EKGConduction abnormalitiesPart I

Sandra Rodriguez, M.D.

RBBB

QRS > 120msec. Terminal forces oriented rightward and

anteriorly. rSR’ complex in V1. Terminal S waves in I, AVL, V6. Terminal R wave in aVR. Normal axis. ST-T should be negative in leads with

terminal R forces (secondary).

RBBB with ST-T abnormalities

LBBB

QRS >120msecs. Terminal forces oriented leftward and

posteriorly. Terminal S wave in V1. Terminal R wave in I, aVL, V6.

LBBB

Left Fascicular Anterior Block

QRS axis -45 to -90 degrees. QRS duration <120msecs unless RBBB. rS complexes in II, III, aVF. Small q wave in I, aVL. Poor R progression in leads V1-V3 and

deeper S waves in leads V5 and V6. R-peak time in lead aVL >0.04s, often

with slurred R wave downstroke

Differential

Some cases of inferior MI with Qr complex in lead II (making lead II 'negative')

Inferior MI + LAFB in same patient (QS or qrS complex in lead II)

Some cases of LVH Some cases of LBBB Ostium primum ASD and

other endocardial cushion defects. Some cases of WPW syndrome (large negative delta wave in lead II)

LAFB

Left Posterior Fascicular Block

Right axis deviation in the frontal plane (usually > +100 degrees)

rS complex in lead I qR complexes in leads II, III, aVF, with R

in lead III > R in lead II   QRS duration usually <0.12s unless

coexisting RBBB Very Rare defect.

Differential

Many causes of right heart overload and pulmonary hypertension

High lateral wall MI with Qr or QS complex in leads I and aVL

Some cases of RBBB Some cases of WPW syndrome Children, teenagers, and some young

adults

Bifascicular Blocks

RBBB plus either LAFB (common) or LPFB (uncommon)

Features of RBBB plus frontal plane features of the fascicular block (axis deviation, etc.)

RBBB plus LAFB

Method

Measurements Rhythm Analysis Conduction Analysis Waveform Description ECG Interpretation Comparison with Previous ECG (if any)

Case 1

Case 2

Case 3

Case 4

Case 5