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Electrocardiogram. Wendy Blount, DVM Nacogdoches TX. ECG – What it Detects. Heart chamber enlargement Eccentric hypertrophy Dilation and growth of heart chambers Due to volume overload Concentric hypertrophy Wall thickening of heart chambers Due to pressure overload

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Electrocardiogram

Electrocardiogram

Wendy Blount, DVM

Nacogdoches TX


Ecg what it detects
ECG – What it Detects

Heart chamber enlargement

  • Eccentric hypertrophy

    • Dilation and growth of heart chambers

    • Due to volume overload

  • Concentric hypertrophy

    • Wall thickening of heart chambers

    • Due to pressure overload

      Conduction Disturbances


Ecg what doesn t detect
ECG – What Doesn’t Detect

Type of Heart chamber enlargement

  • Eccentric vs. Concentric hypertrophy

  • Congestive Heart Failure

    A Short ECG won’t detect many arrhythmias

  • Arrhythmias can be intermittent

  • 10 minutes is <1% of the day


Ecg when to do
ECG – When to Do

  • Pulse deficits detected on exam

  • Chaotic heart sounds (arrhythmia) detected on exam

  • Tachycardia

  • Bradycardia

  • Episodes of weakness or collapse

  • Pre-anesthetic in sick or geriatric animal

    • Abdominal mass (especially spleen)

    • Heart murmur


Ecg when to do1
ECG – When to Do

Event Recorders

  • Owner/witness starts recording during an event

    Holter Monitors

  • Continuously record ECG for 24 hours

  • Can rent for Dr. Kate Meurs at Washington State Vet School

    http://www.vetmed.wsu.edu/deptsVCGL/holter/requestform.aspx


Ecg helpful hints
ECG – Helpful Hints

  • Always in right lateral recumbency

  • Patient on a towel or rubber mat

  • Metal tables are more problematic

  • Limbs perpendicular to body

  • Place leads at the elbow and knee

  • No one moves while the ECG is being recorded

  • Enhance lead contact with gel or alcohol

    Alcohol is FLAMMABLE!!


Ecg helpful hints1
ECG – Helpful Hints

Which lead goes where

  • “Snow and Grass are on the ground”

    • White and green leads are on the bottom (R)

  • “Christmas comes at the end of the year”

    • Red and green are on the back legs

  • “Read the newspaper with your hands”

    • White and black are on front legs

      White – RF Green – RR (ground)

      Black – LF Red – LR


Ecg the cardiac cycle
ECG – The Cardiac Cycle

P wave

  • SA node fires

    • Atrial depolarization

      (contraction)

      • HS4

        2. Iternodal tracts

        (shortcut to

        AV node)


Ecg the cardiac cycle1
ECG – The Cardiac Cycle

PR interval

  • Beginning of P wave to

    beginning of QRS

  • AV node

    • *most of the PR interval

      is here*

  • Bundle of HIS

  • bundle branches (R&L)

  • Purkinje fiber network


Ecg the cardiac cycle2
ECG – The Cardiac Cycle

QRS complex

  • ventricular

    depolarization

    (systole)

  • Q wave 1st negative

    deflection

  • R wave 1st positive

    deflection

  • S wave 2nd negative

    deflection


Ecg the cardiac cycle3
ECG – The Cardiac Cycle

QRS complex

  • HS1

    • AV valves closing

    • beginning of QRS

  • HS2

    • Semilunar valves

      closing (AoV, PV)

    • end of QRS

  • Pulse is generated


Ecg the cardiac cycle4
ECG – The Cardiac Cycle

T wave

  • Ventricular

    repolarization

    (diastole)

  • HS3

    • Ventricular filling

    • if myocardium is

      stiff


Ecg the cardiac cycle5
ECG – The Cardiac Cycle

QT interval

  • beginning of QRS to

    end of T wave

  • ventricular depolari-

    zation & repolarization

  • HS1, HS2, HS3

  • Pulse generated


Ecg the cardiac cycle6
ECG – The Cardiac Cycle

ST segment

  • Between S & T waves

  • Between ventricular

    contraction

    (depolarization – systole)

    and ventricular

    relaxation

    (repolarization – diastole)

