Heart Rhythm

Question 1

What is the function of the sinus node?

Answer 1

It acts as the heart’s pacemaker, initiating electrical impulses under neurohormonal control.

Question 2

What is the function of the AV node?

Answer 2

It relays electrical impulses from atria to ventricles and slows conduction to protect ventricles from excessively fast rates.

Question 3

What happens in the His bundle and Purkinje fibres?

Answer 3

The His bundle splits into right and left Purkinje fibres, conducting impulses through the ventricles.

Question 4

What do cardiac myocytes do in response to depolarisation?

Answer 4

They contract (shorten).

Question 5

What two electrical processes define conduction in the heart?

Answer 5

Depolarisation and repolarisation.

Question 6

What does an ECG record?

Answer 6

Electrical conduction through the heart.

Question 7

How many electrodes and signals are used in a 12-lead ECG?

Answer 7

10 electrodes produce 12 signals.

Question 8

How many chest and limb leads are used in an ECG?

Answer 8

6 chest leads and 4 limb leads.

Question 9

What three main waves are seen on an ECG?

Answer 9

P wave, QRS complex, T wave.

Question 10

What does the PR interval represent?

Answer 10

Conduction from sinus node through atria to AV node.

Question 11

What is the normal PR interval?

Answer 11

Less than 200ms (about 5 small ECG squares).

Question 12

What does QRS duration represent?

Answer 12

Conduction from AV node through His bundle and Purkinje fibres into ventricles.

Question 13

What is the normal QRS duration?

Answer 13

Less than 120ms (about 3 small ECG squares).

Question 14

What does the QT interval represent?

Answer 14

Time of ventricular depolarisation and repolarisation.

Question 15

What is a normal QT interval?

Answer 15

Less than ~450ms.

Question 16

What is sinus rhythm?

Answer 16

A heart rhythm that originates from the sinus node and starts with a P wave.

Question 17

What are the two rules of sinus rhythm?

Answer 17

Every P wave is followed by a QRS; every QRS is preceded by a P wave.

Question 18

How does increased parasympathetic activity affect the heart?

Answer 18

It decreases sinus node depolarisation (slows heart rate).

Question 19

Name situations that increase parasympathetic tone.

Answer 19

Sleep, fitness, digoxin use, fainting.

Question 20

How does increased sympathetic activity affect the heart?

Answer 20

It increases sinus node depolarisation (increases heart rate).

Question 21

Name situations that increase sympathetic tone.

Answer 21

Exercise, fear, heart failure.

Question 22

What is an ectopic beat?

Answer 22

A heartbeat originating outside the sinus node, from atria or ventricles.

Question 23

List some causes of ectopic beats.

Answer 23

Electrolyte imbalance, SNS/PSNS activation, caffeine, alcohol.

Question 24

What ECG finding suggests an atrial ectopic beat?

Answer 24

Premature P wave followed by normal QRS.

Question 25

What is bundle branch block?

Answer 25

A delay (not block) in conduction through either the right or left bundle.

Question 26

How to identify LBBB on ECG?

Answer 26

Broad QRS >120ms, negative in V1.

Question 27

How to identify RBBB on ECG?

Answer 27

Broad QRS >120ms, positive in V1.

Question 28

What defines SVT?

Answer 28

Tachycardia originating at or above the AV node, producing narrow QRS complexes.

Question 29

Name types of SVT.

Answer 29

Sinus tachycardia, atrial flutter, atrial fibrillation, AVRT, AVNRT, atrial tachycardia.

Question 30

What happens to atrial activity in AF?

Answer 30

Disorganised, with no P waves on ECG.

Question 31

Why does AF increase stroke risk?

Answer 31

Blood pools in atria → clots form → risk of embolism.

Question 32

What drugs are used for rate control in AF?

Answer 32

Beta-blockers, digoxin, calcium channel blockers.

Question 33

What drugs are used for rhythm control in AF?

Answer 33

Amiodarone, or DC cardioversion.

Question 34

Where is the re-entrant circuit in AVRT?

Answer 34

Outside the AV node.

Question 35

Where is the re-entrant circuit in AVNRT?

Answer 35

Inside the AV node.

Question 36

What is the typical atrial rate in flutter?

Answer 36

~300 bpm.

Question 37

What is the classic ECG sign of atrial flutter?

Answer 37

Saw-tooth pattern.

Question 38

What defines first-degree heart block?

Answer 38

Prolonged PR interval; every P wave conducts.

Question 39

What defines second-degree heart block?

Answer 39

Some P waves conduct, others do not.

Question 40

What defines third-degree heart block?

Answer 40

No relationship between P waves and QRS complexes.

Question 41

Name some causes of heart block

Answer 41

Beta-blockers, calcium channel blockers, amiodarone, ageing, hyperkalaemia.

Question 42

What are temporary treatments for bradycardia?

Answer 42

Atropine, pacing.

Question 43

What is definitive treatment for high-grade AV block?

Answer 43

Pacemaker implantation.

Question 44

What defines ventricular tachycardia?

Answer 44

Broad, regular, bizarre QRS; life-threatening.

Question 45

What defines ventricular fibrillation?

Answer 45

Chaotic ventricular activity; always fatal unless treated.

Question 46

What are the three mechanisms of tachyarrhythmias?

Answer 46

Enhanced automaticity, triggered activity, re-entry.

Question 47

What is a Class I antiarrhythmic?

Answer 47

Sodium channel blocker (e.g. flecainide).

Question 48

What is a Class II antiarrhythmic?

Answer 48

Beta-blocker (e.g. bisoprolol).

Question 49

What is a Class III antiarrhythmic?

Answer 49

Potassium channel blocker (e.g. amiodarone).

Question 50

What is a Class IV antiarrhythmic?

Answer 50

Calcium channel blocker (e.g. verapamil).

Question 51

Why avoid flecainide in structural heart disease?

Answer 51

It increases risk of arrhythmias.

Question 52

What are key side effects of amiodarone?

Answer 52

Lung fibrosis, thyroid dysfunction, skin discoloration, corneal deposits.

Question 53

What’s a major risk of digoxin toxicity?

Answer 53

Arrhythmias, visual changes (xanthopsia).

Question 54

What does atropine do in bradycardia?

Answer 54

Blocks vagal (PSNS) input to increase SA and AV node conduction.

Question 55

What ion causes depolarisation in atrial/ventricular myocytes?

Answer 55

Sodium influx (phase 0).

Question 56

What ion maintains plateau phase?

Answer 56

Balance of calcium influx and potassium efflux.

Question 57

What ion causes depolarisation in SA/AV node?

Answer 57

Calcium influx (L-type).

Question 58

What is the effective refractory period (ERP)?

Answer 58

Time during which a new impulse cannot propagate an action potential.

Question 59

Why is synchronisation needed in cardioversion?

Answer 59

To avoid shocking during the vulnerable supranormal period → prevents VF.