(07)

Question 1

1. answer the question
2. what is threshold?
3. what is unique about phase 4? what does this give heart?
4. what allows for pacemaker potential?
5. why do we get slower phase four upstroke?

Answer 1

1. not as negative (maximum diastolic potential about -65 mV)

we don’t have resting membrane potential

phase 0 doesn’t go up as abruptly

2. around - 40 mV
3. spontaneous diastolic depolarization (‘pacemaker potential) - phase 4; its automaticity
4. less and less K leaks out - more positives acculumate in cell - membrane gets less negative - a few calcium channels activate - then upon activation get a lot of calcium coming in

Also (funny current) allow Na and K in

5. dependent on calcium and not sodium

Question 2

(Pacemaker action potential)

1. the sinus node is the normal pacemaker of the heart.. why?
2. Subsidiary pacemakers (latent pacemakers) are normally what?

Answer 2

1. sinus node cells have the fastest rate of diastolic depolarization
2. overdrive suppressed (takes them longer to reach threshold - these take over if SA node gets messed up)

Question 3

answer this

1. the ecg represents the summation of what?
2. what kind of APs will you be able to find on body surface?

Answer 3

yes

they are connected

1. summation of all cardiac APs through time as recorded on the body surface
2. ventricular and atrial muscle activation

Question 4

(Electrocardiography)

(Electrocardiogram (ECG, EKG)

1. what is it?
2. what on Y axis?
3. on X axis?
4. What does QRS complex represent?
5. What is T wave?
6. P wave?

Answer 4

1. average electrical potential through time
2. voltage (mV)
3. Time (sec)
4. summation of all the action potentials coming from ventricular muscle cells
5. repolarization of ventricular cells
6. electrical activation of atrial muscle cells (repolarization covered up by QRS)

(look at this diagram)

QRS waves don’t always look this way

Question 5

1. Which tissues depend on the slow current (action potentials)?

2 on fast?

Answer 5

1. sinus node, AV node
2. atria and ventricle and purkinje fibers

Question 6

top is outside of cell in upper left diagram

picture on the bottom right is in an instant of time as wave of depolarization sweeps through heart

from P1 see postive deflection

from P2 see negative deflection (weaker cause not head on)

from P3 (isoelectric - no net change in voltage)

Question 7

1. signals stronger closer to heart - get weaker once you get out to body’s surface
2. when we aligned with axis of dipole - we get the strongest defelctions - but if perpendicular - get zero

Question 8

(Concept: Lead Systems)

1. Bipolar lead: both electrodes influenced by what?
2. Unipolar lead: what is this?
3. What aoccurs in potential as move away from axis of the dipole?

Answer 8

1. dipole (ex: AB) will record positive 2 in B if B is the recording electrode - if A is recording you will get -2
2. 1 “expolring” electrode, 1 “indifferent” (ex: VA)
3. potential decreases

Question 9

understand what is going on here

Question 10

(Basic EKG concepts)

1. Cardiac dipole - represented as what? wave of what? has what two values?
2. Direction of the wave of activation (vector) moves what to what over time?
3. Cofiguration of the recorded tracing of that wave depends on what?
4. If the positive side of the vector (interface of dipoles/activation wave) is oriented toward the recording (+) electrode –> what kind of deflection?

Answer 10

1. a vector; activation; magnitude and direction
2. negative to positive
3. the location of our recording electrodes as compared to the depolarizing tissue
4. positive deflection (and vice versa)

Question 11

(Basic EKG concepts)

1. What orientation will deliver the greatest ampltiude trace?
2. What will give you an isoelectric trace?

Answer 11

1. orientation dircelty toward (o deggres) or away (180 o) from th erecording electrode
2. orientation an 90 degress to recrding lead axis

Question 12

(Ventricular Depolarization)

1. complex - several areas depolarized simulataneously and in differnt directions
2. what is the sum of all vectors at that instant called?
3. QRS represents what?
4. Sum of all QRS instantaneous vectors = ?

Answer 12

2. mean instantaneous vector (there is much…much cancellation)
3. a series of mean instantaneous vectors (the various QRS deflections reflect the changing direction and magnitude of the vectors)
4. mean QRS vector

Question 13

know this - R especially - remember that is by definition a positive deflection

can look very different from this