  • Isn’t measured per se

  • But it’s relationship with

    baseline is noted


Ecg 6 leads
ECG – 6 Leads

Bipolar leads

  • I – LF+ RF-

  • II – LR+ RF-

  • III – RR+ LF-

    Unipolar leads

  • aVR – RF+ (summation lead III)-

  • aVL – LF+ (summation lead II)-

  • aVF - LR+ (summation lead I)-


Ecg systematic interpretation
ECG – Systematic Interpretation

  • Heart Rate and Rhythm

  • Measurements of the parts

    • P wave - width and height

    • PR interval - length

    • QRS - width and height

    • QT interval – length

      • ST segment – relative to PR interval

    • T wave - width and height

  • Mean Electrical Axis

    Form


Ecg measurements
ECG – Measurements

  • Take 3-5 measurements and average

  • All measurements done in lead II

  • Use calipers

  • Measure from the

    center of the line


Ecg heart rate
ECG – Heart Rate

At 25 mm/sec, 150mm = 6 sec

  • “Bic Pen Times Ten”

  • Accurate within 10 beats per minute

    At 50 mm/sec, 300mm = 6 sec

  • A Bic Pen times Twenty

  • Accurate within 20 beats per minute


Ecg heart rate1
ECG – Heart Rate

Normals

  • Giant dogs 60-140 Med-Lg dogs 70-160

  • Toy dogs 80-180 Puppies 70-220

  • Cats 100-240

    Get Baseline heart rates for individuals on every visit


Ecg rhythm
ECG – Rhythm

Normal Sinus rhythm

  • Regular heart rate

    • Measure from one P wave to the next with calipers

  • P, QRS and T waves in each complex

    Respiratory Sinus Arrhythmia

  • heart rate regularly irregular

    • Speeds up with inhale, slows with exhale (vagal tone variance, in a regular cycle)

  • P, QRS and T waves in each complex

  • Variable P wave – wandering pacemaker

  • Heart rate less than 200

    Arrhythmia


Ecg rhythm1
ECG – Rhythm

Respiratory Sinus Arrhythmia


Ecg p wave measurements
ECG – P Wave Measurements

  • Atrial depolarization

    (contraction)

  • Normal Dog:

    <0.4 mV x <0.04 sec

    <0.5 sec in giant breeds

    • 4 boxes tall

    • 25 mm/sec 1-1.25 boxes wide

    • 50 mm/sec 2-2.5 boxes wide

  • Normal Cat:

    <0.2 mV x <0.04 sec

    • 2 boxes tall


Ecg p wave measurements1
ECG – P Wave Measurements

  • Wide P wave (Sometimes Notched)

    • 25 mm/sec > 1 box wide

    • 50 mm/sec > 2 boxes wide

    • LA enlargement

  • Tall P wave (often spiked)

    • Dog > 4 boxes tall, cat > 2 boxes tall

    • RA enlargement

  • Variable P wave – normal variation

    • “wandering pacemaker” – increased vagal tone

  • Lack of P wave

    • Atrial standstill


Ecg p wave measurements2
ECG – P Wave Measurements

Wandering pacemaker


Ecg pr interval
ECG – PR Interval


Ecg pr interval1
ECG – PR Interval

Conduction from atria to ventricles (AV node)

Establishes the ECG baseline

Normal Dog: 0.06-0.13 sec

Normal Cat: 0.05-0.09 sec


Ecg pr interval2
ECG – PR Interval

Conduction from atria to ventricles (AV node)

Establishes the ECG baseline

Normal Dog: 0.06-0.13 sec

Normal Cat: 0.05-0.09 sec


Ecg pr interval3
ECG – PR Interval

  • Short PR Interval (tachycardia)

    • AV node is bypassed

    • “Accessory pathway” (Wolff-Parkinson-White)

    • Congenital or acquired

    • Treated in people by radioablation of the pathway

    • Sudden onset of tachycardia in a dog

    • Can try calcium channel blockers

      • Diltiazem SR (Plumb dose)

