Electrocardiogram ECG Part 1 Made for understanding

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ElectrocardiogramECGPart 1Made for
understanding

• By Mandy Gutliph
• Stephanie Feldman

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Electrocardiography or ECG is a important
diagnostic tool for Veterinary Medicine. ECGs
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 DepolarizationThe T wave represents
Ventricular Repolarization
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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!
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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)
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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
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A Recap Of Heart Anatomy

• SA or Sinoatrial node
• AV or atrioventricular node
• Bundle of His
• Purkinje fibers

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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.
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What Does it Diagnose?

• Cardiac Arrhythmias
• Heart Rate
• Axis Deviations
• Chamber enlargement
• Conduction abnormalities

This is a irregular rhythm
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questions

• 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

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Answers

• 1 D
• 2 D
• 3 A
• 4 B
• 5 C
• 6 C

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Basic ElectrocardiographyPart 2

• By Mandy Gutliph
• And Stephanie Feldman

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Producing a Diagnostic ElectrocardiogramPosition
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

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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.

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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.

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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.

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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.

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Artifacts
Artifacts

• Artifacts are common, and must be recognized to
  be corrected.
• There are 3 common types
• Sixty-cycle interference
• Muscle tremors
• Wandering Baseline

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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.

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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.

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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.

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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.

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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?

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Answers

• Sympathetic nervous stimulation increases the
  heart rate
• Parasympathetic nervous
• stimulation occurs through
• the vagal nerve and lowers
• the heart rate.

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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.

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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.)

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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 ?

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Determining What is Normal

• There are Three normal rhythms that we see.
• Sinus rhythm
• Respiratory sinus rhythm
• Wandering Pacemaker

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1. Sinus Rhythm
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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.

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2. Respiratory Sinus Arrhythmia
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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.

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3. Wandering Pacemaker
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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.

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SUMMARY

• So remember
• Proper position is crucial
• And that patient comfort is part of this!
• Artifacts occur on the ECG
• 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!

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Basic ElectrocardiogramPart 3

• By Mandy Gutliph
• Stephanie Feldman

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• 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.

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• 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.
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• 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?
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• Finally, look for anything abnormal.
• Arrhythmias
• Escaped beats
• And anything else that doesnt produce the
  classic PQRST complex.

Arrhythmia
BAD! Asystole! No heartbeat!
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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)
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Ventricular Premature Contraction

• Ventricular premature contractions are
  characterized by wide, bizarre QRS complexs
  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 complexs 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
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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.
• 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.

Note how the backwards P wave is after the QRS
complex
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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
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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.

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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.

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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
• The AV node is flooded with depolarizations from
  the atria, and thus the AV node may not be able
  to repolarize.
• So, it cannot accept the impluses from the atria.
• Once it finally repolarizes, the AV node can then
  take the impulse, and it passes to the
  ventricles.
• Thus the rate of the atria is different than the
  rate of the ventricles.

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Atrial Flutter
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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.

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Atrial Fibrillation
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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.

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Junctional Rhythm
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Bundle Branch Blocks

• The right and left branches of the ventricular
  conduction system take impulses from the
  atrioventricular node to the Purkinjes 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.

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Bundle Branch Blocks
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Ventricular Arrhythmias

• These are arrhythmias that originate within the
  ventricles.
• ALL of the rest of the arrhythmias listed are
  ventricular arrhythmias!

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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.

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Idioventricular Arrhythmias
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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
  patients normal rhythm.

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Ventricular Tachycardia
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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!

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Ventricular Fibrillation
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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.

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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.

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First-Degree Atrioventricular Block
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Second-Degree Atrioventricular Block

• This is when some of the atrial impulses are not
  conducted to the ventricles. There are two
  types.
• 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.
• Type 2 is characterized by constant P-R intervals
  that have normal duration, but occasional dropped
  beats.

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Second-Degree Atrioventricular Block

• Type 1
• Type 2

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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.

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Third Degree Atrioventricular Block
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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.

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Atrioventricular Dissociation
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Conclusion

• Cardiac arrhythmias can be diagnosed when you
  examine the P waves in comparison to the QRS
  complexes.