Cardiac Rhythms

Transcription

Cardiac Rhythms

Kingston General Hospital
May 2008
In
INDEX
Introduction
Page 2
Cardiac Conduction System
Page 3
Introduction to Cardiac Monitoring
Page 5
Recording Electrical Events
Page 9
Waves of the ECG Complex
Page 10
Intervals and Segments
Page 16
Rhythm Regularity
Page 22
Measurement of Heart Rate
Page 23
Systematic Analysis of Rhythm Strips
Page 25
Describing Rhythms
Page 26
Normal Sinus Rhythm
Page 27
Arrhythmias- Patient Assessment
Page 28
Arrhythmias originating in the sinus node
Page 29
Junctional Rhythms
Page 33
Ventricular Rhythms
Page 37
Atrial Arrhythmias
Page 42
Atrio-ventricular blocks
Page 45
Practice Strip Answers
Page 52
References
Page 56
INTRODUCTION
The electrocardiogram (ECG or EKG) is a recording of the electrical activity of the heart.
The heart has it’s own electrical or conduction system.
Normally the electrical signals are initiated and travel through the heart’s conduction
system in a specific order. This is accomplished by a process known as depolarization
. The pathway receiving the electrical stimulus is negatively charged (polarized). It must
be made positive so that the impulse can be conducted. This process is called
depolarization. These cells later recharge or repolarize in preparation for receiving the
next electrical impulse. As depolarization and repolarization occur, certain electrical
signals are seen on the ECG.
This learning guide will help you identify those signals on the ECG.
The patient will be hooked up to an ECG monitor that is at the bedside (hardwire), or a
battery operated system (telemetry). Telemetry(softwire) is a portable box that is worn
by the patient , and the rhythm is displayed centrally at the nursing desk.
CARDIAC CONDUCTION SYSTEM
The heart has both electrical and mechanical properties.
The electrical event occurs first followed by the mechanical event.
Normal electrical conduction:
•the cardiac impulse begins in the sinoatrial (SA) node and travels to the right and left
atria
•the atria depolarize and generate the p wave on the electrocardiogram
•the conduction then travels to the atrioventricular (AV) node where the conduction
speed is reduced
•conduction then speeds up and travels down the Bundles of His, and the right and left
bundle branches to the Purkinje fibers
•the Purkinje fibers distribute the impulse rapidly and uniformly and ultimately depolarize
the ventricular myocardium- this generates the QRS wave on the electrocardiogram
Mechanical Events:
•after the P wave is generated the atria contract. This contraction contributes 20% of
the blood flow to the ventricle. This is called atrial kick
•after the QRS wave is generated the ventricles contract
•the reduction in depolarization speed at the AV node allows time after the atrial
mechanical contraction for the ventricles to fill before they contract.
CARDIAC CONDUCTION SYSTEM
Escape
rhythms
Automatic Cardiac Tissues
There are different conduction tissues in the heart that can act as pacemakers and
initiate the electrical sequence. These are: SA node, atrial tissues, AV node, and the
ventricles.
These tissues each have their own intrinsic or pre-set rate. Normally the SA node
initiates the electrical sequence because it has the highest intrinsic rate. If the SA node
cannot sustain this rate for some reason, the pacemaker with the next highest rate
would then take over as the pacemaker of the heart. This is called an escape rhythm
and is the heart’s emergency pacing system.
It is very uncommon to see an atrial escape rhythm , even though they are the next
pacemaker in line. The AV node (junction) is the pacemaker that most often escapes
when the SA node fails.
INTRODUCTION TO CARDIAC MONITORING
The ECG monitor:
The patient must be attached to a heart monitor in order to see the electrical signals
from the heart. This is done by applying electrodes (sticky sensors) to the patient’s
skin. Wires attached to a cable are snapped on to the electrodes. The cable is
attached to the monitor. A signal will now appear on the monitor.
Monitoring Guidelines:
1) Electrodes:
•prepare skin- shave if required, cleanse with alcohol and abrade skin with
backing on electrode
•electrodes will dry out over time:
•change if monitor signal is poor or patient is complaining of itchiness underneath
electrode
•use new unopened package of electrodes each time
2) Documentation:
•6 second monitor strips are placed on the chart on each shift and when
arrhythmias are detected
•evaluation of the rhythm strip by the nurse is documented with the strip
*pt’s name and CR number on strip
*do not tape over important information- it will fade and disappear over time
The electrodes detect the heart’s electrical activity.
There may be 3 or 5 electrodes attached to your patient.
Placement of electrodes:
•RA-right arm-below right clavicle
white
•LA-below left clavicle
black
•LL-left leg-left lower rib cage or abdomen
red
•RL-right lower rib cage or abdomen
green
•C- 5 th ICS anterior axillary line
brown
3 lead
5 lead
3 lead system: RA LA and LL electrodes
•these electrodes form a triangle around the heart
•you can choose to monitor leads I, II, or III with a 3 lead system-these are called limb
leads
5 lead system: RA
LA
LL
RL
C
electrodes
•the C electrode can be positioned in any one of 6 designated positions on the left
anterior chest- these are called the V1-V6 positions and are called chest leads
•the RL electrode is a ground electrode and is not used as a recording electrode
•with a 5 lead system you can choose to monitor leads I,II,III,aVR,, aVL , aVF , V1-V6
The electrical activity is picked up between 2 electrodes. A different pair is used to
record each lead. One electrode is considered negative and one positive. It is the
positive one that is recording the electrical activity.
