EKG Week 1

Cardiac Anatomy
& Physiology
• The Heart
• Cardiac Cycle
• Coronary Arteries
• Cardiac Output (CO)
The Heart
• Hollow, coneshaped
muscular
organ
• About size of a fist
& weighs about 11
oz.
• Located in the
middle of the
thoracic cavity
• Attached to thorax
via great vessels
Base
Apex
Layers of the Heart
• Endocardium - inner layer
– Lines inside of heart &
covers heart valves
• Myocardium – middle layer
– Responsible for contraction
& pumping
• Epicardium - external layer (Visceral pericardium)
– Contains coronary arteries
• Pericardium - outer covering (Parietal pericardium)
– Encloses the entire heart
– Approx. 10ml of serous fluid between 2 inner layers
1
Heart
Chambers
Atria
• Low-pressure
chambers receive
blood from body
• Responsible for
“Atrial kick”
Ventricles
• Pump blood to lungs & body
• LV: high-pressure chamber
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3
4

Atrioventricular
(AV) Valves
• Separate atria &
ventricles, prevent
backflow of blood
• Tricuspid valve -
between R Atrium & R ventricle, has 3 leaflets
or cusps
• Mitral (bicuspid) valve - between L Atrium & L
Ventricle, has 2 leaflets/cusps
Semilunar
Valves
• Prevent backflow
of blood from
aorta &
pulmonary
arteries into
ventricles during
diastole
• Pulmonic valve
• Aortic valve
5
6
Cardiac Cycle
(Mechanical Activity)
• Systole “Contract &
eject” time
• Atria relax, ventricles
contract
• 1/3 of cardiac cycle
• Period of systolic BP
(SBP)
Cardiac Cycle
(Mechanical Activity)
• Diastole “Relax &
fill” time
• Ventricles & atria
relax, atria fill
• 2/3 of cardiac cycle
• Period of diastolic
BP (DBP)
7
8

Coronary Arteries
Autonomic Nervous System (ANS)
• Located at the base of aorta, supply heart with O 2
• Coronary arteries fill during diastole when vascular
resistance is lower
• Need DBP of 60 or > to perfuse coronary arteries
• Right coronary artery (RCA)
– Supplies AV Node, SA node (50% of pop), & HB
• Left coronary artery (LCA)
– Left Anterior Decending (LAD)
– Left Circumflex (LC)
– Supplies SA node (50% of pop), BBs, & Purkinje
fibers
Sympathetic (Û)
• Accelerates
• β 1 receptor sites
• Epi/Norepinephrine
• Stimulation results:
– Û contraction
– Û conduction
– Û CO, HR, BP
Parasympathetic (Ü)
• Inhibits
• Vagus nerve
• Acetylcholine
• Stimulation results:
– Ü HR (SA node)
– Ü AV conduction
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10
Cardiac Output (CO)
S/Sx of Decreased CO
• CO = SV (stroke volume) X HR (heart rate)
• CO = amount of blood ejected (pumped) by
the ventricles in 1 minute (LPM)
• Normal adult CO = 4-8 LPM
• SV = amount of blood ejected by ventricles w/
each contraction - 1 heartbeat = 70 ml/beat
• CO is affected by a change in HRÓ
or Ô, or stroke volume Ó or Ô
• Cold, clammy skin
• Color changes in skin
or membranes
• Dyspnea
• Orthopnea
• Crackles (rales)
• Restlessness
• Changes in mental
status
• Changes in BP
• Dysrhythmias
• JVD
• Fatigue
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12

Preload & Afterload
Preload: force exerted by the walls of
ventricles at the end of diastole
–Amount of blood (in the heart) that it has to
“push” out or “up the hill”
–Volume of venous return influences preload
–Hypovolemia (Ôpreload)
–Heart failure (Ópreload)
Preload & Afterload
Afterload: pressure against which ventricles
must pump to eject blood
–“The hill” the heart has to push against
(SVR)
–Ó afterload = Ó heart workload
Frank-Starling Law of the Heart:
–More myocardial muscle is stretched
(to a limit), the greater the force of
contraction
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14
Questions ?
15

