ECG- Recognising Common Abnormalities

Question 1

What are causes of abnormal rhythms? (2)

Answer 1

Abnormal impulse formation

Abnormal conduction (AV block)

Question 2

Where in the heart can rhythms arise from and what are they called?

Answer 2

SAN-supraventricular rhythms
Atrium- supraventricular rhythms
AV node- supraventricular rhythms
Ventricle- ventricular rhythms

Question 3

What are the features of supraventricular rhythms?

Answer 3

• conducted into and within ventricles by His-Purkinje system
• normal ventricular depolarisation
• normal (narrow QRS) complexes

Question 4

What are the features of a ventricular rhythm?

Answer 4

• from foci in ventricle
• conduction not via usual His-purkinje system
• depolarisation takes longer
• wide and bizarre QRS complex (different foci produce different shapes)

Question 5

What are the 3 types of ventricular rhythms?

Answer 5

Ventricular premature beats
Ventricular tachycardia
Ventricular fibrillation

Question 6

What is atrial fibrillations?

Answer 6

Random impulses causing chaotic depolarisation- cardiac cannot contract in a coordinated way

Question 7

What effect does atrial fibrillation have on CO?

Answer 7

It drops it slightly

Question 8

What is the ECG of atrial fibrillations?

Answer 8

No p waves just wavy baseline (atria quiver rather than contract)

Narrow QRS at irregular intervals

Question 9

What happens to the heart rate and pulse rate during atrial fibrillations?

Answer 9

They become irregularly irregular

Question 10

Why would blood thinners be given to those who have atrial fibrillations?

Answer 10

Clots can form in the striatum because there is static blood this can cause strokes etc

Question 11

What is AV conduction blocks?

Answer 11

Delay/failure of conduction of impulses from atrium to ventricles via AV node and bundle of His

Question 12

What are the two main causes of AV conduction block?

Answer 12

Acute MI - full recovery within a few days

Degenerative changes

Question 13

What are the 3 types of heart blood?

Answer 13

First degree block

Second degree heart block: type 1 and type 2

Third degree heart block (complete heart block)

Question 14

What happens in complete heart block?

Answer 14

A pacemaker in the ventricle will take over (ventricular escape rhythm)

Question 15

What is first degree heart block defined by?

Answer 15

Slow conduction in AV node and His Bundle

Normal P wave
Prolonged PR interval (>5 small squares)
Normal QRS

Question 16

What is type 1, 2nd degree heart block?

Answer 16

Progressive lengthening of PR interval until one P is not conducted (this allows time for AVN to recover) then cycle begins again

Question 17

What is type 2, 2nd degree heart block?

Answer 17

PR interval normal
Sudden non-conduction of a beat (dropped beat without warning- ie no QRS)

High risk of progression to complete heart block

Question 18

What is 3d degree heart block?

Answer 18

Atrial depolarisation normal but no impulses are conducted to ventricles

Ventricular pacemaker takes over-wide QRS (ventricular escape rhythm)

No relationship between the P and the QRS wave of an ECG

Question 19

What are the problems with 3rd degree heart block?

Answer 19

Heart rate is too slow- 30/40
Too slow to maintain BP and perfusion
Urgent pacemaker insertion required

Possible for someone to go into asystole

Question 20

What are the features of ventricular ectopic beats?

Answer 20

Impulses not spread via the His-purkinje system

Much slower depolarisation of ventricles

Wide QRS complex, different in shape to usual

Question 21

What is ventricular tachycardia?

Answer 21

Run of 3 or more consecutive ventricular ectopics

Broad complex tachycardia

Question 22

Why is persistence ventricular tachycardia so dangerous?

Answer 22

Because the person is at high risk of ventricular fibrillation

They will need to be electrically shocked back into rhythm

Question 23

What is ventricular fibrillation?

Answer 23

Abnormal, chaotic, fast, ventricular depolarisation

Caused by impulses form numerous ectopic site in ventricular muscle

No co-ordinated contraction causing ventricles to quiver

Question 24

What effect doe VF have on CO?

Answer 24

No cardiac output, cardiac arrest

Question 25

Ischameia and MIs can effect any part of the heart, how can you tell where the damage is?

Answer 25

Changes seen in leads facing affected area. Look at which ECG lead is abnormal

Question 26

What region of tissue in the heart is most vulnerable from lack of perfusion?

Answer 26

Sub-endocardial region

Question 27

What changes will you see in an ECG lead facing an area of ischaemic cardiac tissue?

Answer 27

ST segment depression Or T wave inversion Due to abnormal current during repolarisation *ischaemic ECG changes may only be seen during exercise but if severe reduction of lumen: ischaemic changes at rest

Question 28

What is STEMI?

Answer 28

ST segment elevation myocardial infarction Due to complete occlusion of lumen by thrombus Occurs when muscle injury extends 'full thickness' from endocardium to epicardium

Question 29

What defines a pathological Q wave?

Answer 29

Wider than 1 small square (longer than 0.04 seconds) Deeper than 2 small squares (Depth more than 1/4 of the height of the subsequent R wave

Question 30

What effect does hyperkalaemia have on the heart?

Answer 30

RMP less negative which inactivates some voltage gates Na+ channels - heart is less excitable

Question 31

What are the ECG changes seen with hyperkalaemia?

Answer 31

High T wave Prolonged PR interval, depressed ST segment P wave absent Ventricular fibrillation

Question 32

What ECG changes are seen in hypokalaemia?

Answer 32

Low T wave

Question 33

What is the cardiac axis?

Answer 33

The average direction of spread of ventricular depolarisation Usually Downwards and left (-30 to +90 degrees)

Question 34

What is left axis deviation?

Answer 34

When overall direction of ventricular depolarisation is upwards and to the left (less than -30 degrees)

Question 35

What is left axis deviation associated with?

Answer 35

Conduction block of anterior branch of left bundle Inferior MI Left ventricular hypertrophy

Question 36

What is right axis deviation?

Answer 36

When overall direction of ventricular depolarisation is downwards and to the right (more than +90 degrees)

Question 37

What is right axis deviation associated with?

Answer 37

Right ventricular hypertrophy

Question 38

How can you spot left axis deviation?

Answer 38

Look at leads I and aVF (or III) If QRS is upright in lead I an inverted in aVF (or in III), it is LAD

Question 39

How can you spot righ axis deviation?

Answer 39

Look at leads I and aVF/III If QRS is inverted in lead I and upright in lead III (aVF) then it is RAD

Question 40

In an ECG of complete heart block what its he relationship between the P waves and the QRS complex?

Answer 40

No relationship between them because the atria and ventricle are being stimulated by different pacemakers

Question 41

What might have happened to cause a widened QRS complex?

Answer 41

Problems with ventricle wall, bundle branch block, ischaemia, drugs, metabolic abnormalities, hypokalaemia

Question 42

What do pathological Q waves suggest?

Answer 42

Indicates an area of muscle necrosis following ischaemia

Question 43

What does ST depression suggest?

Answer 43

Reduced perfusion to the myocardial muscle

Question 44

If a p wave can be seen on an ECG, it is possible for someone to be having AF?

Answer 44

No