•Lead 1- uses the RA (neg) and LA (positive) for electrical recording
•Lead 2 -uses the RA(neg) and LL(positive) for recording
•Lead 3-uses the LA(now neg) and LL (positive) for recording
•These limb leads record the electrical conduction of the heart from three different
viewpoints. They are called bipolar leads because they use a pair of electrodes to
record the activity
Remember it is the positive electrode that records the heart’s electrical activitythink of the positive electrode like a camera, watching the electrical activity of the
heart.
• The electrical activity of the heart remains the same but each lead views this
activity from a different angle.
•Recording the electrical
waves:
•an upward deflection will be
recorded on the monitoring
paper if the conduction goes
towards the positive electrode
•a downward deflection will be
recorded on the monitoring
paper if the conduction goes
away from the positive electrode
•Lead 2- the positive electrode is the LL which is positioned just below the heart
•normal conduction in the heart is down and to the left, therefore Lead 2 will pick up the
conduction (or depolarization) coming towards it -the waves will be recorded as upright
on the monitoring paper
•Lead 2 is the limb lead usually used in monitoring
RECORDING ELECTRICAL EVENTS
1 mm
.04 sec
The recording paper is graph paper which records at a specific speed.
The horizontal lines measure the amplitude of events in millimeters or millivolts
One horizontal line measures 1 mm
The vertical lines measure the duration in seconds of any events.
Between 2 vertical lines the measure is .04 of a second. This is called a small box.
You’ll notice that every 5th vertical line is bolded. This is called a large
box and measures .04x5= .20 of a second.
The next section discusses what events will be seen on the recording paper.
WAVES OF THE ECG COMPLEX
The P wave represents the depolarization of the atria. Atrial depolarization begins in
the SA node and spreads through both atria.
The p wave is small, rounded and usually upright.
Atrial repolarization is usually not seen on the ECG because it is hidden in the
subsequent QRS waveform and is of low voltage.
The largest wave in the ECG is the QRS complex.
The electrical impulses spreading through the ventricles produce the QRS complex.
Therefore the QRS represents ventricular depolarization.
Normal QRS duration (interventricular conduction time )is .05-.10 seconds
Abnormal QRS duration is > .12 seconds.
•Indicates that conduction has been delayed in the ventricles
Q wave
•the first downward wave of the QRS complex
•precedes the R wave
•often absent on the ECG
R wave
•the first upward wave of the QRS complex
•an upward wave is always called an R wave
•a second upward wave is called an R prime ( R’)
S wave
•the downward wave following the R wave
An upward wave is always called an R wave
The downward wave before the R is called the Q wave
The downward wave after the R wave is called the S wave
Ventricular contraction following the QRS creates the pulse.
2 small squares= .08 seconds
A
NORMAL
B
A
2 small squares= .08 seconds NORMAL
B
3 ½ small squares= .14 seconds WIDE
Even though we call this complex the QRS complex, not all QRS complexes have all
three components.
The examples above illustrate different QRS complexes and the names of all the
components.
The T wave represents ventricular repolarization or recovery.
The T wave follows the QRS and is smooth and rounded. It is usually upright.
Inverted T waves:
If a T wave is upside down (inverted) this is usually an abnormal finding.
It can indicate myocardial ischemia.
Notched or pointed T waves:
Heavily notched or sharply pointed T waves in adults may indicate MI or pericarditis.
Tall T waves:
Tall T waves suggest an MI or hyperkalemia
If any of the above are new findings on the monitor a 12 lead ECG should be
done
PRACTICE YOUR Ps and Qs!
QRS
QRS
QRS
T P
QRS
T
P
QRS
T
P
T P
QRS
T
T
T P
QRS
P
QRS
T
P
QRS
QRS
T
T
P
P
P
P
INTERVALS AND SEGMENTS
This is the segment between the P wave and the QRS.
•This represents the time interval between when the atria depolarize and when the
ventricles depolarize. The electrical impulse is spreading to the AV node, Bundle of His
and Purkinje fibers.
•This is considered a baseline from which we measure changes in the ST segment.
INTERVALS AND SEGMENTS The PR interval is measured from the beginning of the P to the beginning of the QRS.
If there is no Q wave then it is measured from the beginning of the P wave to the
beginning of the R wave.
• It represents atrial and atrioventricular conduction time. This includes atrial
depolarization, the normal conduction delay in the AV node, and the passage of the
electrical impulse through the bundle of His and the bundle branches.
