Electrocardiography Flashcards
What does electrocardiography do
measures electrical activity in the heart
What is an ECG used for
determine heart rate
conduction disturbances due to:
chamber enlargement
electrolyte disturbances
myocardial ischemia (mainly in humans)
What is the flow of normal electrical impulses in the heart
starts at SA node→AV node→Bundle of His→L & R bundle branches and lastly to the Purkinje fibers
what are the different parts of an ECG and what do they represent
SA node fires sending signal to atria to contract, that gives the P wave
then the signal continues through AV node, bundle of His, bundle branches & Purkinje fiber and the QRS complex starts representing ventricular depolarization (which should in turn lead to ventricular contraction)
then when the ventricles repolarize the T wave appears
and the cycle starts again
Name this part of ECG
P wave
Name this part of ECG segment
R-R interval
Name this part of ECG segment
R wave
Name this part of ECG segment
ST segment
Name this part of ECG segment
S wave
Name this part of ECG segment
QRS wave
where do you put the leads for an regular ECG on a dog
with animal in R lateral position on non metallic surface
white lead on right elbow
black lead on left elbow
red lead on left stifle
green lead on right stifle
where do you put ECG leads on horse
White at base of neck cranial to shoulder on R side
Red on left stifle
Black on PMI of apical beat on L chest
Use Lead I to record
what is normal speed of ECG
what is voltage of 1 small box on ECG strip
what is voltage of 2 big boxes on ECG strip
50mm/sec → 1mm = 0.02sec
1 mm = 0.1mV
1 cm = 1 mV
what are some artifacts that can interfere with ECG interp
60 Hz electrical interference
Motion
Purring
What type of artifact is seen here
60 Hz
What artifact is seen here
purring
What artifact is seen here
muscle tremors/motion
what are the steps in interpreting and ECG
- determine if artifacts present
- figure heart rate
- assess atrial size
- assess ventricular size
- assess ST segment
- asses QT segment
- assess T wave
Measuring complexes & intervals, why
differences from normal range can indicate where the abnormality lies
what are we looking for when we look at P wave
why
whether it is too tall or wide or both
gives an idea of atrial size
what are the mnemonics for P wave
P pulmonlale = peak (think pulmonary valve → R atria)
P mitrale = mound (think mitral valve → L atria)
what is considered normal for P wave
no taller than 0.3 mV (3 boxes)
no wider than 0.04 sec (2 boxes)
what does this ECG indicate
L atrial enlargement
what does this ECG indicate
Right atrial enlargement
How can you see ventricular enlargement on ECG
R wave that is greater than 3.0 mV (3.5 in giant breed dogs)
measured from baseline
Is it possible to see RV enlargement on ECG
Not really since the greater muscle mass of LV shows the most electrical activity (is most prominent), it hides the electrical impulses of the RV
LV enlargement detected?
YES! counting from baseline R wave is 3.5 mV tall
LV enlargement detected in a cat?
What could it be caused by?
YES! When measured the R wave is greater than 0.9 mV!
Hypertrophic Cardiomyopathy (HCM)
What may indicate RV hypertrophy in a dog?
Most common cause?
Deep S wave in lead II (>3.5mm)
Heartworms
What is R bundle branch block (RBBB)?
There is a lesion along the right bundle branch which prevents normal conduction down to the right ventricle. As a result, the left ventricle depolarizes normally and then its wave of depolarization spreads to the right ventricle. Therefore, the depolarization of the ventricles during bundle branch block takes longer to occur, resulting in wider QRS complexes.
What does ECG look like for RBBB?
Supraventricular origin
Wide/bizzare QRS complexes:
wider than normal QRS
reduced R wave
deep S wave
What is L bundle branch block (LBBB)?
During Left Bundle Branch Block there is a lesion along the left bundle branch which prevents normal conduction down to the left ventricle. As a result, the right ventricle depolarizes normally and then its wave of depolarization spreads to the left ventricle. Therefore, the depolarization of the ventricles during bundle branch block takes longer to occur, resulting in wider QRS complexes.
What does ECG look like for LBBB?
Is the CO affected?
Can you hear other names for this?
Wide QRS
Normal R wave height
No, normal CO
Yes, Block or VPDs
What is a VPD
and what is it exactly
Ventricular Premature Depolarization
new term for VPC (Ventricular Premature Contraction)
it is when the ventricles depolarize/contract before getting a signal from the normal channels
usually the heart rate with VPDs is slower due to speed of conduction of self generated signal vs normal route (SA→AV etc)
What is a low voltage complex?
When the QRS complex is shorter than normal, meaning there is not a lot of muscle contraction going on
R wave = 1.0-1.5 mV
What conditions can cause low voltage complexes?
obesity
pleural effusion
pericardial effusion
pneumothorax
hypothyroidism
diffuse myocardial dz
where does the normal ST segment lie in relation to the baseline of ECG?
What does ST segment depression indicate?
Should be the same position as PR interval but, can vary up to 2 mm below baseline or 1.5 mm above and still be normal range
Myocardial hypoxia
What is normal QT segment?
Where is it measured?
What happens if it’s to long? (Why?)
7.5-12.5 boxes
From beginning of QRS to end of T wave
Can indicate electrolyte disturbances, be sure to check potassium, calcium (since the QRS is depolarization of ventricles & T is repolarization it make sense because muscle contraction is regulated by potassium & calcium for nerve impulse speed!)
What drug is known to prolong QT interval?
Is this good (expected/normal)?
Digoxin
Yes, for certain heart conditions it is the tx of choice!
What is the only rule we have regarding T wave morphology
That it shouldn’t be too big!
Normal is considered < ¼ R wave height or 0.3 mV
it can be a negative deflection also, as long as it’s consistent throughout ECG. (if negative it cant change its mind and become positive!)
