Physiological Basis Of ECG

Question 1

How is an Electrocardiogram set up?

Answer 1

9 electrodes (12 readings) placed on skin surface at various location on torso

Question 2

What does the ECG record?

Answer 2

Voltage difference b/w itself and another electrode

(Differences in region of either the ventricles or the atria)

Measures EXTRA-cellular potential

Question 3

What does the ECG illustrate?

Answer 3

Changes in electrical activity of the cardiac msucle tissue

Question 4

When will deflection occur on the ECG trace?

Answer 4

When

1. Part of cardiac excitable tissue is at different membrane potential than rest of heart
2. Current flow can occur b/w those regions

Question 5

What are the standard limb leads?

Answer 5

1-3

Question 6

Where is lead 1?

Answer 6

RA to LA

Looks at heart from L to R

Question 7

Where is lead 2?

Answer 7

RA to LL

Question 8

Where is lead 3?

Answer 8

La to LL

Question 9

Where is aVF?

Answer 9

At foot

(RA + LA) to LL

Question 10

Where is aVR?

Answer 10

Right arm

(LL + LA) to RA

Question 11

Where is aVL?

Answer 11

left arm

(LL+RA) to LA

Question 12

What does a positive tracing deflection show?

Answer 12

Depolarization going toward apex

Question 13

What does a negative tracing deflection show?

Answer 13

Depolarization going toward base

Question 14

What phase does the P wave coordinate w/ ?

Answer 14

Phase 0 in atrial muscle (depolarization of atria)

Question 15

What phase does the QRS complex coordinate w/?

Answer 15

Phase 0 (depolarization) in ventricular muscle

Question 16

What does an elevation in the ST segment show?

Answer 16

Injury, infarction

Question 17

What does a depression in ST segment show?

Answer 17

Ischemia

Question 18

What does the ST segment represent?

Answer 18

All cells are depolarized

Time b/w Ventricular DEpolarization and REpolarization

Question 19

What phase does the T-wave coordinate w/ ?

Answer 19

Phase 3 (repolarization) in Ventricular m.

Question 20

What does the QT segment represent?

Answer 20

When all Ventricular myocytes are depolarized

Question 21

What is a “segment” on an ECG?

Answer 21

Duration of a single event

Question 22

What is an “interval” on the ECG?

Answer 22

Duration of 2 or more events

Question 23

What do 5 large boxes horizontally on the ECG represent?

Answer 23

1 sec

Question 24

What do 2 large boxes VERTICALLY on the ECG represent?

Answer 24

1.0 mV

Question 25

What is the usual length of the PR interval?

Answer 25

Usually 0.16 sec

Question 26

What are the chest/precordial leads assigned to?

Are they positive or negative?

Answer 26

Assigned to regions of the heart

Positive electrodes

Question 27

What are the leads in the Inferior regions?

Answer 27

2, 3, aVF

Question 28

What are the leads in the Septal region?

Answer 28

V1 & V2

Question 29

What are the leads in the anterior region ?

Answer 29

V2, V3, V4

Question 30

What are the leads in the Lateral region?

Answer 30

V4, V5, V6, 1 and aVL

Question 31

What does a prolonged PR interval indicate?

Answer 31

First degree AV block

Question 32

How long is a normal QT interval?

Answer 32

0.35 ms

Question 33

What is the Mean electrical axis showing?

Answer 33

Average direction of spreading AP in ventricles

Question 34

How do you estimate the Mean Electrical axis?

Answer 34

Uses average amplitude of QRS in leads 1 and aVF

Question 35

What can shift the mean electric Le axis?

Answer 35

Hypertrophy
MI
Physical heart placement
Bundle branch blocks

Question 36

What does a RIght Axis Deviation indicate?

Answer 36

Right ventricle hypertrophy

Question 37

What does a LEft Axis Deviation indicate?

Answer 37

Left ventricle hypertrophy

Question 38

What does the PR interval represent?

Answer 38

AV node delayed signal from SA