RBBB with Right and Left Axis

Report:

Sinus rhythm

SVEBs, bigeminal

Left axis deviation in sinus beats, probably LAHB

Right axis deviation in SVEBs due to LPHB

Right bundle branch block throughout

Borderline T wave changes

Comment:

With RBBB the frontal axis is determined by the initial 0.06” – the “unblocked” part of the QRS. In the sinus beats it is decidedly left, approximately –40o. There are probably small R waves in 3 and aVF and there is no Q of any size in 2: LAHB is more likely cause of LAD here (despite smallish voltages) than inferior infarction.

The interesting part is the aberrancy in SVEBs: huge axis swing to about +130o! Only LPHB can explain it. While the right bundle branch is permanently out of use, on the left side one or the other fascicle is always faster than the other, depending on the cycle length. If they were synchronous, there would be no axis deviation – just plain RBBB.

The overall rate is just over 100/min; the bigeminy of sinus and supraventricular ectopic beats thus constitutes, technically, a bidirectional tachycardia. This of course is not what is normally meant by this term and most bidirectional tachycardias are ventricular in origin (classically with RBBB-like complexes like the ones here in V1). This case illustrates how easily the frontal axis can be made to swing and how at least some cases of bidirectional tachycardia are supraventricular in origin. In this case, too, the existing morphologies could easily be misdiagnosed as bidirectional VT if a faster rate obscured atrial activity: the qR in V1 suggests ventricular ectopy rather than RBBB. Thus an SVT or flutter from these short-coupling SVEBs would look like VT.

The right precordial Q waves are most likely due to the hemiblocks, but an old anteroseptal infarction cannot be excluded. The hemiblocks also tend to produce qR or R waves where RBBB alone had the classical RSR’ morphology.

Below, in a different patient (Fig 64a), the sinus beats are normally conducted while the aberrant SVEBs (of atrial origin) have atypical RBBB/LPHB morphology, again with new q or Q waves.