Left Bundle Branch Block

ECG interpretation of Left Bundle Branch Block

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» The duration of the QRS complex is 0.12 secs or greater in limb leads
» No Q wave is seen in leads I, aVL, and V6
» Broad slurred R in V6 with absent q, depressed ST segment and inverted T wave. Tall R wave is seen in lead V6. Usually a broad slurred R in I and avl
» Prominent QS pattern is observed in lead V1 with or without a small initial R wave. Deep S wave in V1-V2
» There may be minor regular variation in heart rate and pulse pressure associated with respiration (sinus arrhythmia)


Diagnosis of Acute MI in the Setting of Left Bundle Branch Block (NLM Medline)

ECG of Left Bundle Branch Block with MI

"The three electrocardiographic criteria with independent value in the diagnosis of acute infarction in these patients were an ST-segment elevation of 1 mm or more that was concordant with (in the same direction as) the QRS complex; ST-segment depression of 1 mm or more in lead V1, V2, or V3; and ST-segment elevation of 5 mm or more that was disconcordant with (in the opposite direction from) the QRS complex."
Sgarbossa E, et. al. N Engl J Med 1996 Feb 22;334(8):481-7

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