الفهرس 
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Abstract
Left ventricular ejection fraction (LVEF) is a major determination of clinical outcome in many cardiovascular diseases that’s why accurate estimation is crucial. Left bundle branch block (LBBB) causes a dyssynchronized contraction of left ventricle (LV) in form of abnormality in the sequence of activation which results in non-coordinated contraction LV; causing a kind of regional wall- motion abnormality which cause measuring left ventricular ejection fraction (LVEF) by two-dimensional echocardiography 2DE could be less reliable in this particular condition.
2DE measurement also has disadvantages like apical foreshortening and false assumption of LV geometry and it’s not optimal to assess three dimensional structure like cardiac muscle with two dimensional imaging modality . Those limitation could be overcome by real time three dimensional echocardiography (RT3DE) with 16 segments SDI obtained by sequential analysis and frame to frame assessment of endocardial borders.
Our aim was to evaluate the role of dyssynchrony index (SDI), measured by RT3DE, in assessment of LVEF and left ventricular volumes accurately in patients with LBBB.
In this study, we included 65 participants with LBBB and normal LVEF or nonischemic cardiomyopathy. LVEF and left ventricular volumes indexed by BSA were assessed by 2DE (modified Simpson’s rule) and RT3DE (four beats full volume analysis) and the impact of SDI on results were evaluated. In patients with SDI >7%, LVEF measurements were significantly different (45.61% [34%-66 %] vs 37.18% [24 %– 55.6 %], P < .0001) between 2DE and RT3DE respectively, and significant difference in LVESVI ( 33.33 ml/m2 vs 41.31 ml/m2 ) , P= 0.002 while there was no significant difference in LVEDVI (68.10 ml/ m2 vs 70.34 ml/m2) , P = 0.501 between 2DE and RT3DE respectively. In patients with SDI < 7%, there were no significant differences between two modalities in terms of LVEF measurements (46.73% [35% -57 %] vs 44.58% [33.4 % –55.6%], P = .158) between 2DE and RT3DErespectively. LV diastolic volumes were not significantly different while systolic volumes were underestimated by 2DE, and this finding was more pronounced when
SDI > 7. and we found positive correlation between duration of QRS complex and SDI .
Conclusion: In patients with LBBB and high SDI (>7%), LVEF values were overestimated and systolic volumes were underestimated by 2DE compared to RT3DE so it might be reasonable to assess LV systolic function by RT3DE rather than 2DE in this particular population .
Our limitation was in small sample size of our study and long duration of the study during Era of Covid-19 and not comparing with CMR .
So we recommend further larger cohort studies in this topic with inclusion of CMR which considered our golden standard of left ventricular systolic function assessment.