Download Electrocardiography Heart Anatomy

PEAK 485
Exercise Test and Prescription
The Heart of the Matter

Cardiovascular health is key

Poor blood supply = damage / death

Cardiac muscle is the ultimate slow twitch fiber

Cardiac function predicts health and performance
Cardiology
Cardiac Function

Two cycle pump
 Receives blood from lungs and body
 Sends blood to lungs and body
 Closed circuit (“leaky” / volume changes)
 Arterial (systemic) vs. venous vascular
systems
Cardiac Anatomy

Four Chambers
 2 Atria and 2 Ventricles
 Left side vs. right side

Key Features
 Left Ventricle is primary pump (systemic circulation)
 Right Atrium
 Sinoatrial node (SA node)
Cardiac Anatomy

Great Vessels
 Sup. & Inf. Vena Cava
 Pulmonary Arteries
 Pulmonary Veins
 Aorta
 Blood source for coronary arteries
Cardiac Diagram
Cardiac Anatomy

Coronary Arteries (lesser vessels)
 Left Coronary Artery
 Anterior Descending Art. (ant. supply) (LAD)
 Left Circumflex Art. (lat. left V. supply)
 Right Coronary Art. (right A. & V.)
 Runs infer. to post.
 AV node supply
 Each supplies given part of myocardium with
blood flow (nutrients and oxygen).
Left
Circumflex
Cardiac Anatomy

Coronary Arteries (lesser vessels)
 Capillary Beds
 Site of oxygen diffusion
Capillary Beds
Cardiac Anatomy

Heart Layers
 Endocardium
 Myocardium*
 Epicardium
 Pericardium
Cardiac Anatomy

Myocardium – Heart Muscle
 Myocytes
 Intercalated discs
 Cell orientation
 Nervous stimulation
 Sympathetic system
 Parasympathetic system
 Cell communication
Cardiac Anatomy

Conduction System
 SA node
 AV node
 Bundle of His
 Bundle Branches (septal to apex to walls)
 Left Bundle Branch (LBB)
o Right Bundle Branch (RBB)
 Purkinje fibers
Cardiac Physiology
Cardiac Physiology

Properties of myocardial cells:
 Contractility
Strength of contraction (tension) can vary
 Extensibility / Elasticity
Cardiac Physiology

Properties of myocardial cells cont’d
 Excitability / Irritability
 Can be electrically or chemically stimulated
 Balance of chemicals creates membrane potential
 Disruption of chemical balance leads to stimulation
 Ionotropic effect – speed up
Ca
Cardiac Physiology

Automaticity
 Leaky / channels
 Spontaneous depolarization.
 Pacemaker Cells (SA Node)
 This tissue normally initiates the cardiac cycle.
Cardiac Physiology

Conductivity
 Action potential travels to other cells within the
atria (or other cells) causing them to contract.
Cardiac Physiology

Properties of myocardial cells cont’d

Extensibility / Elasticity
Electrical Conduction
AV Node – Delay station for electrical impulse. Delay
allows atrial contraction to complete before ventricles
begin.
 Bundle of His – Transmits electrical impulse across the
annulus fibrosis (cartilage framework of atrioventricular
valves).
 Bundle Branches (and fascicles) – conduct impulse
rapidly throughout ventricles.
 Note: Process allows for sequential contraction of the
myocardium to pump blood effectively in the proper
direction.

Questions So Far?
ECG Principles
ECG Principles
ECG Principles
ECG Paper
 Standard paper speed = 25 mm/s
 Small and large boxes
 Horizontally - time


Small boxes represent .04 sec (40 msec)
Large boxes represent .20 sec (200 msec)
 Vertically – strength of electrical activity (voltage)


Small boxes represent .1 mV
Large boxes represent .5 mV
ECG Principles
Electrical & Mechanical Events

P wave
 Atrial depolarization
 Atrial contraction begins midway

QRS wave
 Ventricular depolarization
 Ventricular contraction begins midway/late

T wave
 Ventricular repolarization
 Ventricular relaxation
ECG Tracing Diag.
ECG Principles
Timing of Electrical Events