•If conduction is occurring normally then this will take between 0.12 and .20 of a
second or 3 to 5 small boxes
•Short P-R interval:
•AV conduction time is shortened: could be due to:
•initial impulse in the junction (AVnode) or
•another (faster)conduction pathway betweeen atria and ventricles
•Long P-R interval:
•AV conduction time is longer than normal: could be due to:
•a conduction delay in the AV junction
•a conduction delay through the atria
INTERVALS AND SEGMENTS The ST segment is the segment after the QRS and before the T wave.
This segment represents ventricular repolarization.
Normal ST segment:
•horizontal and flat
•level with the PR segment or baseline
•J point:
•the junction between the ST segment and the QRS is called the J point
If the ST segment is more than 1 mm (1 small square) above the baseline it is
considered elevated
If the ST segment is more than 1 mm below the baseline for .08 seconds
(2 small squares) after the J point, it is considered depressed
•ST depression:
•The ST segment falls below the baseline for .08sec (2 small squares) past the J
point
•indicates myocardial ischemia
•ST elevation:
•The ST segment is above the baseline
•acute ST elevation indicates myocardial injury
•prolonged ST elevation may indicate something other than myocardial injury:
pericarditis, ventricular aneurysm or cardiac contusion
If any of the above are new findings on the monitor a 12 lead ECG should
be done
The QT interval is measured from the beginning of the QRS until the end of the T wave.
•The QT interval represents ventricular depolarization and repolarization.
• Normal QT interval:
• usually between 0.36 and 0.44 second
• varies greatly according to age, gender ,heart rate, and whether the patient is
asleep
• should be less than 1/2 the distance between two consecutive R waves (R-R
interval) when the rhythm is regular
Prolonged QT interval:
Repolarization means that the muscle cell resets itself so it can depolarize again.
Measured on an ECG, the time between the Q wave and the T wave is prolonged in this
condition. This leads to a longer vulnerable period. If the next QRS begins before the
end of repolarization, an arrhythmia or irregular heart beat could occur, such as
ventricular fibrillation, or Torsades de Pointes which could be fatal. This condition is
diagnosed on a 12 lead ECG.
A 12 lead ECG should be done if the QT appears prolonged
•Cause:congenital, medications (Amiodarone, Haldol, Procainamide,Sotalol,
some antibiotics ), hypokalemia and hypomagnesemia, intracranial or
subarachnoid hemorrhage
PR=.16 sec NORMAL
ST-depressed 1mm for .08 sec
past the J point-ABNORMAL
QT- less than ½ the R-R
NORMAL
PR
J point
ST
QT
PR= .32 sec
PROLONGED
ST- slightly depressed, but not
1mm- baseline-NORMAL
QT- less than ½ the R-R
NORMAL
PR
ST
QT
PR= .20 seconds NORMAL
ST- baseline-NORMAL
QT- more than ½ the R-R
PROLONGED
PR
ST
QT
RHYTHM REGULARITY
Rhythm Regularity:
• Refers to the regularity of the QRS complexes
• Measure the distance between the QRS complexes-this is referred to as
the R-R interval
There are three ways to describe regularity:
Regular rhythms
• R-R intervals are all the same or vary slightly.
• In regular rhythms the QRSs usually look alike
Regular but interrupted
• Most of the R-R intervals are constant
• Interrupted by premature beats or a pause
Irregular
• R-R intervals vary
• Not due to premature beats or pauses, but because the actual rhythm is
irregular
MEASUREMENT OF HEART RATE 6 seconds
3 seconds
1
2
3
4
5
6 SECOND METHOD
To determine HR:
• There are small line markers on the top of the graph paper
• These occur every 3 seconds
Count # of QRS complexes in a 6 second strip.
Multiply by 10.
Above example:
QRS’s in 6 seconds = 6
6 X 10 = 60 beats/min
6
MEASUREMENT OF HEART RATE
How to calculate the heart rate on ECG paper
300
150
100
75
60
50
43
37
1 big box
33
30
BIG BOX METHOD
Alternate method to determine HR (for regular rhythms only)
•
•
•
There are 300 big boxes in one minute
If there was one big box between each QRS the HR would be 300 / minute
If there were 2 big boxes between each QRS the HR would be 300/2=
150/min
•
•
•
Try to find a QRS on a bolded line
Count the number of big boxes to the next QRS
Divide into 300
SYSTEMATIC ANALYSIS OF RHYTHM STRIPS
The key to identifying rhythms correctly is to systematically analyze the cardiac rhythm
strip.
1. Determine the atrial and ventricular rate (HR)
If these rates are different then you know to look more closely a the relationship between the p
and the QRS
2. Measure R-R.
a. Is the rhythm regular, regular but interrupted, or irregular?
3. P waves
a. Are they present and do they all look the same?
b. Is there a QRS after each one?
4. PR interval
a. Normal is .12-.20 seconds (3-5 small boxes)
b. Is each PR interval the same?
5. QRS duration
a. Normal is <.12 seconds or 3 small boxes
b. Are they all the same and point in the same direction?
6. Examine the ST segment
a. Is it at baseline (even with the PR segment)
b. Is there ST elevation or ST depression?
