ECG Basics

Question 1

Rate =

Answer 1

300/N large squares in one R-R interval
OR
N QRS complexes on rhythm strip x6

Question 2

1 small square =

Answer 2

0.04 seconds

Question 3

1 large square =

Answer 3

0.2 seconds

Question 4

1 second =

Answer 4

5 big squares

Question 5

Normal QRS =

Answer 5

3 small squares (<0.12 seconds)

Question 6

Normal P-R interval

Answer 6

3 to 5 small squares (0.12 to 0.20 seconds)

Question 7

Normal QTc interval

Answer 7

<0.44 seconds in men (11 small squares)
<0.47 seconds in women (11-12 small squares)

Question 8

Left axis deviation:

Answer 8

Look at leads I + II
Left axis deviation = R waves leaving each other

Question 9

Right axis deviation:

Answer 9

Look at leads I + II
Right axis deviation. = R waves reaching towards each other

Question 10

What is poor R wave progression?

Answer 10

R wave should be small in V1 and get progressively larger through to V6.
An R wave that remains small/doesn’t grow in V3 and V4 = ‘poor R wave progression’
A dominant/large R wave in V1 might indicate RBBB

Question 11

What does a NEW LBBB with ACS symptoms indicate?

Answer 11

STEMI with proximal LAD occlusion

Question 12

Signs of LBBB on ECG: (2 important/obvious + 3 others)

Answer 12

“WiLLiaM”
1. W shape in V1
2. M shape in V6
3. Broad QRS (delayed overall conduction time to LV)
4. Tall R waves in lateral leads
5. Deep S waves in right precordial leads (V1-V3)

Question 13

Signs of RBBB on ECG: (2 obvious + 2 others)

Answer 13

“MaRRoW”
1. M shaped complexes in V1
2. W shaped complexes in V6
3. Wide slurred S wave in lateral leads (I, aVL, V5-V6)
4. Broad QRS

Question 14

Inferior leads:

Answer 14

II, III, aVF

Question 15

Lateral leads:

Answer 15

I, aVL, V5, V6

Question 16

Anterior leads

Answer 16

V1, V2, V3, V4

Question 17

Second degree heart block: Mobitz I

Answer 17

AKA Wenckebach
Progressive prolongation of the PR interval until a P wave occurs without a resulting QRS complex

Question 18

Second degree heart block: Mobitz type II

Answer 18

Constant PR interval but some P waves are not conducted (i.e. followed by a QRS.
Increased risk of progression to complete AV block + asystole

Question 19

2:1 AV Block

Answer 19

Only alternate waves are followed by a QRS
Can be due to type I or II 2nd degree heart block

Question 20

Third degree heart block

Answer 20

No relationship between P and QRS complexes

Question 21

What is an escape rhythm?

Answer 21

If the normal cardiac pacemaker (SA node) fails or operates abnormally slowly, cardiac depolarisation may be initiated from a subsidary pacemaker in the atrial myocardium, AV node conducting fibres or ventricular myocardium.
These pacemaker cells are found at various sites throughout the conducting system, with each site capable to independently sustaining a heart rhythm.
Under normal circumstances subsidiary pacemakers are supressed by the more rapid impulses from above (i.e. sinus rhythm). Junctional and ventricular escape rhythms arise when the rate of the supra-ventricular impulses arriving at the AV node or ventricle in less than the intrinsic rate of the ectopic pacemaker.

Question 22

What is an agonal rhythm?

Answer 22

Occurs in dying patients, often seen in the later stages of an unsuccessful resuscitation.
Characteristics: slow, irregular, wide ventricular complexes, often varying in morphology.
Unlikely to produce a pulse

Question 23

Characteristics of AF: (4)

Answer 23

Tachycardic
Irregularly irregular
No p waves
Narrow QRS

Question 24

Define the following:
- Recurrent AF
- Paroxysmal AF
- Persistent AF

Answer 24

Recurrent = more than 2 episodes
Paroxysmal = self-terminating episode lasting <7 days
Persistent = not self-terminating, duration >7 days

Question 25

First line tx in AF:

Answer 25

Rate control monotherapy with a beta-blocker or CCB

Question 26

When might you use digoxin monotherapy in AF?

Answer 26

If the patient does very litte/no exercise or other rate limiting drugs are ruled out due to co-morbidities/personal preference

Question 27

Second line AF tx:

Answer 27

Dual therapy with any two of: beta-blocker, diltiazem or digoxin

Question 28

What is wolff-parkinson white?

Answer 28

The presence of a congenital accessory pathway and episodes of tachyarrhythmias.
Associated with a small risk of sudden cardiac death.

Question 29

ECG features of wolff-parkinson white: (3)

Answer 29

1. Sinus rhythm with a short PR interval (<3 small sqs)
2. Broad QRS with a slurred upstroke to the QRS complex (= delta wave)
3. Negative delta wave in aVL simulating Q waves of a lateral infarction (referred to as ‘pseudo-infarction’ pattern)

Question 30

Atrial flutter

Question 31

Monomorphic ventricular tachycardia:

Answer 31

Most common VT
Associated with MI

Question 32

Supra-ventricular tachycardia

Question 33

ECG changes seen in PE:

Answer 33

1. Sinus tachycardia (most common)
2. Complete or incomplete RBBB
3. Right ventricular strain pattern (TWI in V1-4 +/- II, III, aVF)
4. P pulmonale (peaked P wave in lead II)

Question 34

What is p pulmonale?

Answer 34

Peaked P wave in lead II (>2.5mm)
Sign of right atrial enlargement, sometimes seen in a PE

Question 35

What is right ventricular strain pattern?

Answer 35

TWI in right precordial leads (V1-4) +/- inferior leads (II, III, aVF).
Associated with high pulmonary artery pressures in PE.

Question 36

6 stage approach:

Answer 36

1. Is there any electrical activity?
2. What is the ventricular rate?
3. Is the QRS rhythm regular or irregular?
4. Is the QRS narrow or broad?
5. Is there atrial activity present?
6. Is the atrial activty related to the ventricular activity and if so, how?

Question 37

Ventricular tachycardia - 3 ECG features:

Answer 37

1. Regular
2. Broad QRS
3. Tachycardic
   Most commonly a re-entry VT

Question 38

Toursades de Pointes:
- 2 ECG features
- Causes (2)
- Tx

Answer 38

• Polymorphic VT, QRS complexes “twist” around the isoelectric line
• Most commonly caused by MI, can occur due to QT prolonging agents
• Wait for it to self-terminate, protect the cardiac membrane with IV Mg, rate control with isoprenaline, defibrillate if unstable

Question 39

Ventricular fibrillation:
- ECG features

Answer 39

No identifiable P waves, QRS complexes or T waves
Rate 150-500 bpm
Amplitude will decrease with duration (coarse -> fine VF)
Prolonged VF will degenerate into asystole

Question 40

What is electrical alternans?

Answer 40

Electrical alternans refers to a beat-to-beat variation in the QRS complex height, with alternating taller and shorter QRS complexes. It is thought to be due to the heart swinging backwards and forwards within a fluid-filled (in a pericardial effusion).