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ECG Overview and Interpretation
NUR 351/352
Professor Diane E. White RN MS CCRN
MEASUREMENTS
1. ECG PAPER
• Horizontal boxes measure time and the vertical boxes measure voltage or amplitude
• Small boxes = .04 seconds
• Large boxes = .20 second or 5 small boxes
• Hatch marks at top of paper = 3 seconds usually want a 6 second strip to analyze
• Low voltage is represented by small waves & vice versa
• Small waves from artria and large from ventricles
Waveforms & Intervals
** a flat baseline called isometric line means neither –/+
** any waveform above the line is positive and below is negative
P Wave: indicates atrial depolarization; upright in leads I and II
•PR Interval: connects P wave & QRS complex; measured from beginning of p wave where + deflection begins to where QRS begins; time it takes impulse to depolarize atria & travel to AV node and Bundle of His; normal .12-.20 seconds
•QRS Complex: ventricular depolarization; Q wave is negative deflection after the p wave; the first positive following the p wave is the R wave, normally tall and positive in lead II; the S wave is a negative waveform that follows the R wave
•QRS Interval: measured from beginning to end of QRS complex; first deflection after the p wave is the beginning of the QRS complex and measured until final deflection returns to baseline; normally less than .12 seconds
•T Wave: represents ventricular repolarization and follows the QRS complex
•ST Segment: usually isoelectric; may be elevated or depressed
INTERPRETATION OF ECG
1. Rhythmicity: is the rate regular or irregular?
2. Rate: atrial (p waves) & ventricular rates (R waves)
methods to determine rate:
• The rule of 1500 - 1500/#small boxes b/w 2 waves
• The rule of 10 - # of P or R waves in 6 second strip multiplied by 10
• The rule of 300 - 300/ # large boxes b/w 2 waves
3. Location: is there a P wave for every QRS?
4. Intervals: does the PR = .12-.20 & the QRS less than .12?
PRACTICE PRACTICE PRACTICE!
MEMORIZE THE RULES FOR VARIOUS DYSRHYTHMIAS
PRACTICE, PRACTICE, PRACTICE!
Normal Sinus
Sinus Bradycardia
Sinus Tachycardia
Sinus Arrhythmia