“Spry” Woman Reports Rapid Heart Rate

ANSWER
The correct interpretation includes atrial fibrillation with a rapid ventricular response and aberrantly conducted complexes, left axis deviation, and a left bundle branch block.

Atrial fibrillation is evidenced by the irregularly irregular heart rhythm without a measurable PR interval, and the rapid ventricular response is indicated by a ventricular rate > 100 beats/min.

Aberrant conduction, caused by conduction delay down the His-Purkinje system, is evidenced by the wide QRS complexes with a normally conducted beat (see first beat in leads V₁-V₃). Criteria for left axis deviation include an R axis between –30° and –90°, and left bundle branch block criteria include a QRS duration > 120 ms, a dominant S wave in V₁, and broad monophasic R waves in leads I, aVL, and V₅-V₆.