PR Interval - My EKG

• 
• Home
• Basic Principles
• Read an EKG
• Disorders
• Arrhythmias
• Calculations

• Read an EKG:
• Heart Rhythm
• Heart Rate
• PR
• QT
• Heart Axis
• ST Segment
• Abnormal Waves

PR Interval

Advertising

The PR interval is measured from the beginning of the P wave to the beginning of the QRS complex. It comprises the P wave and the PR segment.

The interval should be measured in the lead with the largest, widest P wave and the longest QRS duration 1.

The PR interval includes the atrial depolarization and the propagation of the impulse through the AV node and the Conduction System until the ventricular myocardium begins to depolarize 1.

It does not include the duration of conduction from the Sinus Node to the right atrium (Sinoatrial conduction).

The PR interval also includes the atrial repolarization (atrial T wave), which is directed opposite to the P wave axis, but atrial repolarization usually has low amplitude and the PR segment is frequently isoelectric 1.

Normal and Abnormal PR Interval

Normal PR Interval:

In adults the normal PR interval is 0.12 s to 0.20 s (3 to 5 small squares).

Normal PR interval (0.14 s).

It is generally shorter in children (see pediatric EKG) and in pregnant women, and it is longer in older persons.

Prolonged PR Interval:

Prolongation of the PR interval above 0.20 s (5 small squares) is called first degree AV block.

First degree AV Block with prolonged PR interval (0.36 sec).

It indicates a conduction delay from the sinus node to the ventricles. The atrioventricular node is the most commonly involved site in adults.

In type I 2nd degree AV block there is a progressive PR lengthening until a P wave is not conducted (Wenckebach phenomenon).

Short PR Interval

A short PR interval (<0.12 sec) may be caused by a pre-excitation syndrome (Wolff-Parkinson-White), ectopic atrial pacemaker or AV junctional rhythm.

Wolff-Parkinson-White with short PR interval (0.08 sec) and delta wave (red arrows).

The most important findings in Wolff-Parkinson-White syndrome are a short PR interval, the presence of the delta wave and wide QRS complex.

In ectopic atrial pacemaker or AV junctional rhythm may be seen a short PR interval with an abnormal P waves with narrow QRS complex.

Elements of the PR Interval

P Wave

Related articles: EKG waves, abnormal waves and intervals.

The P wave represents atrial depolarisation, it is the result of overlaying the electrical activity of both atria.

P wave duration is less that 0.10 s and its maximum voltage is 0.25 mV. Normal P wave is positive in all leads except aVR where it is negative, and V1, where P wave is biphasic.

More information: EKG waves, abnormal waves and intervals.

PR Segment

Related article: Segments and intervals.

PR segment is the isoelectric segment between the end of the P wave and the start of the QRS complex. It is included in the PR interval (read difference between segments and intervals).

Causes of PR Segment Depression:

• Exercise-induced tachycardia.
• Presences of taller P waves.
• Acute pericarditis.
• Atrial ischemia.

More information: Segments and intervals.

We hope we have been able to help you with the PR interval. For further details on the analysis of QT interval, click Next.

previous | next

References

• 1. Surawicz B, Knilans TK. Chou’s electrocardiography in clinical practice, 6th ed. Philadelphia: Elservier; 2008.

If you Like it... Share it.

Share on Facebook Tweet

Can’t Miss

How to read an EKG

Heart axis calculation

EKG electrodes

EKG waves

Right bundle branch block

MOST POPULAR

Simple guide to reading and reporting an EKG step by step.

Calculate the heart axis by entering the QRS amplitude in I and III.

Calculates the QTc interval by entering QT interval and HR

How not to overlook EKG changes in acute myocardial infarction

Detailed description of each of the EKG wave

Advertising

Folow us:

Facebook Twitter Books on EKG?

My EKG team recomends you the books that we used to create our website.

Advertising

Topics

Initial concepts

• Cardiac conduction system
• Cardiac cycle
• Coronary arteries

Basic principles

• Basic principles
• How to do an EKG
• EKG paper
• Electrodes
  • Tips EKG electrodes
  • Electrode color coding
• EKG leads
  • Right-side and posterior
• EKG waves
  • The P wave
  • The Q wave
  • The U wave
• Intervals and segments
• Locating walls
• QRS morphology
• Is an EKG performed correctly?

Read an EKG

• Read an EKG
• Heart rate
• Heart rhythm
  • Normal sinus rhythm
• PR interval
• QT interval
• Heart axis
  • Right-axis deviation
  • Left-axis deviation
  • Extreme axis deviation
• ST-segment
• Abnormal waves

Arrhythmias

• Arrhythmias
• Sick sinus syndrome
• Sinus arrhythmia
• AV blocks
  • 1st degree AV block
  • 2nd degree AV block
  • 3th degree AV block
• Atrial flutter
• Atrial fibrillation
• Supraventricular tach.
  • AVNRT
  • Inappr. sinus tach.
• Pre-excitation synd.
• Ventricular arrhythmias
  • PVCs
  • Ventricular tachycardias
  • VT criteria
  • Torsades de pointes
  • Fascicular left VT
  • Ashman phenomenon

Bundle branch blocks

• Bundle branch blocks
• Right BBB
• Incomplete RBBB
• Left BBB
• Incomplete LBBB
• Left hemiblocks
• Bifascicular blocks

Ischemia

• Ischemic heart disease
• Chest pain and EKG
• Ischemia, injury and infarction
• Acute coronary syndromes
• NSTE-ACS
• Acute myocardial infarction
• Atypical presentations
• Occluded artery
• Modified Sgarbossa criteria
• Wellens syndrome

Hypertrophy & dilation

• Left atrial enlargement
• Right atrial enlargement
• Left ventricular hypertrophy
• Right ventricular hypertrophy
• Sokolow-Lyon criteria

Metabolic & drugs

• Hyperkalemia
• Hypokalemia
• Hypercalcemia
• Hypocalcemia
• Digoxin
• Hydroxychloroquine

Pacemaker

• Pacemaker & EKG
• Read an EKG with pacemaker
• Pacemaker nomenclature
• Pacemaker malfunction

Pediatric EKG

• Pediatric EKG
• Read a pediatric EKG
• Atrial septal defect
• Ventricular septal defects
• Tetralogy of Fallot
• Pulmonary stenosis

Other articles

• Pericarditis
• Early repolarization
• Brugada syndrome
• Arrhythmogenic cardiomyopathy
• Bayés syndrome
• Dressler syndrome
• Pulmonary embolism
• Hypothermia
• Pregnancy
• Normal EKG in athletes
• Abnormal EKG in athletes
• Poor R wave progression
• Mitral prolapse

Calculations

• Heart axis
• Heart rate
• CHA2DS2-Vasc
• Corrected QT
• Romhilt-Estes
• R-R interval
• Aortic valve

Procedures

• Holter EKG?