Cardiac
Electrophysiology
• Cardiac action potential
• Depolarization cycle
• Refractory periods
• Conduction system
Properties of Cardiac Cells
Automaticity (electrical event)
• Ability to spontaneously initiate an electrical
impulse
Excitability (electrical event)
• Ability to respond to an electrical stimulus
Conductivity (electrical event)
• Ability to receive & conduct an electrical
stimulus
Contractility (mechanical event)
• Ability to shorten or contract
Cardiac Action Potential
• Electrical impulses are a result of rapid flow of
ions back & forth across cell membrane
• Ion exchange/movement (K, Na, Ca) in heart
cells creates electrical activity that appears on
the EKG as waveforms
• Major electrolytes (ions) affecting cardiac
function:
– Potassium (K), Sodium (Na), Calcium (Ca)
• Ü K, Ca = Û automaticity
• Û K, Ca = Ü automaticity
Refractory Periods
Absolute Refractory Period (ARP)
• From onset of QRS to approximate
peak of T wave
• Cells are depolarized & can’t be stimulated to conduct
an impulse no matter how strong the stimulus
Relative Refractory Period (RRP)
• Known as the “Vulnerable Period”
• Corresponds with the downslope of T wave
• Cells can be stimulated if stimulus is strong enough
• Can result in ventricular chaos (VT, VF)

Main Refractory Periods
Conduction System
•Sinoatrial (SA) Node
(Internodal Atrial Pathways)
•Atrio-Ventricular (AV) Junction
•Bundle of His (HB)
•Right & Left Bundle Branches (RBB, LBB)
•Purkinje Fibers/Network (Ventricles)
Sinoatrial (SA) Node
• Located at the junction of
the SVC & RA
• Initiates electrical
impulses at a rate of 60
to 100 beats/min
• Normally the primary
pacemaker of the heart

AV Junction
• Area of AV node & Bundle of
His down to branch of R & L
Bundles
• Impulse delayed here to
allow atrial contraction
(“atrial kick”) & complete filling of ventricles
• First escape pacemaker of the heart
• Inherent rate of junction is 40 – 60 beats/min.
Bundle of His (HB)
• Electrical connection
between the atria & the
ventricles
• Conducts impulses
between AV Junction &
R & L Bundles
R & L Bundle Branches
• RBB: Innervates the R
Ventricle
• LBB: Innervates the L
Ventricle & the intra-
ventricular septum
(from L to R)
• LBB divides into 3 fascicles
Purkinje Fibers
• Web of fibers that
penetrate into the
ventricular muscle
• Receive impulses from
R & L Bundle Branches
& conducts impulse to
ventricles

Ventricles
• Second escape
pacemaker of the heart
• Inherent rate of
Purkinje fibers -
Ventricles is
20 to 40 beats/min
Questions ?

Basic
Electrocardiography
• Lead Systems
• EKG Paper
• EKG Components & Waveforms
The Electrocardiogram (ECG/EKG)
• Records electrical voltages generated by
depolarization of cardiac cells thru skin
electrodes connected by cables to an ECG
machine
• Provides information about conduction
disturbances, electrical effects of meds &
electrolytes, & ischemic damage & injury
• Does not provide information about contractility
of myocardium - that must be evaluated by
assessment of pulse & BP
ECG Electrodes & Lead Systems
• Disposable electrode patches
contain conductive gel that conduct skin
voltage thru lead cables to the monitor.
• An EKG lead is a record of current flow
between two electrodes (+ & -).
• Electrodes & lead wires are applied at
specific locations on the chest wall &/or
extremities.
3 Lead Pt.
Cable -
White,
Black, Red

3 Lead
Electrode
Positions
5 Lead Pt.
Cable -
White,
Black, Red,
Green,
Brown
5 Lead
Electrode
Positions
Waveform Deflections
• An ECG waveform (deflection) is movement
away from the baseline either in a positive
(upward) or negative (downward) direction
• When depolarization wave moves toward
positive electrode, waveform on ECG will be
positive (upright)
• When depolarization wave moves toward
negative electrode, ECG waveform will be
negative (inverted)

