Unit 1 - CV System The Heart PART E

Question 1

Electrical activity in the heart can be measured using _______ placed on the surface of the skin.

Answer 1

ELECTRODES

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

Describe the different triangles/electrodes used in Einthoven’s triangle?

Answer 3

sides of triangles are #’ed to correspond with the 3 leads/leeds, or pairs of electrodes, used for recording

• recorded from 1 lead at a time
• 1 (+) WAVE GOES UP, 1 (-) WAVES GOES DOWN, 1 (inactive) electrodes

Question 4

____ electrodes are typically used in clinical practice

Answer 4

6-12

Question 5

What does an electrocardiogram show?

Answer 5

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

Question 6

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

Answer 6

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 7

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

Answer 7

WAVES

SEGMENTS

Question 8

Waves

Answer 8

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

Question 9

Segments

Answer 9

sections of baseline b/t 2 waves

Question 10

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

Answer 10

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

Question 11

1. P wave

Answer 11

atrial depolarization, quickly followed by atrial contraction

Question 12

2. PR Segment

Answer 12

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

Question 13

3. QRS Wave (Complex)

Answer 13

– Ventricular depolarization

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

Question 14

4. ST segment

Answer 14

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

Question 15

5. T wave

Answer 15

Ventricular repolarization

Question 16

6. TP segment

Answer 16

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

Question 17

What can you NOT tell about an ECG recording?

Answer 17

CANNOT tell if an ECG recording represents depol. or repol. by looking at the SHAPE of the waves relative to the baseline
Ex:
- P wave represents atrial depol.
- T wave represents ventricular repol.
BUT both are ABOVE the baseline in lead I

B/c REMEMBER that the direction of the ECG trace reflects ONLY the direction of the current flow relative to the axis of the lead

Question 18

What do ECG’s provide info on?

Answer 18

• heart rate & rhythm
• conduction velocity
• condition of tissues in the heart

Question 19

Interpretation of ECGs – questions to ask:

Answer 19

1. What is the heart rate? Is it within normal range (60-100 bpm)? Higher than 100 bpm at rest = TACHYCARDIA. Lower than 60 bpm at rest = BRADYCARDIA.
2. Is the rhythm regular?
3. Are all waves and segments present in a recognizable form?

Question 20

What do ECG Abnormalities result in?

Answer 20

result in arrythmias

Question 21

Arrythmias

Answer 21

electrical problems that arise during the generation or conduction of APs through the heart

• irregular rhythm
• resulting from a benign extra beat or more seriously perhaps, atrial fibrillation (where the SA node has lost control of the pacemaking)

Question 22

What are 2 different ECG abnormalities?

Answer 22

1. Heart Block

2. Ventricular fibrillation

Question 23

Heart Block

Answer 23

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

AKA APs from the SA node sometimes fail to be transmitted through the AV node on the ventricles
- therefore, 1 or more P waves may occur without initiating a QRS complex

Question 24

What are the 2 kinds of Heart Blocks?

Answer 24

1st degree

3rd degree

Question 25

1st Degree Heart Block

Answer 25

all waves present, but PR segment (AV node delay) longer than normal.

Question 26

3rd Degree Heart Block

Answer 26

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.

AKA the atria depolarize regularly at 1 pace while the ventricles contract at a much slower pace

Question 27

Ventricular fibrillation

Answer 27

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