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
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