ECG Clinic


David H Spodick, MD, DSc, FACC, Section Editor Am Heart Hosp J. 2010;8(1):50–1


Left Bundle Branch Block—


Significance of the Spatial QRS Axis (Vector) David H Spodick, MD, DSc, FACC


n electrocardiogram (ECG) of an 82-year-old woman (see Figure 1) showed complete left bundle branch block (LBBB: QRS duration 148ms), left axis deviation to -52º, rS complexes in V1–V6, absence of septal Q-waves, and first-degree atrioventricular block (PR 236ms). The textbook diagnosis of LBBB includes wide (≥120ms) QRS and late (45ms or longer) intrinsicoid deflection in V5 and/or V6;


A I ID 45ms II aVL V2 V5


however, in this case rS (rather than R–R1) complexes yield an approximately 20ms ‘intrinsicoid deflection’ (ID) for these leads (ID is lead-dependent and equal to the onset of the final R, r, or R’ downstroke in a unipolar lead; the only possible unipolar lead in this case is aVL, with ID onset at 45ms). This is common with, and a function of, left axis deviation. All ECG complex axes (mean vectors) exist in 3D space, i.e. they have spatial


Figure 1: Electrocardiogram of an 82-year-old Woman Showing Left Bundle Branch Block aVR


V1


V4


III


aVF


V3


V6


II


• From Medical Service/St Vincent Hospital, Worcester, MA


• Correspondence: David H Spodick, MD, DSc, FACC, Medical Service/St Vincent Hospital, 123 Summer Street, Worcester, MA, 01608. E: david.spodick@stvincenthospital.com


50 Left Bundle Branch Block Summer 2010


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