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