7. Examine the T waves
a. Normal is upright and rounded
b. Are they inverted or flattened
8. Measure the QT interval
a. Normal is < ½ the R-R interval
b. Is it changed from previously
9. Are there premature beats.
a. Is there a p in front of the QRS?
b. Is the QRS normal or widened?
10. Analyze the rhythm.
Rhythms are always described by the above format.
The first part of the description tells us where the rhythm originates.
The second part of the description tells us how fast the rhythm is.
Examples:
Sinus bradycardia:
• The rhythm originates in the sinus node and the rate is < 60 beats per minute
Ventricular tachycardia:
• The rhythm originates in the ventricles and the rate is > 100 beats per minute
NORMAL SINUS RHYTHM
Normal Sinus Rhythm
Rhythm
Rate
P wave
PRI
QRS
(seconds)
(seconds)
0.12-0.20
0.06-0.10
(per minute)
Regular
60 -100
Upright
Sinoatrial node
Uniform
The only rhythm that is considered normal is normal sinus rhythm.
Mechanical events are optimal in normal sinus rhythm.
An arrhythmia is any cardiac rhythm that is not normal sinus rhythm.
Arrhythmias fall into the following categories:
• Arrhythmias originating in the sinus node
• Junctional rhythms
• Ventricular rhythms
• Atrial arrhythmias
• AV conduction disturbances
ARRYTHMIAS- PATIENT ASSESSMENT
Arrhythmias can occur for a number of reasons.
If the patient is symptomatic, then there must be immediate intervention
Guide your nursing assessment with the following questions:
1. Is the patient oxygenating well?
a. Check the O2 saturation
2. Is there evidence of ischemia ?
b. Is the patient having chest pain?
c. Check for high blood pressure.
d. Assess for heart failure.
3. Are the electrolytes abnormal?
a. Check the potassium, magnesium and calcium levels
4. What medications is the patient on?
a. Check for medications that can cause bradycardia
b. Check for medications that can cause prolonged QT intervals and may
precipitate tachycardia
Arrhythmias Originating in the
Sinus Node






Sinus Tachycardia
Sinus Bradycardia
Sinus Arrhythmia
Sinoatrial (SA) Block
Sinus Arrest
Sick Sinus Syndrome
Sinus Tachycardia
Rhythm
Rate
P Wave
(per minute)
Regular
100 -160
Upright
Uniform
Sinoatrial node
PRI
QRS
(seconds)
(seconds)
0.12-0.20
0.06-0.10
Causes
Exercise, anxiety, fever, pain, hyperthyroidism, medications
Nursing Implications
Treat the cause
Sinus Bradycardia
Rhythm
Rate
P Wave
(per minute)
Regular
40-60
Upright
Uniform
Sinoatrial
node
PRI
QRS
(seconds)
(seconds)
0.12-0.20
0.06-0.10
Causes
Sleep, athletic heart, increased vagal tone, beta-adrenergic blockade
Treat if there is hemodynamic compromise
Sinus Arrhythmia
Rhythm
Rate
P Wave
(per minute)
Irregular
 irregular
Usually
60 -100
Upright
Uniform
Sinoatrial node
PR Interval
QRS
(seconds)
(seconds)
0.12-0.20
0.06-0.10
rhythm associated with respiratory cycles;
 HR á with inspiration &
 HR âwith expiration
Sinoatrial (SA) Block
Rhythm
Rate
P Wave
(per minute)
Regular but Usually
interrupted 60-100
Upright, uniform
but entire cycle
missing
PRI
QRS
(seconds)
(seconds)
0.12 – 0.20
<0.12
Causes
Coronary artery disease, medications, carotid sinus sensitivity and increased
vagal tone
Treat if the pauses are long and there is hemodynamic compromise
Sinus Arrest
Escape rhythm
Rhythm Rate P Wave
PRI
QRS
(per minute)
(seconds)
(seconds)
Regular but Any rate No sinus
interrupted
P’s
N/A
<0.12 (junctional)
>0.12 (ventricular)
Causes
Coronary artery disease, medications, carotid sinus sensitivity and increased
vagal tone
Treat if the pauses are long and there is hemodynamic compromise
Sick Sinus Syndrome
A cluster of symptoms arising from a pathology in the sinus
node. Results in dramatic changes in heart rate -bradycardia "
tachycardia, interspersed with sinus arrests, pauses and blocks.
Escape beats common after long sinus pauses.
Rhythm
Rate
P Wave
(per minute)
Irregular
PRI
QRS
(seconds)
(seconds)
Varies wildly May or may not If present,
be present,
varies
Too fast –
shape
varies
too slow
Varies
See answers beginning on page 52
Causes
Ischemic disease, medication, inflammatory disease, surgical injury, idiopathic
Treat underlying cause (digoxin, beta blockers), pacemaker
Junctional Rhythms
Junctional Rhythm
 Premature Junctional Contraction
 Accelerated Junctional Rhythm
 Junctional Tachycardia
 Junctional Escape Rhythm

Junctional Rhythm
AV node
2nd
1st
Simultaneous
Atrium depolarized
1st, then ventricles.
Upside down P wave
BEFORE QRS
Atria & ventricles
depolarized
simultaneously.
