ECG Pathologies

Question 1

What are the 2 ways by which arrhythmias can arise?

Answer 1

Re-entry loops
Ectopic pacemaker

Question 2

How can you tell if the depolarisation is travelling via the normal conducting pathway or if it is a ventricular ectopic?

Answer 2

The width of the QRS complex

Broad = ventricular ectopic

Question 3

What are re-entry loops?

Answer 3

Damage to the conducting myocardium causes a unidirectional conduction block
Impulses can only travel via the 1 way and end up not cancelling out so the impulse travels retrogradely back through the damaged tissue forming a continuous loop

Question 4

What can AV node re entry loops cause?

Answer 4

Supra-ventricular tachycardia

Question 5

What can atrioventricular re-entry lead to?

Answer 5

An accessory pathway between atria and ventricles leading to a re-entry loop like in Wolff-Parkinson-White syndrome

Question 6

What can causes atrial tachycardia?
How does it appear on ECG?

Answer 6

Digoxin
Ischaemic heart disease
Rheumatic heart disease

Tachycardia and P and T waves can merge together

Question 7

What causes atrial flutter?

Answer 7

Re-entry loop in Atria

Question 8

What is an example of a type of Atrial Flutter?

How does it appear on an ECG?

Answer 8

2:1 AV block
2 atrial contractions per 1 ventricular contraction

2 p waves before a QRS complex

Question 9

What is Atrial Fibrillation?

How does it appear on ECG?

What problem is commonly associated with AFib?

Answer 9

Irregularly irregular impulses in atria

Causes irregular R-R intervals but normal shaped QRS complexes

Stasis of blood in atria, leading to formation of thrombus leading to embolism (high risk in left atrium due to structure of left oracle)

Question 10

What can ventricular tachycardia degenerate into?

Answer 10

Ventricular fibrillation

Question 11

What causes ventricular fibrillation?

What is bad about VF?

Answer 11

Multiple (3) ectopic foci in ventricles

Severely reduced Cardiac Output leading to cardiac arrest

Question 12

What is Torsades de Pointes?

How is it treated?

Answer 12

Polymorphic ventricular tachycardia meaning the QRS complex’s are all very different in the Ventricular fibrillation

There’s twisting around the axis

Treated with Mg

Question 13

What is First Degree AV block (heart block)?

How does it appear on ECG?

Answer 13

Delayed conduction through the AV node causing a consistently prolonged PR interval (>5small boxes)

Question 14

What are the 2 types of Second Degree AV block?

Answer 14

Mobitz type I

Mobitz type II

Question 15

What is Mobitz type I second degree AV block?

Answer 15

PR interval gets progressively longer until one of the QRS complexes gets dropped
Then PR interval back to normal then cycle continues

Question 16

What is Mobitz type II second degree AV block?

Answer 16

PR interval is normal and constant but occasionally P wave not conducted so a QRS gets dropped

Question 17

What is Third Degree AV block?

Answer 17

When no impulses are transmitted between the atria and ventricles so they work independently to each other (no relationship between P waves and QRS complexes)

Question 18

In Third degree heart block how is blood pressure and heart rate affected and why?

Answer 18

They are both reduced

The escape rhythm produced by the ventricular pacemaker depolarises much slower

Question 19

What is a pathological Q wave?

Where are pathological Q waves seen?

Answer 19

When the Q wave is more than 1 small box wide, more than 2 small boxes depp and more than a quarter of the depth of the R wave

A couple of hours after a STEMI

Question 20

What is a STEMI?

Answer 20

Full thickness myocardial infarction caused by a full occlusion of a coronary artery

Question 21

What ECG changes and investigations are seen with a STEMI?

Answer 21

ST elevation (acutely)
Pathological Q waves (after a few hours)
Raised Troponin I and T
T wave inversion after 1-2 days

Question 22

What is a NSTEMI?

Answer 22

Partial thickness MI as a result of a coronary artery being almost completely occluded

Question 23

What ECG changes and investigations are seen with a NSTEMI?

Answer 23

ST depression or T wave inversion
Raised Troponin I and T

Question 24

What affects does Hyperkalaemia have on the heart?

How does it appear on an ECG?

Answer 24

RMP now less negative
So always partially depolarised
This inactivates some voltage gated Na+ channels so slower upstroke of ventricular AP and so slower heart rate

First tall peaked T waves
Tall peaked T wave, flattened P wave anad prolonged PR interval
Tall peaked T wave, absent P wave and a widened QRS
Widened QRS. The ST segment merges with the T wave causing a sine-wave pattern.

Question 25

What affect does Hypokalaemia have on the heart?

How does it appear on an ECG?

Answer 25

Causes lengthen ventricular action potential (PR interval) delaying repolarisation
This can lead to early after depolarisations causing oscillations in membrane potential which can result in VF

First low T-wave
Then low T-wave and high U-wave
Then low T-wave, high U-wave and a low ST segment

Question 26

What is Delayed afterdepolarisations?

What causes it?

Answer 26

When membrane spontaneously depolarises quickly after it repolarised

Usually happens when there’s a high intracellular calcium level

Question 27

What is Early Afterdepolarisations?

What makes it more likely?

What can it lead to?

Answer 27

When membrane depolarises while it is repolarising

More likely with longer QT intervals

Consecutive EADs can result in VF