Electrocardiography

Question 1

What does electrocardiography do

Answer 1

measures electrical activity in the heart

Question 2

What is an ECG used for

Answer 2

determine heart rate

conduction disturbances due to:

chamber enlargement

electrolyte disturbances

myocardial ischemia (mainly in humans)

Question 3

What is the flow of normal electrical impulses in the heart

Answer 3

starts at SA node→AV node→Bundle of His→L & R bundle branches and lastly to the Purkinje fibers

Question 4

what are the different parts of an ECG and what do they represent

Answer 4

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

Question 5

Name this part of ECG

Answer 5

P wave

Question 6

Name this part of ECG segment

Answer 6

R-R interval

Question 7

Name this part of ECG segment

Answer 7

R wave

Question 8

Name this part of ECG segment

Answer 8

ST segment

Question 9

Name this part of ECG segment

Answer 9

S wave

Question 10

Name this part of ECG segment

Answer 10

QRS wave

Question 11

where do you put the leads for an regular ECG on a dog

Answer 11

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

Question 12

where do you put ECG leads on horse

Answer 12

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

Question 13

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

Answer 13

50mm/sec → 1mm = 0.02sec

1 mm = 0.1mV

1 cm = 1 mV

Question 14

what are some artifacts that can interfere with ECG interp

Answer 14

60 Hz electrical interference

Motion

Purring

Question 15

What type of artifact is seen here

Answer 15

60 Hz

Question 16

What artifact is seen here

Answer 16

purring

Question 17

What artifact is seen here

Answer 17

muscle tremors/motion

Question 18

what are the steps in interpreting and ECG

Answer 18

1. determine if artifacts present
2. figure heart rate
3. assess atrial size
4. assess ventricular size
5. assess ST segment
6. asses QT segment
7. assess T wave

Question 19

Measuring complexes & intervals, why

Answer 19

differences from normal range can indicate where the abnormality lies

Question 20

what are we looking for when we look at P wave

why

Answer 20

whether it is too tall or wide or both

gives an idea of atrial size

Question 21

what are the mnemonics for P wave

Answer 21

P pulmonlale = peak (think pulmonary valve → R atria)

P mitrale = mound (think mitral valve → L atria)

Question 22

what is considered normal for P wave

Answer 22

no taller than 0.3 mV (3 boxes)

no wider than 0.04 sec (2 boxes)

Question 23

what does this ECG indicate

Answer 23

L atrial enlargement

Question 24

what does this ECG indicate

Answer 24

Right atrial enlargement

Question 25

How can you see ventricular enlargement on ECG

Answer 25

R wave that is greater than 3.0 mV (3.5 in giant breed dogs) measured from baseline

Question 26

Is it possible to see RV enlargement on ECG

Answer 26

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

Question 27

LV enlargement detected?

Answer 27

YES! counting from baseline R wave is 3.5 mV tall

Question 28

LV enlargement detected in a cat? What could it be caused by?

Answer 28

YES! When measured the R wave is greater than 0.9 mV! Hypertrophic Cardiomyopathy (HCM)

Question 29

What may indicate RV hypertrophy in a dog? Most common cause?

Answer 29

Deep S wave in lead II (\>3.5mm) Heartworms

Question 30

What is R bundle branch block (RBBB)?

Answer 30

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.

Question 31

What does ECG look like for RBBB?

Answer 31

Supraventricular origin Wide/bizzare QRS complexes: wider than normal QRS reduced R wave deep S wave

Question 32

What is L bundle branch block (LBBB)?

Answer 32

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.

Question 33

What does ECG look like for LBBB? Is the CO affected? Can you hear other names for this?

Answer 33

Wide QRS Normal R wave height No, normal CO Yes, Block or VPDs

Question 34

What is a VPD and what is it exactly

Answer 34

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)

Question 35

What is a low voltage complex?

Answer 35

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

Question 36

What conditions can cause low voltage complexes?

Answer 36

obesity pleural effusion pericardial effusion pneumothorax hypothyroidism diffuse myocardial dz

Question 37

where does the normal ST segment lie in relation to the baseline of ECG? What does ST segment depression indicate?

Answer 37

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

Question 38

What is normal QT segment? Where is it measured? What happens if it's to long? (Why?)

Answer 38

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!)

Question 39

What drug is known to prolong QT interval? Is this good (expected/normal)?

Answer 39

Digoxin Yes, for certain heart conditions it is the tx of choice!

Question 40

What is the only rule we have regarding T wave morphology

Answer 40

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!)