Download PowerPoint - Electrocardiography

Electrocardiogram
Wendy Blount, DVM
Nacogdoches TX
Dr. Callan Video
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
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
• Holter Monitor is more thorough
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 Do
Event Recorders
• Owner/witness starts recording during an event
Holter Monitors
• Continuously record ECG for 24 hours
• Can rent various places
– NCSU – Kate Meurs, DACVIM Cardiology – Vets only
• http://cardiologycarenetwork.com/network/holter_request.php
• $150 12 hours, $250 24 hours, $340 48 hours; recheck $150
– Pet Cardiology.com – breeders and vets
• http://www.pet-cardiology.com/online-enrollment (form)
– Alba Medical – breeders and vets
• http://www.albamedical.com/animalhealth.html
• Sell Holter Monitors, interpretation $40-80 (form)
ECG – Helpful Hints
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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 touching the dog can move while
the ECG is being recorded
• Enhance lead contact with gel or alcohol
Alcohol is FLAMMABLE!!
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
Black – LF
Green – RR (ground)
Red – LR
ECG – The Cardiac Cycle
P wave
• SA node fires
1. Atrial depolarization
(contraction)
• HS4
2. Iternodal tracts
(shortcut to
AV node)
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 Cycle
QRS complex
• ventricular
depolarization
(systole)
• Q wave 1st negative
deflection
• R wave 1st positive
deflection
• S wave 2nd negative
deflection
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 Cycle
T wave
• Ventricular
repolarization
(diastole)
• HS3
– Ventricular filling
– if myocardium is
stiff
ECG – The Cardiac Cycle
QT interval
• beginning of QRS to
end of T wave
• ventricular depolarization & repolarization
• HS1, HS2, HS3
• Pulse generated
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
Bipolar leads
• I – LF+ RF• II – LR+ RF• III – RR+ LFUnipolar leads
• aVR – RF+ (summation lead III)• aVL – LF+ (summation lead II)• aVF - LR+ (summation lead I)-
ECG – Systematic Interpretation
1. Heart Rate and Rhythm
2. Measurements of the parts
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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
3. Mean Electrical Axis
Form
ECG – Measurements
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Take 3-5 measurements and average
All measurements done in lead II
Use calipers
Measure from the
center of the line
• 50mm/sec
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 Rate
Normals
• Giant dogs 60-140
• Toy dogs 80-180
• Cats 100-240
Med-Lg dogs 70-160
Puppies 70-220
Get Baseline heart rates for individuals on
every visit
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 in normal range
Arrhythmia
ECG – Rhythm
Respiratory Sinus Arrhythmia – 10 mm/sec
ECG – P Wave Measurements
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Atrial depolarization
(contraction)
Normal Dog:
<0.4 mV x <0.04 sec
<0.5 sec in giant breeds
– 4 boxes tall (10mm=1mV)
– 50 mm/sec 2-2.5 boxes wide
– 25 mm/sec 1-1.25 boxes wide
•
Normal Cat:
<0.2 mV x <0.04 sec
– 2 boxes tall
ECG – P Wave Measurements
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Wide P wave (Sometimes Notched)
– 50 mm/sec > 2.5 boxes wide
– 25 mm/sec > 1.25 box wide
– LA enlargement
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Tall P wave (often spiked)
– Dog > 4 boxes tall, cat > 2 boxes tall
– RA enlargement
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Variable P wave – normal variation
– “wandering pacemaker” – increased vagal tone
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Lack of P wave
– Atrial standstill
ECG – P Wave Measurements
Wandering pacemaker
ECG – PR Interval
Conduction from atria to ventricles (AV node)
Establishes the ECG baseline
Normal Dog: 0.06-0.13 sec
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50mm/sec – 3-6.5 boxes
25mm/sec – 1.5-3.25 boxes
Normal Cat: 0.05-0.09 sec
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50mm/sec – 2.5-4.5 boxes
25mm/sec – 1.25-2.25 boxes
ECG – PR Interval
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Short PR Interval (tachycardia)
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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 Interval
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Short PR Interval (tachycardia)
