Key result
In a patient undergoing left bundle branch pacing, a paced QRS morphology transition from nonselective to selective pacing did not always indicate LBBP, requiring assessment of high-output pacing.
Case Report (n=1)
A paced QRS morphology transition from nonselective to selective pacing does not always indicate true left bundle branch pacing, making high-output pacing assessment mandatory.
Clinicians should not rely on QRS transition alone to confirm LBB capture; this case challenges criterion specificity and leaves validation to prospective studies.
We report a patient who underwent left bundle branch pacing (LBBP) because of intermittent complete heart block. During unipolar pacing at a deep septal site, a transition in QRS morphology from nonselective to selective pacing (presence of a discrete component on the intracardiac electrogram) was observed, but this was accompanied by concomitant prolongation of the stimulus-to-left ventricular activation time (Stim-LVAT) from 96 to 116 ms. However, with several additional turns of the lead, a transition from nonselective to selective LBBP with a short and constant Stim-LVAT of 78 ms was achieved. Our case suggests that a paced QRS morphology transition from nonselective to selective pacing does not always indicate LBBP. Assessment of high-output pacing is mandatory to achieve LBBP.
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Iida et al. (2022) conducted a case report in Intermittent complete heart block (n=1). Left bundle branch pacing (LBBP) was evaluated on QRS morphology transition and stimulus-to-left ventricular activation time (Stim-LVAT). In a patient undergoing left bundle branch pacing, a paced QRS morphology transition from nonselective to selective pacing did not always indicate LBBP, requiring assessment of high-output pacing.
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