17 Interpretation of ECG

Question 1

What is a normal sinus rhythm?

Answer 1

60-100 beats /min

RR interval 3-5 large boxes

Question 2

What is sinus bradycardia?

Answer 2

a slow sinus rhythm; <60/min

(RR interval >5 large boxes).

Question 3

What is sinus tachycardia?

Answer 3

a fast sinus rhythm; >100/min

RR interval <3 large boxes

Question 4

What is sinus arrhythmia?

Answer 4

an irregular sinus rhythm; difference between the longest and the shortest PP or RR interval is more than 0.16 s (equivalent to 4 small boxes)]

Question 5

First method to measure heart rate is by using the RR interval.
How can we obtain the heart rate?

Answer 5

60/ (number of small boxes x 0.04 )

Question 6

How to derive heart beat by the rule of 300?

Answer 6

Count the number of large boxes between RR intervals and divide it by 300.

e.g. 4 large boxes between 2 RR intervals > 300/4 = 75 beats /min

Question 7

What is the triplicate method?

Answer 7

Use the heart rate ruler

and sample 3 consecutive RR intervals

Question 8

What is the 6 second count method?

Answer 8

every 15 large boxes = 3 seconds

30 large boxes = 6 seconds

number of RR intervals in 30 large boxes x 6

Question 9

How to identify Premature contraction in ECG?

can be ventricular

Answer 9

no P wave/

wider than normal QRS complex

Question 10

How to identify escape beats in ECG?

Answer 10

T wave is shown late

Question 11

What is the definition of 1st degree atrioventricular or heart block?

What can be seen in the ECG?

Answer 11

lengthening of PR interval

normal = 0.08-0.12s within a large box!

Question 12

What is the definition of 2nd degree atrioventricular or heart block?

What can be seen in the ECG?

Answer 12

Intermittent failure of excitation to pass from atria to ventricles

• long PR intervals, disappeared QRS sometimes

Question 13

What is the definition of 3rd degree atrioventricular or heart block?

What can be seen in the ECG?

Answer 13

Atria and ventricles beat independently

no relationship between P waves and QRS complexes, QRS rate is slower than P rate.

Question 14

How can a bundle branch block/ aberrant pathway be identified on ECG?

Answer 14

QRS > 0.1s

Question 15

What is the difference on the ECG of right and left bundle branch block?

Answer 15

right: QRS complex with Bunny ears in V1, V2 leads
left: QRS complex with bunny ears in lead1, V6, and sometimes V1 and V2

Question 16

____ is defined as additional deflection with inverse

polarity, within the Q, R or S wave of the QRS complex..

Answer 16

Notching

> inverted bunny ears

Question 17

_____ is a “slight notching”

without change of polarity.

Answer 17

Slurring

> bunny ears

Question 18

Other than bundle branch block and aberrant pathway of conduction, what else is a possible cause to lengthened QRS complex? > 0.12s

(normal = 0.08-0.12s)

Answer 18

Ventricular hypertrophy

Delay intrinsicoid
deflection means it takes longer time for R
wave to reach its peak as it requires more
time to spread the depolarization through the
thickened ventricular wall.

Question 19

The cardiac/ QRS axis indicates the direction
of the mean ventricular depolarization vector
in the frontal (vertical)
plane when averaged over time.

What is the normal range of cardiac axis?

Answer 19

0 degree starts at 3 oclock > clockwise

-29 - +90 degrees

lower half positive
upper half negative

Question 20

What does it mean by right and left axis deviation?

Answer 20

right: > +90 degrees
left: < -30 degrees

Question 21

What factors will affect the cardiac axis?

A. Age
B. Gender
C. Body position 
D. Position of diaphragm (e.g. pregnancy, obesity)
E. Anatomical position of heart
F. Hypertrophy

Answer 21

All except B

C: Cardiac axis must be determined in supinated position

Question 22

How can cardiac axis be determined? (using which leads?)

Answer 22

using ANY TWO of the Lead I, II and III.

with larger QRS complex

e.g. Lead I:
R = +16; Q=-2.5
Sum = +13.5 > draw perpendicular line at lead I

Question 23

A simple way of estimating the electrical axis of the heart is to divide into four quadrants and consider
the positivity and negativity of only ____ and _____.

Answer 23

Lead I and Lead aVF

normal: ++
right axis deviation: -+
left axis deviation: +-
Extreme right axis deviation: –

Question 24

Rotation of heart: normal should be V3 is the transition zone.
QRS complex can be seen clearly from V3 leads onwards.

If QRS complex can be seen already in V2/ earlier than V3, what does it mean?

Answer 24

Shift to the right.

Counterclockwise rotation

Question 25

If QRS complex appears in leads from V4 onwards, what does it mean?

Answer 25

Shift to the left

Clockwise rotation.

Question 26

Where should the 6 chest leads be put?

Answer 26

V1 4th intercostal space at right
border of sternum
V2 4th intercostal space at left
border of sternum
V4 5th intercostal space in left
mid-clavicular line
V3 Midway between V2 and V4
V6 Same level as V4 in midaxillary
line
V5 Midway between V4 and V6,
in anterior axillary line