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Flashcards in Intro to ECG Deck (17)
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1

What do the P, QRS and T waves correspond with in the cardiac cycle?

What does the PR segment represent?

P wave= atrial systole

P-R: time taken from SA node to AV node

QRS complex = ventricular systole

T wave= repolarisation

2

What do upward (positive) and downward (negative) deflections on an ECG represent?

 

Downward (negative): depolarisation wave away from electrode

Upward (positive): depolarisation wave towards electrode

The electrical signal generated by an action potential reduces as the distance to the recording lead increases. 

3

What does the signal amplitude represent?

Which ventricle normally predominates?

Represents myocardial mass (increased mass = more amplitude)

  • Signal amplitude will therefore change in conditions affecting muscle mass

Left ventricle normally predominates as it usually has a larger myocardial mass (represented by normal QRS axis of -30-90°)

 

4

What is the QRS axis?

How is it determined?

What is a normal QRS axis?

 

The measure of ventricular electrical activity in the vertical plane.

Determined by observing the QRS complex in leads I, II, III, AVF, AVR, AVL:

  • First look for lead whose deflections sum closest to 0 (equiphasic)
  • The main QRS axis will be at right angles to this
  • The dominant deflection in this lead (positive or negative) will indicate axis direction

Normal= -30-90°

 

5

What do leads I, II and III record?

What do leads AVF, AVR and AVL record?

I = difference in electrical potential between the right and left arms

II = difference in electrical potential between the right arm and left foot

III = difference in electrical potential between the left arm and left foot 

AVF = the difference between the combined electrical signal between the two arms and the left foot. 

AVR = the difference between the combined electrical signal between the left arm and left foot and right arm 

AVL = the difference between the combined electrical signal between the right arm and left foot and the left arm 

 

6

Where are the leads of a 12 lead ECG placed?

 

V1: 4th right intercostal space at sternal margin 

V2: 4th left intercostal space at sternal margin

V3: Midway between V2 and V4

V4: 5th intercostal space in mid-clavicular line

V5: left anterior-axillary line, same horizontal plane as V4.

V6: left mid-axillary line on same horizontal plane as V4 and V5

Red: right arm

Yellow: left arm

Green: left leg

Black: right leg 

7

What are 5 small squares equal to on an ECG?

1 small square: 0.04 seconds and 0.1 mV

5 small squares (1 large square): 0.2 seconds 

5 large squares: 1 second 

8

What is an indicator of sinus rhythm on an ecg?

p waves will be equidistant from regularly spaced QRS complexes 

9

How can you calculate the heart rate on a ECG?

300/ number of large squares between QRS complexes

10

What are some common ECG abnormalities caused by changes in muscle bulk? 

  • Hypertrophy due to hypertension or stenotic valves
  • Muscle destruction due to coronary artery disease or myocarditis

 

11

What are some common ECG abnormalities caused by electrical conduction?

  • Ischaemic damage to conduction system
  • Damage to sinus node
  • Abherrant foci of generation
  • Multiple foci of generation (atrial fibrillation)

12

What axis would indicate left axis deviation?

 

+90 - +180°

13

What axis would indicate right axid deviation?

-90 - 0°

14

What view of the heart do leads II, III and AVF represent?

What arteries are likely to be blocked if ST elevation is detected in these leads?

Inferior

Right Coronary Artery

15

What view of the heart do leads I, AVL, V5 and V6 give?

Lateral

16

What view of the heart do leads V1 and V2 give?

Septal

17

What view of the heart do leads V3 and V4 give?

Anterior