Narrow Complex Tachycardias (AFib, Aflutter, AVRT, AVNRT)

Question 1

Common tx pathway for all narrow-complex tachycardias (emergency vs. non-emergency)

Answer 1

emergency:
1. ABCDE
2. DC cardioversion
3. Medical cardioversion: dronedarone, amiodarone

non-emergency
1. Carotid massage, vasalva manoeuvre
2. Adenosine, verapamil

Question 2

Definition of narrow-complex QRS

Answer 2

QRS duration of 120 ms or less

Question 3

Definition of Afib

Answer 3

Afib: disorganised, rapid and irregular activation in atria, discharge at 300-600bpm, AV node responds intermittently, hence irregular ventrocular rate

Question 4

Causes and RFs of Afib

Answer 4

Causes: idiopathic, HTN, HF, MI, cardiac surgery

RFs: >60, T2DM, high BP

Question 5

Signs and Sx of Afib

Answer 5

Sx: chest pain, palpitations, dyspnoea, faintness

Signs: irregularly irregular pulse, apical HR >radial HR

Question 6

Ix for Afib

Answer 6

ECG:
- absense of P waves
- irregularly irregular rhythm
- lack of isoelectric baseline

Question 7

Tx for Afib (acute and non-acute, haemodynamically unstable vs stable)

Answer 7

1. Identify if acute cause is treatable: alcohol toxicity, chest infection, hyperthyroidism
2. Unstable:
   - immediate heparin
   - attempt cardioversion: synchronised DC shock
   - if this fails/Af recurs: IV amiodarone
   - then attempt cardioversion again
3. Stable
   - first line: rate control with BBlockers and rate-limiting CCB like verapamil, maybe digoxin
   - second line: rhythm control with DC cardioversion + BBlockers, dronedarone or amiodarone

Question 8

Which AFib medication is avoided in pts with structural heart defects?

Answer 8

Oral flecainide

Question 9

Which medication is used to prevent thromboembolism in Afib patients?

Answer 9

Aspirin is no longer used
Anticoagulants instead: DOACs like apixaban

Warfarin no longer used as need to monitor INR closely

Question 10

What is used to calculate stroke risk in Afib patients?

Answer 10

CHA2DS2-Vasc
CHF
HTN
Age >75
Age 65-74
Diabetes
Stroke/TIA
Sex (F)
Vascular disease

Score 1/2 (in Fs): start Tx with NOAC

Question 11

What score must be used in Afib before DOAC is started?

Answer 11

ORBIT assessment

Question 12

Definition of Aflutter

Answer 12

Much less common than Afib, organised atrial rhythm with atrial rates of up to 350bpm

Question 13

Signs ans Sx of Aflutter

Answer 13

Not as well-tolerated as Afib
Palpitations
fatigue
dyspnoea
chest pain
dizziness
syncope

Question 14

Ix for Aflutter

Answer 14

ECG: regular sawtooth-like atrial flutter waves between QRS complxes - best seen in leads ll, lll and aVF

regularly irregular

Question 15

What can unmask Aflutter waves on ECG?

Answer 15

Slowing AV conduction by cartoid sinus massage or IV adenosine

Question 16

Tx for Aflutter + Risk of medically treating Aflutter

Answer 16

Same as Afib (rate and rhythm control, cardioversion)

Risk: as atrial rate slows down from 300, AV node may allow 1:1 conduction, so you MUST monitor pt.

Also consider radiofrequency ablation, very effective

Anticoagulation

Question 17

What’s the difference between Afib and SVT?

Answer 17

In Afib, atria does not contract –> risk of blood stasis, clots

In SVTs, atria contract excessively fast, so no risk of clots and arrhythmia is relatively benign

Question 18

What is the pathophysiology of atrioventricular nodal re-entrant tachycardia (AVNRT)

Answer 18

The AV node has 2 pathways:
- slow pathway, with short refractory period
- fast pathway, with long refractory period

In sinus rhythm, impulses travel down both pathways simultaneously.

In pathophysiology, premature atrial contraction arrives while fast pathway is still refractory –> slow pathway takes over –> when premature impulse reaches end of slow pathway, fast pathway is no longer refractory –> impulse recycles retrogradely up fast pathway –> self-sustaining circulation movement, overriding sinus discharge

Question 19

Difference between AVNRT and AVRT

Answer 19

In AVRT, there’s an accessory pathway that allows impulses to travel antrogradely or retrogradely –> leading to 2 pathways transmitting impulses from atria to ventricles –> setting up re-rentry circuit

Question 20

What’s an example of AVRT?

Answer 20

Wolff-Parkinson-White syndrome

Question 21

What are the hallmarks of WPW on an ECG?

Answer 21

Short PR intervals
Wide QRS complex that looks slurred, known as a delta wave
HR 200-300bpm, regular

Question 22

Tx for AVRT/AVNRT

Answer 22

BBlockers, radio-frequency ablation