Electrocardiography of the Dog and Cat

Question 1

action potential

Answer 1

membrane potential across individual cardiac cells
consists of:
- resting membrane potential
- depolarization
- repolarization

Question 2

cardiac dipole

Answer 2

• electrical field generated by wave of depolarization or repolarization
• changes with time
• duration, magnitude and direction in space

Question 3

how are small animal ECGs recorded?

Answer 3

right lateral recumbency
4 limb electrodes and 6 precordial electrodes

Question 4

an electrocardiogram is a recording of

Answer 4

amplitude of the cardiac dipole vs time
time: x axis, sec
amplitude: y axis, mV

Question 5

P wave

Answer 5

atrial depolarization

Question 6

QRS complex

Answer 6

ventricular depolarization
very thin, quick spike

Question 7

T wave

Answer 7

ventricular repolarization

Question 8

what are the bipolar limb leads?

Answer 8

leads 1, 2, 3
frontal plane

Question 9

lead 1

Answer 9

comparing 2 forelimb leads

Question 10

einthoven’s triangle

Answer 10

looking at exact same electrical events from 3 different angles
bipolar limb leads

Question 11

what lead do we usually go straight to in vetmed?

Answer 11

lead 2: gives biggest wave/angle

Question 12

augmented limb leads

Answer 12

aVR, aVL, aVF
take 2 leads and compare them to a third

Question 13

6 lead ECG

Answer 13

• lead 2: axis of normal depolarization
• lead aVF: superior (-) to inferior (+)
• lead 1: right (-) to left (+)

Question 14

what are the inferior leads?

Answer 14

2, 3, aVF: these are positive
compatible with sinus origin if they are +
if negative, something is wrong!

Question 15

what are the negative leads?

Answer 15

aVR, aVL

Question 16

lead 1

Answer 16

positive or biphasic

Question 17

what is the recording speed of an ECG (we use Lead 2)

Answer 17

• 25 mm/sec
• 50 mm/sec

Question 18

what is the voltage calibration of an ECG (we use lead 2)

Answer 18

• 1/2 x - 5mm/mV
• 1 x - 10 mm/mV (standard)
• 2 x - 20 mm/mV

Question 19

ECG recording paper

Answer 19

small box: 1 mm
heavy box: 5 mm

standard calibration: 10 mm/mV
paper speed: 25mm/sec

Question 20

a tall P wave indicates

Answer 20

• P pulmonale
• right atrial dilation

Question 21

a wide P wave indicates

Answer 21

• P mitrale
• left atrial dilation

Question 22

how long is a normal P-Q interval? (sinus node into ventricles; ie what is the delay of the AV node)

Answer 22

dog: 0.06 to 0.13 sec
cat: 0.05 to 0.09 sec

Question 23

what is first degree atrioventricular block?

Answer 23

prolonged P-Q interval

Question 24

a prolonged P-Q wave indicates

Answer 24

first degree AV block
AV node slowing impulse more than it should: high vagal tone or the AV node is abnormal = higher degrees of block

Question 25

a tall R wave in lead 2 is compatible with

Answer 25

left ventricular enlargement > 2.5 mV vector got bigger, so deflection on lead 2 became higher

Question 26

what are the 2 reasons that you can have a widened QRS complex?

Answer 26

1. most common: ventricular in origin: impulse that originates in ventricle doesn't use the HIs purkinje: it travelsa s a uniform wave across the heart. takes time and travels in single direction. the impulse will be wide and have a tall T wave of opposite polarity because it is traveling in exactly the same direction, but is repolarization 2. supraventricular origin with abnormal conduction: can be + or - depending on if it is the R or L bundle that got blocked

Question 27

if your QRS is narrow

Answer 27

then the origin started ABOVE the AV node

Question 28

if the QRS is wide

Answer 28

maybe it came from ventricle, OR it came from above the AV node and was conducted abnormally

Question 29

what are the numbers for wide QRS complexes in dogs and cats

Answer 29

dogs: > 70ms cats: > 40ms