Transcript Electrocardiagram ECG

Electrocardiogram
ECG
Part 1
Made for understanding
By Mandy Gutliph
Stephanie Feldman
Electrocardiography or ECG is a important diagnostic tool for Veterinary
Medicine.
ECG’s measure the electrical activity of the heart.
These measurements are called Lead Polarity and are represented by P,Q,R,S,
and T (as shown below)
The P wave represents Atrial Depolarization
The QRS wave represents Ventricular Depolarization
The T wave represents Ventricular Repolarization
Patient Set-up
Your patient, any mammal, should be sedated or anesthetized for this
procedure
THE ANIMAL MUST ALWAYS BE IN RIGHT LATERAL
RECUMBENCY!
Use a rubber mat between metal tables and patient to prevent any
electrical interference!
Cables
The Basics
Black cable- Attaches to Left Front Leg!
White cable- Attaches to Right Front Leg!
Red cable- Attaches to Left Rear Leg!
Green cable- Attaches to Right Rear Leg!
*Remember Snow (white) and Grass (green) are
always on the ground (right side)
* Remember you always read the newspaper (black and
white) at the beginning of the day (front legs)
Negative and Positive Poles
You can change the Lead (I,II,III) to measure different parts of electrical activity (heart) to
better diagnosis the patient.
Lead I- Causes the cables at the Right forelimb – Negative Pole
Causes the cables on the Left forelimb – Positive Pole
Lead II – Causes the cable on the Right forelimb – Negative Pole
Causes the cable on the Left hind limb – Positive Pole
Lead III- Causes the cable on the Left hind limb – Positive Pole
Causes the cable on the Left forelimb – Negative Pole
A Recap Of Heart Anatomy
•
•
•
•
SA or Sinoatrial node
AV or atrioventricular node
Bundle of His
Purkinje fibers
What does those lines mean?
The P wave or atrial depolarization is a small bump
because the walls of the atria are thinner than the
walls of the ventricle, therefore, the total amount of
electrical activity is smaller than the ventricle, or QRS
wave.
The individual squares measure time and
amplitude.
What Does it Diagnose?
•
•
•
•
•
Cardiac Arrhythmias
Heart Rate
Axis Deviations
Chamber enlargement
Conduction abnormalities
This is a irregular rhythm
questions
1)
Which of the following types of information can be gathered from an ECG?
A. Heart rate
B. Axis deviation
C. conduction abnormalities
D. All of the above
2) Which one of these important heart structures is not measured in an ECG?
A. AV Node
B. SA Node
C. Purkinje Fibers
D. Posterior vena cava
3) The P wave represents Depolarization of:
A. Atria
B. Ventricle
C. Aorta
D. vena cava
4) The QRS wave measures Depolarization of:
A. Atria
B. Ventricle
C. Aorta
D. Vena cava
5) The T wave measures
A. Depolarization of the atria
B. Depolarization of the ventricle C. Repolarization of ventricle
6) Lead II is:
A. + on Right Forelimb, - on Left forelimb
B. – on right forelimb, + on left forelimb
C. – on right forelimb, + on left hind limb
Answers
1
2
3
4
5
6
D
D
A
B
C
C
Basic Electrocardiography
Part 2
By Mandy Gutliph
And Stephanie Feldman
Producing a Diagnostic
Electrocardiogram
Position and Lead Placement
• Animal should be in right lateral
recumbency
• Their front legs should be perpendicular to
their spine.
• Animal should be comfortable
• Animals that have trouble breathing can
be done standing up or in ventral
recumbency
Alligator Clips
•Flattened alligator clips are placed below the elbow on the forelimbs
and below the stifle on the hind limbs.
• Remember to make sure the clip is on the skin, not just on the hair.
•You can use alcohol or electrode paste as a contact solution.
•Alcohol usually works well, but needs to be put onto the skin at
regular intervals because it evaporates
•Electrode paste should be used if the readings are not working well
with just the alcohol.
Checking ECG Machine
1. The sensitivity setting- a setting of 1 makes a
1cm deflection of the pen, when the millivolt
button is pushed.
The standard sensitivity is 1milivolt.
Remember that 1 millivolt = 1cm.
So you can change the sensitivity with the
sensitivity selector to either 0.5cm or 2cm.
When you do this, then 1 millivolt = .5cm or 2cm.
This should be done if your waves are too small or
too large to interpret.
