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First-degree AV block

3

First-degree AV block

• PR interval measured from onset of P wave to onset of QRS
• Normal PR duration is 0.12 to 0.20 s

Non-pathologic Q waves

• Less than 0.04 s (one square) wide
• Less than two squares deep
• Usual leads
1. I
2. aVL
3. V5
4. V6