ECG

Question 1

how many seconds are in a small square?

Answer 1

0.04 seconds or 40 milliseconds

Question 2

how many seconds are in a large square?

Answer 2

1 large square = 5 small squares. Therefore 1 large square = 0.2 seconds or 200 milliseconds

Question 3

how many mm is 1 small square?

Answer 3

1mm

Question 4

how can you calculate rhythm and rate?

Answer 4

regular vs irregular: if there is even amount of squares between each R wave, it is regular.

regular rhythm: count how many small squares in RR interval.
1. 60s/0.04s = 1500
2. 1500/(no. of small squares) = ___ bpm

irregular rhythm: 10s strip
1. count how many R waves x 6 = ___ bpm

Question 5

What are the steps of ECG interpretation?

Answer 5

1. Rate
2. Rhythm
3. P waves
4. PR Relationship
5. QRS
6. ST segment
7. T waves
8. Axis
9. R wave progression

Question 6

what are the different rhythms?

Answer 6

regular: RR intervals are consistent and evenly spaced

irregularly irregular: no consistent pattern to RR intervals

regularly irregular: irregularity with a recurring cycle or pattern to the irregularity

regular underlying rhythm with early beat: mostly regular RR intervals, interrupted by early QRS complexes (occasionally a premature (early) beat)

Question 7

what are the normal observations in P waves?

Answer 7

should be upright (inverted in lead aVR and sometimes biphasic in V1)

<0.12s
<2.5mm
should be all the same shape

Lead II, III, aVF, V1

Question 8

What is the relationship between P wave and QRS?

Answer 8

QRS after every P wave
0.12 - 0.2s

Question 9

what are the normal observations of QRS?

Answer 9

small, narrow Q waves
<0.10 - 0.12s
amplitude varies with leads

Question 10

what are the normal observations of ST segment?

Answer 10

There should be a flat isoeletric line
may be elevated 1-2mm in early chest leads

Question 11

Which leads are lateral, inferior and anterior?

Answer 11

lateral: I, aVL, V5, V6
inferior: II, III, aVF
anterior: V1-V2 (septal), V3-V4 (anterior)

Question 12

what are the normal observations of T waves?

Answer 12

upright (except in aVR and V1)

<5mm in limb leads (I, II, III, aVR, aVL, aVF)

<10mm in chest leads (V1-6)

Question 13

what direction should the cardiac axis be?

Answer 13

normal is between -30 and 90 degrees

quadrant method:
1. assess deflections of waves in lead I and aVF.
- if both are positive –> normal (normal, 0-90)
- if lead I is negative and aVF is positive –> right axis deviation (180-90)
- if lead I is positive and aVF is negative –> places the axis in upper left quadrant (possible left axis deviation, -90-0)
- If both leads are negative, this is indicative of extreme axis deviation

isoelectric method (more accurate):
1. identify the most isoeletric (biphasic) lead
- the axis line is perpendicular to the direction of the isoelectric lead
2. find the lead that runs nearest to the axis line.
- if the QRS complex is positive in that lead, the axis points to roughly the same direction as that lead, vice versa.

Question 14

what do deflections mean?

Answer 14

depolarisation towards a lead produces a positive deflection (upright).

depolarisation away from a lead produces a negative deflection (downward)

depolarisation moving at a 90 degree angle (↑ or ↓) produce an isoelectric or biphasic waves with positive and negative deflections of similar amplitude.

Question 15

What are the normal observations of R wave progression?

Answer 15

mostly negative in early chest leads

mostly positive in late chest leads

• switches around V3-4.