CR: PBL 1 (ECG and Atrial Fibrillation)

Question 1

Define cardioversion

Answer 1

Use of electric shock to convert dangerous, rapid fluttering of heart beat to its normal rhythm

Question 2

Define atrial fibrillation

Answer 2

Irregularity of heart beat caused by involuntary contractions of small areas of heart muscle walls

Question 3

Describe the ECG of someone in atrial fibrillation

Answer 3

No P wave, no identifiable PR interval, normal QRS complex

Question 4

What are heart palpitations?

Answer 4

Sensation where a person is aware of an irregular, hard or rapid heart beat

Question 5

What is cardiovascular disease?

Answer 5

Any disease of the heart or blood vessels e.g. Atherosclerosis, CHD and peripheral vascular disease

Question 6

What is systolic blood pressure?

Answer 6

Blood pressure during contraction of the ventricles

Question 7

What is diastolic blood pressure?

Answer 7

Minimum level of blood pressure measured between heart contractions

Question 8

What is rivaroxaban?

Answer 8

An oral anticoagulant

Question 9

What does a P wave represent?

Answer 9

Atrial depolarisation

Question 10

What does a QRS complex represent?

Answer 10

Ventricular depolarisation

Question 11

What does a T wave represent?

Answer 11

Ventricular repolarisation

Question 12

What does the PR interval represent?

Answer 12

Activation of AVN, bundle of His and Purkinje fibres

Question 13

How can you calculate ventricular rate from ECG?

Answer 13

Duration between R waves (RR interval)

Question 14

How can you calculate atrial rate from an ECG?

Answer 14

Duration between P waves (PP interval)

Question 15

How do atrial and ventricular rates differ in atrial fibrillation?

Answer 15

Atrial rate >360bpm whereas ventricular rate 60-150bpm

Question 16

Why are blood tests used in the diagnosis of atrial fibrillation?

Answer 16

To check for factors which may have led to AF such as hyperthyroidism or electrolyte imbalance

Question 17

How can hyperthyroidism lead to greater risk of atrial fibrillation?

Answer 17

Thyroid hormone contributes to arrhythmogenic activity by altering electro physiological characteristics of atrial myocytes by shortening the duration of atrial depolarisation

Question 18

How can blood tests diagnosis cardiac failure?

Answer 18

Pro-brain natriuretic peptide is released in higher than normal levels (PNP)

Question 19

Where is the SAN located?

Answer 19

Lateral to the junction where the superior vena cava enters the atrium

Question 20

What is the function of the AVN?

Answer 20

Initiate wave of excitation in the ventricles following atrial contraction as the septum blocks the AVN impulse from being transmitted directly to ventricles

Question 21

Define ‘automaticity’

Answer 21

Ability to depolarise spontaneously

Question 22

What percentage of ventricular filling is done by atrial contraction at rest and during exercise?

Answer 22

Rest = 10%
Exercise = 40%

Question 23

Why would atrial fibrillation limit exercise capacity?

Answer 23

Because atrial systole effectively doesn’t occur and therefore there is poor ventricular filling leading to poor stroke volume which is insufficient to supply the active muscles and therefore this will lead to quick fatigue and lactic acid build up (cramp)

Question 24

Why are patients with atrial fibrillation placed on anticoagulants?

Answer 24

AF increases chance of stroke due to slow blood flow (pooling) which increases the likelihood of clots forming and therefore anti coagulants are used to prevent clot formation and reduce stroke likelihood, or may be used prior to cardioversion (also increases risk of stroke)

Question 25

What is atrial fibrillation?

Answer 25

Atria are experiencing chaotic external signals from the SAN meaning the AVN is bombarded with impulses trying to get through the septum and therefore this causes an irregular ventricular rate also

Question 26

Explain why irregular radial pulse is a sign of atrial fibrillation

Answer 26

The pulse is too weak as a result of low blood volume being pumped per unit of time

Question 27

Explain why low blood pressure is a sign of atrial fibrillation

Answer 27

There is a smaller volume of blood being pumped in systole (stroke volume) and therefore the blood pressure decreases

Question 28

Describe the normal clotting cascade

Answer 28

1) Blood exposed to collagen
2) Factor XII activated –> XIIa
3) Factor XIIa activates factor (with HMW kininogen) XI –> XIa
4) Factor XIa binds calcium and activates factor IX –> IXa
5) Platelets release PF3 and thrombin activates factor VIII –> VIIIa
6) Xa factor (help of PF3) joins VIIIa to form factor X activating factor (tense)
7) Tenase activates X –> Xa (prothrombinase)
8) Tenase binds to Ca2+, Xa and prothrombin –> thrombin
9) Thrombin: Factor XIII –> XIIIa and binds to fibrinogen –> fibrin
10) Fibrin activated by XIIIa –> cross-linking –> clot formed

Question 29

Describe how the anticoagulant rivaroxaban works

Answer 29

Inhibits free and bound (to prothrombinase complex) factor Xa to stop production of thrombin

Question 30

What is catheter ablation?

Answer 30

Carefully destroys diseased areas of heart by using thin wires through vein into heart –> record electrical activity and energy source transmitted to destroy abnormal tissue (in terms of electricity)

Question 31

What is a pacemaker?

Answer 31

Battery powered device implanted in chest below collar bone to stop heart beating too slowly (or to regulate)

Question 32

Are athletes at a greater risk of atrial fibrillation?

Answer 32

Most common arrhythmia in athletes, and are 2-3x more likely to have than ordinary person

Question 33

Why may athletes be more predisposed to atrial fibrillation than an ordinary person?

Answer 33

Cardiovascular stresses causing structural changes to atrial muscle (involved in abnormal electrical activity, increased firing of ANS nerves may promote disruption OR low level chronic inflammation that accompanies exercise

IT’S UNKNOWN WHY.

Question 34

What does suffering atrial fibrillation increase your risk of?

Answer 34

Stroke, by 4-5x

Question 35

What are the different types of atrial fibrillation?

Answer 35

Intermittent - intervals of AF
Persistent - in AF for longer than one week
Permanent - always in AF

Question 36

Which drugs affect heart rate?

Answer 36

Chronotropic - affect the nerves controlling heart or the SAN

Question 37

Which drugs affect force of heart contraction?

Answer 37

Ionotropic drugs - involved in muscular contraction (depolarisation), especially of cardiac myocytes