• Normal PR and QRS intervals
• AV blocks
• Bundle branch block

Normal PR and QRS intervals

Measuring intervals: Note landmarks for pr, QRS, and QT intervals.

The PR interval:

Measure from start of P to start of QRS. WNL if 0.12-0.20 seconds (3-5 small boxes)

QRS interval

Measure from the start to the end of the QRS complex! WNL = 0.1 seconds or less (2.5 small boxes or less)

AV blocks

1st Degree AV block

Features: P wave for every QRS, but P-R interval >0.20 (>5 small boxes)

2nd Degree AV block

Two classifications:

• Wenckebach
• Mobitz

2nd Degree AV block/ Wenckebach

Progressive lengthening of PR interval until a QRS is ‘dropped!

2nd Degree AV block/ Mobitz

PR intervals are constant, but QRS is dropped suddenly.

3rd Degree AV block

Features: AV dissociation! The P-P intervals are dissociated from R-R intervals.
Escape rhythm below AV node paces at its inherent rate

Bundle branch blocks

Right BBB

Features: QRS 0.12 sec or more. RR’ in V1, V2

Left BBB

Features: QRS width 0.12 sec or more… Big S in V1 and wide R in V5 and other lateral leads. ST segment abnormalities

 

FOR THE GRAND FINALE... Analyze the tracing below for:

Rate____________________

Rhythm____________________

Conduction:

pr interval _______ sec.
QRS interval_______sec.
Other characteristics which confirm your suspision? ___________

Conclusion____________________________________________