    • If you don’t treat right away, the myocardium will poop out & rapidly progressive CHF will ensue


Ecg pr interval4
ECG – PR Interval

Normal Dog: 0.06-0.13 sec

Normal Cat: 0.05-0.09 sec

  • Long PR Interval

    • Slow conduction through abnormal AV node

    • AV Blocks


Ecg pr interval5
ECG – PR Interval

Normal Dog: 0.06-0.13 sec

Normal Cat: 0.05-0.09 sec

1st degree AV Block

  • Every P wave is followed

    by a QRS

  • Due to increased vagal tone

  • Non-pathogenic

50 mm/sec


Ecg pr interval6
ECG – PR Interval


Ecg pr interval7
ECG – PR Interval

2nd degree AV Block

Some P waves not followed by a QRS

  • Mobitz type I – PR progressively longer until QRS dropped (Wenkebach Phenomenon)


Ecg pr interval8
ECG – PR Interval

2nd degree AV Block

Some P waves not followed by a QRS

  • Mobitz type 2 – no pattern

  • PR interval does not change

  • P-P interval is consistent, so SA node is working fine

  • PR interval may be prolonged and may be normal

  • Occasionally, a P wave is not followed by a QRS

  • Not necessarily pathogenic


Physiology cardiac pacemakers
Physiology - Cardiac Pacemakers

Automatic cells in the heart

  • Depolarize on their own during phase 4 of the cardiac cycle

  • Rate of depolarization affected by autonomic nervous system

    • SA node (60-180 beats/min dog) (100-240 cat)

    • AV node (40-60 beats/min dog) (80-130 cat)

    • Purkinje fibers (20-40 beats/min)

    • Bundle of HIS (20-40 beats/min)

    • Ventricular myocytes (20-40 beats/min)


Physiology cardiac pacemakers1
Physiology - Cardiac Pacemakers

Automatic cells in the heart

  • The fastest functioning pacemaker in the heart takes over, by default

  • The closer to the AV node, the more the escape beat will resemble normal QRS

  • The closer to the ventricle, the more wide and bizarre the QRS will appear

  • Escape rhythm – pacemaker other than SA node takes over, because SA node fails to fire


Ecg pr interval9
ECG – PR Interval

3rd degree AV Block (complete AV block)

No relationship between P waves and QRS

  • P waves have their own rate (faster), determined by the normal SA node

  • QRS has its own rate (slower), determined by the automaticity of the fastest remaining functioning pacemaker

  • Treatment

    • pacemaker

  • Prognosis

    • Cats – without anesthesia, potentially very good

    • Dogs – eventual asystole is likely, if no pacemaker implanted


Ecg pr interval10
ECG – PR Interval

3rd degree AV Block (complete AV block)

  • Pacemaker above bifurcation of bundle of His

  • Pacemaker left ventricle


Ecg qrs complex measurements
ECG – QRS Complex Measurements

Normal Dog:

<40 lbs: <0.05sec x <3.0 mV

  • 30 boxes tall

  • 25 mm/sec 1.25 boxes wide

  • 50 mm/sec 2.5 boxes wide

    >40 lbs: <0.06sec x <3.0 mV

  • 25 mm/ sec 1.5 boxes wide

  • 50 mm/sec 3 boxes wide

    Normal Cat:

    <0.04sec x <0.9 mV

  • 9 boxes tall

  • 25 mm/sec 1 box wide

  • 50 mm/sec 2 boxes wide


Ecg qrs complex measurements1
ECG – QRS Complex Measurements

R wave measured from

baseline to top

  • Tall R wave, wide QRS

    • LV enlargement

    • Left Bundle branch block

  • Deep S wave in leads

    I, II & III

    • RV enlargement


Ecg bundle branch blocks
ECG – Bundle Branch Blocks

  • Depolarization wave through myocardium rather than through Purkinje network on affected side

    • takes longer

    • “appears bigger” on ECG

  • Can be persistent or intermittent

    • Intermittent often precipitated by increased heart rate (delayed refractory period)

