ECG: Identifying some basic disturbances of rhythm

Question 1

What heart rate is considered bradycardia and tachycardia?

Answer 1

Bradycardia = < 60 bpm
Tachycardia = > 100 bpm

Question 2

What is the difference between segments and intervals?

Answer 2

Segments are isoelectric (straight) regions between two waveforms.
Interval is the time between the start of one wave and the start of the next.

Question 3

What is the sweep speed of ECG?

Answer 3

25 mm/s

Question 4

How wide is a small square and a large square and what time interval does that represent?

Answer 4

Small Square = 40ms (1 mm)

Large Square = 200ms (5 mm)

Question 5

What’s the duration and amplitude of a normal P wave?

Answer 5

Duration = < 110ms
Amplitude = < 2.5 mm (0.25 mV)

Question 6

What is the duration of a normal PR interval?

Answer 6

120 - 200 ms (1 large square)

Question 7

What is the duration and amplitude of a normal QRS complex?

Answer 7

Duration = < 120 ms
Amplitude = < 25 mm (2.5mV)

Question 8

What is the normal range for the cardiac axis?

Answer 8

-30 to + 90

Question 9

What is the duration and amplitude of a normal Q wave?

Answer 9

Duration = < 40 ms 
Amplitude = < 25% of the total QRS complex

Question 10

What is the duration of a normal QT interval?

Answer 10

0.38-0.42 ms

Question 11

What does a QRS complex with a large amplitude indicate?

Answer 11

Ventricular Hypertrophy

Question 12

What are the ECG features of sinus tachycardia?

Answer 12

Normal waveforms
Abnormally fast resting heart rate
Atrial and Ventricular Rate = 200 bpm

Question 13

What are the ECG features of atrial fibrillation? Include atrial rate and ventricular rate in your answer.

Answer 13

ABSENT P WAVES (may get an oscillating baseline)
Irregular ventricular rhythm (duration between QRS varies)
Could be high or normal ventricular rate
QRS complexes are normal
Atrial Rate = 350-600 bpm
Ventricular rate = 100-180 bpm

Question 14

What are the ECG features of atrial flutter?

Answer 14

SAW-TOOTHED BASE LINE
No isoelectric line - shows constant atrial activity
Regular ventricular rhythm - one in every few atrial depolarisations will get conducted down to the ventricles
QRS normal + regular ventricular rhythm
Atrial Rate = 250-350 bpm
Ventricular Rate = 150 bpm (with 2:1)
4:1 is also common

Question 15

How is atrial fibrillation different to atrial flutter?

Answer 15

Atrial flutter has a regular ventricular rhythm

Question 16

What is atrioventricular nodal reentrant tachycardia?

Answer 16

When a local circuit is created within the AV node

Question 17

What is atrioventricular reentrant tachycardia?

Answer 17

Local circuit is within the atria and the ventricles

Question 18

What are the ECG features of AVNRT and AVRT?

Answer 18

Lots of QRS complexes
No clear P wave
QRS complexes are RAPID and IRREGULAR
You get simultaneous depolarisation of the atria and ventricles so you get instantaneous P wave and QRS complexes

Question 19

What happens in AVNRT?

Answer 19

Depolarisation is rotating within the AV node

Then it re-enters and causes simultaneous atrial and ventricular contraction

Question 20

What is preexcitation syndrome and what is a defining feature of the ECG?

Answer 20

Defining Feature = DELTA WAVES
Some people are born with a congenital connection between the atria and the ventricles called an ACCESSORY PATHWAY
This allows early depolarisation of the ventricles leading to slurring of the QRS complexes
This gives an abnormally short PR interval

Question 21

What syndrome causes preexcitation syndrome?

Answer 21

Wolff-Parkinson-White Syndrome

Question 22

What is the treatment to remove the accessory pathway?

Answer 22

Radio frequency ablation

Question 23

What are the three types of atrioventricular nodal block and how do they vary?

Broad QRS complexes that are VOID OF ANY PATTERN

Answer 23

1st degree = prolonged PR interval 
2nd degree (Mobitz type 1 and type 2) = some conduction gets there but it's slow 
3rd degree = complete heart block

Question 24

What is an ECG feature of grade 1 AVN block?

Answer 24

Prolonged PR interval

Question 25

What is the difference between Mobitz type 1 and Mobitz type 2 atrioventricular nodal block?

Answer 25

2nd degree block = some of the beats from the atria do NOT reach the ventricles
Mobitz type I = gradual prolongation of the PR interval culminating in a dropped beat
Mobitz type II = fixed PR interval and then a dropped beat (you do NOT see gradually prolonging of the PR interval)

Question 26

What is the ECG feature of 3rd degree atrioventricular nodal block?

Answer 26

There is NO conduction from atria to ventricles
ECG shows COMPLETE DISSOCIATION between QRS complexes and P waves
Ventricles fire on their own as a protective mechanism

Question 27

What is the main ECG feature of bundle branch blocks?

Answer 27

QRS complex WIDENS

It takes longer to depolarise the ventricles

Question 28

How do you distinguish between RBBB and LBBB?

Answer 28

WilliaM MarroW
RBBB = V1 + V2 = rabbit ears
LBBB = V1 + V2 = deep S waves

Question 29

What are the ECG features of ventricular tachyarrhythmia?

Answer 29

Rapid, regular, broad QRS complex pattern

Question 30

What are the ECG features of ventricular fibrillation?

Answer 30

Broad QRS complexes that are VOID OF ANY PATTERN

Question 31

What does the steepness of the ECG lines represent?

Answer 31

Velocity of action potential

Question 32

What does the sharpness of the ECG lines represent?

Answer 32

Rapid changes in direction of the action potential

Question 33

What is the name of the triangle used to describe the lead arrangement?

Answer 33

Einthoven’s Triangle

Question 34

Describe the positioning of each of the 3 leads

Answer 34

Rule of Ls
Lead 1 = Right arm to Left arm
Lead 2 = Right arm to Left Leg
Lead 3 = Left arm to Left Leg

Question 35

Describe the general positioning of the electrodes

Answer 35

There are 10 electrodes and 12 leads in total. 2 leads are artificial pathways.
V1-V6 are on the chest. V1 starts on in the right 4th intercostal space and work sideways downwards

Question 36

Which electrode is technically not useful other than for reference?

Answer 36

Right leg electrode

Question 37

Give the left and right mediated cardiac axis ranges

Answer 37

Left deviated = -90 –> -30
Right deviated = +90 –> +180
Normal deviation = -30 –> +90

Question 38

What does one small square generally represent on a ECG?

Answer 38

1 small square = 40 ms

1 small square = 0.1 mV

Question 39

What does the cardiac axis tell you?

Answer 39

MAIN DIRECTION OF VENTRICULAR DEPOLARISATION