Standard Limb Leads
• Leads I, II, & III
make up the
standard limb leads
• In the bipolar leads,
the R arm electrode
is always negative
& the L leg
electrode is always
positive
Lead I
• Records the
difference in
electrical potential
between the LA (+)
& RA (–) electrodes
• Views the lateral
wall of the LV
• Lead axis:
RA Ú LA
Lead II
• Records the difference
in electrical potential
between the LL (+) &
RA (–) electrodes
• Views the inferior
surface of the LV
• Lead Axis:
RA Ú LL
Lead III
• Records the
difference in
electrical potential
between the LL (+)
& LA (–) electrodes
• Views the inferior
surface of the LV
• Lead Axis:
LA Ú
LL

Lead *MCL 1
• Variation of precordial
lead V 1
• MCL 1 - Negative
electrode below L
clavicle & positive
electrode R of sternum,
4th intercostal space
• Main depolarization
wave is away from
positive electrode, so
QRS appears negative
MCL 1
Lead
Summary
with EKG
Rhythm
Strips
ECG Paper
Vertical Axis = Voltage/Amplitude (mm)
– Small squares = 1 mm high, 1 mm wide
– Large squares = 5 mm high, 5 mm wide
ECG Paper
Horizontal Axis = Time
– Small box = 0.04 second (40 millisec, ms)
– Large box = 0.20 second (200 millisec, ms)

ECG Paper
• Time markers = 1 second, 3 second,
&/or 6 second (“hash marks”)
• Appear on top or bottom of ECG paper
Questions ?
0 1 2 3 4 5 6
0 3 6

ECG
Waveforms
& Intervals
(P, PRI, QRS,
ST, T, QT)
Baseline
P Wave
• Represents atrial
depolarization and spread
of impulse across R & L
atria
• Usually upright &
rounded in leads I, II,
aVF, & V 2 to V 6
• But may be positive,
negative, or biphasic in
leads III, aVL, & V 1
2
1
Abnormal P waves
• May be notched, pointed (peaked), inverted
(negative), or biphasic
• Seen in COPD, CHF, or heart valve disease
PR Segment
• Horizontal line between end of the P wave &
the beginning of QRS complex
• Normally isoelectric (flat)
• Helpful to determine true baseline to evaluate
ST segment elevation or depression
3
4

PR Interval (PRI)
• Begins with the start of the P wave & ends at beginning
of QRS complex
• Normal range = 0.12 - 0.20 second (120 - 200 ms)
• Reflects impulse travel time from SA node thru AV node,
HB, R & L bundles, & into Purkinje fibers
QRS Complex
• QRS complex normally
follows each P wave
• Represents ventricular
depolarization and HR
• Normal QRS duration is
0.06 - 0.12 second
(< 0.12)
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6
Q Wave
• First negative Ü deflection following the P wave
• Usually a negative waveform
• Physiological Q waves
– Normal Q wave is < 25% of the amplitude of the
R wave
– Normal Q wave duration not > 0.04 second
• Pathological Q waves
– More than 0.04 sec (sm. box) in duration
– More than 25% of the amplitude of the following
R wave
R Wave
• First positive Û
deflection following the
P wave (or Q wave if
present)
• Usually positive
• R wave may be tall or
short
7
8

S Wave
• Negative waveform that
follows R wave
• Usually negative Ü
• R & S waves represent
depolarization of Left &
Right ventricles
• Ventricular Enlargement-
➢RV = big R wave
➢LV = big S wave
ST Segment
• Starts at end of QRS
complex & ends at
beginning of T wave
• Point where S wave &
ST segment meet is
called the “J point”
• Normally isoelectric
(flat) in the limb leads,
but usually not more
than 1 mm Ó or Ô
in any lead
9
10
J Point
• Used to
measure ST Ó
or Ô
• Find J point,
• Go right 1 small
box,
• Count down #
of sm. boxes to
baseline
(3.5mm STÓ)
ST Segment Displacement
• Use PR segment to assess degree of elevation or
depression of the ST segment from baseline
• Measure over one small box after the J point &
count number of boxes down/up to baseline
• ST elevated if segment 1 mm > above baseline
• ST depressed if segment 1mm > below baseline
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12

Abnormal ST Segment
ST Segment Variations
• ST segment depression of more than 1
mm is suggestive of myocardial ischemia,
or digoxin toxicity (“Dig “dip”), or ÔK.
• ST segment elevation of more than 1 mm
is suggestive of myocardial injury, infarct,
pericarditis, or cardiac tamponade.
• The “3 I’s of MI” (ischemia, injury, infarct)
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ST Segment Variations
T Wave
14
• Starts when T wave slope
leaves baseline & ends
when T wave returns to
baseline
• Represents ventricular
repolarization
• May be difficult to clearly
determine the start & end
of T wave
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16

