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Lecture Notes
Chapter 19
Electrocardiogram and
Cardiac Arrhythmias
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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Helpful Hints
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Depolarize = Depolarize = Contracts
Systolic
Afterload
Repolarize = Repolarize = Recover
Diastolic
Preload
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Normal Electrocardiogram (ECG)
EKG
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Electrocardiograph
 Detects micro-voltage changes as the heart
depolarizes and repolarizes
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How? - Leads
ECG “leads” (electrode configurations)
• Plots electrical activity that creates depolarization and
repolarization
• Leads are placed on chest, arms, and legs
• Bipolar standard limb leads
• Unipolar limb and chest leads
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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Wave is considered one wave… A complex is considered
multiple waves or letters…
For example, the P Wave that we’ll see is comprised of one
letter… the P… and it shows us the “kick” of the atria…
shooting that last 20% into the ventricle…
Then the QRS wave is considered a complex because there’s
three stages… and this is when the Ventricle contracts or
depolarizes…
The T wave represents the Ventricle Relaxing….
Pg 344
AMPLITUDE = VOLTAGE
Ventricles are much larger in muscle mass, they generate
more voltage when they depolarize or contract… You will see
that the voltage or height that the Ventricles generate is much
higher than the atria..
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ECG Components
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Waves and complexes
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P wave = atrial depolarization
QRS complex = ventricular depolarization
• 0.08 to 0.10 sec
T wave = ventricular repolarization
Wave height (amplitude) = voltage
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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ECG Components
Fig. 19-2
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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ConceptQuestion 19-1
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A high amplitude P wave may be associated
with what type of abnormality?
Let’s think about the right atrium for a moment…
What can cause the Right Atrium CVP to be high?
ANSWERS:
Right heart failure
Cor Pulmonale
Tricuspid Stenosis
Tricuspid Regurg.
An abnormally high P-wave amplitude means the
atrial muscle mass is greater than normal
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ECG Components
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Intervals and segments
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PR interval • From SA node to ventricles
• 0.12 to 0.20 sec ( slower the HR – longer PR)
(longer HR – shorter PR)
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point
• QRS -represents the ventricular contraction… Q is
the beginning of ventricles… S would represent the
end of the contraction… The point in which after the
S, the tracing reaches baseline… this is known as
the J point…
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ST segment Represents the Ventricle beginning it’s
recovery phase… or its diastolic phase
• Flat, lying on baseline is normal
• Depressed >0.5 mm = Myocardial ischemia
• Elevated >2 mm = myocardial injury
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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ECG Components
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Intervals and segments
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QT interval
• Beginning of the QRS complex to the End of the Twave…
• Usually less than 40 seconds
• The ventricle is in the refractory period
 Refractory Period
Refractory Period = When ventricle is contracting,
should another electrical activity try to come
quickly, the ventricle will not respond… It cannot
accept another depolarizing/contracting signal
during this phase… It can’t stack it’s contraction…
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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ECG Graph Paper
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Grid
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1 mm (smallest square) vertical = 0.1 mV
1 mm horizontal = 0.04 sec
Heavy 5 mm lines (big square) = 0.20 sec & 0.5
mV
5 large squares = 25 mm (about 1 inch) = 1 sec
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25 mm/sec graph speed
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Clinical Focus 19-1 pg 347
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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ECG Graph Paper
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
Fig. 19-5 12
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ECG Leads
pg 349
Fig. 19-9
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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Normal Sinus Rhythm
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Sinus node initiates each depolarization
Rate: 60 to 100 beats/min
P wave-QRS complex ratio is 1:1
Spacing between QRS is constant
PR interval is <0.16 sec
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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Normal Sinus Rhythm
Heart Rate _______
Fig. 19-16
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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Abnormal Sinus Rhythms
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Tachycardia
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Sinus tachycardia
• HR >100 beats/min
• Regular and rhythmic
• Causes
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Exercise, fever, anxiety, pain, coffee, smoking, hypoxia
Beta adrenergic drugs
• Treatment: OXYGEN… Then, focus on underlying cause
• Additional Treatment: Vagal Stimulation
• = Carotid Massage
 A rapid heart rate will icrease workload of heart
and increase O2 requirements
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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Abnormal Sinus Rhythms
Tachycardia
Heart Rate _______
Fig. 19-17
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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Abnormal Sinus Rhythms
Bradycardia
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Bradycardia
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Sinus bradycardia
• HR <60 beats/min
• Regular and rhythmic
• Normal in sleep, physically conditioned individuals
• Carotid sinus syndrome; overly sensitive pressure
receptors (vagal) in the neck… If stimulated = syncope
• SYNCOPE = _________________
• Gagging can also cause bradycardia (Suctioning)
• Symptomatic bradycardia
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hypotension, weakness, sweating, syncope
• Treatment: atropine; pacemaker
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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Abnormal Sinus Rhythms
Bradycardia
Heart Rate _______
Fig. 19-18
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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Abnormal Sinus Rhythms
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Sinus arrhythmia
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Irregularly generated sinus node impulses
Alternate between fast and slow rates
Irregular spacing between QRS complexes
Follows inspiration & expiration (↑rate insp.; ↓exp.)
No clinical significance and do not require
treatment
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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Abnormal Sinus Rhythms
Fig. 19-19
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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ConceptQuestion 19-4
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Why do chronic congestive heart failure and
high atrial pressures predispose a person to
the development of atrial fibrillation?
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Ventricular Tachycardia
Fig. 19-28
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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Ventricular Arrhythmias
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Ventricular fibrillation (VF)
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Most lethal arrhythmia = cardiac arrest; CODE BLUE
Ventricles nonfunctional, quivering, no pumping ability
No recognizable waves or complexes
Requires electrical defibrillation—no drug can convert to
normal rhythm
Equivalent to Cardiac Arrest. CPR must be initiated
SHOCKABLE RHYTHM
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Along with a shock, use:
• Epinephrine, Amiodarone, Lidocaine
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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Ventricular Fibrillation
Fig. 18-29
Copyright © 2007, 1998 by Mosby, Inc., an affiliate of Elsevier Inc.
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ASYSTOLE
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