– AV node is bypassed by abnormal myocardium that
passes through the fibrous tissue that normally
insulates the atria from the ventricles
– “Accessory pathway” (Wolff-Parkinson-White)
– Congenital or acquired
– Sudden onset of tachycardia in a dog
ECG – PR Interval
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Short PR Interval (tachycardia)
– AV node is bypassed by abnormal myocardium that
passes through the fibrous tissue that normally
insulates the atria from the ventricles
– “Accessory pathway” (Wolff-Parkinson-White)
– Congenital or acquired
– Sudden onset of tachycardia in a dog
ECG – PR Interval
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WPW Syndrome - ECG shows SVT
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Fused T and P wave
Heart rate 250-350 bpm+
Normal QRS
ECG – PR Interval
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Exam
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Generalized weakness
Heart rate often too fast to count
Pale mucous membranes
Weak pulses, pulse deficits
No heart murmur, normal bloodwork, x-rays and echo
Treatment
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Can try calcium channel blockers (Class 2 or 4 antiarrhythmics)
• Diltiazem SR 3-5 mg/kg PO BID
If you don’t treat right away, the myocardium will poop out &
rapidly progressive CHF will ensue
Refer for as an emergency radioablation of the pathway
ECG – PR Interval
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Types of SVT – all have high heart rate with
narrow/normal QRS
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Sinus tachycardia (normal P waves)
Atrial tachycardia (bizarre P waves negative in I & aVF)
Junctional tachycardia (unrelated P wave)
Atrial flutter (coarse atrial fibrillation)
Atrial fibrillation (chaotic baseline)
Wolff-Parkinson-White Syndrome (SVT + re-entry
rhythm)
ECG – PR Interval
Normal Dog: 0.06-0.13 sec (3-6.5 boxes)
Normal Cat: 0.05-0.09 sec (2.5-4.5 boxes)
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Long PR Interval
– Slow conduction through abnormal AV node
– AV Blocks
ECG – PR Interval
Normal Dog: 0.06-0.13 sec
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50 mm/sec
3-6.5 boxes
Normal Cat: 0.05-0.09 sec
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2.5-4.5 boxes
1st degree AV Block
• Every P wave is followed
by a QRS
• Due to increased vagal tone
• Non-pathogenic
ECG – PR Interval
2nd degree AV Block
Some P waves not followed by a QRS
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Mobitz type I – PR progressively longer until QRS
dropped (Wenkebach Phenomenon)
ECG – PR Interval
2nd degree AV Block
Some P waves not followed by a QRS
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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
ECG – PR Interval
Physiology - Cardiac Pacemakers
Automatic cells in the heart
• Depolarize on their own during phase 4 of
the cardiac cycle (escape beat)
• Rate of depolarization affected by
autonomic nervous system
– SA node (60-180 beats/min dog) (100-240 bpm cat)
– AV node (40-60 beats/min dog) (80-130 bpm cat)
– Purkinje fibers, Bundle of HIS, Ventricular
myocytes (20-40 beats/min) (60-80 bpm cat)
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 Interval
3rd degree AV Block (complete AV block)
No relationship between P waves and QRS
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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
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Pacemaker, if escape rhythm rate doesn’t support normal
activity
Prognosis
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Cats – without anesthesia, potentially very good, as they
usually escape from the AV node
Dogs – eventual asystole is likely, if no pacemaker implanted,
as they escape from Purkinje fibers, HIS or ventricles
ECG – PR Interval
3rd degree AV Block (complete AV block)
•Pacemaker
above
bifurcation
of bundle of
His
•Pacemaker
left ventricle
ECG – QRS Complex Measurements
Normal Dog:
<40 lbs: <0.05sec x <3.0 mV
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30 boxes tall
50 mm/sec 2.5 boxes wide
25 mm/sec 1.25 boxes wide
>40 lbs: <0.06sec x <3.0 mV
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50 mm/sec 3 boxes wide
25 mm/ sec 1.5 boxes wide
Normal Cat:
<0.04sec x <0.9 mV