Ventricles
depolarized 1st, then
atria.
NO visible P wave,
obscured by QRS
Upside down P wave
AFTER QRS
Premature Junctional
Contractions (PJC)
Rhythm
Rate
P Wave
(per minute)
Regular but Occurs
interrupted at any
rate
Inverted before
or after QRS or
not visible
PRI
QRS
(seconds)
(seconds)
<0.12 if P
precedes QRS
<0.12
Causes
MI, Digoxin toxicity, hypoxia, stimulants
Remove the cause eg. Digoxin toxicity
AV node
Junctional Rhythm
Rhythm
Rate
P Wave
(per minute)
Regular
40-60
If visible, inverted
(before or after
QRS)
PRI
QRS
(seconds)
(seconds)
If able to
measure
<0.12
<0.12
Causes
MI, Digoxin toxicity, Hypoxia, vagal stimulation
If symptomatic- atropine. Treat the cause eg. Digoxin toxicity
AV node
Accelerated Junctional
Rhythm
Rate
P Wave
(per minute)
Regular
60 -100
If visible,
inverted (before
or after QRS)
PRI
QRS
(seconds)
(seconds)
If able to
measure
<0.12
<0.12
Causes
MI, stimulant drugs, caffeine, dig toxicity
Remove the cause
Junctional Tachycardia
Rhythm
Rate P Wave
(per minute)
Regular
>100
PRI
QRS
(seconds)
(seconds)
If visible, inverted If able to
(before or after
measure
QRS)
<0.12
Causes
Digoxin toxicity, heart disease, stimulants
Identify and treat the cause eg. Digoxin toxicity
<0.12
Junctional Escape Rhythm
Rhythm
Rate P Wave
(per minute)
Regular
Irregular
40-60
If present
inverted before
or after QRS
PRI
QRS
(seconds)
(seconds)
<0.12
<0.12
Causes
MI, Digoxin toxicity
Identify and treat the cause eg. Digoxin toxicity
Ventricular Arrhythmias
 Premature
Ventricular Contraction
(PVC)
 Accelerated (Idio)ventricular rhythm
 Ventricular Tachycardia
 Ventricular Fibrillation
 Ventricular Escape Rhythm
 Bundle Branch Blocks
Premature Ventricular
Contraction
Rhythm
Rate P Wave
(per minute)
Regular but Occurs
interrupted at any
by PVC’s
rate
PRI
(seconds)
Not seen on N/A
PVC’s
QRS
T wave
(seconds)
>0.12
In opposite
direction of
QRS
Causes
Heart disease, hypokalemia, hypoxia, hypomagnesemia, stimulants,
caffeine, stress, anxiety,digoxin, significant anemia
Assess frequency of PVC’s and potential cause(s).
Bigeminy
Multifocal PVC’s
Accelerated Ventricular
Rhythm
Rhythm
Rate
P Wave
(per minute)
Usually
regular
40-100
Usually not
seen
PR Interval
QRS
(seconds)
(seconds)
Not measureable
>0.12
Causes
Common after MI, administration of fibrinolytics
Usually well tolerated. This is the patient’s escape rhythm, so
antiarrhythmics are not used
Ventricular Fibrillation (VF)
Rhythm
Rate
P Wave
PR Interval
(per minute)
Not
detectable
Can’t be
counted
(seconds)
None
Not detectable
Causes
Significant underlying cardiac disease, AMI,
hypokalemia, hypoxia, hypomagnesemia, drugs
Code Blue- defibrillation
QRS
(seconds)
Not
detectable
Ventricular Escape Rhythm
Rhythm
Rate
P Wave
(per minute)
Usually
regular
20-40
Usually not
seen
Causes
Massive MI, hypoxia
Usually pulseless- CODE BLUE, CPR
PR Interval
QRS
(seconds)
(seconds)
Not measureable
>0.12
Atrial Arrhythmias
 Premature
Atrial Contractions (PAC)
 Atrial Tachycardia
 Atrial Flutter
 Atrial Fibrillation
Premature Atrial Contractions
Rhythm
Rate
P Wave
(per minute)
Interrupted
by PAC
Varies
P of PAC
different from
underlying
rhythm P’s
PRI
QRS
(seconds)
(seconds)
Differs from
underlying
rhythm
Causes
Electrolyte imbalance, stress, hypoxia, digoxin toxicity
Check electrolytes, O2 saturation. Remove the cause.
<0.12
Atrial Fibrillation
Rhythm
Rate
P Wave
(per minute)
Irregular
A: 350-650 Fibrillatory
V: slow to (fine to
coarse)
rapid
PRI
QRS
(seconds)
(seconds)
N/A
<0.12
Causes- Valvular HD,MI , thyrotoxicosis, lung disease
Assess BP as patient has lost atrial kick.
Lack of co-ordinated contraction in the atria predisposes patients to embolic
events- anticoagulation required
Acute-cardiovert or control rate with beta blockers, calcium channel blockers
>48 hours- anticoagulation required x 3 weeks prior to cardioversion
Heart Blocks
1. What is heart block?
Heart block is an arrhythmia usually caused by ischemia or an MI. It can also be
caused by drugs such as beta blockers, calcium channel blockers, digoxin or any drug
trying to slow down a fast rhythm and overshoots the mark!
