Slide 1: What’s wrong with this patient’s his-purkinje system?

Slide 2: There’s a left anterior fascicular block (LAFB). Formal criteria for LAFB. 1. Left axis deviation (-45 degrees and -90 degrees). Specifically, left axis deviation without LVH or inferior q-waves (suggestive of old MI) 2. qR pattern in lead aVL. 3. R-peak time in lead aVL of 45 ms or more. 4. QRS duration less than 120 ms.

Other common findings: rS in II, III, aVF. S in V5-V6.

Slide 3: Anatomy review! How does the left bundle conduct? The left bundle separates into 2 fascicles: anterior fascicle (LAF) and posterior fascicle (LPF).

What’s the underlying pathophysiology of LAFB? Fibrosis of the left anterior fascicle leads too slowed electrical conduction and LAFB. What causes fibrosis? Any condition with increased pressure in the LV can result in fibrosis, including: hypertension (most common), cardiomyopathy, infiltrative disease, and degenerative conduction disease.

Slide 4: How should I proceed after identifying a LAFB? Fortunately, no immediate work-u p or treatment is needed, but…

Ask why? If no known hypertension, consider home blood pressure monitoring and ordering an echocardiogram for structural heart disease.

Stay vigilant! LAFB suggests a maladaptive response to hypertension or structural heart disease, with corresponding increased risk of cardiac problems like atrial fibrillation or heart failure.


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