Paper Speed
• Most ECGs are run at 50mm/sec.
• To change this, use the speed selection
knob.
• There are normally just two choices,
50mm/sec and 25mm/sec.
Lead Selections
• The different lead selections are marked at
the top of the paper.
• Normally, 1 dot means lead 1
– 2 dots mean lead 2
– 3 dots mean lead 3
– Just remember that there are a whole bunch
more lead selections, that we do not have to
know.
Artifacts
Artifacts
•
Artifacts are common, and must be
recognized to be corrected.
•
There are 3 common types
1. Sixty-cycle interference
2. Muscle tremors
3. Wandering Baseline
1 Sixty Cycle Interference
• This is an electrical interference pattern that
occurs when the electrical equipment is not
properly grounded
• Looks like continuous electrical stimulations on
readout.
• To fix, try one of the following
– Make sure power cord is grounded, clips are
contacting skin, clips are clean and securely attached
to cable, pull plugs on nearby equipment, turn off
fluorescent lights, make sure cables are not touching
one another, and that no one else is touching cables.
2 Muscle Tremors
• This looks like rapid and random
movements of the baseline.
• To fix, calm animal.
– Sometimes placing a hand on them will help
them to relax.
Also, cats that are purring can cause this.
3 Wandering Baseline
• This is commonly caused by the animals
chest movement when they breath.
• To fix, allow them to stand, or go into
ventral recumbency, or hold mouth closed
for 3-5seconds to get a quick reading.
• It looks on the readout like the baseline is
looping down.
Interpreting The Electrocardiogram
• This is pretty complicated, and takes a lot
of training and practice.
• Technicians should how to calculate a
heart rate by looking at an ECG.
Heart Rate
• Hear Rate is regulated by a balance of
sympathetic and parasympathetic inputs.
• REVIEW– Sympathetic nervous stimulation does what to
the heart rate?
– Parasympathetic nervous stimulation is done
through which nerve, and does what to the
heart rate?
Answers
• Sympathetic nervous stimulation increases
the heart rate
• Parasympathetic nervous
stimulation occurs through
the vagal nerve and lowers
the heart rate.
More about Heart Rate
• Remember the sinoatrial node is the
biological pacemaker of the heart, and
under normal conditions the heart beats
between 80 and 120 times per minute.
• The next node is the atrioventricular.
Calculating Heart Rate
1. Count the R waves registering within 6 seconds
and multiply by 10. (quick yet inaccurate
method)
2. Count the number of large squares between two
R waves and divide by 300. (this loosed
accuracy when used to calculate fast heart rates
and can only be used with regular rhythms)
3. Count the number of small squares between two
R waves and divide by 1500. (most accurate
method but can only be used with normal
rhythms.)
Interval and Amplitude
Measurements
• These are usually done with lead II.
• At 50mm/sec each small box horizontally
measures 0.02seconds.
• Measurements of P-R interval and ST
segment etc. are things we do not need to
understand 
Determining What is Normal
•
There are Three normal rhythms that we
see.
1. Sinus rhythm
2. Respiratory sinus rhythm
3. Wandering Pacemaker
1. Sinus Rhythm
Sinus Rhythm
• Sinus rhythm occurs when the heart rate
falls between 60 and 140 beats/min in
dogs and 120 -200 beats/min in cats.
• There is a P wave every QRS complex,
the rhythm is regular and the intervals
have normal values.
2. Respiratory Sinus Arrhythmia
Respiratory Sinus Arrhythmia
• This is the same heart function of a sinus
rhythm, except that the heart rate is
variable because it corresponds with
respiration.
• As patient inhales, the heart rate increases
• As patients exhales, the heart rate
decreases.
3. Wandering Pacemaker
Wandering Pacemaker
• This is when the P waves have varied
conformations and sizes within the same
lead.
• The pacemaker site may shit locations
within the sinoatrial node, causing the
vectors to shift slightly. This can be seen
commonly with respiratory sinus rhythm.
SUMMARY
•
So remember
–
Proper position is crucial
•
–
Artifacts occur on the ECG
•
–
–
And that patient comfort is part of this!
Three common ones are 60-cycle interference, muscle
tremors, wandering baseline
Heart rate is a function of several variables and is
regulated by a balance of sympathetic and
parasympathetic outputs.
Evaluation of intervals also plays a role, and you
should know three normal rhythms
•
They are the sinus rhythm, the respiratory sinus
arrhythmia, and the wandering baseline!
