Left anterior fascicular block electrocardiogram
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]
Overview
Electrocardiogram
Criteria for LAHB
- Left axis deviation (usually between -45° and -90°), some consider -30° to meet criteria
- QRS interval < 0.12 seconds
- qR complex in the lateral limb leads (I and aVL)
- rS pattern in the inferior leads (II, III, and aVF)
- Delayed intrinsicoid deflection in lead aVL (> 0.045 s)[1]
Exceptions
It is important not to call LAFB in the setting of a prior inferior wall myocardial infarction which may also demonstrate left axis deviation due to the initial forces (Q wave in a Qr complex) in leads II, III, and aVF. As opposed to LAHB, the left axis shift is due to terminal forces (i.e., the S wave in an rS complex) being directed superiorly.
Effects of LAHB on Diagnosing Infarctions and Left Ventricular Hypertrophy
LAHB may be a cause of poor R wave progression across the precordium causing a pseudoinfarction pattern mimicking an anteroseptal infarction. It also makes the electrocardiographic diagnosis of LVH more complicated, because both may cause a large R wave in lead aVL. Therefore to call LVH on an EKG in the setting of an LAHB you should see the presence of a “strain” pattern when you are relying on limb lead criteria to diagnose LVH.[2]
EKG Examples
Shown below is an example of an EKG demonstrating left axis deviation with rS pattern in lead III and QRS complex < 0.12 seconds indicating a left anterior hemiblock. A qR complex is also seen in lead aVL.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Shown below is an example of an EKG showing rS pattern in lead III, qR complex in lead aVL and QRS complex < 0.12 seconds along with left axis deviation indicating left anterior fascicular block.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
References
- ↑ Mirvis DM, Goldberger AL. Electrocardiography. In: Braunwald E, Zipes DP, Libby P, eds. Heart disease: a textbook of cardiovascular medicine, 6th edn. Philadelphia: WB Saunders; 2001:82–125.
- ↑ Surawicz B, Knilans TK. Chou’s electrocardiography in clinical practice: adult and pediatric, 5th edn. Philadelphia: W.B. Saunders; 2001.