PR interval – atrial depol. .12 - .20 sec.
PR segment – AV/His depol. – isoelectric
QRS complex - < .12 sec
ST segment –vent. cells depolarized - isoelectric
QT interval - < .36 sec
P-P / R-R - Atr. & Vent. rate dependent cycles
ECG Tracing Diag.
Timing changes (fast or slow) =
Normal response
Abnormal response
ECG Waves and Electrodes

Reference point is the positive electrode.
 Depolarization wave moves toward the positive
electrode, recorded depolarization wave is
positive.

Depolarization wave moves away from the
positive electrode, recorded depolarization wave is
negative.
ECG Waves and Electrodes

If the positive electrode is perpendicular (sits
across the axis) to the depolarization wave, the
recording is biphasic (both positive and negative).
ECG Waves and Electrodes
Limb Leads:
 I, II, III: each has two electrodes (bipolar
leads – one positive; one negative)
Limb Leads Diag.
ECG Waves and Electrodes
Limb Leads:
 Augmented Voltage Leads (AVR, AVL, AVF)
- each has a positive electrode but shares an
averaged (common) negative pole made up of
the other electrodes.
Augmented Leads Diag.
ECG Waves and Electrodes
Limb Leads:
 These six leads view the electrical activity in
the vertical plane.
ECG Waves and Electrodes
Hexaxial Reference System
 Measured in degrees starting with positive
side of Lead I being 0°.
 Rotation clockwise from 0° is positive;
counterclockwise is negative.
Hexaxial Diag.
AVR
AVL
AVF
ECG Waves and Electrodes
Precordial Leads
 V1, V2, V3, V4, V5, V6 – each is a positive
electrode with the entire body serving as the
negative pole.
 These six leads view the electrical activity in
the horizontal plane.
Precordial Leads Diag.
Heart level Xsect. Diag.
Cross Section of the Heart at Level of T4 - T5 (Image from the Visible
Human Project-NLM)
V1
Horiz. Hexaxial Diag.
V6
Cross Section of the Heart at Level of T4 - T5 (Image from the Visible
Human Project-NLM)
Vectors and Waveforms
Vector = average electrical activity – direction
 Atria – downward & leftward
 AV Node & BB’s – not strong enough to detect
 Septum – leftward
 Ventricles – downward & leftward
 V. Repolarization – same direction

Vector Diag.
P
Vectors and Waveforms

Remember
– Waveform changes for each lead
– Tallest toward + electrode
– Inverted away from + electrode
– Biphasic perpendicular to line of + to –
– View of multiple leads tells direction of
depolarization
Questions So Far?
ECG Interpretation
Basic Questions?
ECG Interpretation

What do you assess?
 What order do you follow?
 What meaning does a deviation have?
 What should be done?
ECG Interpretation

Rate
 Rhythm
 Axis
 Hypertrophy
 Infarction
ECG Interpretation
Rate
 Methods to determine heart rate:
 1500/# small boxes between R waves.
o
o
Most accurate; best for fast rhythms.
Question: How much time is one small box?
 300/# large boxes between R waves.
o
o
o
Good for slow rhythms.
300, 150, 100, 75, 60, 50 rule
Question: How much time is one large box?
 # R waves in 6.0 s (30 large boxes) x 10 (3 sec. marks)
o
Good for irregular rhythms.
ECG Interpretation
Quick Visual: Rate at each heavy line (large box)
0 300 150 100 75 60 50 43 38 33 30
350
250
(4th)
(6th)
Heart rate determination
ECG Interpretation

Ventricular Rate
 Atrial Rate
 Nodal Rate
What’s The Rate?
What’s The Rate?
What’s The Rate?
ECG Interpretation





Source? – atria, junction, ventricles?
Normal rate = 60-80 bpm
Tachycardia = > 100 bpm
Bradycardia = < 60 bpm
Flutter = > 250 – 350 “bpm”
– Atrial source – “sawtooth” appearance
– Ventricular pacing is not connected

Fibrillation = > 350 “bpm”
– Either atrial or ventricular source – “bag of worms” – no cardiac output
– V. Fib. = immediate syncope, asystole is soon!!!!
What’s the rate? – What’s it called?
Sinus tachycardia
What’s the rate? – What’s it called?
Anything else you can see?
Sinus bradycardia
ECG Interpretation
Rhythm
 Lead II is often best to observe rhythm.
 Analysis:
1. Determine regularity of rhythm.


