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EKG Detective: Sinus arrhythmia

Eliminate EKG rhythms until there is only one probable interpretation

Figure 2 - Sinus Arrhythmia.jpg

Welcome back to the EKG Detective. This column is dedicated to illustrating the benefits of utilizing deductive logic as a method for interpreting ECG tracings. For this month’s article, we will be looking at sinus arrhythmia. Before jumping into sinus arrhythmia, let’s review the differences between inductive and deductive logic. If you read last month’s article, you can skip directly to the interpretation section.

Focus on what you can identify within an ECG tracing, rather than the criteria

Inductive logic

Inductive logic is based upon gathering evidence until you have acquired enough data to make an ECG interpretation. The challenge with utilizing inductive logic is you may not acquire the piece and/or pieces of evidence you need to interpret the ECG. It also requires the practitioner to memorize all the criteria for every EKG interpretation.

Deductive logic

The premise behind deductive logic is reducing options based upon what you can identify within the EKG tracing. This helps the practitioner to focus on the EKG tracing rather than the criteria required to interpret the EKG. The greatest benefit of deductive logic is it frees the practitioner from having to memorize all the criteria required to interpret an EKG tracing.

Throughout this series, we will be using the EKG Detective Interpretation Checklist (see Figure 1). This checklist is intended to prompt providers through five sequential elements associated with basic EKG interpretation while working through the specific criteria for each element:

  1. Rhythm regularity
  2. Rhythm rate
  3. P-wave criteria
  4. PR interval
  5. QRS criteria

EKG rhythms will be eliminated as we identify criteria within the EKG tracing until there is only one probable interpretation. We will use this checklist to illustrate how deduction is used to interpret an EKG tracing. More practically, it can be used as an EKG interpretation job aid.
Fill out the form on this page to download your copy of the EKG Detective Interpretation Checklist.

ECG Category.png

Sinus arrhythmia

For this article, we will be looking at sinus arrhythmia to illustrate the principle behind the EKG Detective (see Figure 2).

Figure 2 - Sinus Arrhythmia.jpg

  • EKG Category 1: “Rhythm regularity”
    • Sinus arrhythmia is characterized by an irregular rhythm that changes with the patient’s respirations. When the patient breathes out, the rate decreases, and when he or she breathes in, the rate increases.
    • As sinus arrhythmia is irregular, we should eliminate any rhythm that is regular.
    • To identify a pause, you will have a gap in the rhythm with regular R-to-R intervals before and after the pause. There is a small gap in our example rhythm, but there are no regular R-to-R intervals before or after the gap so we can eliminate sinus pause and sinus arrest.
    • There are no ectopic beats because none of the complexes have abnormal P-wave criteria that are typically associated with PAC(s) or PJC(s), nor do they have different looking QRS complexes that are associated with PVC(s) (see Figure 3 for all eliminated rhythms from regularity of rhythm).
April 2024-Fig3.png

  • ECG Category 2: “Rhythm rate”
    • The ventricular rate for our example is approximately 80 beats/minute. As there is an identifiable rate, we can eliminate ventricular fibrillation because the rate for ventricular fibrillation cannot be determined.
    • Sinus arrhythmia can present with any heart rate, so no other rhythms can be eliminated due to the rate associated with this rhythm (Figure 4).
April 2024-Fig4.png

  • ECG Category 3: “P-wave criteria”

    Working through the “Specific Criteria” for P-waves:

    • Do the P-waves appear to be saw-toothed and/or flutter waves? As sinus arrhythmia does not have flutter-waves, we should eliminate atrial flutter.
    • Are the P-waves discernible? As P-waves are discernible in a sinus arrhythmia, we should eliminate atrial fibrillation because it has no discernible P-waves.
    • Are there 3 or more different looking P-waves? As sinus arrhythmia has just one P-wave morphology, we should eliminate wandering atrial pacemaker.
    • Is there more than one P-wave for every QRS complex? As sinus arrhythmia has one P-wave for every QRS, we should eliminate all the heart blocks except for sinus arrhythmia with 10.
    • Are the P-waves in front or after the QRS complex? P-waves in sinus arrhythmia are in front of the QRS. Based upon identification of this criteria, none of the remaining rhythms should be eliminated (see Figure 5 for all the eliminated rhythms from P-wave criteria).
April 2024-Fig5.png

  • ECG Category 4: “PR interval”
    • As PR intervals for sinus arrhythmia are typically between 0.12-0.20 seconds and constant, we should eliminate sinus arrhythmia with 10 and junctional rhythm (see Figure 6).
April 2024-Fig6.png

There is no need to move onto ECG Category 5 – QRS Criteria – because the only remaining choice is the sinus arrhythmia we have been working from.

Using deductive logic to interpret sinus arrhythmia

This example illustrates how deductive logic is used to interpret sinus arrhythmia. The difference between sinus arrhythmia and sinus rhythm revolves around regularity of the R-to-R intervals. The irregularity of sinus arrhythmia is usually caused by the patient’s breathing, with the rate typically increasing upon expiration and decreasing during expiration.

See you next month and remember, it is always better to practice as a clinician rather than a technician.

Learn how to become an EKG Detective.

Bob Matoba, M.Ed., EMT-P is an associate professor at the College of Central Florida in Ocala. Bob’s career has spanned almost every aspect of the EMS profession, first as an EMT and paramedic for private ambulance companies, EMS coordinator for medical oversight, EMS system consultation in the private and public sector, all the way to the EMS chief for a metropolitan fire department. He has made it his mission to educate clinicians, rather than technicians. Bob is a monthly columnist for and has been a featured and contributing author for EMS World Magazine and JEMS.