Alteration in Perfusion: Analyzing ECG Rhythm Strips

Systematic Approach to Arrhythmia Interpretation

Calculating Heart Rate – Regular Rhythms

• Count number of large squares between two R waves and divide into 300, or

• Count number of small squares between two R waves and divide into 1500

Calculating Heart Rates: Method A

• Count the number of R waves in a 6- second strip and multiply by 10 

  • Not very accurate 

  • Used only with very quick estimate 

Calculating Heart Rates: Method B

• Count the number of large squares between two consecutive R waves and divide into 300 

• Or 

• Memorize this scale 

  • 1 large square= 300 bpm 

  • 2 large square= 150 bpm 

  • 3 large square= 100 bpm

  • 4 large square= 75 bpm 

  • 5 large square= 60 bpm 

  • 6 large square= 50 bpm 

• Very quick 

• Not very accurate with fast rates 

• Used only with regular rhythms 

Calculating Heart Rates: Method C

• Count the number of small squares between two consecutive R waves and divide into 1500 

  • Most accurate 

  • Used only with regular 

  • Time- consuming 

Figuring Rates Based on the Number of QRS Complexes in a 6-Second Strip (use for Irregular Rhythms)

• Count number of R waves in a 6-second strip and multiply by 10

Regular Rhythm:

• Count the number of small boxes from R to R and then divide into 1500 or Count the number of big boxes from R to R and divide into 300

Determining the Rate

• 1500 divided by the number of small boxes. 1500/20 = 75 beats per minute.

• 300 divided by the number of big boxes. 300/4 = 75

• R to R should always be equal 

Rhythm Strip Analysis Format

• Regularity (Rhythm)

• Rate

• P Waves

• PR Intervals

• QRS Complexes

Regularity (Rhythm)

• Is it regular?

• Is it irregular?

• Are there any patterns to the irregularity?

• Are there any ectopic beats; if so, are they early or late?

P Waves

• Are P waves regular?

• Is there one P wave for every QRS?

• Is P wave in front of QRS or behind it?

• Is P wave normal and upright in Lead II?

• Are there more P waves than QRS complexes?

• Do all P waves look alike?

• Are there any ectopic beats (beats that don’t go side to side, pop up randomly); if so, are they early or late?

PR Interval (PRI)

• Are all PRIs constant?

• Is PRI measurement within normal range?

• If PRI varies, is there a pattern to changing measurements?

• Normal: PRI: 0.12–0.20 seconds

• Beginning of P to beginning of Q

QRS Complex

• Are all QRS complexes of equal duration?

• What is the measurement of QRS complex?

• Is QRS measurement within normal limits?

• Do all QRS complexes look alike?

• Are unusual QRS complexes associated with ectopic beats?

• Normal QRS: Less than 0.12 seconds

• Beginning of Q to end of S