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9 boxes tall
50 mm/sec 2 boxes wide
25 mm/sec 1 box wide
ECG – QRS Complex Measurements
R wave measured from
baseline to top
• Tall R wave, wide QRS
– LV enlargement
– Left Bundle branch block
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Deep S wave in leads
I, II & III
– RV enlargement
ECG – Bundle Branch Blocks
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Depolarization wave through myocardium rather
than through Purkinje network on affected side
– takes longer
– “appears bigger” on ECG
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Can be persistent or intermittent
– Intermittent often precipitated by increased heart
rate (delayed refractory period)
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Left side, right side or both
– Bilateral BBB looks like 3rd degree AV block
ECG – Bundle Branch Blocks
Right Bundle Branch Block (RBBB)
• Causes:
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primary conduction system disease
Disruption of moderator band
RV enlargement
Congenital (especially beagles)
ECG
– Deep S wave leads I, II, III, aVF
– Wide QRS
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May cause a split S2
ECG – Bundle Branch Blocks
Left Bundle Branch Block (LBBB)
• Causes:
– primary conduction system disease
– Widespread LV myocardial disease
– Unlike RBBB, not usually benign
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ECG
– Tall R wave
– Wide QRS
– Looks like a VPC, but follows
normal PR interval
ECG – Bundle Branch Blocks
Ventricular Premature Complexes
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Depolarization wave through myocardium rather
than through Purkinje network on affected side
– takes longer
– “appears bigger” on ECG
Ventricular Premature Complexes
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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)
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Multiform VPCs are more serious
– Multifocal areas of LV pathology
ECG – ST Segment
ST segment depression or
elevation
• >0.2mV (2 boxes) between
baseline and ST segment
• hypothermia
• hypokalemia
• Digitalis toxicity
• Bundle branch block
• Myocardial infarction
– Rare in dogs
– Can be seen in feline HCM
ECG – Mean Electrical Axis (MEA)
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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 (MEA)
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Lead II is most perpendicular
to the normal MEA
– largest deflections
– best for measurements
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aVL is most often the
isoelectric lead
– Approximates MEA in normal
dogs
aVL
+
II
+
ECG – Mean Electrical Axis (MEA)
Calculating MEA by graph
• Calculate the net deflection in lead I
– Graph on “x axis”
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Calculate net deflection in lead aVF
– Graph on “y axis”
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Draw the vector between the two (MEA)
ECG – Mean Electrical Axis (MEA)
+3 - 5 = -2
+10 -1.5 = +8.5
-
MEA = 105o
+
ECG – Mean Electrical Axis (MEA)
Estimating MEA
• Find the isoelectric lead
– NOT necessarily the lead with smallest
deflections
– Lead with smallest NET DEFLECTION
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MEA is perpendicular to that, in the direction of
net deflection
ECG – Mean Electrical Axis (MEA)
Estimating MEA
Isoelectric lead = aVR
+3
+8
+13
+2
+1
+9.5
-5
-0
-2
-2
-8
-1
-2
+8
+11
0
-7
+8.5
MEA = +120o
Right Axis Shift
ECG – Mean Electrical Axis (MEA)
Normal Canine MEA
Normal Feline MEA
40-110o
0-160o
ECG – Mean Electrical Axis (MEA)
Right Axis Shift
• Right ventricular enlargement
– RV hypertrophy or dilation
• Right bundle branch block
Left Axis Shift
• Left ventricular enlargement or dilation
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LV hypertrophy or dilation
Hyperkalemia
Left Bundle Branch Block
Acknowledgements
Open.osmosis.com (WPW Video)
Kittleson, Mark, DACVIM - Cardiology
• Small Animal Cardiovascular Medicine,
Veterinary Information Network. Chapter
5 – Electrocardiography
Edwards J
• Bolton's Handbook of Canine & Feline
Electrocardiography
Acknowledgements
Larry Tilley, DACVIM - Cardiology
• Essentials of Canine and Feline
Electrocardiography
Tilley L, Miller M, Smith FWK
• Canine and Feline Cardiac Arrhythmias – A
Self Assessment