ECG Rhythms

What does it mean to say a rhythm is regular?

It means that there is constant spacing between each beat, which is how you can say NSR and Sinus Brady and Sinus Tach are all regular, even if the actual rates are different

Normal Sinus Rhythm (Strip)

Regular rhythm, 60–100 bpm, normal P before every QRS

Normal Sinus Rhythm (Rate)

60-100 bpm

Normal Sinus Rhythm (P Wave)

P waves are present, upright, uniform, and occur before every QRS.

• One P wave for every QRS.

Normal Sinus Rhythm (PR Interval)

PR interval is normal and constant: 120–200 ms.

Normal Sinus Rhythm (QRS Complex)

QRS is narrow and normal-looking: <120 ms.

• Each QRS follows a normal P wave.

Normal Sinus Rhythm (Regularity)

R-R interval regular. P-P interval regular. Rhythm is regular because the SA node fires at a steady rate.

Sinus Bradycardia (Strip)

Regular rhythm, normal P before every QRS, but rate <60 bpm

Sinus Bradycardia (Rate)

<60 bpm

Sinus Bradycardia (P Wave)

P waves are present, upright, uniform, and occur before every QRS.

• Same as NSR, but rate is slow.

Sinus Bradycardia (PR Interval)

PR interval is usually normal and constant: 120–200 ms. Same as NSR, but rate is slow.

Sinus Bradycardia (QRS Complex)

QRS is usually narrow: <120 ms. Same as NSR, but the rate is slow.

Sinus Bradycardia (Regularity)

R-R irregular but P-P regular

Sinus Tachycardia (Strip)

Regular rhythm, normal P before every QRS, but rate >100 bpm

Sinus Tachycardia (Rate)

>100 bpm

Sinus Tachycardia (P Wave)

P waves are present, upright, uniform, and occur before every QRS. Same as NSR, but rate is fast. At very fast rates, P waves may blend into the previous T wave.

Sinus Tachycardia (PR Interval)

PR interval is usually normal and constant: 120–200 ms.

• At faster rates, P waves may blend into T waves, making PR harder to measure.

Sinus Tachycardia (QRS Complex)

QRS is usually narrow: <120 ms. Same as NSR, but the rate is fast.

Sinus Tachycardia (Regularity)

R-R regular. P-P regular. Same as NSR, but faster than 100 bpm.

Sinus Arrhythmia (Strip)

Normal sinus P waves, but R-R intervals vary

Sinus Arrhythmia (Rate)

Usually 60-100 bpm, but rhythm is irregular

Sinus Arrhythmia (P Wave)

P waves are present, upright, uniform, and occur before every QRS. The rhythm is irregular, but the P waves still look sinus.

Sinus Arrhythmia (PR Interval)

PR interval is usually normal and constant: 120–200 ms. The rhythm is irregular, but conduction from atria to ventricles is still normal.

Sinus Arrhythmia (QRS Complex)

QRS is usually narrow: <120 ms. QRS complexes occur irregularly because the sinus rate varies, but conduction through the ventricles is normal.

Sinus Arrhythmia (Regularity)

R-R irregular. P-P irregular. The rhythm is irregular, usually varying with breathing, but P waves are still sinus and occur before every QRS.

Sinus Pause (Strip)

Sinus Pause (Rate)

Rate varies depending on pause length, though underlying rate is typically 60-100 bpm

Sinus Pause (P Wave)

P waves are normal when present, but there is a temporary missing P-QRS-T complex during the pause. After the pause, sinus P waves resume.

Sinus Pause (PR Interval)

PR interval is usually normal when beats are present: 120–200 ms.

• During the pause, there is no P wave or QRS, so no PR interval to measure.

Sinus Pause (QRS Complex)

QRS is usually narrow: <120 ms when beats are present. During the pause, the expected QRS complex is missing.

Sinus Pause (Regularity)

Underlying rhythm is usually regular, then there is a temporary pause.

• R-R and P-P are interrupted by a missing beat.

• The pause is usually not an exact multiple of the normal P-P interval.

Sinus Arrest (Strip)

Sinus Arrest (Rate)

Rate varies depending on pause length, though underlying rate is typically 60-100 bpm

Sinus Arrest (P Wave)

P waves disappear during the arrest because the SA node fails to fire.

• When rhythm resumes, P waves may return normally, or an escape beat may occur.

Sinus Arrest (PR Interval)

PR interval is usually normal when sinus beats are present: 120–200 ms. During arrest, the SA node fails to fire, so there is no PR interval.

Sinus Arrest (QRS Complex)

QRS is usually narrow: <120 ms when sinus beats are present. During arrest, QRS complexes are absent until sinus rhythm resumes or an escape beat occurs.

Sinus Arrest (Regularity)

Underlying rhythm may be regular before arrest, then the rhythm stops temporarily.

