Xylocaine & BBBB

Report:

Atrial tachycardia, possibly sinus, 174/min

2:1 AV block

Left bundle branch block

Period of 1:1 conduction

Comment:

The exact doubling and then halving of the ventricular rate should have steered the CCU staff away from xylocaine. Broad complex arrhythmias always look more scary on the screen than on paper. At any rate, the drug was probably responsible for the asystole that followed50 (below).

It is unlikely xylocaine promoted AV nodal conduction from 2:1 to 1:1 in this example, for two reasons: (i) episodes of 1:1 conduction occurred before exposure to the drug and (ii) the locus minoris resistentiæ here are the bundle branches, not AV node. The patient had both RBBB/LAHB and LBBB at different times and the current 2:1 AV block + LBBB was almost certainly a manifestation of bilateral bundle branch block (BBBB), as was the ventricular standstill below.

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