The ECG was recorded from a 44 year old man during an employment medical.
ECG. Rhythm: Sinus rhythm is present
Morphology: The QRS complexes are abnormally wide at .12 seconds. There is a secondary R wave in lead VI, the QRS complex has an rSR’ appearance. There is a delayed S wave in lead I, aVL, V5 and V6. Right bimdle branch block is present. The QRS axis is 0 degrees – within normal limits.
Comment. The bundle branch blocks which represent a form of conduction disturbance rather than an arrhythmia per se, are considered in this section for two reasons. Firstly bundle branch block is indicative of disturbed conduction that may precede or be associated with more serious degrees of heart block; this is particularly true of right bundle branch block. In the second place recognizing the patterns of QRS morphology associated with bundle branch block is especially important in the interpretation of broad complex tachycardias which are considered later.
The main ECG features of RBBB are the presence of a broad QRS complex reflecting delayed ventricular depolarization, and an M shaped rSR’ complex in lead VI. The initial part of ventricular activation is depolarization of the interventricular septum, and this normally occurs from left to right: VI therefore registers a positive R wave. Left ventricular acdvadon then occurs from right to left and a negative S wave is recorded in a lead recording from the right ventricle such as VI. The last part of the ventricle to be activated is the right ventricular free wall and activation spreads towards VI giving rise to the broad and often slurred secondary R wave.
Right bundle branch block may occur in apparently normal individuals. It is also seen in ischaemic disease and in conditions affecting the right ventricle – including several types of congenital heart disease.