The rhythm is best analyzed by looking at a rhythm strip. On a 12 lead ECG this is usually a 10 second recording from Lead II.
- Confirm or corroborate any findings in this lead by checking the other leads.
- A longer rhythm strip, recorded perhaps recorded at a slower speed, may be helpful.
7 step approach to ECG rhythm analysis
1. Rate
- Tachycardia or bradycardia?
- Normal rate is 60-100/min.
2. Pattern of QRS complexes
- Regular or irregular?
- If irregular is it regularly irregular or irregularly irregular?
3. QRS morphology
- Narrow complex: sinus, atrial or junctional origin.
- Wide complex: ventricular origin, or supraventricular with aberrant conduction.
4. P waves
- Absent: sinus arrest, atrial fibrillation
- Present: morphology and PR interval may suggest sinus, atrial, junctional or even retrograde from the ventricles.
5. Relationship between P waves and QRS complexes
- AV association (may be difficult to distinguish from isorhythmic dissociation)
- AV dissociation
- complete: atrial and ventricular activity is always independent.
- incomplete: intermittent capture.
6. Onset and termination
- Abrupt: suggests re-entrant process.
- Gradual: suggests increased automaticity.
7. Response to vagal manoeuvres
- Sinus tachycardia, ectopic atrial tachydysrhythmia: gradual slowing during the vagal manoeuvre, but resumes on cessation.
- AVNRT or AVRT: abrupt termination or no response.
- Atrial fibrillation and atrial flutter: gradual slowing during the manoeuvre.
- VT: no response.
Differential Diagnosis
Follow links below for examples of individual rhythms.
Narrow Complex (Supraventricular) Tachycardia
ATRIAL – REGULAR
ATRIAL – IRREGULAR
ATRIOVENTRICULAR
Broad Complex Tachycardia (BCT)
REGULAR BCT
Note: All regular BCTs should be considered to be VT until proven otherwise.
IRREGULAR
Bradycardia
P WAVES PRESENT
1. Every P wave is followed by a QRS complex (= sinus node dysfunction)
2. Not every P wave is followed by a QRS complex (= AV node dysfunction)
P WAVES ABSENT
For escape rhythms to occur there must be a failure of sinus node impulse generation or transmission by the AV node.
Advanced Reading
Online
Textbooks
- Zimmerman FH. ECG Core Curriculum. 2023
- Mattu A, Berberian J, Brady WJ. Emergency ECGs: Case-Based Review and Interpretations, 2022
- Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
- Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
- Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
- Hampton J, Adlam D. The ECG Made Practical 7e, 2019
- Kühn P, Lang C, Wiesbauer F. ECG Mastery: The Simplest Way to Learn the ECG. 2015
- Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
- Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004
LITFL Further Reading
Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.
His one great achievement is being the father of three amazing children.
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