pacing and that of right ventricular apex (RVA) pacing on the ventricular wall motion and cardiac function. It is confirmed that TDI could assess the coordinate of cardiac motion without damage and rapidly and instantly. It provides a new and reliable method to choose the pacing mode for patients and assess the effect of curing the heart diseases.Methods: The study is divided into two parts. In the first part, 30 healthy volunteers participated in our study. To measure the time to systolic peak(Ts) which is used to assess the myocardical synchronical motion. SPSS 10.0 statistics software is used in our study. In the second part, RVA pacing was conducted in 15 patients(9 males and 6 females), of whom hadⅡ—Ⅲ°atrioventricular block, and, underwent RVA pacing was conducted in 10 patients (6 males and 4 females) , of whom hadⅡ—Ⅲ°atrioventricular block. Twelve months after installment of the dual-chamber pacemakers, tissue Doppler imaging was used to evaluate Ts of interventricular septum and left ventricular. CO, CI, SV, SVI and LVEF were also measured by conventional 2-Dimensional echocardiography.Results : Ts in left ventricular was measured by the six-basal-six-mid-six-apical-segmental mode. The result shows that the different of Ts has no significant meaning(P>0.05).QTVI shows that the ventricular motor direction keep coincident in all volunteers and present the same regular pattern: ECG R wave in the rise and decline of the S wave , QTVI show a rapid rise and decline in the baseline near the two-way wave; followed by a rapid rise and slow decline in the positive wave period Sm; ejection in the ECG T-wave, QTVI shows rapid downward after the peak of negative rapid return to the baseline early diastolic wave of Em; ECG in the P wave, QTVI also showed a rapid downward trend. The peak of negative rapid return to baseline systolic wave of atrial Am. It is useful to assess the cardiac synchronization by this regular pattern. The time to systolic peak of the left ventricular wall motion in the normal adult are conformity. Compared with RVA pacing, RVOT pacing better improved CO (4.68±1.06 vs 5.59±1.02,t= 2.134,P=0.044 ),CI (3.05±0.72 vs 3.65±0.54,t=2.230,P=0.036),SV (69.73±13.51 vs 77.70±10.73, t=2.376,P=0.026),SVI (41.60±9.11 vs 48.60±9.35,t=2.737,P=0.012),LVEF (45.53±7.42 vs 57.30±14.71, t=2.338, P=0.037) . RVOT pacing significantly shortened Ts and improved the consistency of wall motion as compared with the RVA pacing. In RVOTP group, Ts is approach to the normal numerical value.Conclusion: Ts in left ventricular of the normal adult has no significant deviation. The systolic time interval in every left ventricular wall keeps synchronic. The regular pattern is completely consistent with the normal cardiac physiological contraction. Compared with RVA pacing, RVOT pacing with a more physiological depolarization pattern and theoretically better hemodynamics , significantly improves ventricular performance , including cardiac function and cardiac synchronism. Tissue Doppler imaging is useful in evaluating the synchronism of ventricular wall motion and cardiac function. The conventional echocardiography in the past is impossible to do it. Therefore, TDI possesses spcious application in choosing the pacing mode.