3. Pearls
• Treat the patient not the paper.
• Electrical activity triggers mechanical activity. No
electrical activity = no mechanical activity
• But electrical activity does not guarantee mechanical
activity.
• The more cells involved the larger the deflection on the
ECG.
• If the wave of electrical activity is moving toward the
electrode, the wave will be positive (above the baseline);
if the wave is moving away from the electrode the wave
will be negative (below the baseline).
4. NORMAL ECG
Cardiac Conduction System
Conduction picture courtesy of New Mexico Heart Institute
One small box = .04 seconds
One large box = .20 seconds
5. Anatomy and the ECG
• The P wave = atrial activation (SA
node to AV node).
• The PR interval = onset of atrial
activation to onset of ventricular
activation.
• The QRS complex = electrical
ventricular activation.
• The ST-T segment = ventricular
repolarization.
• The QT interval = the duration of
ventricular activation and recovery.
6. Calculation Of Heart Rate
• Method 1: Count the number of large (0.2-
second) time boxes between two successive R
waves, and divide the constant 300 by this
number OR divide the constant 1500 by the
number of small (0.04-second) time boxes
between two successive R waves.
• Method 2 best for irregular rhythms: Count the
number of cardiac cycles that occur every 6
seconds, and multiply this number by 10.
7. The Rule Of 300
It may be easiest to memorize the following table:
# of big
boxes
Rate
1 300
2 150
3 100
4 75
5 60
6 50
10. Definition of Normal Sinus Rhythm
• Heart rate
• 60-100 Adult
• 80-160 Infant
• 80-130 Toddler
• 75-115 6 year old
• Regular rhythm
• P waves round, same shape and before each QRS
• Normal PR interval (0.12-0.20 sec or 3-5 small boxes)
• Normal QRS interval (< 0.12 sec or < 3 small boxes)
• QRS positive in leads I, II, aVF, V3-V6
12. Where Does The Impulse Come From?
Electrical
Impulse
Formation
Initiation
Point
Rate
Regularity
Onset
SA Node, Atrial, Junction, Ventricles
Normal, Tachycardic, Bradycardic
Regular, Irregular, Irregularly irregular
Passive escape, active
13. Where/How Does The Impulse Travel?
I, II, III
RBBB
Electrical
Impulse
Conduction
Sinus Node
Atria
AV Junction
Ventricular
SA Block
Intra Atrial Block
LBBB
LAH, LPH
Complete, Incomplete
14. Combined Flow Sheet
I, II, III
RBBB
Conduction
Sinus Node
Atria
AV Junction
Ventricular
SA Block
Intra Atrial Block
LBBB
LAH, LPH
Complete, Incomplete
Electrical
Impulse
Formation
Initiation Point
Rate
Regularity
Onset
SA Node, Atrial, Junction, Ventricles
Normal, Tachycardic, Bradycardic
Regular, Irregular, Irregularly irregular
Passive escape, active
15. Sinus Rhythm
• The P wave is upright in leads I and II
• Each P wave is usually followed by a Q
• The heart rate is 60-100 beats/min
16. When Is The Rhythm Unstable
Four main signs
• Signs of low cardiac output – systolic hypotension < 90
mmHg, altered mental status
• Excessive rates: <40/min or >150/min
• Chest pain
• Heart failure
• If unstable, electrical therapy: cardioversion for
tachyarrhythmia, pacing for bradyarrhythmia