2. What is being blocked in a heart block?
The signal from the SA node is trying to get through to the AV node (creating a p wave)
and then to the ventricle (creating a QRS). In heart block the signal from the SA node
through the AV node is either slowed down (causing a longer P-R interval) or blocked
altogether , so there is a p wave but no QRS.is triggered by the p wave.
The key to heart blocks:
The signal is getting through:
1 all of the time (but taking longer than normal-.20 sec)
2 some of the time
3
none of the time
These are called first degree (#1), second degree (#2)and third degree (#3) heart
blocks.
PR interval
3. What are the three types or degree of heart block?
Look at a normal sinus rhythm:
You can see the p waves and you can see where the QRS begins- the measurement
from the beginning of the P to the beginning of the QRS is the PR interval. A normal PR interval should be no longer than .20 seconds or one big box on the EKG paper.
The PR interval represents the electrical depolarization from the SA node through the
atria and the AV node. If the PR interval is normal then the signal is taking the normal
amount of time to travel this far.
The signal should then travel to the ventricles to create a QRS.
3.1 First degree heart block:
Measure the PR interval. You will notice that it is longer than .20 seconds or one big
block. It is taking longer than normal time to get from the SA node through the AV
node to the ventricles. It does get to the ventricles all the time.
This is SR with a first degree heart block.
3.2 Second degree heart blocks:
By definition a second degree heart block has signals getting through some of the time.
So you will see p’s with QRS’s after them and you will see p’s without QRS’s after them.
The SA node will fire at a constant rate- some of the time the signal gets through the AV
node to the ventricle and sometimes it doesn’t..
There are 2 kinds of second degree heart block:
The first kind can be called one of two names: Type 1 second degree or Wenckebach.
3.2.1 Second degree type 1-Wenckebach
You can see the p waves without a QRS . The signal is getting through the AV node
some of the time.
Look at the PR intervals before the dropped beat- the PR starts out normal, then gets
longer with the next beat, longer with the subsequent beat and then doesn’t get
through.
So the PRs leading up to the dropped beat get longer and longer then drop.
The heart rate in this patient is still 70 bpm, so the patient probably has a good blood
pressure. Usually this rhythm is benign and is transient due to a MI. However it still
bears watching.
3.2.2 Second degree type 2
d degree type 1- PRs- longer,longer, longer and drop
d degree type 2-PRs- all the same and then drop a QRS without warning
Predictable
Unpredictable
You can see the p’s without the QRS. The other Ps are followed by a QRS and all the
PRs are the same. The signal is getting through to the AV node some of the time. –
therefore it is a second degree heart block.
The PRs of the other beats are all the same.
This heart block is much more serious and can progress to third degree heart block
(complete heart block). This patient requires a pacemaker.
3.3 Third degree heart block (complete)
Third Degree Heart Block
In third degree heart block the SA node is firing a signal at a regular rate. The top
arrows show where the p’s are.
However the signal is not getting through the AV node to create a QRS.
When this happens either the AV node or the ventricle will generate a rate by
themselves. If the AV node generates it the QRS will be narrow. If the ventricle
generates it the QRS will be wide. The QRS is marked by the arrows at the bottom.
If you measure the PR intervals, none of them are the same. There are p’s in the
middle of QRS’s. This tells you that there is no connection between the p and the QRS.
The SA node and the ventricle are depolarizing independently of each other. None of
the p waves are conducted through the AV node to the ventricle.
This heart block is serious as the ventricular rate can go as low as 20 or stop altogether.
This patient requires a pacemaker.
AV Blocks
1 p for every QRS
More p’s than QRS
Constant Prolonged P-R Interval
P-R constant?
10
AV block
NO
YES
type 2 AV block
Includes 2:1 AV conduction
20
Regular R-R?
YES
0 AV block (complete)
3
Diagram: AV blocks
of the diagram are the most serious and
20 on
AV the
blockright
type 1side
(Wenckebach)
require a permanent pacemaker. AV blocks on the left side
are less serious,
QRS normal width?
NO
transient, or the causes can be reversed.
NO
Ventricular escape
YES
Junctional escape
Atrioventricular (AV)
Conduction Disturbances
 First
Degree AV Block
 Second Degree AV Block
 Type
I (Wenckebach)
 Type II
 Third
Degree (Complete) AV Block
First Degree AV Block
Rhythm
Rate
P Wave
(per minute)
Depends on
underlying
rhythm
Can
occur at
any rate
upright
Uniform
Precede QRS
PR Interval
QRS
(seconds)
(seconds)
Prolonged
> 0.20
< 0.12
Causes
AV node ischemia,dig toxicity,drugs (beta blockers, calcium channel
blockers), ablation
Remove the cause. Treat the cause
2nd Degree Heart Block
Type I - Wenckebach
Rhythm
Rate
P Wave
(per minute)
Usually
irregular
Atrial usually
60-100
Ventricular
< atrial
Sinus P’s
PRI
QRS
(seconds)
(seconds)
Gradually #’s
until QRS
dropped
<0.12 if block at
AV
>0.12 if block at
bundle branches
Causes- Drugs , MI, chronic degenerative conduction disease.
