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 ventricular tachycardia and ventricular fibrillation.
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.
Ventricular tachycardia
All normal rhythms originate from the sinoatrial (SA) node. Ventricular tachycardia originates from within the ventricles. These areas within the ventricles lie outside of the “normal” bundle branch and purkinje electrical pathways. As a rule of thumb, ventricular tachycardia originates ectopically in the ventricles and not within the SA node.
EKG Category 1: Rhythm regularity
Ventricular tachycardia is characterized by a regular rhythm.
As ventricular tachycardia is regular, we should eliminate any rhythm that is irregulars (see Figure 2).
We can also eliminate ectopic beats because they will cause the rhythm to be irregular (see Figure 2).
EKG Category 2: Rhythm rate
The rate for ventricular tachycardia starts at 100 beats per minute, but it typically fires between 120-150 beats per minute with the potential to beat faster or slower.
As the rate for ventricular tachycardia is 100 or greater, we can eliminate any rhythm that is not tachycardic (see Figure 3).
EKG Category 3: P-wave criteria
P-waves are created when the atria depolarize via the atrial electrical pathways. Ventricular tachycardia originates in the ventricles and not within the atria. This means P-waves will be absent from the ECG tracing.
As P-waves are absent, we can eliminate any rhythms that are associated with having P-waves (see Figure 4).
EKG Category 4: PR interval
As ventricular tachycardia is missing P-waves, there will not be a measurable PR interval for this rhythm.
EKG Category 5: QRS criteria
Under normal circumstances, the ventricles are depolarized via the bundle branches and purkinje network by an electrical impulse originating from the SA node traveling through the AV junction. When this is the case, the electrical impulse travels through the ventricles at approximately 2 meters per second, resulting in a normal appearing QRS complex measuring less than 0.12 seconds in duration.
In ventricular tachycardia, the electrical impulse originates ectopically within the ventricles and travels at a significantly slower speed. This results in a QRS complex that is wide at 0.12 seconds or greater in duration with a bizarre appearance.
As ventricular tachycardia presents with a wide and bizarre QRS complex, we can eliminate junctional tachycardia. Junctional tachycardia is typically associated with having QRS complexes that appear normal measuring less than 0.12 seconds in duration (see Figure 5).
At this point in the deductive process, the only remaining choice is the ventricular tachycardia we have been working from. As a clinical side note, patients in ventricular tachycardia can present with a pulse or with no pulse in cardiac arrest.
Ventricular fibrillation
Ventricular fibrillation is an abnormal rhythm during which the ventricles within the heart quiver. Patients in ventricular fibrillation will present in cardiac arrest with loss of consciousness and no pulse. It is identified by irregular and chaotic electrical activity with no discernible pattern.
Depending upon its amplitude, ventricular fibrillation may be described as “coarse” or “fine.” Coarse is designated when the electrical deflections are greater than 2 large boxes or 10 mm in amplitude. Fine is designated when the electrical deflections are less than 1 large box or 5 mm in amplitude (see Figure 6). We will not be using the EKG Detective system for this rhythm because it is the only interpretation based upon lack of discernible wave forms.
Identifying ventricular tachycardia
This example illustrates how deductive logic is used to interpret ventricular tachycardia. The key to identifying ventricular tachycardia is to focus on the absence of P-waves and measuring a wide QRS complex that is 0.12 seconds or greater and appears bizarre.
See you next month, and remember it is always better to practice as a clinician rather than a technician.
