Unit 1: CV System Part E

Question 1

How can electrical activity in the heart be measured?

Answer 1

t can be measured using electrodes placed on the surface of the skin

Question 2

At least ___ electrodes are required, placed in a triangular formation (___________) on the arms and legs (6-12 electrodes are typically used in clinical practice).

Answer 2

3

Einthoven’s triangle

Question 3

What does an electrocardiogram show?

Answer 3

the summed electrical activity generated by ALL of the cells in the heart during the cardiac cycle

Question 4

Electrocardiogram (ECG) is NOT the same as what? Explain why

Answer 4

an action potential

ECG is an EXTRAcellular recording that represents the SUM of MULTIPLE APs taking place in MANY heart muscle cells

AP is 1 electrical event in a SINGLE cell, recorded using an INTRAcellular electrode

Question 5

The ECG tracing consists of _____ and ______ that correspond to electrical activity in the heart

Answer 5

WAVES

SEGMENTS

Question 6

Waves

Answer 6

go ABOVE or BELOW the baseline (reflect depol. or repol. of the atria & ventricles)

Question 7

Segments

Answer 7

sections of baseline b/t 2 waves

Question 8

What are the 6 waves/segments called in an ECG?

Answer 8

1. P wave
2. PR Segment
3. QRS Wave (Complex)
4. ST segment
5. T wave
6. TP segment

Question 9

P wave

Answer 9

atrial depolarization, quickly followed by atrial contraction

Question 10

PR Segment

Answer 10

– AV node delay.
- Atria finish contracting and emptying (pushing last 20% of blood into ventricles = active filling of ventricles).

Question 11

QRS Wave (Complex)

Answer 11

– Ventricular depolarization
- atrial repolarization also occurring, but it is hidden/covered up by the larger ventricular depolarization event).
- ventricular contraction begins

Question 12

ST segment

Answer 12

– All fibers in the ventricles are contracted, emptying continues until half-way through T wave

Question 13

T wave

Answer 13

Ventricular repolarization

Question 14

TP segment

Answer 14

atria and ventricles relaxed and passively filling (80% of blood enters ventricles through passive filling)

Question 15

tachycardia

Answer 15

Higher than 100 bpm at rest

Question 16

bradycardia

Answer 16

Lower than 60 bpm at rest

Question 17

What do ECG abnormalities result in?

Answer 17

result in arrythmias

Question 18

What are the different types of ECG abnormalities?

Answer 18

1. Heart Block
2. Ventricular fibrillation

Question 19

Heart Block

Answer 19

conduction through AV node is slowed
(AV node damage) and length of PR segment increases.

a. 1st Degree – all waves present, but PR segment (AV node delay) longer than normal.

b. 3rd Degree - complete blockage of signal from atria to ventricles, ventricles contract at AV bundle action potential rate of 30 APs/min. Results in asynchronous contraction and relaxation of atria and ventricles. Many P waves, fewer QRS waves. P waves not followed by QRS wave

Question 20

Ventricular fibrillation

Answer 20

heart muscle no longer depolarizing
synchronously, making coordinated pumping action impossible