Abnormal T Waves
• T waves may be flat, inverted, or biphasic
• Flat or negative (inverted) T waves suggest
myocardial ischemia or hypokalemia (Ô K)
• Tall, pointed (peaked) T waves are commonly
seen in hyperkalemia (Ó K)
T Wave
Variations
QT Interval
• Reflects time of total
ventricular activity
• Duration of QT interval
varies with gender & HR
• When corrected for HR,
written as QT c
• HRÓ, QT interval Ô
17
● HRÔ, QT interval Ó
• Normal QT Interval (HR 60-90) is 0.44 sec
(440 ms) or less.
18
QT Interval Measurement
• Measured from the beginning of QRS
complex to end of T wave
• Measure the # of boxes bet. 2 R
waves (R-R interval), divide by 2
• Measure the QT interval - if QT is
less than ½ the R-R interval, it’s
probably
normal
(HR 60-90)
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20

QT Interval Measurement
• R to R = 11 small boxes = 0.44 sec
• Divided by 2 = 0.22 sec R to R = 0.22 sec
• QT Interval = 4½ small boxes = 0.18 sec
• QT of 0.18 sec is less than R to R of 0.22 sec
(HR=136)
Normal QT Interval
0.44sec (HR=50)
Prolonged QT
Interval
0.56 sec (HR=40)
QT Interval Charts
• Shows HRs & QT max (ms) for male & female
• QT should not vary above normal max for HR
• QT over max, vulnerable for vent. dys. (VT, VF)
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22
Waveform
Review
Segments &
Intervals
Review
12
23
24

Questions ?
25

Heart Rate
Calculation,
Dysrhythmia Analysis
& Classification
Heart Rate Calculation
“6 Second Strip”
• Count # of R waves between 6 second strip markers
on EKG paper
• Multiply that number by 10 to obtain approx. HR
• Good method for regular and irregular rhythms
0 3 6
1
“6 Second Strip”
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8 9 10 11
Heart Rate Calculation
“300 Count Down” (Sequence)
• Select an R wave on a dark vertical line (big
box) as “R” point (starting point)
• Count big box dark lines L to R & number
each consecutive line as
300, 150, 100, 75, 60, 50 (43, 37, 33)
• Note where next R wave falls in relation to
numbered lines
• Estimate HR where 2 nd R wave falls
• Good for regular rhythms only
2
3
4

“300 Count Down”
Box Count Method
Large Box Method (Regular rhythms)
• Count the # of large boxes between 2 R waves &
divide into 300
Small Box Method (Regular rhythms)
• Count the # of small boxes between 2 R waves &
divide into 1500
s
Dysrhythmia Analysis – “3 Rs”
• Rate
• Rhythm
5
Dysrhythmia Analysis – “3 Rs”
• Determine Rate (Count R waves)
– Normal range (60 - 100)
– Slow (Bradycardia, < 60 bpm)
– Fast (Tachycardia, >100 bpm)
– None
6
• Relation(ships) & Durations
7
8

Dysrhythmia Analysis – “3 Rs”
• Determine Rhythm (Measure distance
between R-R intervals along strip)
Dysrhythmia Analysis – “3 Rs”
•Determine Rhythm (Measure distance bet. R to Rs
–Regular (R to R distances even)
–Irregular (R to R distances not even)
–Absent
Dysrhythmia Analysis – “3 Rs”
• Determine Relations(hips) & Durations
– # of Ps to # of QRSs (1 P for each QRS)
– Present
– Related
– Absent
“Quickie” Analysis:
– QRSs: present? −P waves: normal?
– Ps to QRSs: present, related?
Always evaluate the patient’s clinical status to
determine toleration of rate & rhythm.
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10
Dysrhythmia Classification
• Site Classification:
– Sinus – Junctional
– Atrial – Ventricular
• Mechanism Classification:
– Bradycardia (<60 bpm)
– Tachycardia (>100 bpm)
– Prematurity (early beat, check site of origin)
– Escape (late beat, check site of origin)
– Flutter
– Fibrillation
– Conduction Defects
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12

Questions ?
13