Index card method
Calipers
2. Determine rate.
3. Examine P waves:


Appearance is normal and consistent
P before each QRS; one P wave for each QRS
ECG Interpretation
Rhythm
4. Measure PR interval

Normally < .20 s
5. QRS complex width:

normally narrow (< .12 s)
ECG Interpretation

Arrhythmias
Four basic types of arrhythmias:
1. Sinus origin
2. Ectopic rhythms
3. Conduction blocks
4. Preexcitation syndromes
ECG Interpretation
Arrhythmias
1.
Sinus Origin

Sinus bradycardia (< 60 bts/min)
Sinus tachycardia (>100 bts/min at rest)
Sinus Arrhythmia:


Could be normal rate but rate changes (does not remain
regular)
o

Sinus Arrest
o
Escape beats
ECG Interpretation
Arrhythmias
2.
Ectopic Rhythms – originate outside of the SA node
•
Supraventricular - Atrial focus = 60-80
•
•
When SA node does not fire
Increased irritability of atrial tissue
AV node – does no pacemaking – holds signal
Junctional focus = 40-60
•
•
•
•
•
Idiojunctinal – Bundle of His
No signal from SA or atria
Retrograde depolarization (P wave?)
ECG Interpretation
Arrhythmias
2.
Ectopic Rhythms – originate outside of the SA node
•
Ventricular Focus = 20-40
•
•
•
•
Idioventricular
No signal from SA, atria, or junction
Larg, wide QRS wave
P wave? - none
ECG Interpretation
Arrhythmias
2.
Ectopic Rhythms – originate outside of the SA node
•
Rapid ectopic rhythms - tachyarrythmias
•
Paroxysmal Supraventricular Tachycardia (sudden)


•
Paroxysmal Atrial Tachycardia (PAT)
Paroxysmal Junctional Tachycardia (PJT)
Paroxysmal Ventricular Tachycardia (PVT)
•
Looks like rapid PVCs? It is
ECG Interpretation
Arrhythmias
2.
Ectopic Rhythms – originate outside of the SA node
•
Atrial Flutter – sawtooth pattern
•
Atrial Fibrillation – sine wave pattern
•
MultiFocal Atrial Tachycardia – (rate?)

Note: if a normal rate, then called a wandering pacemaker.
Wandering Pacemaker
ECG Interpretation
Arrhythmias
•
•
Non-sustained abnormal beats
Premature
•
•

Early – ectopic
Focus discharging spontaneously
Premature atrial contraction (PAC)
o
o
o
o
Can occur on T wave
May be nonconducted
P wave may be missing
Check P-P interval & R-R interval for early wave
ECG Interpretation
Arrhythmias
•
•
Non-sustained abnormal beats
Premature

Premature junctional contraction (PJC)
o
o
o
Retrograde P waves
P waves during or after QRS
P wave may be missing
Junctional Rhythm
ECG Interpretation

Arrhythmias
Premature Ventricular Contraction (PVC)





Early-before atria (P) can begin a new cycle
Enormous QRS – deflections are tall, deep, wide
Compensatory pause – refractory period
Unifocal or multifocal
Coupled with normal beats



Bigeminy - every 2nd beat
Trigeminy – every 3rd beat
Quadrigeminy – every 4th beat
ECG Interpretation

Arrhythmias
Premature Ventricular Contraction (PVC)


Sign of parasystole – 2 pacemakers – sinus & vent.
Runs of PVCs- sign of impending danger


