الفهرس 
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Abstract
In spite of the evident improvement in quality of life for most patients with an cardiac pacemakers implant, the left bundle-branch block (LBBB) induced by right ventricular (RV) apical pacing can cause hemodynamic, structural and functional alterations in the heart, with deleterious consequences on the clinical evolution of some patients (265, 266). The cardiac pacing at any point of the ventricle alters the natural heart activation and contraction pattern, as the stimulus conduction velocity is slower across the ventricular myocardium, when compared to that resulting from the specialized His-Purkinje system (3, 17).
Right ventricular apical pacing can induce both interventricular dyssynchrony (between the RV and the LV), as well as intraventricular dyssynchrony (within the LV) (15). It has been demonstrated that the presence of ventricular dyssynchrony is associated with an increased risk of cardiac morbidity (281) and mortality (282) in heart failure patients. In addition, it has been suggested that the presence of mechanical dyssynchrony after long-term RV apical pacing is associated with reduced LV systolic function and deterioration in functional capacity (15). However, there are only a few studies that have demonstrated a direct relation between (pacing-induced) ventricular dyssynchrony and clinical heart failure. At the same time, it has been shown that restoration of normal conduction and “cardiac synchrony” by CRT results in normalization of LV systolic function. This suggests that an abnormal activation pattern (left bundle branch block during RV apical pacing) or ventricular dyssynchrony may be directly related to a deterioration of LV function. Therefore, the assessment of ventricular dyssynchrony may provide important information in patients with permanent RV apical pacing (283,284).
Long-term effects of right ventricular apical pacing have been studied, and no much information is available on the acute and early effects of right ventricular pacing on left ventricle function and left ventricle dyssynchrony. (26) The aim of the study was to compare between early effects of right ventricular apical pacing on left ventricular functions in single and dual chamber pacemakers using echocardiographically determined parameters of systolic and diastolic functions as well as 2D speckle-tracking strain imaging. Another aim was to assess that single brain natriuretic peptide (BNP) after 2 months of implantation is correlated for ventricular dyssynchrony in different cardiac pacing mode.
The study was carried out during the period between April 2012 and November 2013 and included 40 patients with implantation of single and dual chamber permanent pacemakers at electrophysiology unit of national heart institute. The patients enrolled into 2 groups each one includes 20 patients: Group A (n=20): 20 patients with implanted single chamber pacemaker with right ventricular apical pacing (VVI). Group B (n=20): 20 patients with implanted Dual chamber pacemaker (DDD).
All patients were subjected to Full history taking with history of the medications, general and cardiac examination. Patients also were subjected to measurements of QRS duration, Chest X-ray to verify the position of the ventricular lead-electrode,Urea and createnin level and Pacemaker analysis. Samples for BNP were obtained after 2 months and 6 months intervals. Patients were examined before implantation and again after 2 months and 6 months of implantation for left ventricular dimension, left ventricular systolic and diastolic functions, Myocardial performance index , LV dyssynchrony and Pulsed tissue Doppler imaging was used to obtain septal and lateral velocities for both E and S waves. Longitudinal strain was measured with STE using the apical 4-chamber and 2-chamber views. Radial and circumferential functions were assessed with STE using parasternal short axis images of the LV base, mid-ventricle, and apex.
This study showed mean BNP level in VVI pacing (group A) was higher than DDD pacing (group B), after two months Follow up group (A) showed a mean of 196.5± 123 pg/dl compared to 79.35± 65.36 pg/dl in group (B) with highly significant difference between both groups (P value = 0.001) .Comparison of both groups for BNP level after 6 month showed a mean 200.85± 106.6 pg/dl in group (A) and a mean of 121.5± 105.15 pg/dl in Group (B) with statistically significant difference and (P value = 0.023). Also there was statically significant difference between group (A) and group (B) when adding the effect of pacemaker type over time on BNP level, P value = 0 .048.
Regarding ventricular dyssynchrony, our results showed no statistically significant difference between both groups at 2 months, 6 months and for repeated measurements comparisons of septal to posterior wall motion delay and interventricular mechanical delay in both groups over time, (P value of > 0.05). In contrast there was statistically significant difference between both groups appeared in results of aortic preejection delay and radial time to peak difference (P value of < 0.05). We believe that the difference was caused by loss of atrioventricular synchrony and a larger part by ventricular pacing percentage.
Our results showed significant correlation between the BNP level and pacing percentage, QRS duration, septal to posterior wall delay, Aortic preejction delay and radial time to peak dyssynchrony. At multiple linear regression analysis, the pacing percentage and Aortic preejction delay remained only significant and independent predictor of BNP levels, even after adjustment for age and LVEF with P value of 0.007 for Aortic preejection delay and P value of 0.000 for pacing percentage. So we can infer that the higher the percentage of pacing and the longer the preejection delay, the higher the BNP level. In 2002, the results of the DAVID trial revealed that RV paced patients with LV dysfunction, requiring a defibrillator, who were actively paced in DDDR-70 mode had a 60% greater risk for hospitalization or death than patients who received minimal back-up pacing in VVI-40 mode (296). This can infer the strong relationship between pacing percentage and BNP increment.
In our study there was a no statistically significant difference within repeated measurements of left ventricular EF, systolic and diastolic internal dimensions in both group over time (P value >0.05) and this is due to short term of follow up. S wave by pulsed tissue Doppler is another predictor of systolic dysfunction (367). In our study there was no statistically significant difference for septal and lateral S wave by pulsed tissue Doppler in both groups over time (P value >0.05).
In our study we found septal S wave velocity was more affected when compared to lateral S wave velocity within each group after 6 months with (P value of 0.005) for group A and (P value of 0.001) for group B. Ventricular pacing reduces mechanical work in the septum during RV apical pacing by 50% and increases it by 50% in the LV free wall.
We did not find any statistically significant difference between both groups regarding septal and lateral E′ waves by pulsed tissue Doppler. This was the same as previous studies; they also found no significant changes in diastolic function.
Our findings showed increase of myocardial performance index in both groups with statistically significant difference between both groups at 6 months (P value of 0.03). Myocardial performance index incorporates both systolic and diastolic aspects of function and also been shown to correlate well with known invasive indexes of LV systolic and diastolic function (360).
Global longitudinal strain analysis decreased in both groups but comparisons between both groups at 2 and 6 months showed no statistically significant difference with P value >0.05 because both groups used right ventricular apical pacing. Circumferential strain analysis remains unaffected or slightly increased in both groups but comparisons between both groups at 2 and 6 months showed no statistically significant difference with P value >0.05. Comparing basal, mid and apical radial strain analysis of both groups at 2 months showed no statistically significant difference with P value >0.05 while comparing the same levels at 6 months showed statistically significant difference between both groups.