ECG part 2

Question 1

What are the 3 categories of arrhthmias?

Answer 1

1. Conduction abnormalities e.g. blocks
2. Abnormal impulse initiation e.g. ectopics, VT
3. Re-entry

Question 2

How does an ECG look like when there is a sinus arrest?

Answer 2

-No P waves or any associated QRS-T during sinus pause

Question 3

How does an ECG look like when there is a 1st degree AV block?

Answer 3

-PR interval is >0.2

Question 4

How does an ECG look like when there is a 2nd degree AV block?

Answer 4

-P waves may not be followed by a QRS complex

Question 5

How does an ECG look like when there is a 3rd degree AV block/complete AV block?

Answer 5

-P waves have constant P-P and R-R interval
-Lack of apparent relationship between the P waves and QRS complexes
-More P waves are present than QRS complexes

Question 6

What happens in an ECG in left bundle branch blcok?

Answer 6

-QRS duration > 120ms
-Dominant S wave in V1
-Broad monophasic R wave in lateral leads(I, aVL. V5-6)
-Absence of Q waves in lateral leads
-Prolonged R wave peak time > 60ms in leads V5-6

Question 7

What happens in an ECG in right bundle branch block?

Answer 7

-QRS duration > 120ms
-RSR’ pattern in V1-3(‘M-shaped’ QRS complex)
-Wide, slurred S wave in lateral leads(I, aVL, V5-6)

Question 8

When does early afterdepolarization occur and what can this lead to?

Answer 8

occur during late phase 2 or 3 and can lead to a salvo of several rapid
action potentials or a prolonged series of action potentials e.g. VT.

Question 9

When does delayed afterdepolarization occur?

Answer 9

occur in late phase 3 or early phase 4 when the action potential is
nearly or fully repolarised.

Question 10

What happens to ECG in ventricular ecptopic?

Answer 10

-Premature wide QRS with no preceding P wave
-Following and encompassing the QRS is a compensatory pause

Question 11

What is ventricular tachycardia?

Answer 11

Ventricular Tachycardia (VT) is a broad complex tachycardia originating in the ventricles

Question 12

What may VT cause and what does this consequently result in?

Answer 12

Ventricular tachycardia (VT) may impair cardiac output, consequently hypotension, collapse, and acute cardiac failure.

Question 13

What in ventricular fibrillation?

Answer 13

This rapid and irregular electrical activity renders the ventricles unable to contract in a synchronised manner,
resulting in immediate loss of cardiac output The heart is no longer an effective pump and is reduced to a quivering mess

Question 14

What is the most common sustained arrhythmia?

Answer 14

Atrial fibrillation (AF) is the most common sustained arrhythmia

Question 15

What is atrial fibrillation characterised by?

Answer 15

It is characterised by disorganised atrial
electrical activity and contraction.

Question 16

What does the ECG look like for atrial fibrillation?

Answer 16

 P wave – No distinct P waves - fibrillation waves (best seen in V1)
 R-R – Varying
 Fibrillatory waves may be present and can be either fine (amplitude < 0.5mm) or coarse (amplitude > 0.5mm)

Question 17

What is atrial flutter?

Answer 17

Atrial flutter is a form of supraventricular tachycardia caused by a re-entry circuit within the right atrium.

Question 18

What does atrial flutter look like on an ECG?

Answer 18

R-R – Irregular Ventricular rate depends on AV conduction ratio

Question 19

What is ST depression on an ECG caused by?

Answer 19

ST depression caused by injury potential difference

Question 20

What does myocardial ischaemia do to membrane potential in the heart?

Answer 20

Ischaemic myocytes have reduced
membrane potentials compared with
healthy myocytes.
The difference in potential between the
ischaemic region and healthy region
displaces the ST segment.
This is called the ‘injury current’ effect.

Question 21

What happens to ECG from ischaemia?

Answer 21

manifests ECG with ST
depression +/- T wave inversion; result from
altered repolarisation.

Question 22

What happens to ECG from injury?

Answer 22

ST segment elevation +/- loss
of R wave; ‘current of injury’

Question 23

What happens to ECG from infarction?

Answer 23

deep Q waves (>0.06 sec /
> 25% R wave) resulting from absence of
depolarisation current from dead tissue
(transmural). Manifests receding currents
from opposite side of heart as an ‘electrical
window’ is formed.

Question 24

What segments of an ECG indicate an injury in left circumflex artery?

Answer 24

1. I
2. V5
3. V6

Question 25

What segments of an ECG indicate an injury in right coronary artery?

Answer 25

1. II
2. III
3. aVF

Question 26

What segments of an ECG indicate an injury in left anterior descending artery?

Answer 26

1. V2
2. V3
3. V4