6 PVC’s in one minute – warning of possible V tach.
3 or more in a row are technically considered V tach.
ECG Interpretation

Arrhythmias
Premature Ventricular Contraction (PVC)

PVC on T






PVC falling on T is much too early
Vulnerable period
Called R on T phenomenon
Can lead to V tach
Ventricular Tachycardia
Ventricular Fibrillation
R on T phenomenon
Practice Rhythms
Practice Rhythm
V tach
Rate: __________
Rhythm: _____
P-R interval: ____
QRS: ________
P wave: _______
Rhythm interpretation: ____________________________
Practice Rhythm
V tach
Rate: 300
Rhythm: reg./rapid
P-R interval: n/a
QRS: wide
P wave: none
Rhythm interpretation: Vetricular Tachycardia
Practice Rhythms
Rate: __________
Rhythm: _____
P-R interval: ____
QRS: ________
P wave: _______
Rhythm interpretation: ____________________________
Practice Rhythms
Rate: 75
Rhythm: regular
P-R interval: .16
QRS: .08
Rhythm interpretation: normal sinus rhythm
P wave: present norm.
Practice Rhythms
Sinus Bradycardia
Rate: __________
Rhythm: _____
P-R interval: ____
QRS: ________
P wave: _______
Rhythm interpretation: ____________________________
Practice Rhythms
Sinus Bradycardia
Rate: 43
Rhythm: reg./slow
P-R interval: .20
QRS: .08
Rhythm interpretation: sinus bradycardia
P wave: pres. reg.
Practice Rhythms
Rate: __________
Rhythm: _____
P-R interval: ____
QRS: ________
P wave: _______
Rhythm interpretation: ____________________________
Practice Rhythms
Rate: 125
Rhythm: reg./rapid
P-R interval: .16
QRS: .08
Rhythm interpretation: sinus tachycardia
P wave: pres.
Atrial Flutter
Rate: __________
Rhythm: _____
P-R interval: ____
QRS: ________
P wave: _______
Rhythm interpretation: ____________________________
V tach
Rate: __________
Rhythm: _____
P-R interval: ____
QRS: ________
P wave: _______
Rhythm interpretation: ____________________________
V tach
Rate: 300
Rhythm: reg./rapid
P-R interval: n/a
QRS: wide
Rhythm interpretation: v - tach
P wave: n/a
Practice Rhythms
A fib answer
Rate: __________
Rhythm: _____
P-R interval: ____
QRS: ________
P wave: _______
Rhythm interpretation: _____________________
Practice Rhythms
A fib answer
Rate: A – 350+
Rhythm: irreg./rapid P wave: irreg.
P-R interval: n/a
QRS: none
Rhythm interpretation: atrial fibrillation
Atrial flutter
Rate: __________
Rhythm: _____
P-R interval: ____
QRS: ________
P wave: _______
Rhythm interpretation: ____________________________
Atrial Flutter
Rate: a-350/v-125
Rhythm: irreg./rapid P wave: rapid
P-R interval: n/a
QRS: .08
Rhythm interpretation: atrial flutter
Junctional Escape Beat-Rhythm
Rate: __________
Rhythm: _____
P-R interval: ____
QRS: ________
P wave: _______
Rhythm interpretation: ____________________________
Junctional Escape Beat-Rhythm
Rate: a-0/v- 35-60
Rhythm: irreg./slow P wave: none
P-R interval: n/a
QRS: .08
Rhythm interpretation: junctional escape rhythm
PVC
Rate: __________
Rhythm: _____
P-R interval: ____
QRS: ________
P wave: _______
Rhythm interpretation: ____________________________
PVC
Rate: 73
Rhythm: irreg.
P-R interval: .12
QRS: 1 wide (.16)
P wave: 1 missing
Rhythm interpretation: PVC (premature ventricular contraction)
Sinus Arrest
~ 3.5 sec
between
beats
Triplet – run of pvc
Triplet – run of pvc
Trigeminy
Trigeminy
Quadrigeminy
Quadrigeminy
ECG Interpretation
Arrhythmias
3.
Conduction Blocks – electrical blocks which slow
or prevent passage of electrical stimuli
(depolarization)
•
Sinus Block – “sick sinus”
•
•
•
•
Unhealthy SA node may skip or fail for at least one cycle
No P or QRST – “lost beat”
Resumes pacing as if nothing happened
Same P waves before and after
ECG Interpretation
Arrhythmias
Conduction Blocks
3.
•
Atrioventricular Blocks (AV Blocks)

