Alternate Interpretation of Left Bundle Branch Potential – Response to a Research Letter

This reader disagrees with the conclusions stated in Research Letter “Electrophysiological characteristics of left bundle branch potential during implantation” by Ponnusamy et al.1 •A measurement timeline isn’t provided in frame-B, but frames A and B are likely at the same paperspeed. If so, time from LB/PV signal to QRS onset is actually shorter (20 ms) in the “Type-B” vs. “Type A” potential as shown (timeline copied from frame-A): •Histology of the conduction system transitions from proximal “bundle cells” with fibrous sheathing (H&E staining) to distal Purkinje cells that are directly juxtaposed to myocardium (elastica van Gieson staining).2 The PV interval and LV activation time are known to decrease as the pacing site becomes more apical. •Density of Purkinje-myocyte contact differs in different regions of the LV, with highest contact density near the apex, followed by anterolateral, anterior, septal and basal portions.3 Conduction velocity is higher with more dense junctions.4 •Disease processes (fibrosis, fatty infiltration, amyloid deposits, infiltrative diseases and even healthy aging) can affect the conduction system and variably affect PV time. No information is provided regarding underlying pathology/LV function/chamber dilation, factors that could affect PV interval. •There is no analysis of radiographic lead location vs. PV interval. More apical deployment is associated with shorter PV intervals. •Inter-individual variation exists in LBB arborization,5,6,7 but the left septal fascicle has greatest variability and is likely engaged during LBB pacing. The arborization pattern of the septal fascicle is another factor in PV interval. Electrophysiological characteristics of left bundle branch potential during implantationHeart RhythmVol. 20Issue 11PreviewLeft bundle branch pacing (LBBP) provides electrical and mechanical synchrony at low stable thresholds. A left bundle branch (LBB) potential can be demonstrated in all patients with normal anterograde LBB activation during sinus rhythm. Su et al1 noted LBB current of injury (COI) in 67% of patients with LBB potential and documented 3 different types of LBB COI. However, no studies have described the different patterns of LBB potential during implantation. We aimed to analyze the electrophysiological characteristics of the LBB potential and its clinical significance during LBBP. Full-Text PDF Author's reply to Alternate Interpretation of Left Bundle Branch Potential – Response to a Research LetterHeart RhythmPreviewThe accuracy of offline digital magnification and measurement of short intervals (20ms vs 30ms) can be misleading as argued by Prof. Pavri in the example provided. We standby the accuracy of our measurements online at a sweep-speed of 300ms as demonstrated by the attached figure of the same disputed measurement. The PV-interval was consistently measured from the onset of the (positive or negative) deflection from baseline. Full-Text PDF