Basic Electrocardiogram
Part 3
By Mandy Gutliph
Stephanie Feldman
There are 4 steps to interpreting ECG:
• The first step is to evaluate the P wave.
The P wave indicated whether the atrial rhythm is normal.
Questions to ask yourself about P waves:
Are all the P waves occurring at regular intervals?
Do all the P waves have the same appearance on the ECG?
Are the P waves visible at all?
If any of these questions, you answered “no”; further investigation is needed.
P waves occur at regular intervals during normal sinus rhythm.
• The second step is to determine whether the ventricles are
activated from inside the ventricles; or from another location.
This can be done by looking at the duration (time) of the QRS
complex.
A QRS complex of normal duration is 0.04-0.06 seconds.
This indicates that waves are going along normal pathways (conduction tissues)
A QRS complex longer than 0.6 seconds has left normal pathways and occurs within
Ventricular Myocardium.
When it takes longer this is called: Ventricular Complex; and causes the QRS complex
to have a wide and bizarre appearance on the ECG
Ventricular Myocardium: muscular structure of the ventricle.
•The third step is to determine the relationship between the P wave and the QRS
complex.
This determines whether the atria and ventricles are working in sync!
You must determine whether the P wave is always, never or sometimes associated
with the QRS complex.
Does the P wave always come before the QRS complex?
Where's the P wave?
• Finally, look for anything abnormal.
•Arrhythmias
•Escaped beats
And anything else that doesn’t produce the classic PQRST complex.
Arrhythmia
BAD!
Asystole! No
heartbeat!
Premature Beats
•
Atrial premature contraction is a beat that is not synchronized with the rest
of the rhythm.
The P-R interval may be short, normal or long depending on the
origin of the premature beat.
Sites of origin are SA node or ectopic (displaced) locations in the
atria.
It may or may no affect the QRS complex (ventricular contraction)
Ventricular Premature Contraction
•
Ventricular premature contractions are characterized by wide, bizarre QRS
complex’s without including the P wave.
This happens when repolarization and depolarization occurring on a cell – to
– cell basis within the myocardium. This looks very different from other QRS
complex’s of sinus origin.
This can be determined by looking at lead II.
The QRS complex can either deflect downwards or upwards in Ventricular
Premature Contraction.
Sinus: normal
Escaped Beats
•
•
•
The depolarization of other areas of the cardiac anatomy resulting FROM a
failure of the SA (Sinoatrial node) to depolarize is called an escaped beat.
Usually if the SA node fails to depolarize the AV node, or atrioventricular
node, depolarizes to compensate for the pause in blood flow.
When the AV node depolarizes, the current travels both upwards to the atria
and through the ventricles. When it goes through the ventricles the QRS
complex is normal BUT atrial depolarization, or P wave, is spiked
downward.
Note how the backwards
P wave is after the QRS
complex
•
*The difference between Ventricular premature contraction and Ventricular
escaped beats is extremely important. The VPC is an occurrence within the
ventricle that interrupts a normal sinus beat WHILE an escaped beat is a
failsafe mechanism that interrupts a life-threatening arrest.
Supraventricular Arrhythmias
•
Supraventricular arrhythmia are arrhythmias that occur above the ventricles.
Such arrhythmias include sinus bradycardia, sinus tachycardia, atrial flutter,
atrial fibrillation, junctional rhythm and bundle branch blocks.
Sinus Bradycardia
Atrial Flutter
Sinus Bradycardia
•
Sinus bradycardia is a normal sinus rhythm that occurs when the heart
beats less than 60 beats/minute in dogs and less than 70-80 beats/minute
in cats.
•
Sinus bradycardia might be normal for some animals and must be
evaluated case by case.
Sinus Tachycardia
• Sinus tachycardia is a normal sinus
rhythm that is faster than 160 beats/minute
in dogs and faster than 240 beats/minutes
in cats.
Atrial Flutter
•
It is the rapid depolarization of the atria.
•
Looks on ECG like saw tooth waves between QRS complexes.
•
What happens in the heart basically goes like this:
1. The AV node is flooded with depolarizations from the atria, and
thus the AV node may not be able to repolarize.
2. So, it cannot accept the impluses from the atria.
3. Once it finally repolarizes, the AV node can then take the
impulse, and it passes to the ventricles.
4. Thus the rate of the atria is different than the rate of the
ventricles.
