الفهرس 
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Abstract
The aim of this study is making use of the new technique of recording sinus node electrogram in order to:
1- Evaluate sinus node function and sinoatrial conduction in patients with sinus bradycardia including those patients with sick sinus syndrome.
2- Enhance the understanding of the mechanisms underlying the SN function using sinus node electrograms.
3- Measure Atrioventricular and sinoatrial conduction in patients with sinus bradycardia and those with sick sinus syndrome.
4- Re-evaluate sinus node recovery time as a method of assessing sick sinus syndrome.
5- Compare SACT directly measure with that obtained indirectly through continous pacing and premature stimulation.
from this study we conclude the following:
1- SNE is a relatively simple technique that considers the diagnostic quality of the currently used tests for evaluation of SN function.
2- SNRT remains the most reliable test for evaluation of SN function. However, the interpretation of the test should be done in the light of the information gathered from the concomitant use of SNE.
3- SACT estimated by programmed electric stimulation is not reliable and did not correlate with both SACTd and SACTn.
4- Atropine in full dose (0.04 mg/ kg) can separate clearly patients with SSS and those with SB due to high vagal tone.
5- The age and sex of patients with SB are similar to those with SSS.
6- Exercise treadmill test couldn’t separate patients with SSS from those with SB.
7- Testing SN automatically can clearly separate patients with SSS and SB from patients with high vagal tone.
8- Further research is definitely needed for evaluation of:
a) The clinical importance of SACT and it is implication on therapy and on the understanding of SN function.
b) Large trial in which post pacing SACT is evaluated and the relationship between post pacing SACT and the PCL is established.
c) Sinus node automatically needs to be evaluated in different conditions affecting sinus node, especially, the effect of different pharmacologic agents that might affect it. Also, the effect of age on this parameter needs to be evaluated.