Cardiac Conduction System
ECG Components
Vertical Axis
1 Small Square = 1 mm (0.1 mV)
1 Large Square = 5 mm (0.5 mV)
2 Large Squares = 1 mV
Horizontal Axis
1 Small Square = .04 sec (40 msec)
1 Large Square = .2 sec (200 msec)
2 Large Squares = 1 sec (1000 msec)
Electrical and Mechanical Events
Mid Diastole
Atrial Contraction
Isovolumic Ventricular Contraction
Ventricular Ejection
Isovolumic Ventricular Relaxation
Sinus Rhythms
Normal Sinus Rhythm
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
60 - 100 bpm - Regular - Before each QRS, identical Before each QRS, identical - 0.12 to 0.20 - < 0.12
Sinus Arrhythmia
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
60 - 100 bpm - Irregular - Before each QRS, identical - 0.12 to 0.20 - < 0.12
Sinus Tachycardia
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
> 100 bpm - Regular - Before each QRS, identical - 0.12 to 0.20 - < 0.12
Sinus Bradycardia
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
> 60 bpm - Regular - Before each QRS, identical - 0.12 to 0.20 - < 0.12
Sinus Arrest or SA Block
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
40 - 100 bpm - Irregular - Identical before each QRS. P to P interval may be fixed before and after the pause - 0.12 to 0.20 - < 0.12
Supraventricular Rhythms
Premature Atrial Complexes – PACs
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
N/A - Irregular - Premature and abnormal. May be hidden - 0.12 to 0.20 - < 0.12
Premature Atrial Complex – Isolated PAC
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
N/A - Irregular - Premature and abnormal. May be hidden - 0.12 to 0.20 - < 0.12
Premature Atrial Complexes (Atrial Bigeminy) Every other beat is a PAC
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
N/A - Irregular - Premature and abnormal. May be hidden - 0.12 to 0.20 - < 0.12
Premature Atrial Complex with Aberrancy
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
N/A - Irregular - Premature and abnormal. May be hidden - 0.12 to 0.20 - < 0.12 Abnormal Shape
Nonconducted Premature Atrial Complex
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
N/A - Irregular - Premature and abnormal. May be hidden - None - Absent
Atrial Tachycardia
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
140 - 250 bpm - Regular - Abnormal P before each QRS (difficult to see) - 0.12 to 0.20 - < 0.12
Atrial Flutter
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
A:240-350 bpm V: Varies with conduction ratio - A: Regular V: Regular group beating or variable - Flutter (F) waves usually the negative component of the flutter wave in II, III, aVF and positive in V1 - N/A - < 0.12
Atrial Fibrillation
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
A:350-650 bpm - V: Slow to rapid - Irregular - Absent Fibrillatory (f) waves - N/A - < 0.12
Junctional Rhythm
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
40 - 60 bpm - Regular - Inverted in inferior leads; before, during or after the QRS; may be absent - < 0.12 - < 0.12
Accelerated Junctional Rhythm
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
60 - 100 bpm - Usually AV dissociation because of digitalis toxicity - May be sinus P wave (AV dissociation) - < 0.12 - < 0.12
Junctional Tachycardia
Heart Rate - Rhythm - PWave - PR Interval (in seconds) - QRS (in seconds)
Usually < 140 bpm - Regular - Inverted, Absent or after QRS - < 0.12 - < 0.12
Conduction Defects
Right Bundle Branch Block
PWave - PR Interval (in seconds) - QRS (in seconds) - Characteristics
Before each QRS, identical - 0.12 to 0.20 - ≥ 0.12 - RSR’ inV1
Left Bundle Branch Block
PWave - PR Interval (in seconds) - QRS (in seconds) - Characteristics
Before each QRS, identical - 0.12 to 0.20 - ≥ 0.12 - QS or rS inV1 &V2 ST elevation
Pre-excitation Syndrome
PWave - PR Interval (in seconds) - QRS (in seconds) - Characteristics
Before each QRS, identical - < 0.12 - Usually > 0.12 - Delta wave distorts initial QRS
First-Degree AV Block
PWave - PR Interval (in seconds) - QRS (in seconds) - Characteristics
Before each QRS, identical - > 0.20 - < 0.12 - Regular rhythm
Second-Degree AV Block – Type I (AV Wenckebach or Mobitz type I)
PWave - PR Interval (in seconds) - QRS (in seconds) - Characteristics
Conduction intermittent - Increasingly prolonged - < 0.12 - QRS dropped in a repeating pattern
Second-Degree AV Block–Type II (Mobitz type II)
PWave - PR Interval (in seconds) - QRS (in seconds) - Characteristics
Sinus - Usually normal and identical (before and after a blocked impulse) - Broad ≥ 0.12 - Some Pwaves are not conducted
Second-Degree AV Block – 2:1 AV Block
PWave - PR Interval (in seconds) - QRS (in seconds) - Characteristics
Sinus - Normal or prolonged - Narrow or broad - 2:1 AV conduction
Third Degree (Complete) AV Block
PWave - PR Interval (in seconds) - QRS (in seconds) - Characteristics
Normal but not related to QRS - N/A - Narrow or broad - AV dissociation
Arrhythmia Recognition (poster 1 of 2)
This is part one of two posters to assist healthcare professionals in recognizing basic arrhythmias. According to the Practice Standards for Electrocardiographic Monitoring in Hospital Settings (Circulation. 2004;110:2721-2746) in general, the mechanisms of arrhythmias are the same in both adults and children. However, the ECG appearance of the arrhyhmias may differ due to developmental issues such as heart size, baseline heart rate, sinus and AV node function, and automatic innervation.
ECG terminology and diagnostic criteria often vary from text to text and from one teacher to another. There are often several terms describing similar findings (for example: Premature Atrial Contraction, Atrial Premature Complex, Atrial Extrasystole, Supraventricular Ectopic Beat, etc.) It is important to correlate the ECG interpretation with the clinical observation of the patient.
This poster includes Premature Ventricular Conduction, Pacemaker Lead Placement, ST Segment Depression, Ventricular Rhythms, Pacemaker Rhythms, Full Compensatory Pause and ECG Artifact. The ECG rhythm strips display lead II as the top waveform and lead V1 as the bottom waveform. Classic examples are shown for each rhythm to provide basic visualization and avoid complexities. The intended use of this poster is to complement a text and /or course – in addition to a reference guide for arrhythmia recognition.
The most common ECG rate, interval, and duration measurements Are from the following publications:
- Clinical Electrocardiography (Post Graduate Institute for Medicine).
- Understanding Electrocardiography (Mary Boudreau Conover).
- How to Quickly and Accurately Master Arrhythmia Interpretation (Dale Davis).
- Principles of Clinical Electrocardiography (M. J. Goldman).
- Basic Dysrhythmias Interpretation and Management (Robert Huszar).
- An Introduction to Electrocardiography (Leo Shamroth).
- Interpretation of Arrhythmias (Emanual Stein
