16. Normal Sinus Rhythm Rhythm : Regular Rate : 60 – 100 P wave : Normal in configuration; precede each QRS PR : Normal ( 0. 12 – 0.20 seconds ) QRS : Normal ( less than 0.12 seconds )
17. First-degree AV block Rhythm : Regular Rate : Usually normal P wave : Sinus P wave present; one P wave to each QRS PR : Prolonged ( greater than 0.20 seconds ) QRS : Normal
18. Second -degree AV block, Mobitz I Rhythm : Irregular Rate : Usually slow but can be normal P wave : Sinus P wave present; some not followed by QRS complexes PR : Progressively lengthens QRS : Normal
19. Second-degree AV block, Mobitz II Rhythm : Regular usually; can be irreguler if conduction ratios vary Rate : Usually slow P wave : Two, three, or four P waves before each QRS PR : PR interval of beat with QRS is constant; PR interval may be normal or prolonged QRS : Normal if block in His bundle; wide if block involves bundle branches
20. Third-degree AV block Rhythm : Regular Rate : 40 – 60 if block in His bundle; 30 – 40 if block involves bundle branches P wave : Sinus P wave present; bear no relationship to QRS; can be found hidden in QRS complexes and T waves PR : Varies greatly QRS : Normal if block in His bundle; wide if block involves bundle branches
