Electric activity of the heart.

Question 1

What spreads throught the tissues during depolirization and repolarization?

Answer 1

Electrical currents generated by the cardiac muscle.

Question 2

Electrical currents are conducted through?

Answer 2

The body fluids.

Question 3

How is the electrical activity measured?

Answer 3

A small portion reaches the body surface, detected by electrodes.

Question 4

What is the name of the record produced, when measuring theese electrical currents?

Answer 4

Electrocardiogram / ECG

Question 5

What is the method of ECG called?

Answer 5

Electrocardiography

Question 6

Various components of the ECG record can be correlated to?

Answer 6

Specific cardiac events.

Question 7

Bipolar limb leads?

Answer 7

I - RF to LF
II- RF to LH
III- LF to LH

Question 8

Unipolar limb leads?

Answer 8

aVR - RF
aVL- LF
aVF - LH

Question 9

What are chest leads?

Answer 9

They measure the cardiac electric potential at six different locations surrounding the heart (V1-V6)

Question 10

What are the aims for the electric activity of the heart exercise?

Answer 10

Application of leads
ECG- quiescent cond.
ECG- after exercise
Evaluation

Question 11

What is Einthoven’s triangle?

Answer 11

Einthoven’s triangle is an imaginary formation of three limb leads in a triangle used in electrocardiography, formed by the two shoulders and the pubis.

Question 12

Why and how is ECG an important tool?

Answer 12

The heart must sustain a regular cycle of relaxation and contraction if it is to fulfill its objective. This regularity is predicated on a series of complex electrophysiological events within the cardiac tissues that can be monitored using a electrocardiogram.

Question 13

Experimental design - 2 ways of measuring ECG?

Answer 13

Mains-independent system

Conventional ECG measurement

Question 14

3 basic distinct waveforms in ECG?

Answer 14

P wave - atrial depolarisation (systola, started by SA- node)
QRS complex - ventricular depolarization (systola by AV-node) and repolarization & diastola of atria.
T wave - ventricular repolarization (diastola)

Question 15

Y axis of ECG?

Answer 15

Voltage, electric potential (mV)

Question 16

X axis of ECG?

Answer 16

Time (s)

Question 17

Formula for frequency of heart activity?

Answer 17

T= R1-R2 [s]
R1-R2 = 45mm –> set point = 25 mm/s
45mm/25 mm/s = 1,8 s

Question 18

Which three electrode locations form the Einthoven’s triangle?

Answer 18

right arm, left arm, left foot

Question 19

What lies in centre of Einthovens triangle?

Answer 19

Heart

Question 20

Which leads can the vector be calculated from?

Answer 20

Any two limb leeds

Question 21

What does the third lead correspond to?

Answer 21

The vector

Question 22

What does the recording of the vector movement during cardiac cycle form?

Answer 22

Three loops –> vectocardiogram

Question 23

What is cardiac vector?

Answer 23

The vector at the maximal deflexion of QRS complex –> electrical axis of the heart

Question 24

What does ECG represent?

Answer 24

a record of the electrical activity conducted in the body fluids from the cardiac impulses that reaches the body surface (not direct heart activity)

Question 25

What does the ECG display?

Answer 25

The sum of all electrical activity in all the cardiac muscle cells.

Question 26

Why are the results expressed as voltage in mV?

Answer 26

Because it does not represent the actual potential, but comparison at two different points on body surface.

Question 27

1 mV =

Answer 27

10-3 V = 0.001 V

Question 28

What is masked by the QRS complex?

Answer 28

Atrial repolarization, occurs simultaneously with ventricular depolarization.

Question 29

Why is the P wave smaller than the QRS complex?

Answer 29

atria have smaller muscle mass then the ventricles and generate less electrical activity.

Question 30

AV- nodal delay?

Answer 30

current is flowing throughthe AV node but magnitude is too small to be detected by ECG , RP segment

Question 31

Plateu phase

Answer 31

Ventricles are completely depolarized and the cardiac cells undergo plateau (refractory period), ST segment

Question 32

Rest and filling phase?

Answer 32

heart muscle is completely at rest and ventricular filling is taking place. TP interval

Question 33

If no current is detected and the ECG remains at baseline indicates the following?

Answer 33

RP segment
ST segment
TP interval

Question 34

Inotropic effects?

Answer 34

change the strength of the contraction of the heart muscle

Question 35

Chronothropic effect?

Answer 35

change the heart rate

Question 36

Dromotropic effect?

Answer 36

change amount of time it takes for the heart to complete one beat

Question 37

Bathmotropic effect?

Answer 37

influence the excitability of the cardiac muscle.

Question 38

Sympathetic influence on the heart?

Answer 38

Innervation of both atrii and ventriculi
Positive chronotrophy in atrium
Positive inotrophy in ventricles
Noradrenaline, activation of adrenergic receptors

Question 39

Parasympathetic influence on the heart?

Answer 39

SA -node, negative chronotrophy
AV-nodes, negative dromotrophy
Acetylcholine –> activation of K+ channels

Question 40

Humoral stimulation of the heart?

Answer 40

Noradrenaline - sympathetic effects
Acetylcholine - parasympathetic effects
Glucagon - positive inotropic and chronotropic effects
Prostaglandin E2 - positive inotropic effect
Insulin - positive dromotropic and bathmotropic effect
Progesterone - negative ino, chrono and bathmotropic effects.