ECG Part I Flashcards
what is phase 0 of the cardiac action potential?
upstroke
what is phase 1 of the cardiac action potential?
early fast repolarization
what is phase 2 of the cardiac action potential?
the plateau
what are the outward potassium currents for repolarization?
Ito1
ikr
iks
what normally controls the heart rate?
sinus node
what is automaticity a property of?
spontaneous depolarization
altered slope to phase 4 changes ___________________
heart rate
which myocardial tissues have automaticity?
sinoatrial node
internodal pathways
atrioventricular junctional tissue
purkinje fibers in the ventricle
what are some cardiac structures that do not possess excitability?
pericardium
cardiac valves
what is the absolute refractory period?
no stimulus can cause depolarization of the cell
what species have type A ventricular activation?
dog
cat
man
what leads to rapid ventricular activation in type B species?
extensive purkinje fiber network
what is escape depolarization?
comes after a pause
what is ectopic?
impulse originates from focus other than SA node
what is a conduction block?
a pathologic delay or interruption of conduction
what is atrioventricular dissociation?
independent depolarization of the atrial and ventricles
what is paroxysmal tachycardia?
sudden onset and abrupt end
“burst” of tachycardia
what is fibrillation?
totally chaotic activation of atria or ventricles
what can you measure on a dog and cat electrocardiogram?
P wave height
P wave duration
PR interval
R wave height
QRS duration
QT interval
what is the ECG “standard calibration”?
1 cm/mV
at 25mm/sec, how long does one little box represent?
0.04 sec
what are the normal heart rate values for dogs?
60-160 beats/min for adults
up to 180 beats/min for toy breeds
up to 220 beats/min for puppies
what is normal P wave duration for dogs in lead II?
<= 0.04 sec
what is normal P wave height for dogs in lead II?
<= 0.4 mV
what is the range of normal cat heart rate (in the hospital)?
160-240 beats/min
what are the normal cat rhythms on an ECG?
normal sinus rhythm
sinus tachycardia
what is the normal P-R interval in a cat on an ECG?
0.05 to 0.09 seconds
what is a hummingbird heart rate while perching?
500 bpm
what is method 1 to obtain heart rate using an ECG?
50 mm/sec or 25 mm/sec
count number of QRS in 3 seconds
multiply by 20
the first negative wave is a ______ wave
Q
which wave is always positive?
R wave
what are the limb leads?
I
II
III
aVF
aVR
in whom do we use the base-apex lead system?
horses and ruminants
how many leads in chest leads may be used?
4-6
why are base-apex leads used in horses and ruminants?
extensive purkinje sustem
burst activation of ventricle
cannot use ECG to identify cardiac enlargement
what is ECG used mostly for in horses and ruminants?
rate and heart rhythm
does cardiac hyperplasia occur in the adult?
no
what can cause cellular hypertrophy?
physiologic: exercise, anemia
pathologic: systemic hypertension, mitral valve reegurgitation
what is hypertrophy triggered by?
load on myocytes
autocrine, paracrine, and endocrine factors
what are some inadequate responses with cardiac hypertrophy?
cell overload
myocyte failure/death
CHF
what is a concentric hypertrophy pattern caused by?
pressure overload: systemic hypertension, aortic stenosis
what can cardiac hypertrophy be stimulated by?
increasing wall stress
catecholamines
angiotensin II
aldosterone
hypoxia or ischemia
cytokines, or other signaling factors
does cardiac hypertrophy trigger ECG changes?
it can
what is phase 3 of the cardiac action potential?
repolarization to diastolic potential
what is phase 4 of the cardiac action potential?
resting membrane potential
does atropine speed or slow the heart rate?
speeds
what does altered slope to phase 4 do?
changes heart rate
what is the supernormal period?
less than normal stimulus might cause depolarization
there are ________ of the 1mm boxes in 1 second at 50mm/sec
50
what is a normal P-R interval for a dog?
0.06-0.13sec
what is a normal QRS duration for most dogs?
<=0.05 seconds
0.06 seconds giant breeds
what is a normal R wave height for dogs?
<=2.5 mV
<3.0 mV giant breeds
what is a normal P-R interval for a cat?
0.05-0.09 seconds
what is a normal QRS duration for a cat?
<=0.04 seconds
what is a normal R wave height for a cat?
<=0.9 to 1.0 mV
what is the second method to obtain heart rate?
count number of boxes between R waves, divide into 3000 for 50mm/sec or 1500 for 25mm/sec
what is an advantage of chest leads?
search for P waves when not evident in frontal plane leads
does cardiac hyperplasia occur in the adult?
no
when is cardiac hypertrophy an adequate response?
compensated hypertrophy
what causes eccentric hypertrophy?
volume overload: mitral regurgitation, ventricular septal defect, anemia
