SVT with LBBB

Report:

Supraventricular tachycardia 152/min

Left bundle branch block

Comment:

The rS complexes in lead V1 are perfectly ‘normal’ LBBB complexes in that the initial R wave is narrow, the S downstroke is sharp and the upstroke slurred. The frontal plane axis is, again, unremarkable for a LBBB at -20o.

The upstroke is slurred and notched in many other leads, but this happens with LBBB, especially if there is underlying myocardial disease. This is what made the computer diagnose VT in this case.

The intriguing aspect of the trace is the rhythm strip, showing what at first may appear as dissociated atrial activity. This would make the tachycardia ventricular, or junctional with AV dissociation. The notches in the S wave do not, however, show obvious dissociation; they recur at regular intervals at the same place throughout. Further, lesser degree of notching is apparent next to the obvious dents in the S wave: e.g., on either side of the third beat in the rhythm strip. These notches may well be part of the QRS complex, varying with respiration. More pseudo P waves.

This sounds too easy. In this case, it was: the patient was cardioverted with sotalol (after the ubiquitous xylocaine failed) and revealed a pre-existing LBBB. A later trace (83a) shows (almost) normal sinus rhythm with complexes virtually identical to those seen during the tachycardia. The phasic S wave notches are there, too, in the rhythm strip.

His LBBB remained notched after an infarction a month later (Fig 83b), but became smoother the day after (Fig 83c).

83a. Sinus bigeminy, possibly through a sinoatrial exit block. The phasic QRS notching is present as before.

83b. Acute anterior infarction month later preserved the notching. 83c. Smoother LBBB complexes but more obvious infarctional changes 24 hours after 83b. 84. 20 year old with recurrent palpitations associated with weakness and dizziness.