RÉSUMÉ
In order to determine the effect of bundle branch block on the Q-T interval, the electrocardiogram of 115 Jordanian Subjects [55 males, mean age 56 years, and eight females, mean age 53.6 years with right bundle branch block; and 31 males, mean age 59, and 21 females, mean age 56.5, with left bundle branch block] were examined, prospectively, over a period of two years. Lipman and Massie's criteria[1] were used for the selection of bundle branch block cases. No significant difference was found in the Q-T interval or Q-Tc [corrected for conduction defect and heart rate using Bazett's formula][2] between right and left bundle branch block. The Q-T interval measured from the beginning of QRS to the end of the T wave varies with the heart rate, age, and sex. It decreases with increasing heart rates[3], hence a number of formulae have been proposed to express the relationship between the length of the cardiac cycle and the Q-T interval[2,4]. The Q-T interval is prolonged in myocardial infarction[5] and sometimes in rheumatic fever[6,8]..It is also lengthened in hypocalcemia, and hypokalemia when associated with calcium deficit[9]. This study was undertaken to determine the effect of bundle branch block on the Q-T interval, and to compare the results obtained with those in the study of Talbot[10] [United Kingdom]