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
- 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.
Follow links below for examples of individual rhythms.
Narrow Complex (Supraventricular) Tachycardia
ATRIAL – REGULAR
- Sinus tachycardia
- Atrial tachycardia
- Atrial flutter
- Inappropriate sinus tachycardia
- Sinus node re-entrant tachycardia
ATRIAL – IRREGULAR
- Atrioventricular re-entry tachycardia (AVRT)
- AV nodal re-entry tachycardia (AVNRT)
- Automatic junctional tachycardia
Broad Complex Tachycardia (BCT)
- Ventricular tachycardia
- Antidromic atrioventricular re-entry tachycardia (AVRT).
- Any regular supraventricular tachycardia with aberrant conduction — e.g. due to bundle branch block, rate-related aberrancy.
Note: All regular BCTs should be considered to be VT until proven otherwise.
- Ventricular fibrillation
- Polymorphic VT
- Torsades de Pointes
- AF with Wolff-Parkinson-White syndrome
- Any irregular supraventricular tachycardia with aberrant conduction — e.g. due to bundle branch block, rate-related aberrancy.
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)
- AV block: 2nd degree, Mobitz I (Wenckebach)
- AV block: 2nd degree, Mobitz II (Hay)
- AV block: 2nd degree, “fixed ratio blocks” (2:1, 3:1)
- AV block: 2nd degree, “high grade AV block”
- AV block: 3rd degree (complete heart block)
P WAVES ABSENT
For escape rhythms to occur there must be a failure of sinus node impulse generation or transmission by the AV node.
- Wiesbauer F, Kühn P. ECG Yellow Belt online course: Become an ECG expert. Medmastery
- Wiesbauer F, Kühn P. ECG Blue Belt online course: Learn to diagnose any rhythm problem. Medmastery
- Rawshani A. Clinical ECG Interpretation ECG Waves
- Smith SW. Dr Smith’s ECG blog.
- Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
- Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
- Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
- Hampton J. The ECG Made Practical 7e, 2019
- Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography 1e, 2009
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
- Mattu A, Brady W. ECG’s for the Emergency Physician Part I 1e, 2003 and Part II
- Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004
- Smith SW. The ECG in Acute MI. 2002 [PDF]
LITFL Further Reading
- ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
- ECG A to Z by diagnosis – ECG interpretation in clinical context
- ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
- 100 ECG Quiz – Self-assessment tool for examination practice
- ECG Reference SITES and BOOKS – the best of the rest
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.