Electrocardiogram Wendy Blount, DVM Nacogdoches TX Wendy
Blount, DVM Nacogdoches TX Dr. Callan Video
Slide 2
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
Slide 3
ECG What Doesnt Detect Type of Heart chamber enlargement
Eccentric vs. Concentric hypertrophy Congestive Heart Failure A
Short ECG wont detect many arrhythmias Arrhythmias can be
intermittent 10 minutes is
Wide P wave (Sometimes Notched) 50 mm/sec > 2.5 boxes wide
25 mm/sec > 1.25 box 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
Slide 24
ECG P Wave Measurements Wandering pacemaker
Slide 25
ECG PR Interval Conduction from atria to ventricles (AV node)
Establishes the ECG baseline Normal Dog: 0.06-0.13 sec 50mm/sec
3-6.5 boxes 25mm/sec 1.5-3.25 boxes Normal Cat: 0.05-0.09 sec
50mm/sec 2.5-4.5 boxes 25mm/sec 1.25-2.25 boxes
Slide 26
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 dont treat right away, the
myocardium will poop out & rapidly progressive CHF will
ensue
Slide 27
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) Long PR Interval Slow conduction
through abnormal AV node AV Blocks
Slide 28
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 1 st degree AV Block Every P wave
is followed by a QRS Due to increased vagal tone Non-pathogenic 50
mm/sec
Slide 29
ECG PR Interval
Slide 30
2 nd degree AV Block Some P waves not followed by a QRS Mobitz
type I PR progressively longer until QRS dropped (Wenkebach
Phenomenon)
Slide 31
ECG PR Interval 2 nd 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
Slide 32
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 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)
Slide 33
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
Slide 34
ECG PR Interval 3 rd 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, if escape rhythm rate
doesnt support normal activity Prognosis 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
Slide 35
ECG PR Interval 3 rd degree AV Block (complete AV block)
Pacemaker above bifurcation of bundle of His Pacemaker left
ventricle