Usually due to MI, is transient and only requires observation
If symptomatic- atropine, pacemaker
2nd Degree Heart Block
Type II
Rhythm
Rate
P Wave
(per minute)
Regular
Or
Irregular
Atrial usually
60-100
Ventricular
< atrial
PRI
QRS
(seconds)
(seconds)
Sinus P’s
Constant for
2 or > before conducted
beats
each QRS
<0.12 if block
at AV
>0.12 if block
at bundle
branches
Causes- Drugs , MI, chronic degenerative conduction disease, hypoxia
Definitive treatment is a pacemaker as this can progress to complete AV
block or asystole.. Atropine can be tried for symptoms, but may
paradoxically slow the heart rate.
Third Degree AV Block
Rhythm
Rate
P Wave
(per minute)
Regular
Atrial 60 -100
Ventricular
Sinus P’s
with no
Block at AV 40-60 relation to
QRS
Block at bundle
branches 20-40
PRI
QRS
(seconds)
(seconds)
varies
Block at AV
<0.12
Block at bundle
branches
>0.12
Causes- Drugs , MI, chronic degenerative conduction disease, hypoxia
Definitive treatment is a pacemaker . Atropine can be tried for
symptoms, but may paradoxically slow the heart rate.
Rate: Atrial __40____ Ventricular __40______ Regular?___Yes _______________
P waves _Yes-all the same_____Followed by QRS?__Yes__ PRI __0.16 QRS___0.08___
ST segment __baseline__________________ T wave ___upright____________
QT Interval ____less than ½ the R-R interval
PRACTICE STRIP ANSWERS
Interpretation_______sinus bradycardia_____________________________________
Practice Strips page 32
Rate: Atrial __70____ Ventricular __70_______ Regular?___No- slows down and speeds up
P waves ____Yes-all the same Followed by QRS?__Yes_____ PRI __0.14 QRS_0.08_____
ST segment ___depressed_______________ T wave upright______________
QT Interval ______1/2 the R-R interval
Interpretation_______Sinus arrhythmia______________________________________
__none__
Ventricular
__170______
Regular?__yes_________________
Rate:Rate:
AtrialAtrial
__none__
Ventricular
___60______
Regular?___yes________________
P waves
____no____________Followed
by QRS?__no_PRI
PRI
__noneQRS___0.06__
QRS__0.20_(wide)_
P waves
___none___________Followed
by QRS?_no____
_none_
ST segment
____can’tdepressed____
measure___________
T wave __can’ see____________
ST segment
______lightly
T wave __upright_____________
QT Interval
_____can’t
QT Interval
_____less
than ½measure____
the R-R interval
Practice Strips Page 36
Interpretation_________ventricular
tachycardia___________________________
Iterpretation_________junctional
rhythm___________________________________
Rate: Atrial __300___ Ventricular __80_______ Regular?____No________________
P waves __f waves_________Followed by QRS?__sometimes PRI _not measured_____ QRS__0.10________
ST segment ____hard to tell________________________ T wave __can’t see____________________
QT Interval _______can’t measure_________________
Interpretation__________atrial flutter with variable conduction from A to V
3 second
arrows show f waves
hidden in the QRS
Rate: Atrial ___no p_____ Ventricular __90_________ Regular?__irregular____________________
P waves _no________________Followed by QRS?_no______ PRI __none____ QRS__0.08________
ST segment _____hard to tell- could be depressed_____________ T wave _upright_____________________
QT Interval ________0.28 normal________________
Interpretation________atrial fibrillation with controlled ventricular response (less than 100/ minute)
QT interval
Rate: Atrial ____80____ Ventricular __60_________ Regular?____No__________________
P waves _yes-all the same______Followed by QRS?_not all______ PRI _0.16-0.32 prolonging_____ QRS__0.06____
ST segment ____baseline________________ T wave _____upright__________
QT Interval _____0.36 normal_______
Interpretation_______second degree type 1 AV block___(Wenckeback)_____________________
REFERENCES
Arrows indicate p waves hidden in the complex
Rate: Atrial ___80_____ Ventricular __30_________ Regular?____yes__________________
P waves ___upright_______________Followed by QRS?_no______ PRI __all different____ QRS__0.16_(wide)_______
ST segment ______depressed______________________ T wave __inverted____________________
QT Interval ______0.28 normal_________________
rd
Interpretation__________3 degree AV block ___________________________________________________
References
1. Daly, S., Weinstein E., Ambrose, M., Charnow, J., (eds) et al. (1993)
Deciphering Difficult ECG’s. Pennsylvania: Springhouse Corporation.
2. Dubin, D. (2000) Rapid Interpretation of EKG’s. 6th edition. Florida: COVER
Publishing Company.
