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Test Findings

Left Anterior Fascicular Block



  • Left anterior fascicular block occurs due to failure of conduction down the left anterior fascicle.
    • Look For

    • Left axis deviation -45° to -90° in the absence of other causes
    • Normal QRS duration <120ms
    • qR pattern in aVL: small Q wave with large R wave
    • Long R peak time (time from start of QRS to peak of R) ≥45ms in aVL
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