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Right bundle branch block
Right bundle branch block is characterised by an RSR’ pattern with the R’ being slurred, producing a QRS duration of 120 msec or more. This delayed right ventricular activation is reflected as a delayed and slurred S wave in leads oriented to the left ventricle, viz. lead I, aVl, V5 and V6. The same pattern if it occurs with a QRS duration of less than 120 msec, it is generally designated as incomplete right bundle branch block. Mild ST segment depression and inverted T waves in anterior leads are associated with right bundle branch block.
Unlike left bundle branch block which often co-exists with structural heart disease, right bundle branch block can occur in the absence of structural heart disease. In a large study involving 67,375 asymptomatic individuals (Am J Cardiol. 1960;6:143-52), the incidence of right bundle branch block was found to be 0.15% in the age group of 20 to 30 years and 0.29% inthose above 40 years .
Right bundle branch block may complicate acute myocardial infarction of the anterior wall, in which case it has prognostic significance, usually indicative more extensive myocardial infarction and possibility of left ventricular dysfunction. Incomplete right bundle branch block pattern can occur in atrial septal defect, Ebstein’s anomaly of tricuspid valve and acute pulmonary embolism.