First Degree AV Block
 Prolonged P-R interval (> .20 sec) every cycle
 Consistent P-R - prolonged by same amount
First Degree Block
ECG Interpretation
Arrhythmias
Conduction Blocks
3.
•
Atrioventricular Blocks (AV Blocks)

Second Degree AV Block – 2 types
o
Mobitz Type I (Wenckebach)
o P-R interval progressively increases until a P is not
followed by a QRS.
o Last P stands alone
o Always a P but eventually no QRS
Second Degree – Mobitz I- Wenckebach
ECG Interpretation
Arrhythmias
Conduction Blocks
3.
•
Atrioventricular Blocks (AV Blocks)

Second Degree AV Block
o
Mobitz Type II
o QRS is “dropped” - not conducted even though P wave is
present and normal
o All is normal before and after event
o No lengthening P-R (no warning)
o Sign of more serious conduction problems
Second Degree Mobitz II -
ECG Interpretation
Arrhythmias
Conduction Blocks
3.
•
Atrioventricular Blocks (AV Blocks)

Third Degree AV Block
 Total lack of conduction through the AV node
 Rate and the interval between the QRS depend upon the origin
of the escape mechanism.
 May progress to ventricular standstill
 Independent P waves and QRS's with no relationship between
the two (AV dissociation – separate atrial & ventricular rates)
Third Degree Block
AV Block
ECG Interpretation
Arrhythmias
4.


Preexcitation Syndromes
Key Feature: Short PR interval
Wolf-Parkinson-White


(also note wide QRS with delta wave in some leads)
Lown-Ganong-Levine

(normal QRS; no delta wave)
ECG Interpretation
12-Lead ECG

Analysis:
1.
2.
3.
4.
5.
6.
7.
8.
Determine regularity of rhythm.
Determine rate.
Examine P waves
Measure PR interval
QRS complex width
Determine Axis
Examine ST Segment (normal is < 1mm elevation or
depression)
Check T waves (upright except for aVR, V1, and
possibly III)
ECG Interpretation
12-Lead ECG

Common Abnormalities:
Axis Deviation
1.
•
Normal axis between 0° and 90°
Bundle Branch Blocks
2.
•
Right Bundle Branch Block



•
Wide QRS
RSR’ in V1 and V2; T wave inversion and ST depression
Deep S wave in V5/V6
Left Bundle Branch Block



Wide QRS
Broad R waves in V5/V6; T wave inversion and ST depression
Deep S waves in V1/V2
ECG Interpretation
12-Lead ECG
Hemiblocks
3.
•
•
Anterior: left axis deviation
Posterior: right axis deviation
Bifascicular block: right bundle branch block +
hemiblock
5. Ventricular Hypertrophy
• Right: R  S in V1
• Left: R in V1 + S in V5  35 mm
• T wave inversion and ST depression in both.
4.
ECG Interpretation
12-Lead ECG
Ischemia
• ST depression; inverted symmetrical T waves
7. Infarct
• Acute (also referred to as injury)
 ST elevation
• Old
 Abnormal Q waves (.04 sec wide; 1/3
height of R wave)
6.
Diagnostic Value of ECGs
(Chapter 6, pages 124-129 in text)

Sensitivity: percentage of people with CAD who
have a positive ECG test.
 70% for ECG stress test
TP/(TP + FN)

Specificity: percentage of people without CAD
who have a negative ECG test.
 77% for ECG stress test
TN/(TN + FP)
Questions?
End Electrocardiography