A heart with EKG lines

EKG Refresher: Sinus Rhythms

This refresher series will explore the basics of rhythm strip analysis; sinus, atrial, junctional, and ventricular rhythms; blocks, pacemakers, and 12-lead EKGs. This series will not teach you how to proficiently recognize and treat dysrhythmias. To learn EKGs basics and advanced rhythms, RN.com provides two courses on rhythm strip interpretation: Telemetry Interpretation: Rates, Rhythms, and More and Lethal Arrhythmias: Advanced Rhythm Interpretation, please refer to these courses to learn and improve your skills.

Take Course 1 Take Course 2

Strip Interpretation begins with the EKG Paper

EKG paper

As your skills improve, this paper will become your best friend, it will tell you the time, rate, amplitude, and rhythm. Is the heart beating normally or abnormally?

EKG Paper is a Continuous Recording of Electrical Activity.

The Paper is Divided into Small and Large Boxes.

  • Each horizontal small box represents 0.04 seconds
  • Each horizontal large box is comprised of 5 small boxes or 0.20 seconds
  • Five large boxes represent 1 second, and 15 large boxes represent 3 seconds of time

Some EKG paper has the 1-second time segments marked by a hash mark on either the top or bottom of the strip. This will help you determine your heart rate. Always print at least a six-second strip, this will enable you to multiply the “R” waves by 10 to get your rate. A longer strip is often needed to recognize abnormal rhythms.

R waves

This is a six-second strip, let’s use the following steps to interpret the strip.

  1. Determine the Rate

    1. Did you count 8 “R” waves?
    2. Did you multiply by 10 to get a rate of 80?
  2. Is the “R” Wave Regular or Irregular?

    1. Using calipers or a piece of paper, you can show if the “R” waves are regular
    2. Did you determine the “R” waves were regularly spaced?
  3. Is There a “P” Wave before Every QRS?

    1. Did you find a “P” wave before every QRS?
  4. Measure the PR Interval

    1. The PR interval measures 0.12 seconds
    2. Is this normal or abnormal
  5. Measure the QRS Width

    1. The QRS interval is 0.08 seconds
    2. Is this normal or abnormal

Congratulations! You have completed the steps to analyze this strip. So, what do we know from this information?

We have a normal sinus rhythm with a rate of 80.

Sinus Rhythms Arise from the SA Node.

  • The rate should be 60-100 beats per minute and regular.
    • Rates lower or higher than the normal rate should be considered abnormal.
  • There should be a “P” wave before every QRS complex
    • Missing “P” waves indicate an abnormality
  • The interval times should be within the normal ranges

Abnormal sinus rhythms are either too fast, tachycardia, or too slow bradycardia. Always determine the blood pressure of the patient to determine if they are symptomatic because athletes often have a slower heart rate than normal, which does not cause any symptoms.

Sinus bradycardia is a rate below 60 beats a minute with a “P” wave before every QRS, is regular and the intervals are within the normal range. This strip shows a rate of 40, with “P” waves and normal intervals.

P waves

Sinus tachycardia is a rate above 100 beats a minute with a “P” wave before every QRS, is regular and the intervals are within the normal range. The following strips show a regular rate, a “P” wave before every QRS, and intervals within normal ranges.


Starting with these basic rhythms will help you cement your skills in the six basic steps to rhythm interpretation. There are other sinus arrhythmias, sinus arrest, and sinus pause that you will learn about when you take the RN.com courses listed above.

Next month, we will explore atrial and junction rhythms.

EKG interpretation takes time, patience, and repetition. Start with regular sinus rhythms, and practice until you can measure accurately and are proficient at determining rates. Then move on to the next set of rhythms. Practice makes perfect.


Maryniak, K. (2019). Telemetry Interpretation: Rates, Rhythms, and More. 

Miller-Hoover, S. M. (2020). Lethal Arrhythmias: Advanced Rhythm Interpretation