Atrial Flutter:
Atrial Fibrillation
• This is characterized by no recognizable P
waves, a regularly irregular rhythm, and a fast
rate for both the atria and the ventricles. The
atria therefore ‘beats’ at a rate of 350 to 600
beats/min.
• Thus the atria fails to fill with blood and then the
total output of the heart is decreased.
• Ventricular rate is also irregular because the AV
node receives countless impulses from the atria
at erratic intervals.
Atrial Fibrillation
Junctional Rhythm
• Basically, impulses that arise from the AV node,
and the bundle of His are called junctional
rhythms.
• Ex: escape beats, premature beats, or junctional
beats.
• The heart rate with a junctional rhythm will be
between 40 to 60 beats/min (remember normal
sinus rhythm is 100 to 120bpm)
• Accelerated junctional rhythm h as a rate
between 60 to 100 bpm.
Junctional Rhythm
Bundle Branch Blocks
• The right and left branches of the ventricular
conduction system take impulses from the
atrioventricular node to the Purkinje’s fibers (at
the apex of the ventricles)
• Imagine if one of these pathways gets blocked.
• Then the signal from the non-blocked side with
continue to travel to the blocked side and signal
that ventricle to contract. Therefore the
ventricles contract sequentially, rather than
simultaneously. In the ECG, you see normal P
waves and P-R intervals.
• There is a difference in the ECG between left
and right bundle blocks, but that is over our
heads.
Bundle Branch Blocks
Ventricular Arrhythmias
• These are arrhythmias that originate within
the ventricles.
• ALL of the rest of the arrhythmias listed
are ventricular arrhythmias!
Idioventricular Arrhythmias
• This is when both the sinoatrial node and
the atrioventricular node
• This ECG has no p-waves, because the
sinoatrial node is not functioning.
• An ectopic focus within the ventricles
takes over to ensure heart beat, but this is
a life threatening arrhythmia because the
etopic focus is unstable.
Idioventricular Arrhythmias
Ventricular Tachycardia
• This normally indicates an irritable
ventricular myocardium and it may
proceed ventricular fibrillation.
• It is three or more consecutive ectopic
ventricular complexes at a rate of 140
beats/min or faster.
• It also may appear and disappear during
the patient’s normal rhythm.
Ventricular Tachycardia
Ventricular Fibrillation
• This results from chaotic depolarization of
the ventricles with a loss of organized
contractions.
• It has no true QRS complexes.
• UNLESS IT IS CONTROLLED
IMMEDIATELY, VENTRICULAR
FIBRILLATION WILL RESULT IN
CARDIAC ARREST!
• WE NEED TO KNOW THIS ONE!
Ventricular Fibrillation
Disorders of Atrioventricular
Conduction
• Remember: These are also Ventricular
Arrhythmias
• These are identified when you examine the P-R
interval.
• When the P-R intervals are within normal limits,
the atria and ventricles are working in unison.
• When the P-R intervals vary, it means one of the
following disorders of Atrioventricular
Conduction.
First-Degree Atrioventricular Block
• This is when there is a P wave for every
QRS complex, but the P-R interval is
much longer than normal.
• This is caused from a minor conduction
defect because the atrial stimulus may be
delayed, but it always makes it to the
ventricles.
First-Degree Atrioventricular Block
Second-Degree Atrioventricular
Block
•
This is when some of the atrial impulses
are not conducted to the ventricles.
There are two types.
1. Type 1 has progressive lengthening of the
P-R interval on successive beats and then P
waves occurring without QRS complexes.
This is called a drop beat.
2. Type 2 is characterized by constant P-R
intervals that have normal duration, but
occasional dropped beats.
Second-Degree Atrioventricular
Block
• Type 1:
• Type 2
Third Degree Atrioventricular Block
• This is also known as complete heart
block. There is no association between P
waves and QRS complexes.
• Most times, the P waves are at regular
intervals because the sinoatrial node is
functional properly, but the atrioventricular
node is blocked.
• Ventricular rate is approximately 20 to 40
beats/min.
Third Degree Atrioventricular Block
Atrioventricular Dissociation
• This is a form of complete heart block.
• The ventricle rate is faster than the atrial
rate.
• The P waves and QRS complexes occur
independently of one another
• This normally results in irritable ventricular
musculature.
Atrioventricular Dissociation
Conclusion
• Cardiac arrhythmias can be diagnosed
when you examine the P waves in
comparison to the QRS complexes.