Overview
When assessing rhythm on an ECG, look at both the regularity of P waves (sinoatrial rhythm) and R waves (ventricular rhythm).
ECG Rhythm is best assessed using the rhythm strip, which is usually lead II.
Sinoatrial Rhythm
Sinoatrial rhythm can be assessed by examining the P waves on the rhythm strip.
Check whether each QRS complex is preceded by a P wave, as well as the regularity of the interval between P waves (PP interval).
Causes of Irregular Atrial Rhythm
Sinus Node
- Sinus arrhythmia
- Sinus pause
- Second degree sinoatrial exit block
Atrium
- Premature atrial complexes
- Multifocal atria tachycardia
Examples
- Second degree sinoatrial block, Mobitz type I - note progressively shortened PP intervals, followed by a pause:
![Second degree sinoatrial block, Mobitz type I - note progressively shortened PP intervals, followed by a pause]()
- Multifocal atrial tachycardia - a variety of P wave morphologies with variable PP intervals indicates several atrial foci:
![Multifocal atrial tachycardia - a variety of P wave morphologies with variable PP intervals indicates several atrial foci]()
Ventricular Rhythm
Ventricular rhythm can be assessed by examining the QRS complexes on the rhythm strip.
Measure the interval between R waves (RR interval) and whether this interval is regular or irregular across the rhythm strip. This can be assessed by marking the R waves on a separate piece of paper, and then transposing the paper to another part of the rhythm strip to see if the R waves line up.
Interpretation
- Regular rhythm - constant RR interval
- Regularly irregular rhythm - variable RR interval with a predictable pattern
- Irregularly irregular rhythm - variable RR interval with a random pattern
Causes of Irregular Ventricular Rhythm
Tachycardia
- Multifocal atrial tachycardia
- Atrial fibrillation
- Atrial flutter with variable block
- Polymorphic ventricular tachycardia
Bradycardia
- Sinus arrhythmia
- Sinus arrest
- Second or third degree sinoatrial exit block
- Atrial fibrillation with slow ventricular rate
- Atrial flutter with variable block
- Second or third degree AV block
Examples
- Atrial fibrillation - note a baseline fibrillation wave with irregular ventricular rhythm:
![Atrial fibrillation - note a baseline fibrillation wave with irregular ventricular rhythm]()
- Third degree (complete) AV block - bradycardia with complete dissociation between P waves and QRS complexes is characteristic:
![Third degree (complete) AV block - bradycardia with complete dissociation between P waves and QRS complexes is characteristic]()
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