ECG Rhythm Evaluation

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 tachycardiaectopic 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




Broad Complex Tachycardia (BCT)


Note: All regular BCTs should be considered to be VT until proven otherwise.



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)


For escape rhythms to occur there must be a failure of sinus node impulse generation or transmission by the AV node.

Advanced Reading



LITFL Further Reading


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

One comment

    Narrow complex: Junctional escape rhythm
    Broad complex: Ventricular escape rhythm

    Two comments

    In ventricular escape rhythm P wave are present but not conducted.

    One not uncommon cause of bradycardia with absent P waves is Atrial fibrillation with slow ventricular rate P wave are absent.

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