✅✅18 - Cardiac Muscle Contraction I

absolute refractory period (ARP)

No response to a stimulus

effective refractory period (ERP)

Period during which the membrane is not sufficiently repolarized and sodium channels have not completely recovered; non-conducted electrical response to a stimulus

relative refractory period (RRP)

-Requires a larger stimulus

-Conducted response to a stimulus

supernormal period (SNP)

-During which the threshold is lower than typically required to generate an AP

-Clinically referred to as R on T

Einthoven's triangle

base to apex lead

-Used for monitoring heart rhythm in large animals

-"Sees" V → D basilar activation well

-Normal QRS is negative

true

T/F - Every cell in the heart has its own AP

PQRST complex = sum of all APs in the heart

What are you measuring during an electrocardiogram?

P

The SA node and atrial muscle cells generate the _____ wave

no

Would we see electrical activity if we were only activating the SA node?

cow - more muscle mass is being electrically activated

Is the P wave bigger in a cat or cow? Why?

true

T/F - Half the time, you cant see a P wave in a cat

more; more; easier

The bigger the animal, the [more/less] tissue mass, the [more/less] electromotive force, and the [easier/harder] it is to record an electrocardiogram

sum total of every action potential in the heart, leading to a waveform pattern

What is a surface electrocardiogram based on?

atrial contraction/atrial electrical activation & contraction

The P wave is primarily associated with what?

ventricular activation & contraction

The QRS wave is primarily associated with what?

ventricular repolarization

The T wave is primarily associated with what?

U

If the muscle mass is great enough, you may see a _____ wave, which is Purkinje fiber repolarization

Purkinje fiber repolarization

The U wave is primarily associated with what?

reviewed

Review

Jimmy the dog

1st electrocardiogram taken to demonstrate its use

in most species, it is buried in the QRS complex

Why don't you see atrial repolarization on the ECG?

120

1000 milliseconds in 1 second

60,000 milliseconds in 1 minute

2 beats every second

If the RR interval is 500 milliseconds, what is the heart rate?

30

1000 milliseconds in 1 second

60,000 milliseconds in 1 minute

2 beats every second

If the RR interval is 2000 milliseconds, what is the heart rate?

towards the left leg

What is the direction the overall electrical motor force points to?

12

The best diagnostic electrocardiogram incorporates _____ leads

Holter (ambulatory) ECG

Placed under the skin to monitor heart rhythm at any time