• P-P and R-R intervals are interrupted by a pause.

• The pause is usually not an exact multiple of the normal P-P interval.

Sinus Exit Block / SA Block (Strip)

Sinus Exit Block / SA Block (Rate)

Rate varies but tends to stay around 60-100 bpm; pause causes slower overall rate

Sinus Exit Block / SA Block (P Wave)

A whole P-QRS-T complex is dropped. P waves are normal before and after the block, but one expected P wave is missing because the impulse does not exit the SA node.

Sinus Exit Block / SA Block (PR Interval)

PR interval is usually normal on conducted beats: 120–200 ms. The abnormality is the dropped P-QRS-T complex, not the PR interval.

Sinus Exit Block / SA Block (QRS Complex)

QRS is usually narrow: <120 ms on conducted beats. A whole expected P-QRS-T complex is dropped.

Sinus Exit Block / SA Block (Regularity)

Underlying rhythm is usually regular, then a full P-QRS-T complex is dropped. The pause is usually an exact multiple of the normal P-P interval.

Sinus Rhythm w/ Premature Atrial Complexes (PAC) (Strip)

Sinus Rhythm w/ PAC (Rate)

Underlying rate usually 60-100 BPM; PAC occurs early

Sinus Rhythm w/ PAC (P Wave)

Normal sinus P waves are present, but the PAC has an early abnormal-looking P wave.

• The PAC P wave may be hidden in the previous T wave.

Sinus Rhythm w/ PAC (PR Interval)

Underlying sinus beats usually have a normal PR: 120–200 ms. The PAC may have a different PR interval, often slightly abnormal depending on where the ectopic atrial impulse starts.

Sinus Rhythm w/ PAC (QRS Complex)

Underlying QRS complexes are usually narrow: <120 ms. The PAC usually has a narrow QRS too because it comes from above the ventricles.

Sinus Rhythm w/ PAC (Regularity)

Underlying rhythm is regular, but the PAC occurs early, making the rhythm irregular.

• The R-R interval before the PAC is shortened, often followed by a pause.

Atrial Tachycardia (Strip)

Usually paroxysmal, meaning it starts and ends abruptly

Atrial Tachycardia (Rate)

Usually 100-250 bpm

Atrial Tachycardia (P Wave)

P waves are usually present but abnormal in shape because the impulse starts from an ectopic atrial focus instead of the SA node.

• There is usually one P wave before each QRS, but they may be hard to see at fast rates.

• The P waves can be inverted, pointed, oddly shaped, or buried in the previous T wave

Atrial Tachycardia (PR Interval)

PR interval may be normal or slightly abnormal, but usually measurable if P waves are visible. Often around 120–200 ms, but exact value can vary.

Atrial Tachycardia (QRS Complex)

QRS is usually narrow: <120 ms because the rhythm starts above the ventricles and conducts normally through the His-Purkinje system.

Atrial Tachycardia (Regularity)

Usually regular R-R intervals. P-P intervals are usually regular if P waves are visible.

• It is a fast, regular atrial rhythm.

Supraventricular Tachycardia (SVT) (Strip)

Supraventricular Tachycardia (SVT) (Rate)

Usually 150-250 bpm

Supraventricular Tachycardia (SVT) (P Wave)

P waves are often absent, hidden, or buried in the T waves/QRS complexes. If visible, they may be abnormal or retrograde.

Supraventricular Tachycardia (SVT) (PR Interval)

PR interval is often not measurable because P waves are hidden in the QRS or T waves. If visible, retrograde P waves may make the PR interval abnormal.

Supraventricular Tachycardia (SVT) (QRS Complex)

QRS is usually narrow: <120 ms. Key clue: very fast, regular, narrow-complex rhythm. QRS can be wide if there is aberrant conduction, but basic SVT is narrow.

Supraventricular Tachycardia (Regularity)

Usually very regular R-R intervals. P-P intervals are often not measurable because P waves are hidden. Key clue: fast, regular, narrow-complex rhythm.

Atrial Flutter (Strip)

Sawtooth flutter waves

Atrial Flutter (Rate)

Atrial rate 250-350 BPM

• Ventricular rate is often, but not always, around 150 BPM with 2:1 conduction

Atrial Flutter (P Wave)

No normal P waves. Instead, there are flutter waves, often described as sawtooth-shaped F waves.

Atrial Flutter (PR Interval)

PR interval is usually not measurable because there are no normal P waves; flutter waves replace P waves.

Atrial Flutter (QRS Complex)

QRS is usually narrow: <120 ms.

• Multiple flutter waves may appear between QRS complexes.

