Atrial Fibrillation

Question 1

What is atrial fibrillation

Answer 1

• Arrythmia causing heart to pump less effectively
• Supraventricular arrhythmia originates in the heart
• Rapid discharge of ectopic foci causing rapid depolarisation of the atria (300-500bpm)
• The AVN limits the number of impulses sent to the ventricle causing a reduction in cardiac output and leading to heart failure
• May also form blood clots, strokes or embolisms

Question 2

Symptoms

Answer 2

Palpitation, dyspnea, tiredness, weakness, poor exercise intolerance, irregular pulse, dizziness

Question 3

Rate control vs Rhythm control

Answer 3

Rate control:
Controls ventricular rate and relieves symptoms but does not treat

Rhythm control:
Restores and maintains sinus rhythm in order to slow down the progression of AF and stroke

Question 4

Heart electrical pathway

Answer 4

1. SAN in right atrium polarises and sends out electrical impulse that travels through heart wall
2. The atria contracts
3. The impulse travels to the AVN where there is a slight delay allowing the atria to fully empty
4. The impulse travels down the bundle of His which branches into left and right bundle of His
5. Ventricles contract

Question 5

Physiology of cardiac conduction

Answer 5

Phase 4:
Cell is at rest (-90mV). NaKATPase maintains the concentration.
- Pacemaker potential since pacemaker cells are never at rest

Phase 0:
Threshold of -40mV is reached and there is rapid depolarisation. Na channels open causing an infux reaching 0mV and there is a brief overshoot causing further depolarisation from neighbouring cells through gap junctions reaching +50mV

Phase 1:
Rapid inactivation of Na channels and activation of K channels allowing a brief flow of K+ out the cell causing membrane potential to go back to 0mV
- In pacemaker cells this phase is not obvious

Phase 2:
Balance of charge moving into and out of the cell. K+ leaves the cell whereas Ca2+ moves in causing myofibril contractions. At the end the Ca2+ channels close

Phase 3:
Rapid repolarisation where K channels remain open allowing more K+ efflux making the internal more negative

Phase 0:
Hyperpolarised resting state due to ATP pumping of Na+ and Ca2+. Resting potential maintained by NaKATPase

Question 6

Rate control

Answer 6

First line treatment in those except for patients with new onset AF, heart failure secondary to AF or AF with a reversible cause

1. Standard beta blocker
2. Diltiazem/verapamil
3. Digoxin (only in sedentary patients) if AF is accompanied with congestive heart failure

If ventricular function diminished then consider beta blocker and digoxin

If single drug fails then consider combination of any 3 or rhythm control

Question 7

Beta blocker

Answer 7

Inhibit sympathetic influence on cardiac electrical activity
Decrease sinus rate and conduction velocity
Inhibit aberrant pacemaker activity
Increase action potential duration and the effective refractory period

For people with AF alone: atenolol with loading dose 50-100mg

For people with HF: Atenolol, bisoprolol, metoprolol and nebivolol

Side effects: bradycardia, cold extremeties, sleep disturbance or nightmares, fatigue, sexual dysfunction

Do not stop beta blockers abruptly

Question 8

Diltiazem/Verapamil

Answer 8

Block the L type calcium channel causing decreased myocardial force of contraction, decreased heart rate and decreased conduction velocity
Start with low dose and titrate up

Verapamil commonly causes constipation regulated with more fible and drinking fluids
Diltiazem commonly causes dizziness

Question 9

Digoxin

Answer 9

Increases parasympathetic activity reducing SAN firing rate and reduces conduction velocity through the AVN
Loading dose: 250-750mcg a day for a week
Maintanence dose: 125-250mcg a day
*Renal impairment in elderly requires reduced loading dose

Question 10

Rhythm control

Answer 10

• Amiodarone is most effective but considered last due to its adverse effects

Question 11

Amiodarone

Answer 11

Long half life, oral loading
Slow onset and long duration
Contains iodine moeities so causes hepatic and thyroid effects
Protect skin from sunlight
Affects night time lighting

Question 12

Dronedarone

Answer 12

Not as effective as amiodarone but better tolerated due to fewer side effects as it lacks iodine moeities

Question 13

PILL in the pocket

Answer 13

Flecainide or propafenone
Suitable for those who have no history of left ventricular dysfunction, valvular or ischemic heart disease
Given when systolic bp >100mmHg or >70bpm

If AF longer than 5 mins, take one dose and go to hospital if it doesn’t revert within 6-8 hours

MAX ONE DOSE IN 24 HOURS

Flecainide 300mg causes visual disturbances or blurred vision

Propafenone 600mg causes constipation

Question 14

Stroke and bleeding risk assessment

Answer 14

Worked out using CHAD2VASC and HASBLED
- For people with high risk of stroke, anticoagulation is considered

DO NOT USE ASPIRIN

Only give apixaban, rivoroxaban, warfarin and dabigatran