The rhythm of the heart

Question 1

The PR interval is taken from which two points of an ECG?

Answer 1

The PR interval is taken from the beginning of the P wave through to the beginning of the QRS

Question 2

What does the PR interval represent?

Answer 2

This is related to the time that the atria has to contract, so it is related to how long the AVN is holding up the electrical signal
- Atrial depolarisation

Question 3

What does the QRS complex represent?

Answer 3

Ventricular depolarisation

Question 4

T wave on an ECG represents what?

Answer 4

Ventricular repolarisation

Question 5

What is the normal PR interval? (msec)

Answer 5

<200msec

Question 6

How many squares on an ECG is the normal PR interval if each square is 40msec

Answer 6

<5small squares

Question 7

The normal QRS complex is how long? (msec)

Answer 7

<110msec

- <3 little squares

Question 8

A normal QT interval is how long? (msec)

Answer 8

<460msec

- <12 small squares

Question 9

How do you count the rate from an ECG?

Answer 9

Look at the R-R interval and divide the number of big squares by 300

Question 10

How does increased para-sympathetic nervous system (PNS) affect heart rate?

Answer 10

Slows it down

Question 11

How does increased sympathetic nervous system affect heart rate?

Answer 11

Increases heart rate

Question 12

What are the important questions which you need to ask when interpreting an ECG?

Answer 12

1. Are the QRS complexes regular?
2. Is there a P-wave in front of each QRS with a normal AV delay?
3. What is the relationship between the P waves and QRS?
4. Are the QRS complexes regular and >120msec wide?

Question 13

NOTE SLIDE: Look over B13 lecture 19 slide to learn ECG interpretations for each pathology e.g. AF and SVT etc…

Question 14

How do you measure if QRS complexes are regular?

Answer 14

R-R interval distance should be measured

Question 15

What is a sinus rhythm?

Answer 15

Sinus rhythm is any cardiac rhythm in which depolarisation of the cardiac muscle begins at the sinus node, which means that THERE IS A P WAVE BEFORE EACH QRS

Question 16

Causes of bradycardia

Answer 16

Beta blockers
Digoxin
Hypothyroidism
Fitness

Question 17

Treatment of bradycardia

Answer 17

IV atropine

Question 18

COPD patients may have a LBBB or RBBB pattern, which is it and why?

Answer 18

RBBB
- Because the right side of the heart is under pressure from pumping blood through the high pressure pulmonary vasculature

Question 19

LBBB might be due to a significant problem with which ventricle? What can this be a marker for?

Answer 19

LV

- Underlying cardiomyopathy

Question 20

What is atrial tachycardia? Which age range will you more often see with this issue?

Answer 20

The AV node starts to become a little more slow compared to children where it is a lot faster
- You may see atrial tachycardia more often in children compared to 60/70yrs old because of this

Question 21

What is Atrioventricular reentrant tachycardia (AVRT)?

Answer 21

AVRT = electrical pathway is going via the normal route via the AV node, but there is an extra accessory pathway separate to the AV node, the signals go back up this accessory pathway and down back through the AV node and back up through the pathway again, so you end up with a circuit of electricity.

• This is a sort of self-perpetuating electrical depolarisation, as you have fast conduction through this accessory pathway, much faster than the normal AV node conduction

Question 22

How do you treat AVRT?

Answer 22

If you give adenosine and you block the AV node, you will cut through the short circuit and go back to a normal SA node led sinus rhythm

Question 23

What is Atrioventricular nodal reentry tachycardia (AVNRT)?

Answer 23

Other type of tachycardia is AVNRT, meaning that the AV node itself is subject to an extra short little circuit, so within the AV node, you get this short circuit of electricity which drives itself

Question 24

How do you treat AVNRT?

Answer 24

If you give adenosine, you temporarily block the AV node, and the SA node can take over once again

Question 25

Causes of sinus tachycardia?

Answer 25

Hyperthyroidism
Anxiety
Heart failure
Hypovolaemia
Septicaemia

Question 26

Which manoeuvres can be used to terminate an SVT

Answer 26

Vagotonic maneouvres, push against closed glottis or put under cold water.
Also can perform the carotid sinus massage, typically the right carotid, will increase the activity & efficacy of the AVN and you can terminate the SVT like that

Question 27

Atrial fibrillation increases the risk of stroke, true or false?

Answer 27

TRUE

By 4-fold

Question 28

What is atrial fibrillation?

Answer 28

The commonest sustained arrhythmia

Question 29

What is the treatment for AF?

Answer 29

1. Control ventricular rate = commonly beta-blocker

2. Reduce stroke risk = estimate using CHADS2VASC score and give anticoagulation (DOAC) to those who need it

Question 30

Does aspirin protect against stroke caused by AF?

Answer 30

No!

- Anti-platelet therapy does not work for this

Question 31

What are the ways in which one can be put back into sinus rhythm?

Answer 31

1. In the acute setting (if it has not been there for very long), can use a drug called FLECAINIDE
2. If that does not work, it can be done with a DC cardioversion, you want to deliver shock on the QRS complex to get back into sinus rhythm. N.B. do not shock on a T wave as it can put you into VF!
   - The machine delivers the shock at just the right point to get you back into sinus rhythm. This is done under general anaesthetic