• These waves appear in a ratio of, usually, 2:1 or 4:1

Atrial Flutter (Regularity)

Can be regular or irregular depending on AV conduction. With fixed conduction, like 2:1 or 3:1, R-R is regular. With variable conduction, R-R is irregular.

• Flutter waves usually occur at a regular atrial rate.

Atrial Fibrillation (Strip)

Irregularly irregular rhythm with no distinct P waves

Atrial Fibrillation (Rate)

Atrial rate chaotic, often 350-600 BPM; ventricular rate varies with AV conduction

Atrial Fibrillation (P Wave)

No distinct P waves.

• Baseline is chaotic, wavy, or fibrillatory due to disorganized atrial activity.

Atrial Fibrillation (PR Interval)

PR interval is not measurable because there are no distinct P waves.

Atrial Fibrillation (QRS Complex)

QRS is usually narrow: <120 ms, but the R-R intervals are irregularly irregular. QRS can be wide if there is a bundle branch block or aberrant conduction.

Atrial Fibrillation (Regularity)

R-R intervals are irregularly irregular.

P-P intervals are not measurable because there are no true P waves.

• This is the classic irregularly irregular rhythm.

Junctional Rhythm (Strip)

Narrow regular rhythm with absent/inverted/after-QRS P waves

Junctional Rhythm (Rate)

40-60 bpm

Junctional Rhythm (P Wave)

P waves may be absent, hidden in the QRS, or appear after the QRS.

• If before the QRS, the PR interval is usually short.

It will ALWAYS be inverted.

Junctional Rhythm (PR Interval)

PR interval depends on where the P wave appears. If P wave is before QRS, PR is usually short: <120 ms. If P wave is hidden or after QRS, PR is not measurable.

Junctional Rhythm (QRS Complex)

QRS is usually narrow: <120 ms because the impulse still travels normally through the ventricles.

Junctional Rhythm (Regularity)

Usually regular R-R intervals. P-P intervals may be absent or not measurable because P waves may be hidden, inverted, or after the QRS.

Accelerated Junctional Rhythm (Strip)

Notice the inverted P wave

Accelerated Junctional Rhythm (Rate)

60-100 bpm

Accelerated Junctional Rhythm (P Wave)

P waves may be absent, hidden, or after the QRS.

The P wave will ALWAYS be inverted

• Difference is the rate is faster, 60–100 bpm.

Accelerated Junctional Rhythm (PR Interval)

Same as junctional rhythm.

• If P wave is before QRS, PR is usually short: <120 ms.

• If hidden or after QRS, PR is not measurable.

Accelerated Junctional Rhythm (QRS Complex)

QRS is usually narrow: <120 ms. Same QRS appearance as junctional rhythm, but rate is faster.

Accelerated Junctional Rhythm (Regularity)

Usually regular R-R intervals. Same regularity pattern as junctional rhythm, but rate is 60–100 bpm.

Junctional Tachycardia (Strip)

Junctional Tachycardia (Rate)

>100 bpm

Junctional Tachycardia (P Wave)

Same junctional P wave pattern: P waves may be absent, inverted, hidden, or after the QRS. At faster rates, they are often hard to see.

Junctional Tachycardia (PR Interval)

Same junctional pattern. PR interval is often not measurable because P waves are hidden. If P wave appears before QRS, PR is usually short: <120 ms.

Junctional Tachycardia (QRS Complex)

QRS is usually narrow: <120 ms. Fast, regular rhythm with absent/inverted/hidden P waves and narrow QRS.

Junctional Tachycardia (Regularity)

Usually regular R-R intervals. Same junctional pattern, but rate is greater than 100 bpm.

NSR w/ 1st Degree AV Block (Strip)

PR interval >200 ms, but every P conducts

NSR w/ 1st Degree AV Block (Rate)

Usually 60-100 bpm

NSR w/ 1st Degree AV Block (P Wave)

P waves are present, upright, uniform, and every P wave is followed by a QRS. The issue is not the P wave itself; the PR interval is prolonged.

NSR w/ 1st Degree AV Block (PR Interval)

PR interval is prolonged but constant: >200 ms. Every P wave still conducts to a QRS.

NSR w/ 1st Degree AV Block (QRS Complex)

QRS is usually narrow: <120 ms. The issue is a prolonged PR interval, not the QRS complex.

NSR w/ 1st Degree AV Block (Regularity)

R-R regular. P-P regular. Every P wave conducts to a QRS, but the PR interval is prolonged.

2nd Degree AV Block Mobitz I (Wenckebach) (Strip)

PR gets longer, longer, longer, then QRS drops

2nd Degree AV Block Mobitz I (Rate)

Atrial rate usually normal; Ventricular rate often slower/variable

2nd Degree AV Block Mobitz I (P Wave)

P waves are usually present and regular, but not every P wave conducts to a QRS. PR interval gets progressively longer until a QRS drops.