Palpitations of unusual etiology

Written by Pendell Meyers, with edits by Steve SmithA male in his 60s with history of HTN and previous complaint of palpitations but with a negative holter monitor workup, presented to our ED with palpitations for the past hour, associated with lightheadedness and presyncope.He was hemodynamically stable and well appearing, but was symptomatic with palpitations and lightheadedness.Here is his 12-lead on arrival:What do you think?There is a regular, seemingly wide complex tachycardia at 224 beats per minute. The computer QRS duration is calculated at 178ms, but I believe the true QRS duration is much shorter, and in most leads no greater than 100ms. The QRS morphology is similar to RBBB with LPFB. However, the RBBB morphology in V1 is not the classic rSR ' [first wave (r-wave) smaller than the second (R ' -wave)]. Instead, the first R-wave in V1 is taller than the second (the R ' -wave). This " sign " has been described as an indicator of ventricular origin. However, the initial deflection of the QRS complex has undeniably rapid and organized (steep slope) conduction, strongly suggesting that the conduction pattern is utilizing the intrinsic conduction system of the Purkinje fibers.For a QRS complex to have narrow QRS duration, organized initial conduction, and morphology consistent with RBBB + LPFB, it must either:1) be supraventricular with RBBB and LPFBor2) originate in the left anterior fascicle itselfThe differential at this point includes SVT with RBBB and LPFB, ant...
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