ECG Academy

ECG Rhythm Evaluation

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Appcardio ECG Academy

ECG Rhythm Evaluation

A structured approach to identifying cardiac rhythm: assess rate, regularity, QRS morphology, atrial activity, atrioventricular relationships, rhythm onset and termination, and response to vagal manoeuvres.

Core ECG interpretation Intermediate learning level Approx. 10–12 min

Learning Objectives

01Use a rhythm strip systematically and corroborate findings across the 12-lead ECG.
02Apply the seven-step framework to describe rate, regularity, morphology and atrioventricular activity.
03Organise tachycardia differentials by QRS width and regularity.
04Approach bradycardia by assessing P-wave visibility and P-to-QRS conduction.
05Recognise the limitations of onset/termination patterns and vagal response as diagnostic clues.
06Communicate a structured rhythm interpretation without relying on a single ECG feature.

Start With the Rhythm Strip

II

Lead II is a practical starting point. On a standard 12-lead ECG, rhythm assessment commonly begins with the 10-second Lead II rhythm strip. Confirm or challenge what you see by reviewing the other leads.

A longer rhythm strip can be useful when the rhythm is intermittent, when atrial activity is difficult to identify, or when the relationship between atrial and ventricular events is uncertain. A slower recording speed may also help reveal timing relationships.

Original schematic rhythm strip for orientation only. It is not intended to represent a specific rhythm diagnosis or measured interval.

Practical approach

First describe what is present on the tracing. Avoid naming a rhythm before you have assessed the ventricular rate, regularity, QRS morphology, atrial activity and AV relationship.

The Seven-Step Approach to ECG Rhythm Analysis

Work through the same questions in a consistent order. The steps are complementary: no single feature should be used in isolation when the tracing is ambiguous.

1

Rate

Decide whether the ventricular rate is slow, within the usual adult resting range, or fast. The supplied reference describes 60–100 beats/min as the normal range.

Ask: Is this bradycardia, a rate in the usual range, or tachycardia?
2

Pattern of QRS Complexes

Assess the spacing between successive QRS complexes. If the rhythm is irregular, decide whether the irregularity follows a repeating pattern or is unpredictable.

Ask: Regular, regularly irregular, or irregularly irregular?
3

QRS Morphology

Classify the QRS complexes as narrow or broad using the ECG's morphology and calibration. A narrow complex generally points toward a sinus, atrial or junctional origin; a broad complex may be ventricular or supraventricular with aberrant conduction.

Ask: Narrow or broad — and is the morphology consistent?
4

P Waves

Look for atrial activity, then assess its morphology and timing. Visible P waves and the PR relationship may support sinus, ectopic atrial, junctional or retrograde activation. P waves may not be clearly visible in some rhythms.

Ask: Are P waves present, absent, hidden, or of more than one morphology?
5

P-Wave and QRS Relationship

Determine whether atrial and ventricular events are associated or dissociated. Complete AV dissociation means the atria and ventricles are activated independently; intermittent capture may indicate incomplete dissociation.

Ask: Does each atrial event relate consistently to a ventricular event?
6

Onset and Termination

An abrupt start or stop can support a re-entrant mechanism. A gradual acceleration or deceleration can support increased automaticity. These patterns are clues, not stand-alone proof of mechanism.

Ask: Did the rhythm begin/end suddenly or change progressively?
7

Response to Vagal Manoeuvres

When clinically appropriate and performed with suitable monitoring, the response may add information. The supplied reference describes gradual slowing with sinus or ectopic atrial tachycardia and AF/flutter; AVNRT/AVRT may terminate abruptly or show no response; VT is described as showing no response.

Ask: Was there gradual slowing, abrupt termination, or no discernible response?
Safety and interpretation caveat

Do not use a vagal manoeuvre as a substitute for immediate assessment of an unstable patient. A response is not definitive proof of a particular rhythm. Use only an appropriate manoeuvre in a clinically suitable, monitored setting and follow local protocols.

Rhythm Differential: Tachycardia

The supplied lesson groups tachycardias first by QRS width, then by regularity and likely chamber or circuit of origin. Use this as a differential framework rather than a replacement for detailed rhythm-specific criteria.

Narrow-Complex (Supraventricular) Tachycardia

Atrial — Regular

Regular rhythm
  • Sinus tachycardia
  • Atrial tachycardia
  • Atrial flutter
  • Inappropriate sinus tachycardia
  • Sinus node re-entrant tachycardia

Atrial — Irregular

Irregular rhythm
  • Atrial fibrillation
  • Atrial flutter with variable block
  • Multifocal atrial tachycardia

Atrioventricular

AV-related circuit / focus
  • Atrioventricular re-entry tachycardia (AVRT)
  • AV nodal re-entry tachycardia (AVNRT)
  • Automatic junctional tachycardia

Interpretive reminder

A narrow QRS supports a supraventricular origin in the framework presented, but the full tracing and clinical context remain essential. Review atrial activity and the AV relationship rather than relying on QRS width alone.