3. Ellis, Karen (2002) EKG Plain and Simple. New Jersey: Prentice Hall.
4. Hudak, C., Gallo B., Gonce Morton, P.,(1998) Critical Care Nursing: A Holistic
Approach. 7th edition. New York: Lippincott.
4. Stein, E. (1997) Clinical Electrocardiography: A Self Study Course.
Philadelphia: Lea & Febiger.
5.
6.
Vinsant, M., Spence, M. (1989) Commonsense Approach to Coronary Care: A
Program: 5th edition. Toronto: The C.V Mosby Company.
Woods, S., Sivarajan Froeclicher,E., Underhill Motzer, S. (2000) Cardiac
Nursing. 4th edition. New York: Lippincott.
7. Online- the Medstud.com
RHYTHM INTERPRETATION
TEST
Please check with your CE to see which test is appropriate for you to complete
Please evaluate the following strips in a systematic way. Describe the
dysrhythmia by the predominant underlying rhythm and then any other
rhythm or extra beats that are on the strip.
e.g.- SR with PVC’s
or
SR with first degree HB
Filling out the test completely should lead you to an accurate interpretation
Thank you
Marks
1. What is the ventricular rate_________?
• Is it regular?________
• Are there any premature QRS’s?______
• Ask yourself- Are the premature QRS’s wide or narrow?_______
2. P waves
• What is the rate ?
____________
• Are the each followed by a QRS? ________
3. What is the P-R interval ? __________
• Is it constant? __________
• If not constant what is happening to the P-R?
___________________________________
1
1
4. What is the QRS duration?__________
• Is this a normal QRS duration?________
Ask yourself:
Could there be a hidden p wave in the ST segment or T wave? _____
1
5. Identify the conduction pathway for this rhythm on the following diagram
1
6. State the rhythm diagnosis _____________________________
Mark
2
/10
2
2
Marks
• Ask yourself -Are the premature QRSs wide or narrow?_______
2. P waves
• What is the rate?
____________
3. What is the P-R interval? __________
___________________________________
1
1
Ask yourself:
1
1
2
2
2
Mark
2. P waves
____________
___________________________________
/10
Marks
1
1
2
2
Ask yourself:
1
1
Mark
2
/10
2. P waves
____________
___________________________________
Marks
1
1
2
2
Ask yourself:
1
1
Mark
2
/10
Marks
2. P waves
____________
___________________________________
1
1
Ask yourself:
1
1
Mark
2
/10
2
2
Marks
2. P waves
____________
___________________________________
1
1
Ask yourself:
1
1
Mark
2
/10
2
2
Marks
2. P waves
____________
___________________________________
1
1
Ask yourself:
1
1
Mark
2
/10
2
2
Marks
2. P waves
____________
___________________________________
1
1
Ask yourself:
1
1
Mark
2
/10
2
2
Marks
1
1
2. P waves
2
____________
___________________________________
2
Ask yourself:
1
1
Mark
2
/10
Marks
2. P waves
____________
___________________________________
1
1
Ask yourself:
1
1
Mark
2
/10
2
2
Marks
2. P waves
____________
___________________________________
1
1
Ask yourself:
1
1
Mark
2
/10
2
2
RHYTHM INTERPRETATION
Test # 2
Please check with your CE to see which test is
appropriate for you
Please evaluate the following strips in a systematic way. Describe the
dysrhythmia by the predominant underlying rhythm and then any other
rhythm or extra beats that are on the strip.
e.g.Normal Sinus rhythm with Premature Ventricular Contractions (NSR
with PVCs)
or
Normal Sinus Rhythm (NSR) with first degree Heart Block (HB)
For test purposes each rhythm strip will be assumed to be a 6 second
strip.
Identify the normal PR interval as 0.12-0.20 and abnormal as > 0.20
as
in the learning guide
Identify the normal QRS interval as 0.06-0.10 and abnormal as > 0.10
as in the learning guide
Filling out the test completely should lead you to an accurate interpretation.
Each test strip will be marked out of 5 for a total score out of 25.
Thank you
Strip #1
2. a) What is the ventricular rate?
a) Is it regular?
_________
_________
2. P waves
a) What is the rate?
____________
b) Is each P wave followed by a QRS?
3. a) What is the P-R interval?
b) Is it constant?
________
__________
__________
7. a) What is the QRS duration?
__________
b) Is this a normal QRS duration?
8. State the rhythm diagnosis.
________
_____________________________
Strip #2
b) Is it regular?
_________
________
3. P waves
____________
__________
__________
_____________________________
Strip #3
b) Is it regular?
_________
________
2. P waves
____________
__________
7. a) What is the QRS duration? __________
b) Is this a normal QRS duration? _________
_____________________________
Strip #4
b) Is it regular?
_________
________
2. P waves
____________
b) Are they each followed by a QRS?
__________
__________
b) Is this a normal QRS duration?
________
________
_____________________________
Strip #5
b) Is it regular?
_________
________
c) Are there any premature QRS’s?
______
01.701.8402000
2. P waves
____________
b) Is it constant?
__________
__________
__________
_____________________________

Cardiac Rhythms

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