  • Left side, right side or both

    • Bilateral BBB looks like 3rd degree AV block


Ecg bundle branch blocks1
ECG – Bundle Branch Blocks

Right Bundle Branch Block (RBBB)

  • Causes:

    • primary conduction system disease

    • Disruption of moderator band

    • RV enlargement

    • Congenital (especially beagles)

  • ECG

    • Deep S wave leads I, II, III, aVF

    • Wide QRS

  • May cause a split S2


Ecg bundle branch blocks2
ECG – Bundle Branch Blocks

Left Bundle Branch Block (RBBB)

  • Causes:

    • primary conduction system disease

    • Widespread LV myocardial disease

    • Unlike RBBB, not usually benign

  • ECG

    • Tall R wave

    • Wide QRS

    • Looks like a VPC, but follows

      normal PR interval


Ventricular premature complexes
Ventricular Premature Complexes

  • Depolarization wave through myocardium rather than through Purkinje network on affected side

    • takes longer

    • “appears bigger” on ECG


Ventricular premature complexes1
Ventricular Premature Complexes

  • VPCs are like escape beats in that they both originate from the ventricular myocardium

  • VPCs are abnormal due to primary LV pathology or secondary to metabolic disease

  • Escape beats are the normal life saving response to a failure of upline pacemaker

  • VPCs can be persistent or intermittent

    • Intermittent often precipitated by increased heart rate (delayed refractory period)

  • Multiform VPCs are more serious

    • Multifocal areas of LV pathology


Ecg st segment
ECG – ST Segment

ST segment depression or

elevation

  • >0.2mV between baseline

    and ST

  • hypothermia

  • hypokalemia

  • Digitalis toxicity

  • Bundle branch block

  • Myocardial infarction

    • Rare in dogs

    • Can be seen in feline HCM


Ecg mean electrical axis mea
ECG – Mean Electrical Axis (MEA)

  • when a wavefront spreads toward an electrode, the largest possible deflection will occur

  • When a wavefront spreads perpendicular to a lead, the smallest or no deflection occurs

  • ECG shows the sum of all wavefronts relative to the lead being used to measure (MEA)

  • Isoelectric lead

    • lead with the smallest deflection

    • Perpendicular to the MEA


Ecg mean electrical axis mea1
ECG – Mean Electrical Axis (MEA)

  • The normal MEA is 40o to 100o

    in the dog

  • Lead II is most perpendicular

    to the normal MEA

    • largest deflections

    • best for measurements

  • aVL is most often the

    isoelectric lead

    • Approximates MEA in normal

      dogs


Ecg mean electrical axis mea2
ECG – Mean Electrical Axis (MEA)

Calculating MEA by graph

  • Calculate the net deflection in lead I

    • Graph on “x axis”

  • Calculate net deflection in head aVF

    • Graph on “y axis”

  • Draw the vector between the two (MEA)


Ecg mean electrical axis mea3
ECG – Mean Electrical Axis (MEA)

+3 - 5 = -2

+10 -1.5 = +8.5

-

+

MEA = 105o


Ecg mean electrical axis mea4
ECG – Mean Electrical Axis (MEA)

Estimating MEA

  • Find the isoelectric lead

    • NOT the lead with smallest deflections

    • Lead with smallest NET DEFLECTION

  • MEA is perpendicular to that, in the direction of net deflection


Ecg mean electrical axis mea5
ECG – Mean Electrical Axis (MEA)

Estimating MEA

Isoelectric lead = aVR

+3

-5

-2

+8

-0

+8

+13

-2

+11

+2

-2

0

+1

-8

-7

+9.5

-1

+8.5

MEA = +120o

Right Axis Shift


Ecg mean electrical axis mea6
ECG – Mean Electrical Axis (MEA)

Normal Canine MEA

40-110o

Normal Feline MEA

0-160o


Ecg mean electrical axis mea7
ECG – Mean Electrical Axis (MEA)

Right Axis Shift

  • Right ventricular enlargement

    • RV hypertrophy or dilation

  • Right bundle branch block

    Left Axis Shift

  • HCM in cats

  • hyperkalemia


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