الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Abnormalities of cardiac impulse formation and propagation have been recognized as potentially lethal causes of cardiovascular morbidity and mortality. Symptomatic bradycardia is effectively treated with the implantation of a cardiac pacemaker.
A variety of types of pacemakers and modes of pacing has been developed to restore or sustain a regular heartbeat in different ways. Pacemakers can be divided according to the number of device leads into two types, single chamber & dual chamber. The difference between single and dual chamber pacemakers is that a single chamber pacemaker has only one lead implanted in the right ventricle. A dual chamber has two leads, one in the right atrium and one in the right ventricle which can allow a heart rhythm that more naturally resembles the normal activities of the heart and achieving AV synchrony.
The aim of this study was to detect differences between single and dual chamber pacemakers regarding their effects on left ventricular volumes and function using Doppler and 3D echocardiography.
The study included 50 patients with structurally normal hearts undergoing permanent pacemaker implantation for high grade AV block.
2D echocardiography was done before the implantation to exclude patients with reduced LV systolic function (EF<50%), significant valvular heart disease. Patients with IHD, recent cardiac surgery, arrhythmia or poor echocardiographic windows were excluded.
SV was calculated using the Doppler method. Full volume 3D echocardiography was performed to calculate LV volumes, COP and EF. All measurements were repeated after 7-10 days post-pacing and at 6 months.
from the fifty consecutive patients, 27 Patients (54%) received single chamber and 23 patients (46%) received dual chamber pacing. RV lead implanted at RV apex in all candidates. Patients with single chamber pacemakers were programmed to VVIR mode while those with dual chamber pacing were programmed to DDDR mode. Rate responsive mode was selected. In the DDDR group, dynamic AV time delay was selected with resting paced/ sensed AV time delay adjusted to 200/150ms. Device interrogation was done at both follow up visits to inquire ventricular pacing percentage (VP%).
It was found that pacing resulted in a significant reduction in SV. This reduction was detected at 10 days and became more significant at six months. At 10 days, the reduction was due to significant DROP in left ventricular EDV while ESV did not change. Both groups showed a significant increase in COP 10 days post-pacing despite the DROP in SV as it was overcounted by pacing at higher heart rates. Despite achieving AV synchrony in DDDR group, there was no statistically significant difference between both groups regarding the reduction in SV. However, DDDR group showed greater increase in COP than VVIR group. This increase was because DDDR mode of pacing tracks the patient intrinsic heart rate leading to pacing at higher heart rates. Also, there was a DROP in left ventricular EF at 10 days with no significant difference between groups. This DROP is due to the reduction in left ventricular SV and pacing induced LV dyssynchrony.
During the second follow up, at six months, SV continued to decrease as a result of pacing induced remodeling affecting mainly ESV which increased significantly while EDV did not change significantly from 10 days to six months. This DROP in SV resulted in a corresponding DROP in COP and EF. Again, there were no significant differences between single chamber and dual chamber pacing groups regarding all the measured parameters except for COP which was still higher in the DDDR group.
Based on changes on LVEF, six patients developed PICMP with their post-pacing EF dropped to 45% or below, 19 patients developed PIVD with DROP in their EF 10% or more from baseline but still above 45%. 25 patients maintained preserved EF with a DROP less than 10% from baseline.
The study concluded that dual chamber pacing is not superior to single chamber pacing regarding pacing effects on cardiac volumes and function. It provided higher COP due to pacing at higher heart rates not due to achieving AV synchrony. However, pacing at higher heart rates was associated with higher incidence of pacing related LV dysfunction and cardiomyopathy. PICMP may be higher than previously described in the literature and it may occur as early as 6 months post implantation.
The study included GLS measurements for all the patients before and after implantation. It was found that Pre and post-pacing strain reduction was an early predictor for LV dysfunction.
The study revealed the importance of GLS as an early predictor for pacing induced LV dysfunction.
It was found that the use of Doppler method for quantification of SV and COP was not inferior to 3D echocardiography.
Based on the results and conclusions, the study recommends the use of single chamber pacing in elderly population and in patients with limited mobility. Dual chamber pacing should be considered for younger and active patients who need higher COP and for patients with pacemaker syndrome.
The study recommends routine echocardiography at follow up visits for device interrogation for early detection of PICMP. Device programming should be adjusted to decrease the percentage of ventricular pacing in order to decrease the incidence of PICMP.
The study also recommends the use of GLS as an early predictor for PIVD and PICMP.