Editor’s note: The EKG Detective will be a monthly column dedicated to illustrating the benefits of utilizing deductive logic as a method for interpreting ECG tracings. The column will highlight and review all the basic ECG interpretations, before transitioning into a monthly interpretation challenge. See you next month and remember, it is always better to practice as a clinician rather than a technician.
Welcome back to the EKG Detective. This column is dedicated to illustrating the benefits of utilizing deductive logic as a method for interpreting EKG tracings. For this month’s article, we will be looking at premature junctional contractions (PJCs).
If you need a refresher on inductive and deductive logic, check out our introductory article.
Fill out the form on this page to download your copy of the EKG Detective Interpretation Checklist.
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:
- Rhythm regularity
- Rhythm rate
- P-wave criteria
- PR interval
- 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 ECG tracing. More practically, it can be used as an EKG interpretation job aid.
Premature junctional contractions
Premature junctional contractions are given their designation because they originate from within the atrioventricular (AV) node or bundle of HIS and occur early in the cardiac cycle. Prematurity associated with PCJs is determined by measuring the R-to-R intervals of the underlying rhythm with the PCJ and/or PCJs falling prior to the next expected beat — prematurely (see Figure 2 for an early in the cardiac cycle example). For this specific article, we’ll only be focusing on premature junctional contractions and not the underlying rhythms within the ECG tracings.
Ectopic beats
All normal beats originate from the sinoatrial (SA) node. The term “ectopic” means an abnormal place or position. Thus, the term “ectopic beat” means any beat that originates outside of the SA node. PCJs originate ectopically in the AV node or the bundle of HIS but not within the SA node.
As a side note, when you combine the AV node with the bundle of HIS it is referred to as the AV junction.
EKG Category 1: Rhythm regularity
By the nature of where they occur within the cardiac cycle, PJCs tend to look out of place as it pertains to the overall ECG tracing.
Focusing on the P-waves and where they are located is critical for identifying PJCs. A different or missing P-wave when compared to the underlying rhythm’s P-waves is the first criteria required to identify a PJC.
EKG Category 2: Rhythm rate
Again, we are not focusing on underlying rhythms, so the rate category will not apply for this article. As we aren’t looking at underlying rhythms, we will eliminate all the underlying rhythms and go directly to EKG Category 3: P-wave criteria (see Figure 3).
EKG Category 3: P-wave criteria
P-waves for PJCs will be located either immediately before the QRS complex, hidden within the QRS complex or immediately after the QRS complex (see Figure 4). The location of the P-wave is typically associated with where the ectopic beat originates within the AV junction. If the P-wave is located after the QRS complex, this criterion almost always implies the ectopic beat is junctional.
As the focus for PJCs originates within the AV junction, the atria depolarize from the bottom in an upward direction. This frequently causes the P-waves to be inverted, which is referred to as retrograde P-waves.
EKG Category 4: PR interval
If the P-wave is in front of the QRS complex, the PR interval will be less than 0.12 seconds, because the electrical impulse originates in the AV junction and doesn’t have to travel through the atria before reaching the ventricles (see Figure 5).
If the PR interval is 0.12 seconds or greater, you can eliminate premature atrial contractions because PACs have a normal PR interval (see Figure 6).
EKG Category 5: QRS criteria
When the P-wave is hidden within the QRS complex, it will typically appear normal with a measurement of less than 0.12 seconds, whereas the QRS complex for PVCs will not have an associated P-wave and will appear wide and bizarre with a measurement of 0.12 seconds or greater. As PJCs have normal QRS criteria, PVCs can be eliminated because PVCs do not have P-waves and their QRS complexes are wide and bizarre (see Figure 7).
At this point in the deductive process, the only remaining choice is the premature junctional contraction we have been working from.
Identifying premature junctional contractions
This example illustrates how deductive logic is used to interpret PCJs. At a glance, premature junctional contractions can be a challenge to identify. Focus on the P-wave if there is a single PJC or P-waves if there are multiple PJCs. The PCJs will typically have inverted/retrograde P-waves with one of the following criteria:
- P-waves immediate before the QRS complex with a short PR interval of less than 0.12 seconds
- P-waves hidden within the QRS complex with a narrow QRS complex of less than 0.12 seconds
- P-waves immediately after the QRS complex
See you next month and remember, it is always better to practice as a clinician rather than a technician.
