We aimed to determine the relationship between QT interval and QT dispersion with left ventricular systolic function (LVSF), in patients with left or right bundle branch block ( LBBB or RBBB). In this cross-sectional study, 80 convenience samples of patients with LBBB and RBBB were recruited from March to September 2015 in Kerman. The relationship between QT interval and QT dispersion (based on electrocardiogram) with LVSF (basedon echocardiography) was measured using Chi square and student T test. The findings were compared between LBBB and RBBB cases. Left ventricular systolic dysfunction (LVSDF) in LBBB cases was more prevalent than RBBB. (80% vs. 45%). The QT dispersion was seen in 100% and 95% of cases with LBBB and RBBB respectively.
The increased QT interval was more frequent in LBBB (92.5%) than RBBB (80%). In LBBB, with prolonged QT interval, LVSDF was more prevalent than normal QT interval sub group. (81% vs. 66%) but in RBBB only the
prevalence of severe LVSDF had increased in the prolonged QT interval subgroup. (21% vs. 12%). In patients with BBB, especially LBBB, there is a direct significant relationship between prolonged QT interval and left ventricular ejection fraction (LVEF). So after diagnosis of BBB in ECG, it is better to calculate QT interval until if it is prolonged, evaluation of LVEF with echocardiography was done. On the other hand, QT interval is a diagnostic key for estimation of LVSF in patients with BBB.
Keywords: long QT syndrome, Left bundle- branch block, Right bundle- branch block, ventricular function, left.