Broad-Complex Tachycardia

Regular Broad-Complex Tachycardia

  • Ventricular tachycardia (VT)
  • Antidromic AVRT
  • Regular supraventricular tachycardia with aberrant conduction, for example bundle branch block or rate-related aberrancy

Irregular Broad-Complex Tachycardia

  • Ventricular fibrillation
  • Polymorphic VT
  • Torsades de pointes
  • AF with Wolff–Parkinson–White syndrome
  • Irregular supraventricular tachycardia with aberrant conduction
High-stakes broad-complex rule

The supplied reference advises treating every regular broad-complex tachycardia as VT until proven otherwise. This is a safety-oriented working assumption, not a claim that every broad-complex rhythm is ventricular in origin. If the patient is unstable, follow emergency resuscitation protocols without delaying treatment for extended rhythm analysis.

Rhythm Differential: Bradycardia

For a slow rhythm, first look for atrial activity. If P waves are visible, determine whether each P wave is followed by a QRS complex. This separates patterns suggestive of sinus-node dysfunction from those in which AV conduction is impaired.

P Waves Present

Every P Wave Followed by QRS

Sinus-node pattern
  • Sinus bradycardia
  • Sinus node exit block
  • Sinus pause or arrest

The key observation is that each visible atrial depolarisation is followed by ventricular depolarisation.

Not Every P Wave Followed by QRS

AV-conduction pattern
  • Second-degree AV block, Mobitz I (Wenckebach)
  • Second-degree AV block, Mobitz II
  • Fixed-ratio block (e.g. 2:1 or 3:1)
  • High-grade AV block
  • Third-degree (complete) AV block

P Waves Not Clearly Identifiable

Narrow-Complex Escape

A junctional escape rhythm is one differential diagnosis when a narrow-complex escape rhythm is present and sinus impulse generation or conduction has failed.

Broad-Complex Escape

A ventricular escape rhythm is one differential diagnosis when a broad-complex escape rhythm occurs in the setting of failure of higher pacemaker activity or conduction.

Do not over-read an absent P wave

Failure to identify a P wave on a short strip does not by itself establish sinus arrest or a junctional rhythm. Atrial fibrillation with a slow ventricular response is another possible explanation for a slow rhythm without discrete P waves. In addition, atrial activity can occur independently of the QRS complexes. Reassess the full tracing and, when needed, obtain a longer rhythm strip.

Putting the Findings Together

Once the seven observations have been made, summarise the rhythm in a consistent sequence. A structured description makes uncertainty visible and helps another clinician understand how the interpretation was reached.

1. Ventricular rateState the measured rate or describe it as slow, usual-range or fast.
2. RegularityDescribe the QRS pattern as regular, regularly irregular or irregularly irregular.
3. QRS morphologyState whether complexes are narrow or broad and whether morphology is uniform.
4. Atrial activityDescribe P-wave visibility, morphology and timing where identifiable.
5. AV relationshipState whether atrial and ventricular activity is associated or dissociated.
6. Dynamic behaviourInclude abrupt/gradual onset or termination and any observed response to a manoeuvre, if relevant.

Knowledge Check

Test the core principles from this lesson. Select one answer and submit to reveal feedback.

Question 1. What is the recommended starting point for rhythm assessment on a standard 12-lead ECG in the supplied lesson?

Question 2. A regular broad-complex tachycardia should initially be approached as:

Question 3. Complete AV dissociation means:

Question 4. Which onset pattern can support a re-entrant mechanism?

Key Takeaways

  • Start with a rhythm strip, commonly Lead II, and corroborate findings in the remaining ECG leads.
  • Use the seven-step sequence: rate, QRS pattern, QRS morphology, P waves, P–QRS relationship, onset/termination and vagal response.
  • For tachycardia, organise the differential by QRS width and regularity before refining the mechanism.
  • Approach bradycardia by assessing atrial activity and whether P waves conduct to the ventricles.
  • Interpret dynamic features and manoeuvre responses as supporting clues, not definitive diagnoses.
  • Clinical stability and the patient's overall condition take priority over completing a teaching algorithm.

References and Further Reading

Nickson C. ECG Rhythm Evaluation. Life in the Fast Lane (LITFL), ECG Library Basics. Published August 1, 2020. Primary educational source supplied for this lesson. View source article.
Zimmerman FH. ECG Core Curriculum. 2023. Listed in the supplied source as advanced reading.
Mattu A, Berberian J, Brady WJ. Emergency ECGs: Case-Based Review and Interpretations. 2022. Listed in the supplied source as advanced reading.
Straus DG, Schocken DD. Marriott’s Practical Electrocardiography. 13th edition. 2021. Listed in the supplied source as advanced reading.
Brady WJ, Lipinski MJ, et al. Electrocardiogram in Clinical Medicine. 1st edition, 2020. Listed in the supplied source as advanced reading.
Hampton J, Adlam D. The ECG Made Practical. 7th edition. 2019. Listed in the supplied source as advanced reading.
Source and adaptation note

This lesson is an independently written and designed educational presentation based on the supplied LITFL article. The source PDF identifies the LITFL educational material as licensed under Creative Commons Attribution–NonCommercial–ShareAlike 4.0 International (CC BY-NC-SA 4.0). Confirm that the intended use and any adapted material comply with that licence or obtain permission where required. The original article's diagrams and screenshots have not been reused.

Medical education disclaimer: This page is intended for education and revision. It is not a substitute for clinical assessment, expert ECG review, local emergency pathways or institutional protocols. Rhythm interpretation must be integrated with symptoms, haemodynamic status, history and the complete ECG. Management of an unstable patient must not be delayed to complete this educational framework.
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